Chapter 5 | Life Processes | Class 10 Science

Life Processes

In-depth study of fundamental biological systems: Autotrophic & Heterotrophic Nutrition, Aerobic & Anaerobic Respiration, Human & Plant Transportation, and Human & Plant Excretion.

💡 Key Practice: Pair diagrams with anatomical labels and functions: organ/structure → enzyme/fluid → biological role. For physiological pathways, follow the input → steps → output sequence.

Concepts & Visual Theory

Complete chapter progression • detailed explanations • diagrams

What are Life Processes? (Maintenance & Energy)

Direct Board Definition — Life Processes: The basic vital functions and maintenance activities performed by all living organisms to sustain life, maintain order, repair damage, and prevent their breakdown on earth are called Life Processes.

Why Continuous Maintenance is Essential for Living Beings:

Living Organisms are Well-Ordered Structures: They have tissues, tissues have cells, cells have smaller molecular components, and so on. Because of environmental effects, this organized, ordered nature of living structures is very likely to keep breaking down over time.
Need for Continuous Repair: If order breaks down, the organism cannot stay alive. Therefore, living creatures must keep repairing and maintaining their structures continuously.
Maintenance Requires Energy: Since these maintenance processes are needed to prevent damage and breakdown, energy is needed for them. This energy comes from the outside of the individual body in the form of food.
Molecular Movement Criterion: Invisible molecular movements inside cells are the definitive characteristic of life. Viruses do not show any molecular movement until they infect a host cell, which is why controversy persists on whether they are truly alive or not.

Four Core Life Processes in Class 10:
1. Nutrition: Process of transferring a source of energy (food) from outside into the body for maintaining life.
2. Respiration: Process of acquiring oxygen from outside to break down carbon-based food sources for cellular energy.
3. Transportation: System for carrying food, gases, and oxygen from one part of the body to all individual cells.
4. Excretion: Process of collecting and removing toxic chemical by-products produced during metabolic reactions.

Why Simple Diffusion is Insufficient in Multicellular Organisms

Direct Board Question (Classic 2-3 Marker): "Why is simple diffusion insufficient to meet the oxygen requirements of large, multicellular organisms like humans?"

Single-Celled Organisms (e.g. Amoeba)

Entire surface of the single cell remains in direct contact with the external environment.
No specific organs for taking in food, exchange of gases, or removal of wastes are needed.
Simple diffusion across the cell membrane is fast and sufficient to meet all metabolic needs.

Multicellular Organisms (e.g. Humans)

Various body cells are not in direct contact with the surrounding environment.
Body size is large and internal cellular architecture is highly specialized.
Diffusion is an extremely slow physical process across macroscopic multicellular distances.

Detailed Scientific Rationale:

Vast Distance Factor: In large human bodies, internal tissues and vital organs (brain, liver, muscle) lie deep inside, far away from respiratory surfaces.
Calculated Time for Diffusion: Calculations show that if diffusion alone were to move oxygen in our body, it would take an estimated 3 years for a single molecule of oxygen to travel from our lungs down to our toes!
Need for Specialized Organ Systems: To fulfill high metabolic and energy demands rapidly, multicellular organisms evolved specialized respiratory surfaces (alveoli with high surface area), a dedicated blood circulatory pump (heart), and an efficient oxygen-carrying pigment (haemoglobin).

Board Examiner Keyword Alert: Write both points — (1) Cells not in direct contact with environment, and (2) Diffusion is too slow to cover large anatomical distances to meet high metabolic demands.

Nutrition — Autotrophic vs Heterotrophic Nutrition

Direct Board Definition — Nutrition: The biological process by which an organism procures or synthesizes nutrients (food) and utilizes them for energy, growth, maintenance, and cellular repair.

Parameter	Autotrophic Nutrition	Heterotrophic Nutrition
Definition	Organisms synthesize organic nutrients from simple inorganic raw materials ($CO_2$ and $H_2O$).	Organisms obtain ready-made complex organic food derived directly or indirectly from autotrophs.
Energy Source	Solar energy (sunlight) trapped by chlorophyll or chemical energy (chemosynthesis).	Chemical energy obtained through ingestion/absorption of organic molecules.
Chlorophyll Requirement	Essential; contains chlorophyll inside specialized chloroplasts.	Chlorophyll is completely absent.
Stored Form of Food	Carbohydrates stored primarily as Starch.	Carbohydrates stored in animals and fungi as Glycogen.
Examples	Green plants, Euglena, blue-green algae (cyanobacteria).	All animals, fungi (yeast, mushroom), amoeba, non-green plants (Cuscuta).

Board Storage Distinction: Autotrophs store internal energy reserves as Starch, whereas animals store excess glucose as Glycogen in the liver and muscles.

Photosynthesis — The Complete Balanced Reaction & 3 Major Events

Direct Board Definition — Photosynthesis: The physiological process by which green plants containing chlorophyll synthesize organic glucose from carbon dioxide and water in the presence of sunlight, releasing oxygen as a by-product.

Standard Balanced Chemical Equation:

$$6CO_2 + 12H_2O \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} C_6H_{12}O_6 + 6O_2 \uparrow + 6H_2O$$

The 3 Sequential Events During Photosynthesis (Strict NCERT & Board Marking Scheme):

Absorption of Light Energy: Solar radiation is absorbed by the green pigment Chlorophyll located inside the thylakoids of chloroplasts.
Conversion & Photolysis of Water: Light energy is converted into chemical energy (ATP and NADPH), and water molecules are split into Hydrogen and Oxygen ($2H_2O \rightarrow 4H^+ + 4e^- + O_2$). Oxygen released originates strictly from water, not from carbon dioxide!
Reduction of Carbon Dioxide: Carbon dioxide ($CO_2$) is reduced to carbohydrates (glucose, $C_6H_{12}O_6$) using assimilatory chemical energy.

🌵 Desert Plants Adaptation (High-Frequency CBSE Board Question):
Do these three steps take place immediately one after another?
No! In desert xerophytic plants (e.g. Cactus), stomata remain closed during the hot daytime to prevent transpiration water loss. They take up $CO_2$ at night and store it as an intermediate organic acid (malic acid). During the daytime when sunlight becomes available, chlorophyll absorbs light and acts upon this intermediate to complete carbohydrate synthesis!

Stomata & Guard Cells — Gas Exchange Mechanism & Turgor Control

Direct Board Definition — Stomata: Microscopic pores present on the epidermis of green leaves, green stems, and floral parts that facilitate gaseous exchange ($CO_2$ and $O_2$) and transpiration.

Detailed Mechanism of Opening & Closing of Stomatal Pores:

Guard Cells: Each stomatal pore is surrounded and regulated by a pair of specialized kidney-shaped (bean-shaped) Guard Cells (dumbbell-shaped in grasses) containing chloroplasts.
Stomatal Opening (Turgid State): When water enters guard cells from neighbouring epidermal cells by endosmosis, the guard cells swell and become turgid. Because their inner wall facing the pore is thick and inelastic while the outer wall is thin and elastic, the outer wall bulges outward, pulling the inner thick wall apart and opening the stomatal pore.
Stomatal Closing (Flaccid State): When guard cells lose water by exosmosis, turgor pressure drops. The guard cells shrink, become flaccid, and their straight elastic inner walls collapse back together, closing the pore.

Open vs closed stomatal pore

⭐ Stomata solve a trade-off: CO₂ entry for photosynthesis vs water loss by transpiration.

⭐ Evolutionary Dilemma: Stomata serve as the primary gateway for $CO_2$ required in photosynthesis, but inevitably cause substantial water loss through transpiration. Plants tightly regulate guard cell turgidity to close stomata when $CO_2$ is not actively needed for photosynthesis.

Raw Materials for Photosynthesis & Proven Experimental Evidence

Essential Raw Materials for Autotrophs: To perform photosynthesis and build complex cellular structures, autotrophic green plants require four cardinal factors:

Raw Material	Source	Uptake Mechanism & Biological Purpose
Carbon Dioxide ($CO_2$)	Atmosphere (0.03-0.04%)	Enters leaves by simple diffusion through open stomatal pores; acts as the carbon and oxygen source for glucose synthesis.
Water ($H_2O$)	Soil groundwater	Absorbed by root hairs via osmosis and transported upward through xylem vessels; provides hydrogen and electrons during photolysis.
Sunlight	Solar radiation	Electromagnetic radiant energy driving photochemical excitation and photolysis.
Chlorophyll	Internal chloroplasts	Green photosynthetic pigment with a porphyrin ring that traps photons of light.
Mineral Nutrients (N, P, Fe, Mg)	Soil	Absorbed with soil water by roots. Nitrogen is an essential element used in the synthesis of amino acids, proteins, and nucleic acids. Plants take up nitrogen as inorganic nitrates/nitrites or organic forms synthesized by bacteria.

🧪 Board Lab Experiments (Key Questions):
• Chlorophyll is Necessary: Variegated leaf experiment (Croton/Money plant) tested with iodine solution; only green chlorophyll-containing patches turn blue-black.
• $CO_2$ is Necessary: Destarched potted plant experiment with KOH (Potassium Hydroxide); KOH absorbs $CO_2$ in the enclosed bell jar, preventing starch formation in that leaf.

Heterotrophic Nutrition — Holozoic, Saprophytic & Parasitic Strategies

Direct Board Classification — Heterotrophic Modes: Depending on the nature and availability of food material as well as how it is obtained, organisms exhibit three prominent heterotrophic nutritional strategies:

1. Saprophytic (Saprotrophic) Nutrition

Organisms feed on dead, decaying organic matter.
They break down food materials outside the body by secreting digestive enzymes, and then absorb the soluble nutrients.
Examples: Fungi such as Bread Mould (Rhizopus), Yeast, and Mushrooms.

2. Parasitic Nutrition

Organisms derive nutrition from the body of another living organism (the host) without killing it.
Causes harm, weakness, or disease to the host organism.
Plant parasite: Cuscuta (Amarbel).
Animal parasites: Ticks, lice, leeches, tapeworms, roundworms.

3. Holozoic Nutrition:

Organisms take in complex whole organic food material into their body, digest it intracellularly or in a dedicated alimentary canal with internal enzymes, absorb simple soluble nutrients, and egest the undigested residue.
Five Cardinal Steps: Ingestion $\rightarrow$ Digestion $\rightarrow$ Absorption $\rightarrow$ Assimilation $\rightarrow$ Egestion.
Examples: Amoeba, Paramecium, humans, cattle, birds, fish.

Board Examiner Trap: If asked "Name an organism that breaks down food material outside the body before absorption", always write Fungi (Bread Mould / Rhizopus / Yeast / Mushroom).

Amoeba & Paramecium — Nutrition in Single-Celled Organisms

Holozoic Ingestion in Amoeba: Amoeba is a unicellular eukaryotic organism with no fixed mouth or specialized digestive organs. It captures food using temporary finger-like cell surface projections called pseudopodia.

Step-by-Step Sequence of Nutrition in Amoeba (Must-Know Diagram Question):

Ingestion: Amoeba senses a microscopic food particle, extends pseudopodia around it, and fuses them to engulf the particle, forming a temporary spherical Food Vacuole (phagosome).
Digestion: Digestive enzymes from the cytoplasm enter the food vacuole and break down complex insoluble food into simple soluble substances.
Absorption: The digested simple nutrients diffuse directly out of the food vacuole into the surrounding cytoplasm.
Assimilation: Absorbed food is utilized by the cell for obtaining energy through respiration and for growth and protoplasm repair.
Egestion: The undigested waste residue moves to the cell surface; the cell membrane ruptures at any random point to cast the waste outside.

Amoeba nutrition sequence

🧠 “P-F-D-A-E” → Pseudopodia → Food vacuole → Digestion → Absorption → Egestion.

🔬 Nutrition in Paramecium (Contrast with Amoeba): Unlike Amoeba, Paramecium has a definite, fixed slipper shape. Food is taken in at a specific spot called the Oral Groove (Cytostome). Food is driven to this spot by the rhythmic, coordinated beating of thousands of hair-like cilia covering the entire cell surface!

Human Digestive System — Overview & The Alimentary Canal Journey

Alimentary Canal Blueprint: The human alimentary canal is a continuous, muscular, coiled tube roughly 9 metres long extending from the mouth to the anus, accompanied by associated digestive glands (salivary glands, liver, pancreas).

Anatomical Roadmap of Ingested Food:

$$\text{Mouth} \rightarrow \text{Pharynx} \rightarrow \text{Oesophagus} \rightarrow \text{Stomach} \rightarrow \text{Small Intestine} \rightarrow \text{Large Intestine} \rightarrow \text{Rectum} \rightarrow \text{Anus}$$

Alimentary canal flow

Food pathway: Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum/Anus.

🧠 “My Old Sister Sings Like Rap” → Mouth, Oesophagus, Stomach, Small intestine, Large intestine, Rectum.

Key Physiological Principles of the Digestive Tract:

Mechanical Breakdown: Teeth crush and masticate food; tongue mixes it with saliva to lubricate passage through the soft digestive canal lining.
Chemical Breakdown: Specific biological catalysts called enzymes cleave complex non-absorbable macromolecules (polysaccharides, proteins, lipids) into simple absorbable micromolecules (glucose, amino acids, fatty acids + glycerol).
Unidirectional Movement: Coordinated involuntary muscular contractions ensure food travels systematically in one forward direction across specialized digestive chambers.

💡 Board Exam Tip: When asked to draw the digestive system, always label: Oesophagus, Stomach, Liver, Gallbladder, Pancreas, Small Intestine, Large Intestine, Appendix, and Anus.

Mouth & Saliva — First Stage of Digestion & Peristalsis

First Stage of Chemical Digestion: Digestion of carbohydrates begins in the mouth (buccal cavity), catalyzed by the enzyme Salivary Amylase (Ptyalin) secreted by three pairs of salivary glands.

Components & Functions of Saliva:

Salivary Amylase: Breaks down complex insoluble dietary starch (a polysaccharide) into simple reducing sugar maltose (a disaccharide) at an optimum slightly acidic/neutral pH (~6.8).
Mucus & Water: Moisten, soften, and lubricate chewed food particles, rolling them into a cohesive, easily swallowable spherical mass called a bolus.
Lysozyme: Mild antibacterial enzyme in saliva that destroys pathogens entering with food.

$$\text{Starch} \xrightarrow[\text{pH } \approx 6.8]{\text{Salivary Amylase}} \text{Maltose (Sugar)}$$

Starch digestion starts in the mouth

⭐ Iodine + starch gives the characteristic blue-black colour. If saliva digests starch, less starch remains to react.

Peristalsis in the Oesophagus (Food Pipe):

The swallowed bolus enters the oesophagus. No chemical digestion or enzyme secretion occurs in the oesophagus.
Peristaltic Movement: Rhythmic, wave-like contraction and relaxation of the circular and longitudinal muscles in the alimentary canal lining that pushes food forward all along the gut.

🧠 Reasoning Question: Why does a piece of bread taste sweet after chewing it for some time?
Answer: Salivary amylase breaks down tasteless insoluble starch into sweet-tasting soluble maltose sugar.

Stomach — Gastric Glands, HCl, Pepsin & Mucus Function

Stomach Architecture: A large J-shaped muscular organ situated on the left side of the upper abdominal cavity that expands when food enters. It churns food mechanically for 3 to 4 hours and mixes it thoroughly with gastric juice secreted by tubular Gastric Glands present in its muscular wall.

Gastric Secretion	Secreting Cells	Vital Biological Function in Stomach
Hydrochloric Acid (HCl)	Oxyntic (Parietal) cells	1. Creates an essential strongly acidic medium (pH ~1.5 - 2.0) required for inactive pepsinogen to convert into active Pepsin. 2. Kills harmful bacteria and pathogens ingested along with food. 3. Softens tough fibrous food particles.
Pepsin (Proteolytic Enzyme)	Chief (Peptic) cells	Acts in acidic medium to hydrolyse complex dietary proteins into shorter soluble peptide fragments (peptones and proteoses).
Mucus	Goblet (Neck) cells	Forms a continuous protective physical and chemical barrier over the inner stomach lining, preventing corrosion and autodigestion by concentrated HCl and pepsin.

⚠️ Clinical Board Question — Cause of Acidity:
If mucus secretion is compromised or excess HCl is secreted (due to overeating, stress, or irregular meals), the acid attacks the unprotected stomach wall, causing inflammation, heartburn, and painful gastric ulcers. Antacids (mild bases like $Mg(OH)_2$ or $NaHCO_3$) neutralize excess acid to provide relief.

