Q: Which of the following best explains why fermentation is necessary for some microorganisms in the absence of external electron acceptors?

Fermentation enables the cell to oxidize NADH back to NAD\textsuperscript{+}, maintaining redox balance.

Q: During lactic acid fermentation, what is the net ATP yield per molecule of glucose, and what is the fate of NADH?

2 ATP; NADH reduces pyruvate to lactate, regenerating NAD\textsuperscript{+}.

Q: Which of the following statements about chemolithotrophy is correct?

Chemolithotrophs use inorganic compounds such as H\textsubscript{2}S, H\textsubscript{2}, Fe\textsuperscript{2+}, and NH\textsubscript{4}\textsuperscript{+} as electron donors.

Q: Which of the following best describes the Calvin Cycle?

It is an anabolic pathway that fixes CO\textsubscript{2} into organic molecules using ATP and NADPH.

Question 1

Which of the following best explains why fermentation is necessary for some microorganisms in the absence of external electron acceptors?

Accepted Answer

Fermentation enables the cell to oxidize NADH back to NAD	extsuperscript{+}, maintaining redox balance.

Question 2

During lactic acid fermentation, what is the net ATP yield per molecule of glucose, and what is the fate of NADH?

Accepted Answer

2 ATP; NADH reduces pyruvate to lactate, regenerating NAD	extsuperscript{+}.

Question 3

Which of the following is a key difference between aerobic respiration and fermentation in E. coli?

Accepted Answer

Aerobic respiration uses an external electron acceptor, while fermentation does not.

Question 4

A bacterium is growing in an environment with no oxygen but with nitrate available. Which metabolic pathway will it most likely use for energy conservation?

Accepted Answer

Anaerobic respiration using nitrate as the terminal electron acceptor

Question 5

Which of the following statements about chemolithotrophy is correct?

Accepted Answer

Chemolithotrophs use inorganic compounds such as H	extsubscript{2}S, H	extsubscript{2}, Fe	extsuperscript{2+}, and NH	extsubscript{4}	extsuperscript{+} as electron donors.

Question 6

Which enzyme is responsible for the fixation of atmospheric nitrogen (N	extsubscript{2}) into ammonia (NH	extsubscript{3}) in certain bacteria and archaea?

Accepted Answer

Nitrogenase

Question 7

Why is nitrogenase activity highly sensitive to oxygen, and what is one microbial strategy to protect it?

Accepted Answer

Oxygen inhibits nitrogenase; microbes form heterocysts or slime layers to limit O	extsubscript{2} exposure.

Question 8

Which of the following best describes the Calvin Cycle?

Accepted Answer

It is an anabolic pathway that fixes CO	extsubscript{2} into organic molecules using ATP and NADPH.

Question 9

Which of the following is a product of the pentose phosphate pathway and is essential for nucleotide biosynthesis?

Accepted Answer

Ribulose-5-phosphate

Question 10

A mutation in the gene encoding acyl carrier protein (ACP) would most directly affect which cellular process?

Accepted Answer

Fatty acid biosynthesis

Question 11

Which of the following best explains why lactic acid bacteria are important in food preservation?

Accepted Answer

They produce lactic acid, which lowers pH and inhibits spoilage organisms.

Question 12

Which of the following is true regarding the energetics of fermentation compared to aerobic respiration?

Accepted Answer

Fermentation produces only 2 ATP per glucose, while aerobic respiration can produce up to 38 ATP per glucose.

Question 13

Which of the following is a key function of the pentose phosphate pathway in microbial cells?

Accepted Answer

Production of NADPH and ribose-5-phosphate for biosynthesis

Question 14

Which of the following statements about gluconeogenesis is correct?

Accepted Answer

Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors and requires ATP.

Question 15

Which of the following is a direct precursor for the synthesis of most amino acids in bacteria?

Accepted Answer

Intermediates from glycolysis and the citric acid cycle

Question 16

What is the main role of glutamate dehydrogenase in amino acid biosynthesis?

Accepted Answer

Incorporation of ammonia into α-ketoglutarate to form glutamate

Question 17

Which of the following is true about the biosynthesis of purines and pyrimidines?

Accepted Answer

Both are synthesized atom by atom from several carbon and nitrogen sources.

Question 18

Which of the following best describes the effect of temperature on fatty acid biosynthesis in bacteria?

Accepted Answer

Low temperatures promote the synthesis of shorter-chain and unsaturated fatty acids.

Question 19

Which of the following is a distinguishing feature of phototrophy in microorganisms?

Accepted Answer

ATP is generated by photophosphorylation using light energy.

Microbial Metabolism and Biosynthesis: Study Notes for Microbiology

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