Which enzyme catalyzes the primary carboxylation reaction in the Calvin cycle? MCQ with Answer and Explanation

Which enzyme catalyzes the primary carboxylation reaction in the Calvin cycle?
A. RuBisCO
B. Carbonic anhydrase
C. PEP carboxylase
D. Nitrogenase
Answer: Option A
Solution (By JKSSB Mock Tests)
RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is the most abundant protein on Earth and the key enzyme in the Calvin cycle (C3 pathway). It catalyzes the fixation of CO2 by attaching it to Ribulose-1,5-bisphosphate (RuBP) to form a 6-carbon intermediate that immediately splits into two molecules of 3-PGA.

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Practice More Biology Questions

Question #1
The most common species of honeybee used for commercial apiculture in India is:
A. Apis dorsata
B. Apis florea
C. Apis mellifera
D. Apis cerana indica

Correct Answer: Option D


Explanation:
Apis cerana indica (the Indian honeybee) is the most commonly domesticated species for commercial apiculture (beekeeping) in India. It is well-adapted to the local climate and is less aggressive than Apis dorsata (the rock bee). Apis mellifera (the Italian bee) is also widely used globally and in India for its high honey yield and gentle nature. Apis florea is the little bee, which is not suitable for commercial beekeeping.

This question belongs to: Science Biology
Question #2
Consider statements about environment: 1. Carbon dioxide is a greenhouse gas. 2. Methane is a greenhouse gas. 3. Oxygen is a major greenhouse gas. Which are correct?
A. 1 and 3 only
B. 1 and 2 only
C. 2 and 3 only
D. 1, 2 and 3

Correct Answer: Option B


Explanation:
Greenhouse gases trap heat in the Earth's atmosphere, contributing to the greenhouse effect and global warming. Carbon dioxide (CO2) and methane (CH4) are potent greenhouse gases emitted through human activities like fossil fuel combustion and agriculture. Oxygen (O2) and nitrogen (N2), which make up the majority of the atmosphere, are not greenhouse gases as they do not absorb infrared radiation. Thus, statements 1 and 2 are correct.

This question belongs to: Science Biology
Question #3
Assertion (A): The genetic code is universal.
Reason (R): The same codon codes for the same amino acid in all organisms.
A. A false, R true.
B. Both A and R are true, but R is not the correct explanation.
C. Both A and R are true, and R is the correct explanation.
D. A true, R false.

Correct Answer: Option C


Explanation:
Universality means that with few exceptions, codons specify the same amino acids across species. This is the evidence, so R correctly explains A.

This question belongs to: Science Biology