Exit Control into Small Intestine:

Food exits the stomach in small regulated amounts as an acidic, semi-liquid pulp called chyme.
Its release into the duodenum is strictly regulated by a ring-like muscular valve called the Pyloric Sphincter.

Small Intestine — Complete Digestion & The Three Juices

Site of Complete Digestion: The Small Intestine is the longest part of the alimentary canal (~6 metres long in adults, highly coiled to fit in a compact space). It is the site of complete chemical digestion of carbohydrates, proteins, and fats.

Carnivore vs Herbivore Intestinal Length (Frequent Reasoning Question):

Herbivores (e.g. Cows, Deer): Have a longer small intestine to allow complete digestion of tough, fibrous cellulose by symbiotic microflora.
Carnivores (e.g. Tigers, Lions): Have a shorter small intestine because meat is concentrated, protein-rich, and much easier to digest.

The Three Coordinated Secretions Received by the Duodenum:

Digestive Secretion	Source Organ	Enzymes & Specific Action
Bile Juice (Contains no enzymes!)	Liver (Stored in Gallbladder)	1. Alkalinisation: Neutralizes acidic chyme from the stomach, turning it alkaline (pH ~8.0) so pancreatic enzymes can function. 2. Emulsification: Bile salts break down large, insoluble fat globules into tiny microscopic droplets, drastically increasing the surface area for lipase action.
Pancreatic Juice	Pancreas	• Pancreatic Amylase: Hydrolyses remaining starch into maltose. • Trypsin: Digests proteins, peptones, and proteoses into smaller peptides in an alkaline medium. • Pancreatic Lipase: Hydrolyses emulsified fats into fatty acids and glycerol.
Intestinal Juice (Succus Entericus)	Intestinal Gland walls	Contains terminal enzymes that finalize complete breakdown: • Complex Carbohydrates $\rightarrow$ Glucose • Proteins $\rightarrow$ Amino Acids • Fats $\rightarrow$ Fatty Acids + Glycerol

Crucial Board Distinction: Contrast Pepsin (works in acidic pH in stomach) with Trypsin (works in alkaline pH in small intestine). Both are protein-digesting proteases!

Villi — Structural Design of the Small Intestine for Absorption

Direct Board Question (3 Marks): "How is the small intestine designed to absorb digested food? Mention three structural adaptations."

Three Cardinal Structural Adaptations for Absorption:

Tremendous Surface Area via Villi: The inner lining (mucosa) of the small intestine (jejunum and ileum) possesses millions of tiny, finger-like projections called Villi. Each epithelial cell of a villus further bears thousands of microscopic microvilli (brush border), increasing the absorptive surface area by nearly 300 to 600 times (equal to the area of a tennis court!).
Extensive Capillary Blood Network: Each villus is richly supplied with a dense mesh of thin-walled blood capillaries running close to the surface, ensuring rapid uptake of water-soluble glucose, amino acids, vitamins, and minerals.
Central Lacteal for Fat Transport: In the core of each villus lies a specialized lymphatic capillary called a lacteal. Insoluble fatty acids and glycerol are packaged into chylomicrons and absorbed into the lacteal, which eventually empties into the venous bloodstream.

Villus: large area + short transport distance

🧠 VILLI = “Very Increased Large Lining Interface” — think more area + blood supply = better absorption.

🩸 Fate of Absorbed Food (Assimilation): Absorbed nutrients are transported through the hepatic portal vein to the liver, and then circulated to every living cell where they are utilized for obtaining cellular energy (via respiration), tissue repair, and building new protoplasmic structures.

Large Intestine, Water Absorption & Egestion Regulation

Function of the Large Intestine: The unabsorbed and undigested food passes from the small intestine into the Large Intestine (caecum, colon, and rectum). No chemical digestion takes place here.

Step-by-Step Processing of Residual Waste:

Extensive Water Reabsorption: The extensive walls of the colon absorb most of the remaining water and essential mineral salts from the unabsorbed material.
Solid Waste Compaction: As water is progressively extracted, the remaining undigested residue solidifies into semisolid faeces.
Storage in Rectum: The compacted faecal matter is temporarily stored in the terminal chamber called the Rectum.
Egestion (Defecation): The periodic elimination of undigested waste matter from the body through the Anus is called Egestion.

Movement and final removal

🔒 Anal Sphincter Regulation: The exit of faecal waste through the anus is strictly controlled and guarded by the Anal Sphincter muscle, ensuring voluntary regulation of bowel evacuation.

⚠️ Board Concept Contrast — Egestion vs Excretion:
• Egestion: Discharge of undigested, unabsorbed food residues through the anus (part of digestive system).
• Excretion: Elimination of toxic metabolic wastes (like urea, uric acid, $CO_2$) produced inside cells (part of excretory system).

Respiration — Cellular Breakdown of Food & Energy Release

Direct Board Definition — Respiration: The biochemical process occurring within living cells by which organic nutrients (primarily glucose) are oxidatively broken down in a controlled step-by-step manner to release usable chemical energy in the form of ATP.

Breathing (External Respiration)

Physical mechanical process of inhaling oxygen-rich air and exhaling carbon dioxide-rich air.
Involves respiratory organs (nostrils, trachea, lungs, ribs, diaphragm).
Occurs outside the cells (extracellular).
No enzymes are involved; energy is consumed, not released.

Cellular Respiration (Internal Respiration)

Biochemical oxidation of glucose molecules inside cells to release energy.
Involves cellular cytoplasm and mitochondria.
Occurs inside the cells (intracellular).
Catalyzed by a series of specific enzymes; energy is trapped as ATP.

The Universal First Step — Glycolysis:

Occurs in the Cytoplasm of all living cells (both aerobic and anaerobic).
One 6-carbon glucose molecule ($C_6H_{12}O_6$) is cleaved into two 3-carbon molecules of Pyruvate ($CH_3COCOO^-$), releasing a small amount of energy.
This initial step does not require any oxygen!

🧠 Board Summary Formula: Breathing brings $O_2$ to cells and removes $CO_2$; Cellular Respiration uses $O_2$ to burn glucose and produce ATP.

Glucose Breakdown — The Three Metabolic Pathways

Highest-Frequency 3-5 Mark Board Question: "Describe the three pathways of glucose breakdown in living organisms. Draw a flow chart showing the products formed in each case."

Universal Initial Phase (in Cytoplasm):

$$\text{Glucose (6-Carbon)} \xrightarrow{\text{in Cytoplasm}} \text{Pyruvate (3-Carbon)} + \text{Energy}$$

Glucose → pyruvate → three routes

🧠 “Y-M-A” → Yeast = Alcohol, Muscle = Lactic acid, Aerobic = CO₂ + Water.

The Three Fates of Pyruvate:

Path 1 — Absence of Oxygen (Anaerobic / Fermentation in Yeast):
In yeast cells during fermentation, pyruvate is converted anaerobically into Ethanol (2-carbon), Carbon Dioxide ($CO_2$), and low energy (2 ATP).
$$\text{Pyruvate} \xrightarrow[\text{in Yeast}]{\text{Absence of } O_2} \text{Ethanol} + CO_2 + \text{Energy (2 ATP)}$$
Path 2 — Lack of Oxygen (in Human Skeletal Muscle Cells):
During vigorous running, sprinting, or heavy exercise, oxygen is consumed faster than blood can supply it. Skeletal muscle cells temporarily switch to anaerobic respiration, converting pyruvate into Lactic Acid (3-carbon) and energy.
$$\text{Pyruvate} \xrightarrow[\text{in Muscle Cells}]{\text{Lack of } O_2} \text{Lactic Acid} + \text{Energy}$$
Why do athletes experience severe muscle cramps? The rapid build-up and accumulation of lactic acid in muscle fibres causes painful localized cramps. A hot water bath or gentle massage restores blood circulation, brings oxygen, and breaks lactic acid down into $CO_2$ and $H_2O$.
Path 3 — Presence of Oxygen (Aerobic Respiration in Mitochondria):
In the presence of oxygen inside mitochondria, pyruvate undergoes complete oxidation, breaking down into Carbon Dioxide ($CO_2$), Water ($H_2O$), and a huge yield of energy (up to 38 ATP).
$$\text{Pyruvate} + O_2 \xrightarrow[\text{in Mitochondria}]{\text{Presence of } O_2} CO_2 + H_2O + \text{Energy (38 ATP)}$$

🎯 CBSE Flowchart Rule: Always write carbon count: Glucose (6C) $\rightarrow$ Pyruvate (3C) $\rightarrow$ Ethanol (2C) / Lactic Acid (3C) / $CO_2$ (1C).

Aerobic vs Anaerobic Respiration — Comprehensive Comparison

Direct Board Question (3-5 Marks): Differentiate between Aerobic Respiration and Anaerobic Respiration with balanced equations, energy yield, and cellular sites.

Feature	Aerobic Respiration	Anaerobic Respiration
Oxygen Requirement	Strictly occurs in the presence of dissolved/atmospheric oxygen.	Occurs in the total absence or acute deficit of oxygen.
Cellular Location	Initiates in Cytoplasm (glycolysis) and completes inside Mitochondria (Krebs cycle).	Occurs entirely within the Cytoplasm; mitochondria are not involved.
Degree of Oxidation	Complete oxidation of glucose into simple inorganic molecules ($CO_2 + H_2O$).	Incomplete oxidation of glucose into organic end products (Ethanol / Lactic Acid).
Energy Output (ATP Yield)	High energy yield: 36 to 38 ATP molecules per glucose molecule (~2870 kJ).	Low energy yield: only 2 ATP molecules per glucose molecule (~150 kJ).
End Products	$CO_2$, $H_2O$, and abundant ATP.	Ethanol + $CO_2$ (in yeast) OR Lactic Acid (in animal muscles) + low ATP.
Examples	Most higher plants, animals, birds, humans, aerobic bacteria.	Yeast (fermentation), parasitic tapeworms, anaerobic bacteria, overworked muscles.

⚡ Energy Disparity Fact: The release of energy in aerobic process is almost 18 to 19 times greater than in anaerobic process because all carbon-carbon bonds in glucose are completely broken down to $CO_2$.

ATP — The Universal Energy Currency of Living Cells

What is ATP? Adenosine Triphosphate (ATP) is the universal intracellular energy currency for all biological processes. The energy released during cellular respiration is immediately utilized to synthesize ATP from ADP (Adenosine Diphosphate) and inorganic phosphate ($P_i$).

Formation & Hydrolysis of ATP:

$$ADP + \text{Phosphate } (P_i) + \text{Energy} \longrightarrow ADP \sim P = \text{ATP}$$

Cellular energy transfer

🧠 ATP = “A Tiny Power-pack” — immediate usable cellular energy.

Energy Delivery Mechanism:

When the terminal phosphate linkage in ATP is broken using water (hydrolysis), an energy equivalent to $30.5\text{ kJ/mol}$ is released.
This released energy drives diverse endothermic (energy-consuming) cellular reactions in the body:
- Contraction of muscle proteins (enabling movement, heartbeat, breathing).
- Protein and nucleic acid synthesis for cellular growth and repair.
- Conduction of electrical nerve impulses along neurons.
- Active transport of ions and molecules across cell membranes against concentration gradients.

🔋 Battery Analogy (NCERT): Just as a battery can be used to obtain mechanical energy, light energy, or electrical energy, ATP provides stored chemical energy on demand for any cellular activity.

Human Respiratory System — Anatomy & Breathing Mechanism

Anatomical Sequence of Inhaled Air: Nostrils $\rightarrow$ Nasal Passage $\rightarrow$ Pharynx $\rightarrow$ Larynx $\rightarrow$ Trachea $\rightarrow$ Bronchi $\rightarrow$ Bronchioles $\rightarrow$ Alveolar Ducts $\rightarrow$ Alveoli (Air Sacs).

Key Protective Structures in the Respiratory Tract:

Nasal Cavity: Lined by fine mucus and microscopic cilia that filter out dust particles, microbes, and foreign debris, while warming and moistening incoming air.
Cartilaginous Rings in Trachea: The trachea (windpipe) is supported by C-shaped rings of hyaline cartilage. Board Question: What is the function of cartilage rings? They ensure that the air passage does not collapse when there is less air in it.

Air pathway

Physiological Mechanism of Breathing (Inhalation vs Exhalation):

Parameter	Inhalation (Inspiration)	Exhalation (Expiration)
Rib Cage Movement	External intercostal muscles contract, lifting ribs upward and outward.	Intercostal muscles relax, ribs move downward and inward.
Diaphragm Action	Diaphragm contracts and flattens downwards.	Diaphragm relaxes and returns to its dome-shaped resting position.
Chest Cavity Volume	Thoracic cavity volume increases.	Thoracic cavity volume decreases.
Intrapulmonary Pressure	Internal air pressure falls below atmospheric pressure; air rushes into lungs.	Internal air pressure rises above atmospheric pressure; air is pushed out of lungs.

🫁 Residual Volume of Air (NCERT Board Fact): During the breathing cycle, when air is taken in and let out, the lungs always retain a certain residual volume of air so that there is sufficient time for oxygen to be absorbed into blood and carbon dioxide to be released.

Alveoli — Structural Design for Maximum Gaseous Exchange

Direct Board Question (Classic 3-Marker): "How are the lungs designed in human beings to maximize the area for exchange of gases?"

Three Cardinal Structural Adaptations of Alveoli:

Immense Surface Area: The bronchiole branches terminate in millions of microscopic balloon-like air sacs called Alveoli (approx. 300-400 million in both human lungs). If spread out flat, the total alveolar surface area would cover roughly $80\text{ m}^2$ (about the size of a standard tennis court!), providing massive area for rapid gas diffusion.
Extremely Thin Respiratory Membrane: The alveolar wall is composed of a single layer of ultra-thin squamous epithelial cells ($<0.5\ \mu\text{m}$ thick), minimizing diffusion distance for gases.
Rich Capillary Network: Alveoli are enveloped by an extensive, dense mesh of microscopic thin-walled blood capillaries, ensuring immediate contact between air and circulating red blood cells.

Why alveoli are efficient

🧠 “3T” for alveoli: Tons of area, Thin wall, Tight capillary network.

Mechanism of Alveolar Gas Exchange:

Driven purely by differences in partial pressures (concentration gradient).
Oxygen Uptake: Inhaled alveolar air has high $pO_2$; deoxygenated capillary blood has low $pO_2$. Oxygen diffuses across the thin membrane into blood and binds to haemoglobin in RBCs.
$CO_2$ Release: Capillary blood returning from body tissues has high $pCO_2$; alveolar air has low $pCO_2$. $CO_2$ diffuses out of blood into alveoli and is exhaled.

Transport of Respiratory Gases ($O_2$ & $CO_2$) in Human Blood

Board Reason Question: "Why is a respiratory pigment necessary in large multicellular animals like humans? Why can blood plasma alone not carry all the oxygen needed?"

Oxygen Transport — The Role of Haemoglobin:

Low Solubility of Oxygen in Water: Oxygen has very low solubility in aqueous blood plasma. Only about 3% of oxygen is carried in physical solution dissolved in plasma.
Haemoglobin Pigment: The remaining 97% of oxygen is bound to the respiratory pigment Haemoglobin ($Hb$), a conjugated iron-containing protein packed inside Red Blood Cells (Erythrocytes).
Each haemoglobin molecule has four iron atoms, each capable of binding one molecule of oxygen reversibly to form Oxyhaemoglobin:
$$Hb + 4O_2 \underset{\text{in Tissues}}{\overset{\text{in Lungs}}{\rightleftharpoons}} Hb(O_2)_4$$
In lung capillaries where oxygen tension is high, haemoglobin binds $O_2$. In active tissues where oxygen tension is low, oxyhaemoglobin dissociates to release free $O_2$ for cellular respiration.

Carbon Dioxide ($CO_2$) Transport:

High Water Solubility: Carbon dioxide is roughly 20 to 25 times more soluble in water than oxygen.
Therefore, $CO_2$ is mostly transported in dissolved form in blood plasma as soluble Bicarbonate ions ($HCO_3^-$) (~70%), dissolved $CO_2$ in plasma (~7%), and bound to haemoglobin as Carbaminohaemoglobin (~23%).

⚠️ Carbon Monoxide ($CO$) Poisoning Danger: Haemoglobin has nearly 250 times greater affinity for Carbon Monoxide than for Oxygen! Inhaling smoke from burning coal in a closed room forms irreversible Carboxyhaemoglobin, choking cellular oxygen supply and causing painless asphyxiation and death.

