The rate of photosynthesis increases with increasing CO2 concentration only up to a certain point. This point is called:
ASaturation point
BCompensation point
COptimal point
DLight-saturation point
Correct Answer: A. Saturation point
Explanation:
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.
Which of the following is characteristic of monocot roots?
APresence of secondary growth
BAdventitious roots arising from stem nodes
CTap root system with lateral branches
DVascular bundles arranged in rings
Correct Answer: B. Adventitious roots arising from stem nodes
Explanation:
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.
Abscisic acid (ABA) functions primarily as which type of hormone?
AGrowth promoter
BStress hormone
CFlowering hormone
DRipening hormone
Correct Answer: B. Stress hormone
Explanation:
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.
The green color of chloroplasts is due to which property of chlorophyll?
AEmission of green light
BReflection and transmission of green light
CAbsorption of all wavelengths equally
DProduction of green pigment in stroma
Correct Answer: B. Reflection and transmission of green light
Explanation:
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.
The process of nitrogen fixation in legumes is performed by which organism?
ARhizopus
BRhizobium (Nitrogen-fixing bacteria in root nodules)
CAzotobacter in soil
DNitrosomonas in soil
Correct Answer: B. Rhizobium (Nitrogen-fixing bacteria in root nodules)
Explanation:
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.
Which of the following shows the highest photosynthetic efficiency?
AC3 plants in cool, moist climate
BC4 plants in hot, dry climate
CCAM plants during day
DAll show equal efficiency
Correct Answer: B. C4 plants in hot, dry climate
Explanation:
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.
During photosynthesis, the lumenal pH of thylakoids drops to approximately:
A2-3
B4-5
C6-7
D8-9
Correct Answer: B. 4-5
Explanation:
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.
Which of the following is a hydrophobic protein complex involved in photosynthesis?
ARubisco
BPhotosystem I (PSI) in thylakoid membrane
CFerredoxin
DPlastocyanin
Correct Answer: B. Photosystem I (PSI) in thylakoid membrane
Explanation:
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.
