General Science - MCQ Practice Questions

CO2 saturation point is where further increase in CO2 doesn't increase photosynthesis rate because other factors (like enzyme activity) become limiting. Compensation point is where photosynthesis equals respiration.

Monocots typically have fibrous root systems with adventitious roots. They lack secondary growth (no cambium) and have scattered vascular bundles. Dicots have tap roots and show secondary growth.

ABA is a stress hormone that accumulates during drought, regulating stomatal closure and promoting seed dormancy. It antagonizes gibberellins and cytokinins. This is crucial for understanding plant responses to environmental stress.

Chlorophyll absorbs blue and red light but reflects and transmits green light, making plants appear green. This is why plants cannot utilize green light efficiently for photosynthesis - a fundamental physics-biology concept.

Wood is composed of secondary xylem with thick-walled tracheids and vessel elements that provide mechanical support and water transport. Annual rings visible in wood represent secondary xylem produced by vascular cambium.

Rhizobium bacteria form symbiotic associations with legume roots, fixing atmospheric N2 into ammonia. The bacteria live in root nodules. This symbiotic relationship is agriculturally significant and frequently tested in competitive exams.

C4 plants have higher photosynthetic efficiency (~60%) compared to C3 plants (~30%) because they concentrate CO2 around RuBisCO, reducing photorespiration. This adaptation makes them suited for hot climates - important agricultural knowledge.

Protons accumulate in the thylakoid lumen (pH 4-5) due to water photolysis and electron transport, creating a chemiosmotic gradient for ATP synthesis. The stroma maintains pH ~8. This proton gradient is essential for understanding light reactions.

Photosystem I is an integral membrane protein complex with multiple transmembrane domains, making it hydrophobic. Rubisco is soluble, while ferredoxin and plastocyanin are soluble electron carriers. This biochemical distinction is important for understanding photosynthetic mechanisms.

Mitochondria is the powerhouse of the cell and produces ATP through oxidative phosphorylation. Chloroplasts produce ATP through photophosphorylation.

Calcium pumps actively transport Ca²⁺ into vacuoles, serving as a calcium reservoir for second messenger signaling in plant cells.

In the Calvin cycle, RuBP combines with CO₂ to form 3-PGA (3-carbon compound), which is the first stable product detected in C3 plants.

Rubisco is the most abundant enzyme on Earth and catalyzes both carboxylation (photosynthesis) and oxygenation (photorespiration) of RuBP.

The Warburg effect in plants refers to photorespiration, where high O₂ competes with CO₂ for Rubisco binding, reducing net photosynthesis.

Arbuscular mycorrhizal fungi increase plant access to phosphorus and micronutrients (Zn, Cu) through their extensive hyphal networks in soil.

The casparian strip is a hydrophobic barrier of suberin and lignin in the endodermis that prevents apoplastic transport and regulates ion uptake.

Maize is a C4 plant with higher photosynthetic efficiency and drought tolerance compared to C3 crops like wheat and rice.

Quantum yield is the ratio of CO₂ fixed to photons absorbed, typically 0.05-0.1 (5-10 CO₂ per 100 photons).

Guttation is the exudation of xylem sap through hydathodes, caused by positive root pressure, especially in early morning when transpiration is low.

Osmotically active solutes like glucose, sucrose, malate, and K⁺ ions accumulate in vacuoles to maintain turgor pressure and cell rigidity.