Human Circulatory System — Blood, Heart & Blood Vessels

Circulatory Infrastructure: The human cardiovascular transport system consists of three coordinated components: (1) Circulating Fluid (Blood & Lymph), (2) Muscular Pumping Organ (Heart), and (3) Network of Conducting Tubes (Blood Vessels: Arteries, Veins, Capillaries).

Composition of Human Blood:

Blood Component	Proportion	Structure & Primary Physiological Function
Blood Plasma	~55% of blood	Pale yellow fluid matrix containing 90-92% water, plasma proteins (albumin, fibrinogen, globulin), glucose, amino acids, hormones, urea, and dissolved mineral ions. Transports food, $CO_2$, hormones, and nitrogenous wastes.
Red Blood Cells (RBCs / Erythrocytes)	~45% of blood	Biconcave disc-shaped, enucleated (in mature mammals) cells packed with iron-containing Haemoglobin. Specialize in transporting oxygen from lungs to all body tissues.
White Blood Cells (WBCs / Leucocytes)	<1% of blood	Nucleated, amoeboid defence cells (lymphocytes, phagocytes). Defend the body by engulfing foreign pathogens and producing neutralizing antibodies.
Blood Platelets (Thrombocytes)	<1% of blood	Tiny membrane-bound cell fragments derived from megakaryocytes. Circulate in blood and initiate clotting of blood at injury sites to prevent haemorrhage and entry of microbes.

🩸 Blood Clotting Mechanism: Platelets release thromboplastin, converting prothrombin into thrombin, which converts soluble fibrinogen into an insoluble fibrous mesh of fibrin that traps RBCs to plug the wound leak.

Four Chambers of the Human Heart & Complete Double Circulation

The Muscular Pumping Heart: A muscular organ roughly the size of a clenched fist, tilted slightly to the left in the thoracic cavity. It has four distinct chambers to completely prevent mixing of oxygen-rich blood with carbon dioxide-rich blood.

Detailed Step-by-Step Pathway of Blood Through the Four Chambers:

Deoxygenated Blood Collection: $CO_2$-rich blood from the entire body enters the thin-walled Right Atrium via the superior and inferior Vena Cava. The right atrium relaxes while receiving blood.
Entry into Right Ventricle: Right atrium contracts while the Right Ventricle relaxes, transferring blood through the one-way Tricuspid Valve.
Pumping to Lungs (Pulmonary Circuit): Right ventricle contracts, pumping deoxygenated blood through the Pulmonary Artery to both lungs for oxygenation.
Oxygenated Blood Returns: Fresh, $O_2$-rich blood from lungs returns via four Pulmonary Veins into the relaxing Left Atrium.
Entry into Left Ventricle: Left atrium contracts, transferring oxygenated blood into the thick muscular Left Ventricle through the Bicuspid (Mitral) Valve.
Systemic Pumping to Body: Left ventricle contracts powerfully, pumping oxygenated blood into the large main artery, the Aorta, which distributes it across the entire body.

Double circulation route

Double circulation: blood passes through the heart twice in one complete cycle — heart → lungs → heart and heart → body → heart.

🧠 “Right = Receive/Respire; Left = Launch” → right side receives deoxygenated blood and sends it to lungs; left side sends oxygenated blood to body.

❤️ Why Ventricular Walls are Thicker than Atrial Walls (Frequent 2-Marker):
Atria only pump blood into adjacent ventricles beneath them. Ventricles have to pump blood with great force over long distances to distant organs (right ventricle to lungs; left ventricle to the entire body). Hence, ventricles have much thicker, more muscular walls than atria, and the left ventricle has the thickest wall of all!

🔄 What is Double Circulation? (Crucial 3-5 Mark Board Concept):
In human beings, blood passes through the heart twice during one complete cycle through the body. This is known as Double Circulation:
1. Pulmonary Circulation: Right Ventricle $\rightarrow$ Pulmonary Artery $\rightarrow$ Lungs $\rightarrow$ Pulmonary Veins $\rightarrow$ Left Atrium.
2. Systemic Circulation: Left Ventricle $\rightarrow$ Aorta $\rightarrow$ Body Tissues $\rightarrow$ Vena Cava $\rightarrow$ Right Atrium.
Significance: Completely prevents mixing of oxygenated and deoxygenated blood, ensuring highly efficient oxygen delivery required to maintain constant warm-blooded body temperature (homeothermy).

Arteries, Veins & Capillaries — Structural & Functional Distinctions

Rule of Blood Vessels: Never define arteries and veins solely by oxygen content! Arteries carry blood AWAY from the heart; Veins carry blood TOWARDS the heart.

Characteristic	Arteries	Veins	Capillaries
Direction of Flow	Carry blood away from heart to body organs.	Carry blood from organs back to heart.	Connect terminal arterioles to venules inside tissues.
Nature of Blood	Carry oxygenated blood (Exception: Pulmonary artery carries deoxygenated blood).	Carry deoxygenated blood (Exception: Pulmonary veins carry oxygenated blood).	Site of continuous exchange between blood and tissue fluid.
Blood Pressure	Blood flows under high pressure with rhythmic spurts.	Blood flows under low pressure smoothly.	Blood flows slowly under very low pressure.
Vessel Wall	Thick, muscular, and highly elastic walls to withstand high blood pressure.	Thin, less muscular, less elastic walls.	Microscopically thin, one-cell thick endothelial layer.
Internal Lumen	Narrow lumen.	Wide, open lumen.	Extremely narrow lumen (RBCs pass in single file).
Internal Valves	Valves absent (high pressure prevents backflow).	Internal semilunar valves present to ensure unidirectional blood flow towards heart.	Valves absent.

💡 Board Trap Alert: Remember both exceptions: Pulmonary Artery carries deoxygenated blood to lungs; Pulmonary Veins carry oxygenated blood to left atrium.

Blood Pressure, Heart Valves & Lymph (Tissue Fluid)

Blood Pressure (BP) Fundamentals: The lateral force that circulating blood exerts against the elastic wall of an artery is called Blood Pressure. It is measured using an instrument called a Sphygmomanometer.

Systolic Pressure (Contraction Phase)

Pressure of blood inside artery during ventricular contraction (systole).
Normal standard human value: $120\text{ mm of Hg}$.

Diastolic Pressure (Relaxation Phase)

Pressure in artery during ventricular relaxation (diastole).
Normal standard human value: $80\text{ mm of Hg}$.
Standard recorded BP: $120/80\text{ mm Hg}$.

Hypertension (High Blood Pressure):

Caused by the constriction of tiny arterioles, which leads to increased resistance to blood flow.
Persistent high blood pressure ($>140/90\text{ mm Hg}$) can cause rupture of delicate internal blood vessels (cerebral haemorrhage / stroke) and heart attack.

Lymph returns tissue fluid to blood

Lymph (Tissue Fluid / Extracellular Fluid):

How it Forms: Through pores present in capillary walls, some amount of blood plasma, proteins, and white blood cells leak out into intercellular tissue spaces to form tissue fluid (lymph).
Difference from Blood: Lymph is similar to blood plasma but is colourless and contains significantly less protein. RBCs and platelets are completely absent.
Functions of Lymphatic System:
- Carries digested and absorbed fats from the small intestine via central lacteals.
- Drains excess interstitial extracellular fluid back into the major venous bloodstream, preventing oedema (tissue swelling).
- Contains lymphocytes in lymph nodes that trap and destroy invading bacteria.

Transportation in Plants — Xylem vs Phloem Comparison

Why Plants Need Specialized Transport Systems: Plants are stationary, do not move, and have a very large proportion of dead supporting cells (sclerenchyma, tracheids, vessels). As a result, plants have relatively low energy needs and can use comparatively slow transport systems compared to active animals.

Parameter	Xylem Tissue	Phloem Tissue
Substances Transported	Water and dissolved inorganic mineral salts (nitrogen, phosphorus, potassium).	Soluble products of photosynthesis (Sucrose), amino acids, and plant hormones.
Direction of Transport	Strictly Unidirectional (upward from roots to stems, leaves, and buds).	Bidirectional / Multidirectional (from leaves/storage organs to growing points both up and down).
Conducting Elements	Tracheids and Vessels (elongated hollow dead tubes with lignified walls).	Sieve tubes with perforated sieve plates, supported by living companion cells.
Living / Dead Tissue	Composed mostly of dead cells (xylem vessels, tracheids, fibres; only xylem parenchyma is living).	Composed mostly of living cells (sieve tubes, companion cells, phloem parenchyma; only phloem fibres are dead).
Energy Requirement	Transport occurs passively driven by physical forces (root pressure and transpiration pull); no ATP is consumed.	Translocation is an active metabolic process that directly consumes cellular energy (ATP).

🌿 Board Distinction: Always state the driving force — Xylem relies on passive physical gradients (transpiration pull); Phloem relies on active osmotic pressure created by ATP!

Water Transport — Root Pressure & Transpiration Pull

Ascent of Sap in Xylem: The upward movement of water and dissolved minerals from roots to aerial parts against gravity is achieved through two complementary physical mechanisms:

1. Root Pressure (Active Ion Uptake):

Cells of root epidermis in contact with soil actively absorb inorganic mineral ions using ATP.
This creates a concentration difference (osmotic gradient) between root tissue and soil water.
Water continuously moves into root xylem by osmosis, creating hydrostatic root pressure that pushes water upward.
Limitation: Root pressure is relatively weak; it is significant primarily at night and in short herbaceous plants, but insufficient to lift water to the top of tall canopy trees (like Eucalyptus or Redwood).

2. Transpiration Pull (Suction Force):

Definition of Transpiration: The loss of water in the form of water vapour from aerial parts (mainly stomata of leaves) of the plant.
Mechanism of Transpiration Pull (The Suction Pump):
1. Evaporation of water molecules from stomata of leaves creates a strong negative suction pressure in leaf xylem.
2. Because water molecules possess high cohesive (attraction between water molecules) and adhesive forces (attraction to xylem walls), an unbroken, continuous column of water is formed inside xylem vessels from leaves all the way down to roots.
3. This cohesive tension, termed Transpiration Pull, acts as a powerful suction force pulling water upward from roots even in trees over 100 metres tall!

Water movement in a tall plant

⭐ Day: transpiration pull dominates. Night: root pressure becomes relatively more important.

⭐ Dual Benefits of Transpiration:
1. Generates upward pull for absorption and distribution of water and dissolved minerals.
2. Helps in temperature regulation (evaporative cooling), preventing leaf tissues from scorching under direct sunlight.

Phloem Translocation — Active Transport of Photosynthetic Food

Direct Board Definition — Translocation: The transport of soluble products of photosynthesis (primarily sucrose), along with amino acids and phytohormones, from the leaves (or storage organs) to other parts of the plant through the Phloem is called Translocation.

Step-by-Step Mechanism of Phloem Translocation (Requires ATP):

Active Loading of Sugar: Photosynthetic sucrose synthesized in leaves is actively loaded into sieve tubes of phloem tissue using energy derived from ATP.
Osmotic Entry of Water: Accumulation of sucrose inside sieve tubes increases solute concentration, lowering water potential. Water moves into the phloem from adjacent xylem vessels by osmosis.
Hydrostatic Pressure Generation: This influx of water creates high osmotic hydrostatic pressure inside the phloem sieve tube.
Mass Flow to Sink: The high pressure drives the food solution along sieve tubes towards regions of lower osmotic pressure (sinks, such as roots, fruits, seeds, and actively growing shoots/buds).
Active Unloading: At the destination site, sucrose is actively unloaded into consuming or storing cells, and water returns to adjacent xylem.

Source → sink concept

Key sequence: sucrose loading → water enters phloem → pressure develops → food moves toward lower-pressure sink.

🌸 Seasonal Reversal (NCERT Board Example): In early spring, sugar stored in root or stem tissues is actively mobilized and translocated through phloem up to the dormant buds, which need energy to grow into new leaves and flowers!

Excretion — Metabolic Waste Removal & Osmoregulation

Direct Board Definition — Excretion: The biological process of eliminating toxic nitrogenous waste products (urea, uric acid) and excess substances produced during metabolic activities from the body of an organism is called Excretion.

Why Excretion is Critical for Survival:

During metabolic reactions (protein catabolism, nucleic acid breakdown), toxic nitrogenous by-products such as ammonia, urea, and uric acid are continuously generated.
If these nitrogenous wastes accumulate in blood, they disrupt intracellular pH, poison cellular enzymes, cause metabolic acidosis, organ failure, and death.
Osmoregulation: Excretory organs also regulate the precise balance of water and dissolved mineral salts (osmotic balance) in blood and body fluids.

Excretion as the waste-removal pathway

Excretion in Unicellular Organisms (e.g. Amoeba)

No specialized excretory organs.
Toxic soluble wastes ($CO_2$, ammonia) are removed by simple diffusion across the cell membrane directly into surrounding water.
Contractile vacuoles expel excess osmotic water.

Excretion in Complex Animals (e.g. Humans)

Complex multicellular body with trillions of cells located far from the exterior.
Possess a highly specialized Human Excretory System (Kidneys, Ureters, Bladder, Urethra) capable of filtering blood and generating concentrated urine.

Human Excretory System — Organs, Route & Architecture

Anatomy of Human Excretory System: The human urinary excretory system consists of: (1) A pair of Kidneys, (2) A pair of Ureters, (3) A Urinary Bladder, and (4) A Urethra.

Organ	Location & Structure	Excretory Function
Kidneys	Two reddish-brown, bean-shaped organs located in the abdomen, one on either side of the backbone, protected by lower ribs.	Filter circulating blood received from Renal Arteries to remove nitrogenous metabolic wastes (urea, uric acid) and produce urine.
Ureters	Pair of long, narrow, muscular distensible tubes emerging from the hilum of each kidney.	Propel urine downwards from kidneys to the urinary bladder by peristaltic muscular contractions.
Urinary Bladder	Pear-shaped, hollow muscular reservoir located in the lower pelvic cavity.	Stores urine temporarily until pressure dictates micturition. Because its walls are muscular and under nervous control, urination is voluntary.
Urethra	Short muscular tube extending from urinary bladder neck to exterior orifice.	Discharges urine outside the body, guarded by the urethral sphincter.

Urine pathway

🧠 K-U-B-U → Kidney → Ureter → Bladder → Urethra.

🫘 Blood Vessels to Kidney:
• Renal Artery: Brings oxygenated blood containing toxic urea and nitrogenous wastes into the kidney for filtration.
• Renal Vein: Carries clean, deoxygenated filtered blood away from the kidney back to the inferior vena cava.

Nephron — Microscopic Structure & The 3 Steps of Urine Formation

Functional Unit of Kidney: The functional filtration unit of the human kidney is the microscopic tubular structure called the Nephron. Each human kidney contains approximately 1 to 1.2 million nephrons packed together.

Anatomy of a Single Nephron:

Bowman's Capsule: A cup-shaped double-walled sac located in the renal cortex.
Glomerulus: A dense knot of microscopic blood capillaries nestled inside Bowman's capsule, fed by the afferent arteriole and drained by the narrower efferent arteriole.
Renal Tubule: A long, coiled tube divided into:
- Proximal Convoluted Tubule (PCT)
- Henle's Loop (hairpin U-shaped tube dipping into renal medulla)
- Distal Convoluted Tubule (DCT)
Collecting Duct: Receives urine from multiple DCTs and empties into the renal pelvis.

Simplified nephron map

Nephron logic: filter first → keep useful substances → retain/adjust water → remove remaining waste as urine.

🧠 F-R-E = Filter → Reabsorb useful material → Excrete the remainder.

The 3 Sequential Steps of Urine Formation (High-Yield Board Question):

1. Glomerular Ultrafiltration:
Because the efferent arteriole exiting the glomerulus is narrower than the incoming afferent arteriole, blood flows through the glomerulus under extremely high hydrostatic pressure. Non-cellular fluid containing water, glucose, amino acids, urea, uric acid, and mineral salts is forced across the capillary walls into Bowman's capsule to form Initial Filtrate (Nephric Filtrate). Large plasma proteins and blood cells cannot pass and remain in the bloodstream.
2. Selective Tubular Reabsorption:
As the initial filtrate flows down the convoluted tubule, surrounded by peritubular capillaries, all essential substances are selectively reabsorbed back into the blood:
- 100% of Glucose and Amino Acids are actively reabsorbed.
- Major amount of water is reabsorbed by osmosis.
- Major fraction of mineral salts ($Na^+, Cl^-$) are actively reabsorbed based on bodily requirements.
3. Tubular Secretion:
Cells of the renal tubule actively secrete additional wastes ($K^+$, $H^+$, ammonium, drug residues) from peritubular blood into the tubular lumen to maintain precise blood pH and electrolyte balance. The remaining fluid entering the collecting duct is concentrated Urine.

