Plant Physiology

Definition

The process by which plants take up water from the soil and move it through tissues using osmosis and diffusion.

Key Concepts

• Osmosis: Movement of water from high to low water potential.
• Turgor Pressure: Pressure of cell contents against the cell wall, keeping the plant upright.
• Plasmolysis: When a cell loses water and the membrane shrinks from the wall.

Examples & Real-Life Use

• Root Hair Absorption: Maximizes surface area for water intake.
• Wilting: Occurs when turgor pressure drops.
• Food Preservation: Pickling vegetables in salt creates a high-solute environment, drawing water out via osmosis to stop bacterial growth.

Definition

Ascent of Sap: Upward movement of water/minerals from roots to leaves.
Transpiration: Loss of water vapor from leaves.

Mechanism

• Cohesion: Water molecules sticking to each other.
• Adhesion: Water molecules sticking to xylem walls.
• Transpiration Pull: The suction force acting like a "straw" pulling water upward.

Examples & Real-Life Use

• Guttation: Droplets on leaf tips due to root pressure.
• Forest Cooling: Transpiration releases vapor that absorbs heat, acting as a natural air conditioner.

Definition

The movement of organic nutrients (sucrose) from sources (leaves) to sinks (roots, fruits, seeds).

Key Points

• Bidirectional movement (Up and Down).
• Uses energy (ATP) to push sugar into the phloem.

Real-Life Use

Grafting: Ensuring phloem and xylem align between two plant varieties so nutrients can flow to the branch.

Categorization

• Macronutrients: Needed in large amounts (C, H, O, N, P, K, Ca, Mg, S).
• Micronutrients: Needed in tiny amounts (Fe, Mn, Cu, Zn, B, Mo, Cl).

Real-Life Application: NPK Fertilizers

N (Nitrogen): Green leaves | P (Phosphorus): Roots/Flowers | K (Potassium): Disease resistance.

The Process

Converting atmospheric $N_2$ (unusable) into ammonia or nitrates (usable).

• Nitrogen Fixation: $N_2 \rightarrow NH_3$ (via *Rhizobium*).
• Nitrification: $NH_3 \rightarrow NO_2 \rightarrow NO_3$.
• Denitrification: $NO_3 \rightarrow N_2$.

Real-Life Use: Crop Rotation

Rotating nitrogen-consuming crops (corn) with nitrogen-fixing crops (soybeans) to maintain soil fertility naturally.

The Site

Occurs in the Chloroplast (Thylakoids and Stroma).

The Two Stages

1. Light Reaction (Thylakoids): Light $\rightarrow$ splits water $\rightarrow$ produces ATP, NADPH, and Oxygen.
2. Dark Reaction/Calvin Cycle (Stroma): Uses ATP/NADPH $\rightarrow$ turns $CO_2$ into Glucose.

C3 vs C4 Pathways

• C3: Standard; first product is a 3-carbon molecule (e.g., Rice, Wheat).
• C4: Efficient in heat; first product is a 4-carbon molecule (e.g., Maize, Sugarcane).
• Photorespiration: Wasteful process in C3 plants where Rubisco binds to Oxygen.

Real-Life Use: Grow Lights

LEDs emitting Blue and Red wavelengths are used for indoor gardening to optimize photosynthetic efficiency.

Stages of Aerobic Respiration

• Glycolysis: Glucose $\rightarrow$ Pyruvate (Cytoplasm).
• TCA/Krebs Cycle: Pyruvate $\rightarrow$ $CO_2$ + Energy (Mitochondrial Matrix).
• ETS: Massive ATP production (Inner Mitochondrial Membrane).

Comparison

• Aerobic: Needs $O_2$; yields $\sim 36-38$ ATP.
• Anaerobic: No $O_2$; yields only 2 ATP (e.g., Yeast fermentation).

Real-Life Use: Seed Storage

Seeds are dried to lower respiration rates; moist seeds respire too quickly, exhausting energy and failing to germinate.

Growth Processes

• Differentiation: General cell $\rightarrow$ Specialized cell.
• Dedifferentiation: Specialized $\rightarrow$ General (Dividing).
• Redifferentiation: General $\rightarrow$ New Specialized.

Plant Growth Regulators (Hormones)

1. The driving force for the ascent of sap in tall trees is:
   Ans: b) Transpiration pull
2. Which of the following is a micronutrient?
   Ans: c) Zinc
3. The first stable product of the C3 cycle is:
   Ans: b) PGA
4. Kranz anatomy is a characteristic feature of:
   Ans: b) C4 plants
5. Glycolysis occurs in the:
   Ans: c) Cytoplasm
6. Which hormone is responsible for "Apical Dominance"?
   Ans: c) Auxin
7. The "Stress Hormone" in plants is:
   Ans: b) ABA
8. The process of converting $N_2$ gas into ammonia is called:
   Ans: c) Nitrogen Fixation
9. Which of these is a product of the Light Reaction?
   Ans: c) NADPH
10. Vernalization is the promotion of flowering by:
    Ans: b) Low temperature

1. Q: Explain the Cohesion-Tension Theory of water transport.
   Ans: Water molecules stick to each other (cohesion) and xylem walls (adhesion). Transpiration creates negative pressure (tension) that pulls the water column upward.
2. Q: What is the difference between Nitrogen Fixation and Nitrification?
   Ans: Fixation converts atmospheric $N_2$ to $NH_3$; Nitrification converts $NH_3$ to nitrites ($NO_2^-$) and then nitrates ($NO_3^-$).
3. Q: Why are C4 plants more efficient than C3 plants in hot climates?
   Ans: Kranz anatomy concentrates $CO_2$ around Rubisco, preventing photorespiration and allowing stomata to partially close to save water.
4. Q: Describe the steps of Glycolysis.
   Ans: Breakdown of 1 glucose (6C) into 2 pyruvic acid (3C) in cytoplasm, yielding 2 ATP and 2 NADH.
5. Q: What happens during the ETS in mitochondria?
   Ans: Electrons from NADH/FADH2 pass through proteins, pumping protons to create a gradient that drives ATP synthesis.
6. Q: How does ABA help a plant survive drought?
   Ans: ABA signals guard cells to lose turgidity and close stomata, stopping water loss.
7. Q: Explain the concept of Photoperiodism.
   Ans: The plant's response to day/night length; short-day plants flower when nights are long, long-day plants when nights are short.
8. Q: Compare Aerobic and Anaerobic respiration.
   Ans: Aerobic requires $O_2$ and yields $\sim 36-38$ ATP; Anaerobic occurs without $O_2$ and yields only 2 ATP.
9. Q: What is the role of the Calvin Cycle?
   Ans: It uses ATP and NADPH from light reactions to fix $CO_2$ into PGA, eventually forming glucose.
10. Q: Define Differentiation, Dedifferentiation, and Redifferentiation.
    Ans: Differentiation (Meristem $\rightarrow$ Xylem), Dedifferentiation (Xylem $\rightarrow$ Meristem), Redifferentiation (Meristem $\rightarrow$ Cork).

• Macro-nutrients: *"Naughty People Keep Causing Mg (Magic) Stroubles"* (N, P, K, Ca, Mg, S).
• Plant Hormones: *"All Good Crops Eat Air"* (Auxin, Gibberellin, Cytokinin, Ethylene, ABA).
• Nitrogen Cycle: *"Fix Nitrate Denitrify"* (Fixation $\rightarrow$ Nitrification $\rightarrow$ Denitrification).