Stomatal conductance (gs) is the rate of gas diffusion through stomata, dependent on aperture width and inversely on distance (g = A/L).

PSII catalyzes photolysis of water at the oxygen-evolving complex, transferring electrons to plastoquinone in the thylakoid membrane.

Water photolysis occurs in the thylakoid lumen as part of Photosystem II, releasing O2, H+, and electrons that drive the electron transport chain.

For every 3 turns of Calvin cycle (fixing 3 CO2), 9 ATP and 6 NADPH are used. This gives a ratio of 3:2 (ATP:NADPH).

The Casparian strip contains suberin (waxy substance) and lignin, which prevents apoplastic (cell wall) movement of water and minerals, forcing symplastic transport.

The Z-scheme illustrates electron flow from PSII through the cytochrome b6f complex to PSI, showing how electrons are elevated twice to reach NADP+ reduction.

# Transpiration Coefficient in Different Plant Types

The transpiration coefficient measures water loss efficiency relative to biomass production, with lower values indicating more water-efficient plants.

Step 1: Understanding Transpiration Coefficient

The transpiration coefficient is defined as the ratio of water transpired to dry matter produced by a plant.

Step 2: Comparing Photosynthetic Pathways

C4 plants (like maize, sugarcane) have evolved a specialized two-stage carbon fixation process using phosphoenolpyruvate carboxylase, which concentrates CO₂ around RuBisCO enzyme. This reduces photorespiration and allows stomata to remain partially closed, minimizing water loss while maintaining photosynthetic efficiency.

- C3 plants (wheat, rice): Open stomata longer, higher transpiration coefficient (~500-600)

- C4 plants (maize, sugarcane): Efficient CO₂ fixation, lower transpiration coefficient (~200-250)

- CAM plants (cactus): Open stomata at night only, but produce less dry matter per unit time

- Hydrophytes (aquatic plants): Abundant water, no water conservation mechanism

The transpiration coefficient is lowest in C4 plants because they maximize photosynthetic efficiency while minimizing water loss through specialized leaf anatomy and biochemical pathways.

[Final Answer: (B) C4 plants]

While plant cells lack true centrosomes with centrioles, plasmodesmata serve similar intercellular communication functions. However, most plant cells lack a distinct MTOC (microtubule-organizing center).

The azimuthal quantum number (l) determines the shape of the orbital (s, p, d, f)

Resistance R = ρL/A. When length doubles, L becomes 2L and area becomes A/2 (volume constant). New R = ρ(2L)/(A/2) = 4ρL/A = 4R