Regulation of Urine Volume — Hormonal & Osmotic Factors

Direct Board Question (2-3 Marks): "The daily initial filtrate produced in human kidneys is about $180\text{ litres}$, but the volume of urine excreted per day is only $1$ to $2\text{ litres}$. Explain why. How is the amount of urine regulated?"

The $180\text{ Litre}$ Filtrate Paradox:

Both kidneys together filter approximately $180\text{ litres}$ of initial filtrate every day!
However, healthy humans excrete only $1$ to $2\text{ litres}$ of actual urine in a 24-hour period.
Scientific Explanation: More than $99\%$ of the initial filtrate is selectively reabsorbed by the renal tubules back into the blood capillaries surrounding the nephrons.

Two Major Factors Regulating the Amount of Urine Produced:

Amount of Excess Water in the Body:
If a person drinks plenty of water, blood osmotic pressure decreases, less water is reabsorbed by nephron tubules, and a large volume of dilute urine is excreted. If dehydrated (e.g. during summer or fasting), nephrons reabsorb almost all water, producing a small volume of dark, concentrated urine.
Amount of Dissolved Nitrogenous Wastes to be Excreted:
When there is a higher concentration of urea and salts in the body (e.g. after a high-protein diet), more water is required to dissolve and excrete these toxic solutes safely, increasing urine volume.

🧠 Hormonal Control (Board Enrichment): The antidiuretic hormone (ADH / Vasopressin) secreted by the pituitary gland increases water reabsorption in collecting ducts during water deprivation. In summer, sweating also excretes water, reducing urinary volume.

Dialysis (Artificial Kidney) — Principle, Procedure & Limitations

Kidney Failure (Renal Failure): Kidneys may fail due to severe infections, physical injury, chronic diabetes, or restricted blood supply. Renal failure leads to rapid accumulation of toxic urea and fluid in blood (uremia), which is fatal unless treated by a Kidney Transplant or Haemodialysis.

What is an Artificial Kidney (Haemodialysis)?

An artificial kidney is an external clinical device used to remove nitrogenous metabolic waste products from blood through the physical principle of Dialysis.
It consists of numerous cellophane tubes with semi-permeable membranes suspended in a sterile tank filled with dialysing fluid.

Basic dialysis principle

Unlike the normal nephron, dialysis removes wastes by diffusion but does not perform normal tubular reabsorption.

Working Mechanism of Haemodialysis:

Blood drawn from the patient's convenient artery is cooled to $0^\circ\text{C}$ and mixed with an anticoagulant (heparin) to prevent clotting.
The blood is pumped through the coiled semi-permeable cellophane tubes of the dialyser.
Dialysing Fluid Composition: The dialysing fluid has the exact same osmotic pressure and electrolyte composition as normal healthy blood plasma, except that it completely lacks nitrogenous wastes (urea).
Diffusion of Waste: As the patient's blood flows through the tubes, nitrogenous wastes (urea, uric acid) diffuse rapidly across the semi-permeable membrane down their concentration gradient into the dialysing fluid.
Clean, purified blood leaves the dialyser, is warmed to body temperature, mixed with anti-heparin, and pumped back into the patient through a vein.

⚠️ Crucial Board Distinction — Artificial Kidney vs Natural Kidney:
What is the fundamental difference between an artificial kidney and a natural kidney?
In a natural human kidney, filtration is followed by extensive selective tubular reabsorption of useful nutrients (glucose, amino acids, water). In an artificial kidney (dialyser), NO tubular reabsorption takes place!

Excretion in Plants — Multiple Alternative Strategies

Unique Excretory Strategies of Plants: Plants do not possess any specialized excretory organs or circulatory waste disposal system like animals. They employ diverse alternative strategies to eliminate or isolate metabolic wastes:

Plant Waste Product	Metabolic Source	Specific Excretory Mechanism & Route
Oxygen ($O_2$)	By-product of daylight photosynthesis	Diffuses out into the atmosphere through open stomatal pores of leaves and lenticels of stems.
Carbon Dioxide ($CO_2$)	By-product of cellular respiration	Diffuses out through stomata and lenticels (especially at night when photosynthesis is absent).
Excess Water ($H_2O$)	Root absorption & metabolism	Eliminated into the atmosphere as water vapour through stomata by Transpiration.
Dead Tissue Shedding	Cellular waste accumulation	Many waste products are stored in cellular vacuoles of dying leaves, old bark, and senescent twigs that turn yellow and drop off (leaf fall / abscission).
Resins and Gums	Metabolic waste residues	Stored permanently in non-functional old xylem (heartwood) of woody trunks (e.g. pine resin, acacia gum).
Soil Secretion	Organic acids and minerals	Plants actively excrete some chemical waste substances into the surrounding soil through their root systems.

🌱 Board One-Marker Alert: If asked "Where are resins and gums stored in plants?", always write in old xylem!

Chapter-Wide Master Process Map — The Interconnected Web of Life

The Interdependent Loop of Life: The four cardinal life processes do not function in isolation — they form an unbroken, self-sustaining biochemical loop that keeps cells alive and organized.

Life Process	Primary Biological Input	Central Cellular Transformation	Output / Beneficiary Process
1. Nutrition	Food from external environment ($CO_2+H_2O$ for plants; organic matter for animals).	Digestive enzymes hydrolyse food into absorbable micro-nutrients (glucose, amino acids, fatty acids).	Supplies chemical fuel to Respiration; supplies building blocks to growing tissues.
2. Respiration	Glucose from Nutrition + $O_2$ from respiratory organs.	Cellular mitochondria oxidatively cleave pyruvate to generate ATP.	Powers energy-requiring active transport in Phloem, cellular repair, nerve impulses, and muscular motion.
3. Transportation	Absorbed nutrients, respiratory gases ($O_2, CO_2$), hormones, and metabolic wastes.	Heart and blood vessels in animals; Xylem and Phloem in plants distribute molecules rapidly.	Brings fuel and $O_2$ to distant cells; sweeps toxic wastes away to excretory organs.
4. Excretion	Toxic nitrogenous wastes (urea, uric acid) and excess minerals from metabolism.	Nephrons filter blood, selectively reabsorb nutrients, and excrete concentrated urine.	Maintains homeostatic blood pH, osmotic volume, and clean non-toxic internal cellular environment.

How all four life processes connect

🧠 N-R-T-E loop: Nutrition supplies fuel/material → Respiration releases usable energy → Transport distributes materials and collects wastes → Excretion removes wastes.

🧠 Mnemonic for Board Revision — The N-R-T-E Cycle:
• Nutrition supplies the fuel and raw material.
• Respiration breaks down fuel to release energy as ATP.
• Transportation moves fuel, oxygen, and wastes to wherever needed.
• Excretion cleanses internal tissues by throwing toxic wastes out!

NCERT Exercises — Questions + Answers

Complete end-of-chapter exercise set

1. The kidneys in human beings are a part of the system for (a) nutrition (b) respiration (c) excretion (d) transportation.

ANSWER(c) Excretion. Kidneys filter blood and remove nitrogenous wastes by forming urine.

2. The xylem in plants are responsible for (a) transport of water (b) transport of food (c) transport of amino acids (d) transport of oxygen.

ANSWER(a) Transport of water. Xylem conducts water and minerals from roots to other parts.

3. The autotrophic mode of nutrition requires (a) CO₂ and water (b) chlorophyll (c) sunlight (d) all of the above.

ANSWER(d) All of the above.

4. Breakdown of pyruvate to give carbon dioxide, water and energy takes place in (a) cytoplasm (b) mitochondria (c) chloroplast (d) nucleus.

ANSWER(b) Mitochondria. Aerobic breakdown of pyruvate occurs in mitochondria.

5. How are fats digested in our bodies? Where does this process take place?

ANSWERFat digestion occurs mainly in the small intestine. Bile salts emulsify large fat globules into smaller droplets, increasing surface area for enzymes. Pancreatic lipase then breaks fats down; intestinal digestion completes the process to fatty acids and glycerol.

6. What is the role of saliva in the digestion of food?

ANSWERSaliva moistens food and contains salivary amylase, which begins digestion of starch into simpler sugars.

7. What are the necessary conditions for autotrophic nutrition and what are its by-products?

ANSWERAutotrophic nutrition by photosynthesis requires CO₂, water, sunlight and chlorophyll. The main carbohydrate product is formed for the plant's food/energy needs and oxygen is released as a by-product.

8. What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode.

ANSWERAerobic respiration uses oxygen and gives CO₂, water and much more energy. Anaerobic pathways do not require oxygen and give less energy; yeast can produce ethanol + CO₂, while human muscles can produce lactic acid when oxygen is insufficient.

9. How are the alveoli designed to maximise the exchange of gases?

ANSWERAlveoli provide a very large surface area, have thin and delicate walls and are surrounded by a rich network of blood capillaries. Their moist surface and close blood supply make diffusion efficient.

10. What would be the consequences of a deficiency of haemoglobin in our bodies?

ANSWERHaemoglobin carries oxygen in blood. Its deficiency reduces oxygen-carrying capacity, so tissues may receive less oxygen for cellular respiration and energy production, leading to weakness/fatigue and reduced performance.

11. Describe double circulation of blood in human beings. Why is it necessary?

ANSWERDeoxygenated blood travels from body → right side of heart → lungs. Oxygenated blood returns lungs → left side of heart → body. Thus blood passes through the heart twice in one cycle. Separation prevents mixing of oxygenated and deoxygenated blood and supports efficient oxygen delivery in birds and mammals.

12. What are the differences between the transport of materials in xylem and phloem?

ANSWERXylem transports water and minerals, mainly upward from roots, using root pressure and transpiration pull. Phloem transports soluble food such as sucrose and other substances; translocation can occur in both directions according to plant needs and requires energy.

13. Compare the functioning of alveoli in lungs and nephrons in kidneys with respect to their structure and functioning.

ANSWERBoth have specialised structures closely associated with thin blood vessels and exchange/processing substances from blood. Alveoli are thin-walled air sacs for gas exchange; nephrons are filtration units in kidneys where blood is filtered and useful substances are selectively reabsorbed while wastes remain for urine formation.

PYQ Practice

Board-style questions • reveal answers after thinking

1 MARK

Name the process by which plants lose water vapour through stomata.

Answer
Transpiration.

1 MARK

Where does glycolysis/initial glucose breakdown occur?

Answer
Cytoplasm. Glucose is first broken into pyruvate there.

2 MARKS

Why are multicellular organisms dependent on specialised transport systems?

Answer
Many cells are not in direct contact with the external environment, so diffusion alone cannot rapidly supply oxygen/nutrients or remove wastes across long distances.

2 MARKS

Differentiate between arteries and veins.

Answer
Arteries carry blood away from the heart and have thick elastic walls. Veins carry blood toward the heart and have valves to prevent backflow.

3 MARKS

Explain why the small intestine is the main site of absorption.

Answer
It is long and extensively coiled; digestion is completed there; its inner surface has numerous villi that greatly increase surface area and have rich blood supply for transporting absorbed nutrients.

3 MARKS

Explain the three pathways of pyruvate breakdown.

Answer
With oxygen: pyruvate is broken down in mitochondria to CO₂ + H₂O with more energy. In yeast without oxygen: ethanol + CO₂ + less energy. In oxygen-deficient muscles: lactic acid + less energy.

3 MARKS

Why is separation of oxygenated and deoxygenated blood necessary in mammals?

Answer
Mammals have high energy demands for maintaining body temperature. Complete separation prevents mixing and ensures tissues receive efficiently oxygenated blood.

5 MARKS

Explain the formation of urine in a nephron.

Answer
Blood enters the capillary cluster; filtration occurs into Bowman's capsule. The filtrate passes through the tubule. Useful substances such as glucose, amino acids, salts and much water are selectively reabsorbed. Remaining dissolved wastes and excess water form urine, which passes to the ureter and bladder.

5 MARKS

Explain transportation of water in plants.

Answer
Roots absorb ions and water enters root xylem, creating root pressure. Water moves through continuous xylem vessels. During the day, evaporation through stomata creates transpiration pull, which provides the major upward driving force. Water and dissolved minerals reach leaves and other parts.

Competency-Based Questions

CBSE Board practice items with step-by-step solutions

TERM Items (1–28) SAS Case Questions (29–38) CBSE Item Bank (39–53)

SECTION 1

Learning Objective Practice Items

Topic Focus

Explain the process of absorption of $\text{CO}_2$ & $\text{H}_2\text{O}$, in order to understand how autotrophs obtain substances necessary for nutrition

CBQ 1 • Raw Materials for Photosynthesis

The schematic process of photosynthesis in green plants involves light energy, carbon dioxide, water, oxygen, and glucose. Which statement correctly describes how autotrophs obtain their essential raw materials?

(a) Plants absorb $\text{CO}_2$ from air and $\text{H}_2\text{O}$ from the soil as raw materials and convert them into glucose

(b) Plants absorb $\text{CO}_2$ from the soil and $\text{H}_2\text{O}$ from air as raw materials and convert them into glucose

(d) Plants absorb $\text{O}_2$ from air and minerals from the soil as raw materials and convert them into heat energy

Correct Answer: Option (a)

Plants absorb $\text{CO}_2$ from air and $\text{H}_2\text{O}$ from the soil

Terrestrial plants take in gaseous carbon dioxide from the atmosphere through tiny epidermal pores called stomata, while water and dissolved minerals (nitrogen, phosphorus, iron, magnesium) are absorbed from the soil by root hairs via osmosis.

CBQ 2 • Role of $\text{CO}_2$ in Plant Survival

A student sets up an experiment with two identical potted plants. Both pots were placed in the garden and watered properly. Pot 1 was kept open to air, while Pot 2 was sealed inside an airtight bell jar with caustic soda (potassium hydroxide / $\text{KOH}$ or $\text{NaOH}$). Caustic soda absorbs carbon dioxide from the surrounding air. After 2 days, the plant in Pot 1 is healthy while the plant in Pot 2 sheds leaves and droops. What is the primary reason for this observation?

(a) Lack of nutrients in the soil

(b) Absence of oxygen for survival

(d) Absorption of light by caustic soda restricting growth

Correct Answer: Option (c)

Inability to perform photosynthesis

Caustic soda absorbs all the carbon dioxide inside the sealed jar. In the absence of $\text{CO}_2$, the plant cannot perform the carbon-fixation reaction of photosynthesis, starving it of carbohydrates and leading to drooping and leaf shedding.

Topic Focus

Explain the process of conversion of $\text{CO}_2$ & $\text{H}_2\text{O}$ into carbohydrates, in order to understand how autotrophs obtain nutrition

CBQ 3 • Chemical Equation of Photosynthesis

Which equation represents the balanced chemical conversion of carbon dioxide and water into carbohydrates in green plants during photosynthesis?

(a) $6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow[\text{Heat energy}]{\text{Chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 + 12\text{H}_2\text{O}$

(b) $6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow[\text{Sunlight}]{\text{Chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 + 12\text{H}_2\text{O}$

(c) $6\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow[\text{Sunlight}]{\text{Chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 + 6\text{H}_2\text{O}$

(d) $16\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow[\text{Heat energy}]{\text{Chlorophyll}} \text{C}_6\text{H}_{12} + 6\text{O}_2 + 6\text{H}_2\text{O}$

Correct Answer: Option (c)

$$6\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow[\text{Sunlight}]{\text{Chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 + 6\text{H}_2\text{O}$$

During photosynthesis, chlorophyll absorbs light energy, which splits $12\text{H}_2\text{O}$ molecules (photolysis) to release oxygen and provide reducing equivalents that reduce $\text{CO}_2$ into glucose, regenerating 6 water molecules.

CBQ 4 • Moll's Half-Leaf Experiment

A student destarches a potted plant by keeping it in darkness for 3 days. Half of a destarched leaf is placed inside a wide-mouthed bottle containing caustic potash ($\text{KOH}$, which absorbs $\text{CO}_2$), while the other half remains exposed to air. After 5 hours of sunlight exposure, the leaf is boiled in alcohol and tested with iodine. The part inside the bottle shows no colour change, whereas the outside portion turns blue-black. What does this experiment prove?

(a) Carbon dioxide is directly linked with the colour of leaf

(b) Carbon dioxide is necessary for preparing carbohydrate (starch)

(d) Lack of carbon dioxide slows the process of photosynthesis

Correct Answer: Option (b)

Carbon dioxide is necessary for preparing carbohydrate

The portion enclosed with $\text{KOH}$ lacked $\text{CO}_2$ and therefore could not synthesize starch, showing a negative iodine test. The exposed half received $\text{CO}_2$, synthesized starch, and gave a positive blue-black colour with iodine.

