General Science - MCQ Practice Questions

G3P (Glyceraldehyde-3-phosphate) is the final product of the reduction phase where 3-PG is reduced using ATP and NADPH from light reactions.

When O2 concentration is high, RuBisCO catalyzes oxygenase activity, causing O2 to react with RuBP instead of CO2, initiating photorespiration.

Stomata open during the day (when light is available for photosynthesis) and close at night. This reduces water loss during low photosynthetic activity periods.

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

Sugarcane is a C4 plant adapted to high light and temperature conditions. C4 plants first fix CO2 into a 4-carbon compound (oxaloacetate).

Exudation or guttation occurs when root pressure forces water out through specialized pores (hydathodes) as liquid water droplets, typically observed in early morning.

Abscisic acid (ABA) promotes seed dormancy and inhibits germination, acting antagonistically to gibberellins which promote germination.

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).

Osmosis is passive transport of water molecules across a semipermeable membrane in response to water potential differences.

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

The nucleolus within the nucleus is the site of ribosomal RNA (rRNA) synthesis and ribosome assembly in eukaryotic cells.

Ethylene is the major hormone controlling senescence (aging) in plants, promoting leaf yellowing, fruit ripening, and abscission.

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.

Nitrosomonas is a chemosynthetic bacterium that oxidizes ammonia to nitrite, obtaining energy without requiring light (unlike photosynthetic organisms).

# 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.

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 saturation point is the CO2 concentration beyond which photosynthesis rate does not increase further, limited by other factors like temperature or light.

Plasmolysis is the shrinkage of protoplasm away from the cell wall when placed in hypertonic solution. It's reversible if not prolonged.