Which of the following is a C4 plant commonly cultivated in India for fodder and grain production?
A
Wheat
B
Maize (Corn)
C
Rice
D
Barley
Correct Answer:
B. Maize (Corn)
Explanation:
Maize is a C4 plant with higher photosynthetic efficiency and drought tolerance compared to C3 crops like wheat and rice.
The casparian strip in plant roots is composed primarily of:
A
Cellulose and pectin
B
Suberin and lignin
C
Chitin and protein
D
Keratin and elastin
Correct Answer:
B. Suberin and lignin
Explanation:
The casparian strip is a hydrophobic barrier of suberin and lignin in the endodermis that prevents apoplastic transport and regulates ion uptake.
Mycorrhizal associations in plants primarily enhance the uptake of which nutrients?
A
Nitrogen and potassium
B
Phosphorus and micronutrients
C
Calcium and magnesium
D
Sulfur and iron
Correct Answer:
B. Phosphorus and micronutrients
Explanation:
Arbuscular mycorrhizal fungi increase plant access to phosphorus and micronutrients (Zn, Cu) through their extensive hyphal networks in soil.
The phenomenon where plants show reduced photosynthesis when exposed to high oxygen concentrations is called:
A
Warburg effect
B
Crabtree effect
C
Pasteur effect
D
Joule effect
Correct Answer:
A. Warburg effect
Explanation:
The Warburg effect in plants refers to photorespiration, where high O₂ competes with CO₂ for Rubisco binding, reducing net photosynthesis.
Which enzyme catalyzes the carboxylation of RuBP in the Calvin cycle, and what is its full name?
A
Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase)
B
Phosphofructokinase
C
Aldolase
D
Pyruvate dehydrogenase
Correct Answer:
A. Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase)
Explanation:
Rubisco is the most abundant enzyme on Earth and catalyzes both carboxylation (photosynthesis) and oxygenation (photorespiration) of RuBP.
During C3 photosynthesis, the first stable product formed after CO₂ fixation is:
A
Glucose
B
3-Phosphoglycerate (3-PGA)
C
Ribulose-1,5-bisphosphate (RuBP)
D
Pyruvate
Correct Answer:
B. 3-Phosphoglycerate (3-PGA)
Explanation:
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.
The calcium pump in plant cell vacuole membrane is primarily involved in:
A
Maintaining osmotic potential
B
Regulating turgor pressure
C
Sequestering calcium ions for cellular signaling
D
Photosynthesis regulation
Correct Answer:
C. Sequestering calcium ions for cellular signaling
Explanation:
Calcium pumps actively transport Ca²⁺ into vacuoles, serving as a calcium reservoir for second messenger signaling in plant cells.
Which of the following organelles is responsible for synthesizing ATP through oxidative phosphorylation in plant cells?
A
Mitochondria
B
Chloroplast
C
Ribosome
D
Golgi apparatus
Correct Answer:
A. Mitochondria
Explanation:
Mitochondria is the powerhouse of the cell and produces ATP through oxidative phosphorylation. Chloroplasts produce ATP through photophosphorylation.
Which of the following is a hydrophobic protein complex involved in photosynthesis?
A
Rubisco
B
Photosystem I (PSI) in thylakoid membrane
C
Ferredoxin
D
Plastocyanin
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.
During photosynthesis, the lumenal pH of thylakoids drops to approximately:
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.