Topic Focus

List and explain the strategies employed by heterotrophs to take up food, in order to understand how heterotrophs obtain nutrition

CBQ 5 • Saprophytic Nutrition in Fungi

Bread moulds (Rhizopus) and other fungi grow rapidly on moist stale bread. How do these organisms obtain nutrition from the substrate?

(a) By eating the bread on which it is growing

(b) By using nutrients from the bread to prepare their own food

(d) By allowing other organisms to grow on the bread and then consuming them

Correct Answer: Option (c)

By breaking down the nutrients outside the body and then absorbing them (Saprophytic nutrition)

Fungi secrete digestive enzymes externally onto decaying organic matter to break down complex polymers (like starch and proteins) into simple, soluble molecules, which are then absorbed through fungal hyphae.

CBQ 6 • Phagocytosis in Amoeba

Amoeba takes in food particles using temporary finger-like extensions of the cell surface (pseudopodia) which fuse over the food particle to form a food vacuole. How is this process advantageous for Amoeba?

(a) Capturing of food takes less time

(b) Complex food can be digested easily inside an isolated compartment

(d) Fast distribution of nutrition within the body

Correct Answer: Option (b)

Complex food can be digested easily inside a food vacuole

Formation of a food vacuole creates an enclosed digestive vesicle inside which lysosomal enzymes are secreted to break down complex food into simple diffusable substances without damaging other cellular organelles.

Topic Focus

Illustrate the process involved in human digestive system, in order to explain how humans obtain nutrients from food

CBQ 7 • Site of Digestion Initiation

At which organ of the human alimentary canal does the chemical breakdown and digestion of food begin?

(a) Mouth due to the presence of salivary amylase in saliva

(b) Oesophagus that moves the food in gut

(d) Small intestine which helps in mixing food with digestive juices

Correct Answer: Option (a)

Mouth due to the presence of salivary amylase in saliva

Chemical digestion begins in the mouth (buccal cavity), where the enzyme salivary amylase (ptyalin) present in saliva breaks down complex starch molecules into simple disaccharide sugars (maltose) at pH ~6.8.

CBQ 8 • Function of Intestinal Villi

The inner lining of the small intestine possesses millions of tiny finger-like projections called villi supplied richly with blood vessels and lacteals. What will likely happen if the total surface area and number of villi increases in the intestine?

(a) Increase in the absorption of digested food into the bloodstream

(b) Fast elimination of waste from the body

(d) Fast breakdown of larger food particles into smaller ones

Correct Answer: Option (a)

Increase in the absorption of digested food

Villi vastly increase the effective absorptive surface area of the ileum. Each villus contains a dense network of blood capillaries and a central lymph vessel (lacteal) to rapidly absorb amino acids, glucose, and fatty acids into circulation.

Topic Focus

List the enzymes & their functions involved in human digestive system, in order to understand breakdown of food in humans

CBQ 9 • Action of Salivary Amylase

An in-vitro biochemical test is set up with:$$\text{Saliva} + \text{Starch suspension (in test tube at } 37^\circ\text{C)}$$What is the biochemical outcome of this enzymatic reaction after incubation?

(a) Saliva will convert starch into complex fat molecules

(b) Saliva will convert starch into complex sugar molecules

(d) Saliva will breakdown starch into simple protein molecules

Correct Answer: Option (c)

Saliva will breakdown starch into simple sugar molecules

Salivary amylase hydrolyses polysaccharide starch into maltose (a disaccharide sugar). Consequently, the mixture gradually loses its ability to produce a blue-black colour with iodine and gives a positive Benedict’s reducing sugar test.

CBQ 10 • Activation of Pepsin by Gastric Acid

A student sets up an experiment to study the role of gastric enzymes in protein digestion using two test tubes:
• Test tube A: $\text{Egg white suspension} + \text{pepsin}$
• Test tube B: $\text{Egg white suspension} + \text{pepsin} + \text{dilute HCl}$
In which test tube will significant digestion of protein occur, and why?

(a) Test tube A as pepsin will breakdown into simple molecules

(b) Test tube B as HCl provides the acidic medium required to activate pepsin

(d) Test tube B as HCl alone breaks down protein into simple molecules

Correct Answer: Option (b)

Test tube B as HCl activates pepsin for protein breakdown

Pepsin is an endopeptidase that requires a strongly acidic environment (pH ~1.5–2.0) provided by hydrochloric acid ($\text{HCl}$) to function optimally and convert complex proteins into soluble peptones and proteoses.

Topic Focus

Outline and explain the ways of breakdown of glucose by various pathways, in order to explain how energy is obtained in organisms

CBQ 11 • Anaerobic Fermentation in Yeast

The breakdown of glucose in yeast is represented by the pathway:$$\text{Glucose (6-C)} \xrightarrow{\text{In cytoplasm}} \text{Pyruvate (3-C)} + \text{Energy} \xrightarrow{\text{In yeast}} \text{Ethanol (2-C)} + \text{CO}_2 + \text{Energy}$$Under which physiological condition does this metabolic pathway take place?

(a) In the presence of oxygen

(b) In the absence of oxygen (anaerobic conditions)

(d) In the absence of carbon dioxide

Correct Answer: Option (b)

In the absence of oxygen (Anaerobic respiration / Fermentation)

Yeast performs anaerobic respiration (alcoholic fermentation) in the absence of oxygen, decarboxylating pyruvate into acetaldehyde and then reducing it to ethanol with release of $\text{CO}_2$ and a modest yield of 2 ATP per glucose.

CBQ 12 • Respiration in Muscle Cells During Sprinting

Which metabolic pathway occurs in the skeletal muscle cells of an athlete who is performing an intense 100-metre sprint when oxygen supply is insufficient?

(a) $\text{Glucose} \xrightarrow{\text{Cytoplasm}} \text{Pyruvate} \xrightarrow{\text{Absence of oxygen}} \text{Ethanol} + \text{CO}_2 + \text{Energy}$

(b) $\text{Glucose} \xrightarrow{\text{Cytoplasm}} \text{Pyruvate} \xrightarrow{\text{Lack of oxygen (muscle cells)}} \text{Lactic acid} + \text{Energy}$

(c) $\text{Glucose} \xrightarrow{\text{Cytoplasm}} \text{Pyruvate} \xrightarrow{\text{Presence of oxygen (mitochondria)}} \text{CO}_2 + \text{H}_2\text{O} + \text{Energy}$

(d) $\text{Glucose} \xrightarrow{\text{Cytoplasm}} \text{Pyruvate} \xrightarrow{\text{Absence of oxygen}} \text{Lactic acid} + \text{Ethanol} + \text{Energy}$

Correct Answer: Option (b)

$\text{Glucose} \rightarrow \text{Pyruvate} \rightarrow \text{Lactic acid} + \text{Energy}$

During sudden vigorous activity, muscle cells consume $\text{O}_2$ faster than the respiratory and circulatory systems can deliver it. Under this lack of oxygen, pyruvate is converted into 3-carbon lactic acid, the accumulation of which causes muscle cramps.

Topic Focus

Illustrate the process involved in human respiratory system, in order to explain how humans take in oxygen and expel $\text{CO}_2$

CBQ 13 • Consumption of Oxygen in Respiration

A student places a burning candle and a living cockroach in sealed Flask A, and an identical candle and a dead cockroach in sealed Flask B. After 10 minutes, the candle in Flask A extinguishes much faster than in Flask B. What does this observation demonstrate?

(a) Candle produces high amount of carbon dioxide

(b) Living beings consume oxygen during respiration, depleting it faster

(d) Water vapours produced by living beings prevent burning of candle

Correct Answer: Option (b)

Living beings consume oxygen during respiration

Both combustion and cellular respiration utilize molecular oxygen. In Flask A, the living cockroach and the flame competed for the limited $\text{O}_2$, depleting oxygen faster and causing the candle to extinguish earlier.

CBQ 14 • Limewater Test for Exhaled Carbon Dioxide

A student exhales through a straw into a test tube containing freshly prepared clear lime water [$\text{Ca(OH)}_2$]. Within a few seconds, the solution turns milky white. What conclusion is drawn from this observation?

(a) Oxygen is exhaled during respiration

(b) Glucose is produced during respiration

(d) Water vapours are produced during respiration

Correct Answer: Option (c)

Carbon dioxide is exhaled during respiration

Exhaled breath contains ~4.4% $\text{CO}_2$ compared to 0.04% in atmospheric air. The blown $\text{CO}_2$ reacts with limewater to form insoluble calcium carbonate precipitate: $$\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3\downarrow + \text{H}_2\text{O}$$

Topic Focus

Illustrate the process of transport of oxygenated & de-oxygenated blood by human heart, in order to explain how oxygen is transported to cells

CBQ 15 • Pathway of Oxygenated Blood to Body Tissues

Which sequence correctly traces the pathway of oxygen-rich blood from the lungs to the systemic cells of the human body?

(a) $\text{Lungs} \rightarrow \text{pulmonary vein} \rightarrow \text{left atrium} \rightarrow \text{left ventricle} \rightarrow \text{aorta} \rightarrow \text{body cells}$

(b) $\text{Lungs} \rightarrow \text{pulmonary vein} \rightarrow \text{right atrium} \rightarrow \text{right ventricle} \rightarrow \text{aorta} \rightarrow \text{body cells}$

(c) $\text{Lungs} \rightarrow \text{pulmonary artery} \rightarrow \text{left atrium} \rightarrow \text{left ventricle} \rightarrow \text{venacava} \rightarrow \text{body cells}$

(d) $\text{Lungs} \rightarrow \text{pulmonary artery} \rightarrow \text{right atrium} \rightarrow \text{right ventricle} \rightarrow \text{venacava} \rightarrow \text{body cells}$

Correct Answer: Option (a)

$\text{Lungs} \rightarrow \text{Pulmonary vein} \rightarrow \text{Left atrium} \rightarrow \text{Left ventricle} \rightarrow \text{Aorta} \rightarrow \text{Body cells}$

Oxygenated blood returns from the alveoli through 4 pulmonary veins into the left atrium, passes through the bicuspid (mitral) valve into the thick-walled left ventricle, and is pumped under high pressure into the aorta for systemic distribution.

CBQ 16 • Deoxygenated Blood Flow from Right Atrium

What is the subsequent direction of flow of deoxygenated blood received in the right atrium of the human heart from the vena cava?

(a) Towards the lungs (via the right ventricle and pulmonary artery)

(b) Towards the lower body via systemic capillaries

(d) Towards the left atrium through the interatrial septum

Correct Answer: Option (a)

Towards the lungs (via the right ventricle and pulmonary artery)

When the right atrium contracts, deoxygenated blood is pumped across the tricuspid valve into the right ventricle, which contracts to propel the blood through the pulmonary artery to the lungs for oxygenation.

Topic Focus

Outline the process of double circulation of blood in fishes, in order to explain how oxygenated & de-oxygenated blood is compartmentalized

CBQ 17 • Circulatory Pathway in Fish

Which option accurately describes the anatomical pathway of blood circulation in a bony fish?

(a) $\text{Gill capillaries} \rightarrow \text{oxygenated blood} \rightarrow \text{heart} \rightarrow \text{body cells} \rightarrow \text{deoxygenated blood} \rightarrow \text{gills}$

(b) $\text{Gill capillaries} \rightarrow \text{oxygenated blood} \rightarrow \text{body cells} \rightarrow \text{deoxygenated blood} \rightarrow \text{heart} \rightarrow \text{gills}$

(c) $\text{Gill capillaries} \rightarrow \text{heart} \rightarrow \text{oxygenated blood} \rightarrow \text{body cells} \rightarrow \text{deoxygenated blood} \rightarrow \text{heart} \rightarrow \text{gills}$

(d) $\text{Gill capillaries} \rightarrow \text{oxygenated blood} \rightarrow \text{heart} \rightarrow \text{body cells} \rightarrow \text{deoxygenated blood} \rightarrow \text{heart} \rightarrow \text{gills}$

Correct Answer: Option (b)

$\text{Gill capillaries} \rightarrow \text{oxygenated blood} \rightarrow \text{body cells} \rightarrow \text{deoxygenated blood} \rightarrow \text{heart} \rightarrow \text{gills}$

In fish, the heart pumps venous blood directly to the gills where it is oxygenated. From the gills, oxygenated blood flows directly to body tissues without returning to the heart, before returning as deoxygenated blood to the two-chambered heart.

CBQ 18 • Single Circulation vs Double Circulation

How is blood circulation in fish fundamentally different from double circulation in birds and mammals?

(a) The heart in fish is bigger in size relative to body weight

(b) The flow of blood in fish is bidirectional through alternating vessels

(d) The heart of fish has more chambers compared to that of a human

Correct Answer: Option (c)

Blood passes through the heart only once per complete circuit (Single circulation)

Fish possess a 2-chambered heart (one atrium and one ventricle). Blood passes through the heart only once during each cycle, whereas in humans blood passes twice through the 4-chambered heart (pulmonary and systemic circulation).

Topic Focus

Describe the function of blood vessels, arteries, platelets & lymph in human body, in order to understand how human transportation system works

CBQ 19 • Structural Adaptations of Arteries

Arteries have thick, elastic muscular walls and narrow central lumens without valves. Why do arteries possess thick elastic walls compared to veins?

(a) To carry large volumes of slowly moving blood

(b) To allow easy diffusion and exchange of gases with cells

(d) To withstand and sustain the high, pulsatile blood pressure emerging directly from the ventricles

Correct Answer: Option (d)

To sustain the high-pressure blood coming from the heart

When ventricles contract during systole, blood is ejected under high hydrostatic pressure (~120 mm Hg). Thick, elastic tunica media walls in arteries absorb the systolic shock wave and maintain diastolic recoil pressure without rupturing.

CBQ 20 • Role of Platelets in Haemostasis

When an injury causes bleeding, platelets (thrombocytes), clotting factors, and fibrin mesh act together to stop haemorrhage. What is the fundamental mechanism of clot formation?

(a) Platelets adhere and aggregate at the wound site, releasing thromboplastin to form an insoluble fibrin clot

(b) Platelets use components of the broken vessel to form a permanent epithelial lining

(d) Red blood cells and platelets migrate to the site of injury and secrete collagen to build a new artery

Correct Answer: Option (a)

Platelets form a clot by plugging the site of injury

Platelets stick to exposed collagen at the damaged endothelium, form a primary platelet plug, and release thrombokinase/thromboplastin which converts prothrombin to thrombin, ultimately polymerising soluble fibrinogen into an insoluble fibrin mesh that traps RBCs to seal the leak.

Topic Focus

Explain the function of xylem (vessels and tracheids) in plants, in order to explain how plants take up water from soil

CBQ 21 • Osmotic Uptake of Water by Roots

How is water initially absorbed from the soil into the xylem vessels of root hair cells?

(a) Xylem tissue mechanically attracts and absorbs water molecules

(b) Roots act as an active suction pump for taking in water

(d) Active ionic uptake by root cells creates a concentration gradient that draws water in by osmosis

Correct Answer: Option (d)

Difference in ion concentration creates an osmotic gradient for water movement

Root hair cells actively transport mineral ions from the soil into their cytoplasm. This establishes an osmotic potential difference between the root cortex and soil water, causing water to passively flow into the root cells and build root pressure.

CBQ 22 • Eosin Dye Transport Demonstration

An intact balsam plant is kept in a beaker of dilute red eosin dye solution for 3 hours. When a thin transverse section (T.S.) of the stem is cut and examined under a microscope, only the xylem vessels and tracheids show pink coloration. What does this observation demonstrate?

(a) Eosin dye solution is selectively stored in xylem vacuoles

(b) Water and dissolved minerals move upward exclusively through xylem vessels

(d) Most of the plant stem cross section is anatomically composed of xylem

Correct Answer: Option (b)

Water moves through xylem in the plant

The selective staining of xylem vessels proves that water and dissolved solutes are conducted unidirectionally upward from roots to aerial parts via the lumen of tracheary elements (xylem vessels and tracheids).

Topic Focus

Explain the function of transpiration in order to explain how water travels up in plants

CBQ 23 • Significance of Transpiration

Transpiration is the evaporative loss of water vapour from aerial parts of the plant. Which of the following is a major physiological benefit of transpiration for tall trees?

