Question 1

Which of the following is NOT a requirement for biosynthesis (anabolism) in microbial cells?

Accepted Answer

Direct absorption of complex biomolecules from the environment

Question 2

Which enzyme catalyzes the carboxylation of ribulose 1,5-bisphosphate in the Calvin cycle?

Accepted Answer

Rubisco

Question 3

During the Calvin cycle, what is the fate of the majority of glyceraldehyde 3-phosphate (G3P) molecules produced?

Accepted Answer

They are used to regenerate ribulose 1,5-bisphosphate

Question 4

Which of the following best describes the energetic cost of nitrogen fixation in living cells?

Accepted Answer

It is highly energy-intensive, requiring about 16 ATP per N2 fixed

Question 5

Which of the following equations correctly represents the overall reaction for biological nitrogen fixation?

Accepted Answer

$\mathrm{N_2 + 8H^+ + 8e^- + 16\ ATP \rightarrow 2\ NH_3 + H_2 + 16\ ADP + 16\ P_i}$

Question 6

Which of the following is a key regulatory strategy microbes use to minimize the energetic cost of biosynthesis?

Accepted Answer

Regulation of enzyme activity and gene expression

Question 7

In the reverse (reductive) TCA cycle, which molecule is regenerated to allow for the fixation of CO2?

Accepted Answer

Oxaloacetate

Question 8

Which of the following best explains why nitrogen fixation is restricted to specialized cells or structures in some organisms?

Accepted Answer

Nitrogenase is highly sensitive to oxygen

Question 9

Which of the following is a direct product of the Calvin cycle that can be used for biosynthesis?

Accepted Answer

Glyceraldehyde 3-phosphate (G3P)

Question 10

A mutant bacterium lacks the ability to regenerate ribulose 1,5-bisphosphate. Which step of the Calvin cycle will be directly affected?

Accepted Answer

Regeneration phase

Question 11

Which of the following best describes the role of NADPH in biosynthetic pathways?

Accepted Answer

It provides reducing power for anabolic reactions

Question 12

Which of the following is a real-world example of a symbiotic nitrogen-fixing relationship?

Accepted Answer

Rhizobium bacteria in root nodules of legumes

Question 13

Which of the following is a correct description of anaplerotic reactions?

Accepted Answer

They regenerate TCA cycle intermediates by fixing CO2

Question 14

Which of the following best explains why nodulated legumes can grow in nitrogen-poor soils?

Accepted Answer

They form a symbiosis with bacteria that fix atmospheric N2 into ammonia

Question 15

Which of the following is a correct sequence of events in the mechanism of nitrogenase during nitrogen fixation?

Accepted Answer

Fe protein transfers electrons to FeMo center, H2 is released, N2 binds, then N2 is reduced to NH3

Question 16

Which of the following is a major difference between the Calvin cycle and the reverse TCA cycle?

Accepted Answer

The Calvin cycle fixes CO2 using Rubisco, while the reverse TCA cycle fixes CO2 using TCA enzymes in reverse

Question 17

Which of the following best describes the role of leghemoglobin in root nodules?

Accepted Answer

It binds oxygen to protect nitrogenase from inactivation

Question 18

Which of the following is a plausible consequence if a plant lacks the ability to form root nodules with Rhizobium?

Accepted Answer

The plant will have reduced access to fixed nitrogen and may show stunted growth in nitrogen-poor soils

Microbial Biosynthesis, Carbon Fixation, and Nitrogen Metabolism

Study Guide - Practice Questions