Plant Physiology Photosynthesis Transpiration

1. Detailed Mindmap (Plant Physiology)

mindmap
  root((Plant Physiology))
    Photosynthesis
      Light-Reaction
      Dark-Reaction
      Factors
    Transpiration
      Mechanism
      Stomata-Control
      Importance
    Respiration
      Glycolysis
      Krebs-Cycle
      ETC

2. Overview: The Energy Engine of Plants

Plant physiology is the study of plant function and behavior, covering all the dynamic processes that allow a plant to grow, metabolize, and reproduce. At the heart of this lie two critical processes: Photosynthesis (energy capture) and Transpiration (water transport and cooling).पादप कार्यिकी पौधों के कार्य और व्यवहार का अध्ययन है, जिसमें वे सभी गतिशील प्रक्रियाएं शामिल हैं जो पौधे को बढ़ने, चयापचय करने और प्रजनन करने की अनुमति देती हैं। इसके केंद्र में दो महत्वपूर्ण प्रक्रियाएं हैं: प्रकाश संश्लेषण (ऊर्जा कैप्चर) और वाष्पोत्सर्जन (जल परिवहन और शीतलन)।

3. Photosynthesis: The Chemical Foundation

Photosynthesis is a physico-chemical process by which green plants use light energy to drive the synthesis of organic compounds. The primary equation is: 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O. This process occurs primarily in the chloroplasts, specifically within the thylakoid membranes and the stroma.

Key Fact: Chlorophyll 'a' is the primary photosynthetic pigment, while chlorophyll 'b', xanthophylls, and carotenoids are accessory pigments.

4. Light Reaction (Photochemical Phase)

The light-dependent reaction occurs in the thylakoid membranes. It involves light absorption, water splitting (photolysis), oxygen release, and the formation of high-energy chemical intermediates, ATP and NADPH. The process is driven by two photosystems: PS I (P700) and PS II (P680).

Feature	Photosystem I	Photosystem II
Reaction Center	P700	P680
Location	Outer surface of thylakoids	Inner surface of thylakoids

5. Dark Reaction (Biosynthetic Phase)

The biosynthetic phase or Calvin Cycle uses the ATP and NADPH produced in the light reaction to reduce CO2 into sugars. It occurs in the stroma of the chloroplast. The cycle involves three stages: Carboxylation, Reduction, and Regeneration of RuBP.

Note: C3 plants (like wheat/rice) fix CO2 directly via RuBisCO, while C4 plants (like maize/sugarcane) use the Hatch-Slack pathway to minimize photorespiration.

6. Factors Affecting Photosynthesis

Blackman’s Law of Limiting Factors states that if a process is conditioned by a number of factors, its rate is limited by the pace of the slowest factor. Key factors include light intensity, CO2 concentration, temperature, and water availability.

Factor	Optimal Range	Effect
Temperature	25-35°C	Enzyme activity drops if too high
CO2	0.03-0.04%	Rate increases until saturation

7. Transpiration: The Water Pump

Transpiration is the evaporative loss of water by plants, which occurs mainly through the stomata in the leaves. It creates a 'transpiration pull' that facilitates the upward movement of water and minerals from roots to shoots (Xylem transport).

Significance: It maintains turgidity for cell structure and cools the leaf surface by 10-15 degrees.

8. Stomatal Mechanism

The opening and closing of stomata are regulated by the turgor pressure of guard cells. When guard cells become turgid due to K+ ion accumulation and water entry, the stomata open. When they lose water (flaccid), the stomata close.

Type	Stomatal Opening Time	Examples
Apple-Mulberry	Day	Most plants
Potato	Day/Night	Potato
Barley	Day	Cereals

9. Factors Influencing Transpiration

External factors include atmospheric humidity (high humidity decreases rate), wind speed (increases rate), and light intensity (stimulates stomatal opening). Internal factors include leaf surface area, number of stomata, and canopy structure.

Fact: Cobalt chloride paper is used to detect the rate of transpiration as it changes color from blue to pink upon water absorption.

10. C3 vs C4 Pathways

C4 plants exhibit 'Kranz Anatomy', where bundle sheath cells are large and packed with chloroplasts. This allows them to concentrate CO2, effectively eliminating photorespiration, a wasteful process common in C3 plants under high light/heat.

Feature	C3 Plants	C4 Plants
First Product	3-PGA	Oxaloacetic acid
Primary Enzyme	RuBisCO	PEPCase
Efficiency	Lower	Higher

11. Mineral Nutrition & Transpiration Link

Transpiration is essential for the translocation of minerals. Since minerals are absorbed by roots from the soil, the transpiration stream acts as a conveyor belt, moving ions like Nitrogen, Phosphorus, and Potassium upward to growing tissues.

12. Photorespiration

Photorespiration is a light-dependent process where RuBisCO acts as an oxygenase rather than a carboxylase, consuming O2 and releasing CO2 without producing ATP or sugar. This is a net loss for the plant, prevalent in C3 plants under stress.

13. Important Mnemonics for Exam

To remember the limiting factors: 'L-C-T-W' (Light, CO2, Temp, Water). For the Calvin Cycle stages: 'C-R-R' (Carboxylation, Reduction, Regeneration). Remember, RuBisCO is the most abundant protein on Earth!

14. Summary Table: Physiological Processes

Process	Primary Function	Main Organ
Photosynthesis	Food Synthesis	Chloroplast
Transpiration	Cooling/Transport	Stomata
Respiration	Energy Release	Mitochondria

15. Tips for UPSSSC Lower Mains

Focus on the 'Why' and 'Where'. UPSSSC often asks about the location (Stroma vs Thylakoid) and the specific enzymes involved (RuBisCO vs PEPCase). Always review the difference between C3 and C4 plants as it is a high-yield topic.

Plant Physiology Photosynthesis Transpiration Plant Physiology Photosynthesis Transpiration (विज्ञान)