(a) It aids in the downward movement of sucrose from leaves to roots

(b) It generates a negative transpirational pull for sap ascent and regulates temperature by evaporative cooling

(d) It maintains a constant moisture level in the external soil environment

Correct Answer: Option (b)

Generates transpirational pull and aids temperature regulation (cooling effect)

Evaporation of water through stomata creates negative pressure (tension) in mesophyll cells, which pulls continuous water columns upward through xylem vessels (transpiration pull). It also prevents overheating of leaves in intense sunlight via evaporative cooling.

CBQ 24 • Bell Jar Transpiration Demonstration

A well-watered potted plant has its pot and soil tightly enclosed in a waterproof polythene sheet (leaving only the aerial shoot exposed) and is placed under an inverted glass bell jar sealed with Vaseline. After 2 hours in bright sunlight, clear water droplets appear on the inner wall of the jar. What is the source and mechanism of this water accumulation?

(a) Plant leaves release water in the form of water vapour via stomatal transpiration

(b) Heat from the sun melts the Vaseline seal into volatile vapours

(d) Covered soil warms up and forces water through the stem cortex

Correct Answer: Option (a)

Plant leaves give off water in the form of vapours (Transpiration)

Because the soil was sealed with polythene, evaporation from the soil was eliminated. The water droplets on the bell jar could only have originated from water vapour released through leaf stomata, which condensed upon striking the cooler glass surface.

Topic Focus

Explain the function of phloem & ATP, in order to explain how food is transported in plants

CBQ 25 • Bidirectional Translocation from Source to Sink

How are soluble products of photosynthesis (sucrose, amino acids) transported through phloem tissue according to seasonal plant requirements?

(a) Food is transported along with transpiration stream in a strictly upward direction

(b) Food is transported unidirectionally from roots to shoot tips like water in xylem

(d) Food is translocated bidirectionally from regions of synthesis/storage (source) to regions of utilization or growth (sink)

Correct Answer: Option (d)

From source to sink bidirectionally

Unlike xylem transport (unidirectionally upward), phloem translocation is multidirectional. In summer/autumn, leaves act as source and roots/fruits act as sink; in early spring, reserves stored in roots or stems act as source and young growing buds act as sink.

CBQ 26 • Role of ATP in Phloem Loading

During translocation, sucrose is actively loaded into the sieve tubes of phloem against a concentration gradient. How is this initial loading achieved?

(a) With the physical pull of transpirational water loss

(b) Passive diffusion across cell wall pits

(d) Hydrostatic suction created by root pressure

Correct Answer: Option (c)

With the help of ATP molecules (Active transport)

Phloem loading requires metabolic energy: ATP powers proton pumps that transport sucrose into companion cells and sieve tube elements. The resulting high solute concentration lowers water potential, drawing in water by osmosis and generating high hydrostatic pressure that drives mass flow.

Topic Focus

Illustrate the process involved in human excretory system, in order to explain how waste is transported out of humans body

CBQ 27 • Selective Reabsorption in the Nephron

During urine formation in a nephron, initial glomerular filtrate (~180 litres/day) is modified by extensive selective tubular reabsorption. What is the biological advantage of selective reabsorption along the renal tubule?

(a) It makes the process of ultrafiltration in Bowman’s capsule unnecessary

(b) It keeps the daily output of urine fixed at exactly 10 litres regardless of fluid intake

(d) It recovers vital glucose, amino acids, salts, and regulates water balance according to body hydration levels

Correct Answer: Option (d)

Maintains osmoregulation and recovers vital solutes according to body needs

Selective reabsorption in the proximal convoluted tubule and loop of Henle reclaims nearly 99% of filtered water along with essential nutrients (glucose, amino acids, $\text{Na}^+$). The amount of water reabsorbed is tightly regulated by hormones (ADH) to maintain bodily homeostasis.

Topic Focus

Describe transpiration and other ways in which plants shed extra wastes, in order to explain excretion in plants

CBQ 28 • Mechanisms of Plant Excretion

Plants do not possess specialized excretory organs like kidneys. Besides transpiration of excess water and diffusion of metabolic gases ($\text{O}_2$ and $\text{CO}_2$), how do plants eliminate cellular metabolic wastes?

(a) Shortening and thickening of the woody stem

(b) Storage of metabolic wastes in cellular vacuoles and shedding of old, yellowing leaves

(d) Exudation of all cellular cytoplasm into adjacent root tissues

Correct Answer: Option (b)

Shedding of yellow/old leaves containing stored wastes in cellular vacuoles

Plants store insoluble metabolic end-products (such as calcium oxalate crystals, resins, and gums) in older xylem and cellular vacuoles of leaves. When these senescent leaves turn yellow and drop (abscission), the accumulated waste products are safely discarded.

SECTION 2

Case Study & Contextual Questions

Experimental Context

Case Context (Questions 29 & 30):
The process of filtering blood outside the human body to remove harmful nitrogenous wastes (like urea) is called Haemodialysis. Dialysis takes place in an enclosed chamber where blood with metabolic wastes flows through long, coiled hollow tubes immersed in a dialysing fluid, and purified blood returns to the patient’s body.

CBQ 29 • SAS21S100601 • Dialysis Chamber Principles

Which of the following statements must be TRUE for an operational haemodialysis chamber?

1. Used dialysis solution is directly recycled back to the chamber as fresh dialysis solution without replenishment.
2. The hollow pipes through which blood flows must have cellophane semi-permeable walls.
3. The osmotic pressure of the dialysing solution matches normal blood, but lacks nitrogenous wastes.

(a) Only statement 1 is true

(b) Only statement 2 is true

(d) All three statements are true

Correct Answer: Option (c)

Statements 2 and 3 are True; Statement 1 is False

• Statement 1 is FALSE: Used dialysing solution contains accumulated urea and excess salts and is continuously drained away and replaced by fresh dialysing fluid.
• Statement 2 is TRUE: The hollow cellophane tubing is semi-permeable, allowing small waste molecules (urea, uric acid, creatinine) to diffuse outward into the fluid while retaining blood cells and large proteins.
• Statement 3 is TRUE: The dialysing fluid has the same osmotic pressure as normal blood except that it is completely devoid of nitrogenous wastes, creating a steep outward diffusion gradient.

CBQ 30 • SAS21S100602 • Blood Vessel in Dialysis Connection

In clinical haemodialysis, from what type of blood vessel is blood taken out of the patient’s body to enter the dialysis machine, and through what vessel is it returned after purification?

(a) Blood is taken from a vein and returned through an artery

(b) Blood is drawn from an artery (under systemic pressure) and returned through a vein

(d) Blood is taken directly from the vena cava and returned to the aorta

Correct Answer: Option (b)

Drawn from an artery (via an AV fistula) and returned through a vein

Blood carrying nitrogenous wastes is pumped out from a convenient artery (often the radial artery in the arm, heparinised to prevent clotting) into the dialyser tubes, and after ultrafiltration/diffusion of urea, the purified blood is infused back into a vein.

CBQ 31 • SAS21S100603 • Biological Filter in the Human Body

Which vital organ acts as the natural filtration and dialysis chamber in the human body by constantly removing metabolic nitrogenous wastes from circulating blood?

(a) Heart

(b) Brain

(d) Pancreas

Correct Answer: Option (c)

Kidneys

The two kidneys contain approximately 1 to 1.2 million microscopic functional filtration units called nephrons. Nephrons perform ultrafiltration at the glomerulus and selective reabsorption along renal tubules to cleanse the blood and produce urine.

Experimental Context

Case Context (Questions 32 & 33):
Sanjeev wanted to investigate whether plant leaves release water vapour. He took a potted plant, covered the entire shoot system with a transparent plastic bag, tied it at the base of the stem, and observed numerous tiny water droplets on the inside after 2 hours in sunlight.

CBQ 32 • SAS21S100604 • Control Setup in Transpiration Experiment

Sanjeev compared the results of this activity with a second control pot setup to confirm that the water droplets came exclusively from the living leaves and not from evaporation of soil moisture. Which of the following best represents the required control setup?

(a) A pot with moist soil but without a plant, covered with an identical plastic bag

(b) A pot with a plant but left without a plastic bag

(d) An empty, completely dry flower pot without soil

Correct Answer: Option (a)

Pot without plant covered with plastic bag (Control setup)

In a controlled scientific experiment, an identical pot containing moist soil covered with a plastic bag serves as a negative control to verify that evaporation from the soil or pot surface does not account for the heavy droplet condensation seen in the planted pot.

CBQ 33 • SAS21S100605 • Physiological Benefits of Transpiration

How does the continuous loss of water vapour from plant leaves (transpiration) benefit the plant? Identify the two primary physiological functions.

(a) 1. Creation of suction pressure (transpirational pull) for ascent of water and minerals; 2. Temperature regulation via evaporative cooling

(b) 1. Storage of starch in leaf mesophyll; 2. Rapid production of carbon dioxide for cellular respiration

(d) 1. Conversion of sunlight directly into chemical bonds; 2. Active excretion of nitrogenous salts

Correct Answer: Option (a)

Ascent of sap (Transpiration pull) and Evaporative Cooling

1. Suction force (Ascent of sap): Evaporation from leaf mesophyll creates a negative hydrostatic pressure gradient that pulls water and dissolved inorganic ions up from roots to tall canopies.
2. Thermal regulation: The high latent heat of vaporisation of water provides effective cooling to foliage, preventing thermal denaturation of enzymes in direct midday sunlight.

Experimental Context

Case Context (Questions 34 & 35):
Blood transports oxygen and carbon dioxide to and from all tissues in the human body. The exchange of respiratory gases between blood and inhaled alveolar air takes place across the thin capillary walls in the lungs. A closed double circulatory system ensures complete anatomical separation between oxygenated and deoxygenated blood streams.

CBQ 34 • SAS21S100606 • Properties of Capillaries in Double Circulation

Based on the anatomical and physiological principles of the human cardiovascular and respiratory systems, which statement is scientifically valid?

(a) All arteries without exception carry oxygenated blood

(b) Capillaries have single-cell thin endothelial walls that are permeable to diffusing respiratory gases ($\text{O}_2$ and $\text{CO}_2$)

(d) Blood normally flows back and forth bidirectionally between the right atrium and the right ventricle

Correct Answer: Option (b)

Capillaries are permeable to gases

• Capillary walls consist of a single layer of squamous endothelium (~0.5 $\mu$m thick) that allows rapid diffusion of $\text{O}_2$ and $\text{CO}_2$.
• Option (a) is incorrect because the pulmonary artery carries deoxygenated blood.
• Option (c) is incorrect because the septum is solid and prevents mixing.
• Option (d) is incorrect because atrioventricular valves ensure strictly unidirectional flow.

CBQ 35 • SAS21S100607 • Effect of Reduced Pulmonary Gaseous Exchange

Which of the following will be the immediate physiological consequence if gaseous exchange across the pulmonary alveolar capillaries is acutely impaired or reduced?

(a) Blood will flow in reverse direction through the pulmonary veins into lungs

(b) Pulmonary veins will deliver blood with significantly less oxygen (hypoxemia) to the left atrium

(d) The hydrostatic pressure of blood inside pulmonary capillaries will drop to zero

Correct Answer: Option (b)

Pulmonary veins will receive blood with less oxygen

Pulmonary veins carry blood from the alveolar capillary beds directly to the left atrium. If alveolar diffusion of oxygen decreases (due to infection, fluid, or reduced surface area), blood entering pulmonary veins remains poorly oxygenated, reducing arterial oxygen saturation ($S_p\text{O}_2$).

Experimental Context

Case Context:
A schematic diagram of the human alimentary canal and associated glands displays four numbered structures: 1 (Stomach), 2 (Liver), 3 (Pancreas), and 4 (Small intestine / Ileum).

CBQ 36 • SAS21S100608 • Identification of the Liver

Which labelled organ represents the largest accessory gland in the human body—the Liver—which secretes alkaline bile juice for emulsification of dietary fats?

(a) Organ 1

(b) Organ 2

(d) Organ 4

Correct Answer: Option (b)

Organ 2 (Liver)

The liver is located in the upper right quadrant of the abdominal cavity just beneath the diaphragm. It secretes bile (stored in the gall bladder), which contains bile salts that emulsify large fat globules into tiny micelles, increasing surface area for pancreatic lipase.

CBQ 37 • SAS21S100609 • Consequence of Pancreatic Lipase Deficiency

The exocrine pancreas secretes pancreatic juice containing the enzyme lipase along with trypsin and amylase. Mr. Ayub is diagnosed with chronic pancreatitis causing severe hyposecretion of pancreatic lipase. Which major dietary macronutrient will Mr. Ayub have extreme difficulty digesting and absorbing?

(a) Digestion of carbohydrates

(b) Digestion of proteins

(d) Digestion of water-soluble vitamins

Correct Answer: Option (c)

Digestion of fats

Lipase is the principal enzyme responsible for hydrolysing triglycerides (emulsified dietary fats) into monoglycerides and free fatty acids. Malfunctioning of the pancreas impairs fat breakdown, causing steatorrhoea (undigested fatty stools) and poor fat absorption.

CBQ 38 • SAS21S100610 • Destruction of Respiratory Cilia by Smoking

Microscopic, hair-like motile structures called cilia line the pseudo-stratified ciliated epithelium of the human respiratory tract. Working together with mucus-secreting goblet cells (mucociliary escalator), they trap and sweep inhaled dust, germs, and airborne particles toward the pharynx. Chronic cigarette smoking is clinically known to cause frequent, severe respiratory infections. Which statement best explains this pathogenic mechanism?

(a) Cigarette smoke paralyses and permanently destroys the ciliated epithelial cells, preventing the clearance of trapped pathogens

(b) Cigarette smoke stimulates cilia to produce excessive toxic chemicals into bronchial passages

(d) Smoke wets the cilia surface so that they can no longer adhere to dust particles

Correct Answer: Option (a)

Smoking destroys and paralyses the hair-like ciliated structures

Tobacco smoke contains noxious chemicals (acrolein, formaldehyde, hydrogen cyanide) that paralyse ciliary motility (ciliostasis) and eventually lead to the destruction of ciliated columnar cells. Without the mucociliary escalator, trapped bacteria and toxic particles accumulate in the bronchi, leading to chronic bronchitis and frequent lung infections.

SECTION 3

CBSE Item Bank Questions

Item Data & Reference

CBSE Item Bank Reference (Item Science10AP5):
In a detailed anatomical diagram of the human digestive tract, various digestive organs and secretor glands are designated by specific alphabetical letters:
• Mouth / Buccal cavity (A)
• Oesophagus (B)
• Stomach (C)
• Pancreas (E)
• Liver (J)
• Small intestine / Duodenum-Ileum (F)
• Large intestine / Colon (G)
• Anus (H)

CBQ 39 • Science10AP5 — 1(a)(i)-(v) • 5 Marks

Based on the physiological processes occurring along the human alimentary canal, identify the specific anatomical site and letter for each of the following:
(i) The site where chemical digestion of dietary starch begins
(ii) The site where salivary secretion is produced and mixed with food
(iii) The site where a strongly acidic gastric environment ($ ext{pH} \approx 1.5–2.0$) is maintained
(iv) The primary site where excess unabsorbed water is re-absorbed from undigested residue
(v) The terminal opening where egestion (defecation) occurs

Model Answer & Marking Scheme

(i) Mouth / Buccal Cavity (Letter A) [1 Mark]: Salivary amylase begins the hydrolysis of starch into maltose.

(ii) Salivary Glands / Mouth (Letter A) [1 Mark]: Three pairs of salivary glands secrete saliva into the oral cavity.

(iii) Stomach (Letter C) [1 Mark]: Gastric glands in the stomach wall secrete hydrochloric acid ($\text{HCl}$), establishing an acidic medium (pH 1.5–2.0) that activates pepsinogen and kills microbes.

(iv) Large Intestine / Colon (Letter G) [1 Mark]: The extensive mucosal surface of the colon reabsorbs water and electrolytes, consolidating waste into semi-solid faeces.

(v) Anus (Letter H) [1 Mark]: The terminal exit guarded by anal sphincter muscles where unabsorbed faecal matter is egested from the body.

CBQ 40 • Science10AP5 — 1(b) • 2 Marks

State the names of two major accessory organs associated with the alimentary canal: organ E (a pale yellow gland tucked beneath the stomach) and organ J (the large reddish-brown gland on the right side). Give one major digestive secretion produced by each.

Model Answer & Marking Scheme

1. Organ E: Pancreas [1 Mark]
• Secretes pancreatic juice containing trypsin (for proteins), pancreatic amylase (for carbohydrates), and lipase (for emulsified lipids).

