Govt. Exams
Entrance Exams
Plasmolysis is the shrinkage of protoplasm away from the cell wall when placed in hypertonic solution. It's reversible if not prolonged.
The saturation point is the CO2 concentration beyond which photosynthesis rate does not increase further, limited by other factors like temperature or light.
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).
# 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]
Nitrosomonas is a chemosynthetic bacterium that oxidizes ammonia to nitrite, obtaining energy without requiring light (unlike photosynthetic organisms).
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.
Ethylene is the major hormone controlling senescence (aging) in plants, promoting leaf yellowing, fruit ripening, and abscission.
The nucleolus within the nucleus is the site of ribosomal RNA (rRNA) synthesis and ribosome assembly in eukaryotic cells.
The Casparian strip contains suberin (waxy substance) and lignin, which prevents apoplastic (cell wall) movement of water and minerals, forcing symplastic transport.
Osmosis is passive transport of water molecules across a semipermeable membrane in response to water potential differences.