2. Organ J: Liver [1 Mark]
• Secretes bile juice (containing bile salts and bile pigments), which neutralises acidic chyme and emulsifies large dietary fat globules.

Item Data & Reference

CBSE Item Bank Reference (Item Science10CKV3):
Photosynthesis is the foundational biochemical process by which autotrophs synthesise organic biomass from inorganic atmospheric carbon dioxide and soil water using solar energy.

CBQ 41 • Science10CKV3 — 1(a) • 1 Mark

Photosynthesis occurs in chloroplasts of green plants. In terms of chemical energetics and bond transformations, what fundamental type of chemical reaction is photosynthesis?

(a) Exothermic combination reaction

(b) Endothermic oxidation-reduction (redox) reaction

(d) Simple displacement reaction

Correct Answer: Option (b)

Endothermic redox (reduction-oxidation) reaction [1 Mark]

Photosynthesis is an endothermic anabolic process because it absorbs solar photon energy. It is a redox reaction wherein water is oxidised to oxygen gas ($2\text{H}_2\text{O} \rightarrow \text{O}_2 + 4\text{H}^+ + 4\text{e}^-$) and carbon dioxide is reduced to glucose (carbohydrate).

CBQ 42 • Science10CKV3 — 1(b) • 2 Marks

Write down the complete, balanced chemical symbol equation for photosynthesis in green plants, indicating essential catalysts and conditions written above and below the reaction arrow.

Model Answer & Marking Scheme

Balanced Symbol Equation [2 Marks]:

$$6\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 + 6\text{H}_2\text{O}$$

• Reactants: 6 molecules of Carbon Dioxide and 12 molecules of Water.
• Conditions: Sunlight (energy source) and Chlorophyll (photoreceptive pigment) [1 Mark].
• Products: 1 molecule of Glucose ($\text{C}_6\text{H}_{12}\text{O}_6$), 6 molecules of Oxygen ($\text{O}_2$), and 6 molecules of regenerated Water ($\text{H}_2\text{O}$) [1 Mark].

CBQ 43 • Science10CKV3 — 1(c) • 3 Marks

Explain how the two principal inorganic reactants required for photosynthesis—carbon dioxide and water—become available in the palisade and spongy mesophyll cells of plant leaves.

Model Answer & Marking Scheme

1. Availability of Carbon Dioxide ($\text{CO}_2$) [1.5 Marks]:
Atmospheric carbon dioxide enters the leaf through microscopic epidermal apertures called stomata. When guard cells swell (become turgid), stomatal pores open, allowing $\text{CO}_2$ to diffuse down its concentration gradient through intercellular air cavities directly into photosynthetic mesophyll cells.

2. Availability of Water ($\text{H}_2\text{O}$) [1.5 Marks]:
Water and dissolved mineral ions are absorbed from the surrounding moist soil by root hair cells via osmosis. From the root cortex and endodermis, water enters root xylem vessels and is pulled upward through stem xylem and leaf petiole bundles by transpirational pull, finally reaching leaf veins and mesophyll cells.

CBQ 44 • Science10CKV3 — 1(d) • 4 Marks

Explain the precise biological role of transpiration and the regulatory action of guard cells in mediating the upward transport of water from the root xylem to the leaf tip.

Model Answer & Marking Scheme

Role of Transpiration (Transpirational Pull) [2 Marks]:
• Evaporation of water molecules from thin films on mesophyll surfaces into substomatal cavities creates a tension/suction force called transpirational pull.
• Because water molecules possess high cohesive and adhesive forces, this negative pressure draws a continuous, unbroken column of water upward through tracheids and vessels from roots to leaves (ascent of sap).

Role of Guard Cells [2 Marks]:
• Guard cells control the opening and closing of stomatal pores. When water flows into guard cells, they become turgid and their curved outer thin walls bulge outwards, widening the pore to allow gas exchange and transpiration.
• When water availability drops, guard cells lose water, become flaccid, and straighten, closing the stomatal pore to prevent fatal dehydration (wilting).

CBQ 45 • Science10AP1 • 1 Mark

Which anatomical adaptation allows green plant leaves to achieve highly rapid and efficient gaseous exchange with minimal diffusion resistance?

(a) Thick waxy cuticles covering both surfaces of the leaf

(b) Broad, thin laminar surface with numerous stomata and interconnected spongy mesophyll air spaces

(d) Absence of chloroplasts in epidermal cells

Correct Answer: Option (b)

Broad, thin lamina with stomata and extensive intercellular air spaces [1 Mark]

A flat, broad lamina maximises light interception and surface area-to-volume ratio, while large intercellular air spaces in spongy parenchyma provide immediate access for $\text{CO}_2$ and $\text{O}_2$ to diffuse directly into chloroplast-rich cells.

Item Data & Reference

CBSE Item Bank Reference (Item Science10AP3):
The respiratory surface in human lungs comprises approximately 300 to 480 million microscopic balloon-like sacs called alveoli, providing a combined surface area of roughly $80\,\text{m}^2$.

CBQ 46 • Science10AP3 — 1(a) • 3 Marks

Describe three key anatomical adaptations of alveoli that maximise the rate and volume of respiratory gas exchange between alveolar air and pulmonary capillary blood.

Model Answer & Marking Scheme

Three Adaptations of Alveoli [1 Mark each = 3 Marks]:

1. Enormous Surface Area: The millions of folding alveoli provide a massive collective surface area (~$80\,\text{m}^2$) for gas diffusion.

2. Ultra-Thin Respiratory Membrane: Alveolar walls consist of extremely thin single-layer squamous epithelium, meaning gases need to diffuse across a barrier less than 1 micrometre thick.

3. Dense Capillary Network & Moist Lining: Alveoli are enveloped by an extensive web of pulmonary blood capillaries and lined with a thin film of moisture in which oxygen dissolves before rapid diffusion into RBC hemoglobin.

CBQ 47 • Science10AP3 — 1(b)(i) & (ii) • 3 Marks

(i) Differentiate between aerobic respiration and anaerobic respiration in yeast in terms of end products formed.
(ii) Explain why skeletal muscle cells produce lactic acid during vigorous physical exercise, and state its consequence.

Model Answer & Marking Scheme

(i) Difference in End Products [1 Mark]:
• Aerobic Respiration: Complete oxidation yields Carbon Dioxide ($\text{CO}_2$), Water ($\text{H}_2\text{O}$), and a high energy yield (36–38 ATP).
• Anaerobic Respiration (Yeast): Incomplete breakdown yields Ethanol ($\text{C}_2\text{H}_5\text{OH}$), Carbon Dioxide ($\text{CO}_2$), and only 2 ATP.

(ii) Lactic Acid Formation in Muscle Cells [2 Marks]:
• During heavy sprinting or exercise, cellular demand for ATP exceeds the oxygen supply delivered by the bloodstream.
• Muscle tissue temporarily switches to anaerobic glycolysis, converting pyruvate into lactic acid to regenerate $\text{NAD}^+$.
• Consequence: Accumulation of lactic acid in muscle fibres lowers pH, causing muscle fatigue, stiffness, and severe cramps.

CBQ 48 • Science10AP3 — 1(c)(i) & (ii) • 5 Marks

Explain the biomechanical mechanism of human breathing. Detail how synchronized movements of the diaphragm and ribcage (intercostal muscles) bring about (i) Inhalation (inspiration) and (ii) Exhalation (expiration).

Model Answer & Marking Scheme

(i) Mechanism of Inhalation (Inspiration) [2.5 Marks]:
• External intercostal muscles contract, lifting the ribs upwards and outwards.
• Concurrently, the dome-shaped diaphragm contracts and flattens downwards.
• These actions substantially enlarge the volume of the thoracic cavity (antero-posterior and dorso-ventral axes).
• As thoracic volume increases, internal pulmonary air pressure drops below atmospheric pressure, causing outside atmospheric air to rush into the lungs through the trachea and bronchi to inflate the alveoli.

(ii) Mechanism of Exhalation (Expiration) [2.5 Marks]:
• Intercostal muscles relax, causing the ribcage to move downwards and inwards.
• The diaphragm relaxes and returns to its upward-curved dome shape.
• This reduces the volume of the thoracic cage, compressing the lungs.
• Intra-pulmonary pressure rises above external atmospheric pressure, forcing air rich in $\text{CO}_2$ out of the lungs into the atmosphere.

Item Data & Reference

CBSE Item Bank Reference (Item Science10MS5):
ATP (Adenosine Triphosphate) is regarded as the universal energy currency of cellular processes in all living organisms.

CBQ 49 • Science10MS5 — 1(b) • 3 Marks

Explain how the energy released during the step-wise breakdown of glucose in cellular respiration is captured, converted, and stored in the form of ATP molecules, and how cells utilise this energy.

Model Answer & Marking Scheme

Synthesis and Role of ATP [3 Marks]:

• ATP Synthesis: Energy released during oxidation of glucose is used to synthesise ATP from low-energy Adenosine Diphosphate ($\text{ADP}$) and inorganic phosphate ($\text{P}_i$):
$$\text{ADP} + \text{P}_i + \text{Energy} \longrightarrow \text{ATP}$$ [1.5 Marks]

• Energy Release: When the terminal phosphate bond in ATP is broken by hydrolysis using water, approximately $30.5\,\text{kJ/mol}$ of energy is released:
$$\text{ATP} + \text{H}_2\text{O} \longrightarrow \text{ADP} + \text{P}_i + 30.5\,\text{kJ/mol}$$ [1 Mark]

• Cellular Usage: This released free energy powers endothermic metabolic processes including protein synthesis, active trans-membrane transport (sodium-potassium pumps), nerve impulse transmission, and muscle contraction [0.5 Mark].

Item Data & Reference

CBSE Item Bank Reference (Item Science10DP3):
The human heart is a muscular four-chambered organ functioning as a dual pump to drive blood through two separate circuits simultaneously.

CBQ 50 • Science10DP3 — 1(a), (b), (c) • 5 Marks

(a) Describe the pathway of blood flow through the four chambers of the human heart and define the term double circulation.
(b) State the functional importance of valves located within the heart chambers and in systemic veins.
(c) Why do the ventricles have much thicker muscular walls than the atria?

Model Answer & Marking Scheme

(a) Blood Pathway & Double Circulation [2.5 Marks]:
• Systemic Return: Deoxygenated blood from tissues enters the Right Atrium $\rightarrow$ Right Ventricle $\rightarrow$ Pulmonary Artery $\rightarrow$ Lungs.
• Pulmonary Return: Oxygenated blood from lungs enters the Left Atrium $\rightarrow$ Left Ventricle $\rightarrow$ Aorta $\rightarrow$ Body Tissues.
• Definition: Double circulation refers to the physiological pattern where blood travels through the heart twice during one complete cycle through the body—once via the pulmonary circuit (to oxygenate blood) and once via the systemic circuit (to supply body tissues).

(b) Function of Valves [1.5 Marks]:
Valves (cuspid valves between atria and ventricles, semilunar valves at arterial exits, and pocket valves in veins) prevent the backflow of blood when the chambers or tissues contract and relax, ensuring strictly unidirectional forward circulation under varying pressures.

(c) Ventricular Wall Thickness [1 Mark]:
Atria only pump blood into the adjacent ventricles below them, requiring minimal force. In contrast, ventricles must generate immense muscular pressure to pump blood to distant organs—the right ventricle to the lungs and the left ventricle across the entire systemic body—necessitating thick myocardium.

CBQ 51 • Science10CKV1 • 1 Mark

Which class of blood vessels collects deoxygenated blood from systemic capillary beds in organs and carries it back toward the heart under relatively low pressure?

(a) Systemic Arteries

(b) Arterioles

(d) Pulmonary Veins

Correct Answer: Option (c)

Systemic Veins (Vena Cava) [1 Mark]

Veins have thin muscular walls, wide internal lumens, and internal semilunar valves to transport deoxygenated blood from systemic tissue capillary beds back to the right atrium under low hydrostatic pressure.

Item Data & Reference

CBSE Item Bank Reference (Item Science10DP4):
Each human kidney contains over a million functional filtration units called nephrons, each consisting of a Malpighian body (glomerulus and Bowman’s capsule) and an extensive tubular network.

CBQ 52 • Science10DP4 — 1(a)-(d) • 5 Marks

(a) Name the basic structural and functional filtration unit of the human kidney.
(b) State precisely where ultrafiltration occurs, and name two valuable substances selectively reabsorbed as tubular fluid flows through the nephron.
(c) What two primary physiological factors determine the amount of water reabsorbed by renal tubules?
(d) Explain the working principle of an artificial kidney (haemodialysis) in clearing nitrogenous waste from patients suffering from acute kidney failure.

Model Answer & Marking Scheme

(a) Functional Unit [0.5 Mark]: The Nephron.

(b) Ultrafiltration & Reabsorbed Solutes [1.5 Marks]:
• Ultrafiltration occurs across the podocyte slit membranes between the Glomerulus and Bowman’s capsule under high afferent arteriolar pressure.
• Useful substances selectively reabsorbed include glucose, amino acids, sodium salts, and water.

(c) Factors Determining Water Reabsorption [1 Mark]:
1. The amount of excess water present in the body (hydration status).
2. The concentration of dissolved excretory wastes (osmotic load) that must be eliminated.

(d) Artificial Kidney (Haemodialysis) Mechanism [2 Marks]:
• Patient’s blood is diverted from an artery through semi-permeable cellophane tubes submerged in a tank of dialysing solution.
• The dialysing fluid matches normal blood osmolarity and electrolytes but contains zero urea/uric acid.
• Nitrogenous wastes diffuse down their steep concentration gradient from the blood into the dialysing fluid.
• The purified blood is warmed, treated with anti-heparin, and returned to the patient via a vein. (Note: Unlike healthy kidneys, there is no selective reabsorption in artificial dialysis).

CBQ 53 • Science10CKV2 • 1 Mark

Which toxic nitrogenous metabolic waste product, formed in the liver by the deamination of excess amino acids (ornithine cycle), is primarily filtered and excreted in human urine?

(a) Ammonia

(b) Urea

(d) Creatine phosphate

Correct Answer: Option (b)

Urea [1 Mark]

Humans are ureotelic organisms. Highly toxic ammonia generated during amino acid metabolism is converted into less toxic, water-soluble urea ($\text{NH}_2\text{CONH}_2$) by hepatocytes in the liver and subsequently eliminated via glomerular filtration in the kidneys.

Complete Revision Notes

All concepts • mnemonics • tips • traps • formulas

① Life Processes — Core Idea

Life processes are maintenance functions required to keep an organism alive.
Main processes: nutrition, respiration, transportation and excretion.
Multicellular organisms need specialised tissues/organs because diffusion alone is too slow over long distances.
Think of the body as a system: input → energy → distribution → waste removal.

🧠 N-R-T-E = Nutrition → Respiration → Transportation → Excretion.

② Nutrition — Autotrophic & Heterotrophic

Nutrition supplies energy and raw materials.
Autotrophs synthesise complex organic food from simple inorganic materials.
Heterotrophs depend directly/indirectly on organisms that make food.
Heterotrophic strategies include holozoic, saprophytic and parasitic modes.
Fungi can digest food outside the body; parasites obtain nutrition from living hosts.

🎯 Tip: If asked “why different nutrition modes?”, connect food availability + organism's body design + method of obtaining food.

🧠 AUTO = self; HETERO = other.

③ Photosynthesis — Complete Recall

Raw materials: CO₂ + water.
Conditions: sunlight + chlorophyll.
CO₂ enters mainly through stomata; water comes through roots.
Chlorophyll in chloroplasts absorbs light.
Light energy is converted to chemical energy; water is split; CO₂ is reduced to carbohydrates.
Unused carbohydrate may be stored as starch.
O₂ is released as a by-product.
Plants also need mineral nutrients such as nitrogen, phosphorus, iron and magnesium from soil.

CO₂ + H₂O → C₆H₁₂O₆ + O₂ sunlight + chlorophyll

🧠 “CO₂ + H₂O + Sun + Green” → food + O₂.

🎯 Experiment trick: destarch → expose → iodine test. Green area turns blue-black because starch is formed where chlorophyll is present.

④ Stomata & Guard Cells

Stomata are tiny pores for gaseous exchange.
Guard cells regulate opening and closing.
Swollen guard cells → pore opens.
Shrunken guard cells → pore closes.
Stomata allow CO₂ entry but also cause water loss.

🧠 “Swollen = Space; Shrunken = Shut.”

⑤ Human Digestion — Organ-by-Organ

Mouth: teeth crush food; saliva moistens; salivary amylase starts starch digestion.
Oesophagus: food moves by peristalsis.
Stomach: HCl creates acidic medium; pepsin digests proteins; mucus protects lining.
Small intestine: receives bile + pancreatic juice; complete digestion of carbohydrates, proteins and fats; major absorption site.
Bile: makes acidic food alkaline and emulsifies fats.
Pancreas: trypsin acts on proteins; lipase acts on fats.
End products: carbohydrates → glucose; proteins → amino acids; fats → fatty acids + glycerol.
Villi: increase surface area and have rich blood supply.
Large intestine: absorbs more water.
Anus: egestion controlled by anal sphincter.

🧠 “M-O-S-S-L-A” = Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Anus.

🎯 Digestion answer trick: write organ + secretion/enzyme + substrate + product.

⑥ High-Yield Digestion Facts

Salivary amylase → starch → simpler sugars.
HCl → acidic medium → helps pepsin.
Pepsin → protein digestion.
Mucus → stomach protection.
Bile salts → emulsification of fats.
Trypsin → protein digestion.
Lipase → fat digestion.
Villi → absorption.
Peristalsis → forward movement of food.

🧠 “H-P-M” = HCl prepares, Pepsin processes, Mucus protects.

⑦ Respiration — Must-Know Pathway

Glucose is first broken into pyruvate in the cytoplasm.
Pyruvate has three possible pathways depending on oxygen and organism/tissue.
Aerobic: mitochondria → CO₂ + H₂O + much more energy.
Yeast anaerobic: ethanol + CO₂ + less energy.
Muscle oxygen shortage: lactic acid + less energy.
Lactic acid accumulation during sudden activity is associated with cramps.

🧠 “Y-M-A” = Yeast–Alcohol, Muscle–Lactic acid, Aerobic–CO₂ + H₂O.

⑧ Aerobic vs Anaerobic — Quick Table

O₂: aerobic yes; anaerobic no.
Energy: aerobic much more; anaerobic less.
Products: aerobic CO₂ + H₂O; anaerobic depends on pathway.
Site after pyruvate: aerobic in mitochondria; anaerobic pathway does not use mitochondrial aerobic breakdown.

🎯 Trap: Do not write “anaerobic respiration always produces alcohol.” In human muscles, lactic acid is produced under oxygen deficiency.

⑨ ATP — Energy Currency

Respiration energy is used to synthesise ATP from ADP + inorganic phosphate.
ATP provides usable energy for cellular work.
Examples: muscle contraction, protein synthesis, nervous impulses.

🧠 ATP = A Tiny Power-pack.

⑩ Human Respiration — Alveoli & Gas Exchange

Air enters through nostrils; hairs/mucus filter particles.
Cartilage rings prevent collapse of air passages.
Air reaches alveoli through progressively smaller tubes.
Alveoli have large surface area, thin walls and rich blood supply.
O₂ diffuses into blood; CO₂ diffuses into alveoli.
Haemoglobin carries oxygen; CO₂ is transported largely dissolved in blood.
Inhalation: ribs lift + diaphragm flattens → chest volume increases → air enters.
Exhalation reverses these volume changes.

🧠 Alveoli = “3T”: Tons of area + Thin wall + Tight capillary network.

⑪ Transportation in Humans

Blood = plasma + cells.
Plasma transports dissolved food, CO₂, nitrogenous wastes and salts.
RBCs with haemoglobin transport O₂.
Platelets help clot damaged vessels.
Heart is the pump; vessels form the network.
Right side handles deoxygenated blood; left side handles oxygenated blood.
Valves prevent backward flow.

🧠 “Right → Respiratory organs; Left → Life tissues.”

⑫ Double Circulation — Exact Route

Body → vena cava → right atrium → right ventricle → pulmonary artery → lungs.
Lungs → pulmonary vein → left atrium → left ventricle → aorta → body.
Blood passes through heart twice in one complete cycle.
Separation prevents oxygenated/deoxygenated mixing and supports high energy demands.

🧠 “Right sends to lungs; Left launches to body.”

🎯 Trap: artery/vein is defined by direction relative to heart, not oxygen content.

⑬ Blood Vessels — Artery / Vein / Capillary

Artery: away from heart; thick elastic walls; high pressure.
Vein: toward heart; thinner walls; valves.
Capillary: one-cell-thick; exchange with tissues.

🧠 ARTERY = AWAY. VEIN = towards the heart.

⑭ Blood Pressure & Lymph

Blood pressure = force of blood against vessel wall.
Systolic = ventricular contraction.
Diastolic = ventricular relaxation.
Valves ensure one-way flow.
Platelets plug leaks and help clot.
Lymph/tissue fluid forms from material escaping through capillary walls.
Lymph returns excess tissue fluid and transports absorbed fats from intestine.

⑮ Transportation in Plants

Xylem transports water + minerals from roots.
Root pressure contributes to upward movement.
Transpiration is loss of water vapour from aerial parts through stomata.
Transpiration creates suction/transpiration pull.
During day, transpiration pull is the major driving force for upward xylem movement.
Phloem transports soluble photosynthetic products, amino acids and other substances.
Phloem translocation can occur upward or downward according to plant needs.
Phloem loading uses ATP and produces pressure differences that drive movement.

🧠 Xylem = Water; Phloem = Food.

🎯 Plant transport answer: always mention tissue + material + direction + driving force.

⑯ Excretion in Humans

Excretory system: kidneys, ureters, urinary bladder, urethra.
Kidneys remove nitrogenous wastes such as urea/uric acid from blood.
Nephron = functional filtration unit.
Bowman's capsule collects filtrate from capillary cluster.
Selective reabsorption returns useful substances such as glucose, amino acids, salts and much water.
Remaining waste + excess water becomes urine.
Urine → ureter → bladder → urethra.

🧠 K-U-B-U = Kidney → Ureter → Bladder → Urethra.

🎯 Nephron trick: FRE = Filter → Reabsorb → Excrete.

⑰ Urine Regulation & Dialysis

Water reabsorption depends on body water status and dissolved waste requirements.
More water available → less need to conserve it → more may remain in urine.
Kidney failure causes waste accumulation.
Dialysis uses a semipermeable lining and waste-free dialysing fluid.
Waste diffuses from blood into dialysing fluid; purified blood returns to patient.
Normal kidney function includes reabsorption; dialysis does not replicate normal tubular reabsorption.

🧠 Dialysis = “Diffuse waste, Return blood.”

⑱ Excretion in Plants

Plants have no single kidney-like excretory organ.
O₂ can be released during photosynthesis.
Excess water is lost by transpiration.
Wastes can be stored in vacuoles.
Wastes can accumulate in leaves and leave when leaves fall.
Gums and resins can store wastes, especially in old xylem.
Some wastes can be released into surrounding soil.

🧠 V-L-G-S = Vacuoles → Leaves → Gums/resins → Soil.

⑲ Must-Draw Diagrams

Human alimentary canal.
Amoeba nutrition.
Human respiratory system + alveoli.
Human heart / double circulation.
Artery, vein and capillary comparison.
Plant xylem water movement / transpiration pull.
Human excretory system.
Nephron.

🎯 Diagram scoring trick: practise labels separately. In the exam, draw the outline first, then label, then add 1–2 function statements.

⑳ Final 60-Second Memory Grid

Nutrition: obtain/build food.
Photosynthesis: CO₂ + H₂O + light + chlorophyll → carbohydrate + O₂.
Digestion: break large molecules into absorbable molecules.
Respiration: glucose → pyruvate → energy pathway.
ATP: usable cellular energy.
Alveoli: gas exchange.
Heart: pump.
Artery: away.
Xylem: water/minerals.
Phloem: food/translocation.
Nephron: filtration + selective reabsorption.
Plant excretion: vacuoles/leaves/gums-resins/soil/transpiration.

🧠 MASTER CHAIN: “Food → Fuel → Flow → Filter”
Food = Nutrition • Fuel = Respiration/ATP • Flow = Transportation • Filter = Excretion.

Concepts & Visual Theory

Single-Celled Organisms (e.g. Amoeba)

Multicellular Organisms (e.g. Humans)

1. Saprophytic (Saprotrophic) Nutrition

2. Parasitic Nutrition

Breathing (External Respiration)

Cellular Respiration (Internal Respiration)

Systolic Pressure (Contraction Phase)

Diastolic Pressure (Relaxation Phase)

Excretion in Unicellular Organisms (e.g. Amoeba)

Excretion in Complex Animals (e.g. Humans)

NCERT Exercises — Questions + Answers

PYQ Practice

Name the process by which plants lose water vapour through stomata.

Where does glycolysis/initial glucose breakdown occur?

Why are multicellular organisms dependent on specialised transport systems?

Differentiate between arteries and veins.

Explain why the small intestine is the main site of absorption.

Explain the three pathways of pyruvate breakdown.

Why is separation of oxygenated and deoxygenated blood necessary in mammals?

Explain the formation of urine in a nephron.

Explain transportation of water in plants.

Competency-Based Questions

Learning Objective Practice Items

Explain the process of absorption of $\text{CO}_2$ & $\text{H}_2\text{O}$, in order to understand how autotrophs obtain substances necessary for nutrition

The schematic process of photosynthesis in green plants involves light energy, carbon dioxide, water, oxygen, and glucose. Which statement correctly describes how autotrophs obtain their essential raw materials?

Explain the process of conversion of $\text{CO}_2$ & $\text{H}_2\text{O}$ into carbohydrates, in order to understand how autotrophs obtain nutrition

Which equation represents the balanced chemical conversion of carbon dioxide and water into carbohydrates in green plants during photosynthesis?

List and explain the strategies employed by heterotrophs to take up food, in order to understand how heterotrophs obtain nutrition

Bread moulds (*Rhizopus*) and other fungi grow rapidly on moist stale bread. How do these organisms obtain nutrition from the substrate?

*Amoeba* takes in food particles using temporary finger-like extensions of the cell surface (pseudopodia) which fuse over the food particle to form a food vacuole. How is this process advantageous for *Amoeba*?

Illustrate the process involved in human digestive system, in order to explain how humans obtain nutrients from food

At which organ of the human alimentary canal does the chemical breakdown and digestion of food begin?

The inner lining of the small intestine possesses millions of tiny finger-like projections called villi supplied richly with blood vessels and lacteals. What will likely happen if the total surface area and number of villi increases in the intestine?

List the enzymes & their functions involved in human digestive system, in order to understand breakdown of food in humans

An in-vitro biochemical test is set up with:$$\text{Saliva} + \text{Starch suspension (in test tube at } 37^\circ\text{C)}$$What is the biochemical outcome of this enzymatic reaction after incubation?

Outline and explain the ways of breakdown of glucose by various pathways, in order to explain how energy is obtained in organisms

Which metabolic pathway occurs in the skeletal muscle cells of an athlete who is performing an intense 100-metre sprint when oxygen supply is insufficient?

Illustrate the process involved in human respiratory system, in order to explain how humans take in oxygen and expel $\text{CO}_2$

A student places a burning candle and a living cockroach in sealed Flask A, and an identical candle and a dead cockroach in sealed Flask B. After 10 minutes, the candle in Flask A extinguishes much faster than in Flask B. What does this observation demonstrate?

A student exhales through a straw into a test tube containing freshly prepared clear lime water [$\text{Ca(OH)}_2$]. Within a few seconds, the solution turns milky white. What conclusion is drawn from this observation?

Illustrate the process of transport of oxygenated & de-oxygenated blood by human heart, in order to explain how oxygen is transported to cells

Which sequence correctly traces the pathway of oxygen-rich blood from the lungs to the systemic cells of the human body?

What is the subsequent direction of flow of deoxygenated blood received in the right atrium of the human heart from the vena cava?

Outline the process of double circulation of blood in fishes, in order to explain how oxygenated & de-oxygenated blood is compartmentalized

Which option accurately describes the anatomical pathway of blood circulation in a bony fish?

How is blood circulation in fish fundamentally different from double circulation in birds and mammals?

Describe the function of blood vessels, arteries, platelets & lymph in human body, in order to understand how human transportation system works

Arteries have thick, elastic muscular walls and narrow central lumens without valves. Why do arteries possess thick elastic walls compared to veins?

When an injury causes bleeding, platelets (thrombocytes), clotting factors, and fibrin mesh act together to stop haemorrhage. What is the fundamental mechanism of clot formation?

Explain the function of xylem (vessels and tracheids) in plants, in order to explain how plants take up water from soil

How is water initially absorbed from the soil into the xylem vessels of root hair cells?

An intact balsam plant is kept in a beaker of dilute red eosin dye solution for 3 hours. When a thin transverse section (T.S.) of the stem is cut and examined under a microscope, only the xylem vessels and tracheids show pink coloration. What does this observation demonstrate?

Explain the function of transpiration in order to explain how water travels up in plants

Transpiration is the evaporative loss of water vapour from aerial parts of the plant. Which of the following is a major physiological benefit of transpiration for tall trees?

Explain the function of phloem & ATP, in order to explain how food is transported in plants

How are soluble products of photosynthesis (sucrose, amino acids) transported through phloem tissue according to seasonal plant requirements?

During translocation, sucrose is actively loaded into the sieve tubes of phloem against a concentration gradient. How is this initial loading achieved?

Illustrate the process involved in human excretory system, in order to explain how waste is transported out of humans body

During urine formation in a nephron, initial glomerular filtrate (~180 litres/day) is modified by extensive selective tubular reabsorption. What is the biological advantage of selective reabsorption along the renal tubule?

Describe transpiration and other ways in which plants shed extra wastes, in order to explain excretion in plants

Plants do not possess specialized excretory organs like kidneys. Besides transpiration of excess water and diffusion of metabolic gases ($\text{O}_2$ and $\text{CO}_2$), how do plants eliminate cellular metabolic wastes?

Case Study & Contextual Questions

In clinical haemodialysis, from what type of blood vessel is blood taken out of the patient’s body to enter the dialysis machine, and through what vessel is it returned after purification?

Which vital organ acts as the natural filtration and dialysis chamber in the human body by constantly removing metabolic nitrogenous wastes from circulating blood?

Sanjeev compared the results of this activity with a second control pot setup to confirm that the water droplets came exclusively from the living leaves and not from evaporation of soil moisture. Which of the following best represents the required control setup?

How does the continuous loss of water vapour from plant leaves (transpiration) benefit the plant? Identify the two primary physiological functions.

Based on the anatomical and physiological principles of the human cardiovascular and respiratory systems, which statement is scientifically valid?

Which of the following will be the immediate physiological consequence if gaseous exchange across the pulmonary alveolar capillaries is acutely impaired or reduced?

Which labelled organ represents the largest accessory gland in the human body—the Liver—which secretes alkaline bile juice for emulsification of dietary fats?

CBSE Item Bank Questions

State the names of two major accessory organs associated with the alimentary canal: organ E (a pale yellow gland tucked beneath the stomach) and organ J (the large reddish-brown gland on the right side). Give one major digestive secretion produced by each.

Photosynthesis occurs in chloroplasts of green plants. In terms of chemical energetics and bond transformations, what fundamental type of chemical reaction is photosynthesis?

Write down the complete, balanced chemical symbol equation for photosynthesis in green plants, indicating essential catalysts and conditions written above and below the reaction arrow.

Explain how the two principal inorganic reactants required for photosynthesis—carbon dioxide and water—become available in the palisade and spongy mesophyll cells of plant leaves.

Explain the precise biological role of transpiration and the regulatory action of guard cells in mediating the upward transport of water from the root xylem to the leaf tip.

Which anatomical adaptation allows green plant leaves to achieve highly rapid and efficient gaseous exchange with minimal diffusion resistance?

Describe three key anatomical adaptations of alveoli that maximise the rate and volume of respiratory gas exchange between alveolar air and pulmonary capillary blood.

(i) Differentiate between aerobic respiration and anaerobic respiration in yeast in terms of end products formed.(ii) Explain why skeletal muscle cells produce lactic acid during vigorous physical exercise, and state its consequence.

Explain the biomechanical mechanism of human breathing. Detail how synchronized movements of the diaphragm and ribcage (intercostal muscles) bring about (i) Inhalation (inspiration) and (ii) Exhalation (expiration).

Bread moulds (Rhizopus) and other fungi grow rapidly on moist stale bread. How do these organisms obtain nutrition from the substrate?

Amoeba takes in food particles using temporary finger-like extensions of the cell surface (pseudopodia) which fuse over the food particle to form a food vacuole. How is this process advantageous for Amoeba?

(i) Differentiate between aerobic respiration and anaerobic respiration in yeast in terms of end products formed.
(ii) Explain why skeletal muscle cells produce lactic acid during vigorous physical exercise, and state its consequence.