Microbial Metabolism Questions and Answers

Q: Complete oxidation of glucose in aerobic respiration can yield a net output of _____ATP.

Correct answer: 38Complete aerobic oxidation yields about 38 ATP in the classical accounting: 4 from substrate-level phosphorylation, and the rest from reoxidising 10 NADH and 2 FADH2 through the electron transport chain. Modern measurements put the real figure nearer 30, because the proton gradient also pays for transport across the membrane.

Q: Psychrophiles would be expected to grow:

Correct answer: at refrigeration temperaturesPsychrophiles are cold-loving, growing best below about 15°C and often at 0°C. Their enzymes and membranes are adapted to stay flexible in the cold, which is why they spoil refrigerated food while mesophiles cannot.

Q: Radioisotopes are frequently used in the study of cells. Assume a culture of E. coli is grown in a culture medium containing radioactive sulphur. At the end of 48 hours, it is expected to find the radioactive label located in

Correct answer: enzymesSulfur enters the cell chiefly as cysteine and methionine, so a 35S label ends up in proteins, enzymes among them. Nucleic acids contain no sulfur at all, which is exactly what Hershey and Chase exploited when they used 35S to label phage protein and 32P to label its DNA.

Q: Which enzyme is responsible for biological nitrogen fixation ?

Correct answer: NitrogenaseNitrogenase reduces atmospheric N2 to ammonia, an energy-expensive reaction requiring around 16 ATP per molecule fixed. The enzyme is irreversibly inactivated by oxygen, which is why nitrogen-fixing cells protect it inside heterocysts or root nodules.

Q: What is the end product of glycolysis ?

Correct answer: PyruvateGlycolysis splits glucose into two molecules of pyruvate. What follows depends on conditions: pyruvate enters the Krebs cycle by way of acetyl-CoA when a terminal electron acceptor is available, and is reduced to fermentation products when one is not.

Q: A cell exposed to a hypertonic environment will _____by osmosis:

Correct answer: lose waterA hypertonic environment has the higher solute concentration outside, so water moves out of the cell, down its own gradient. In a walled bacterial or plant cell the membrane pulls away from the wall - plasmolysis. Bursting is what happens in a hypotonic solution.

Q: The catabolic reaction, pentose-phosphate exists in

Correct answer: prokaryotic and eukaryotic cells bothThe pentose phosphate pathway is essentially universal, found in bacteria and in eukaryotes alike. Its products are needed everywhere: NADPH for biosynthesis and for defence against oxidative damage, and ribose-5-phosphate for nucleotides.

Q: Which of the following does not produce oxygen as a product of photosynthesis?

Correct answer: Purple sulfur bacteriaPurple sulfur bacteria are anoxygenic photosynthesisers: they use H2S rather than water as the electron donor, so the by-product is elemental sulfur, not oxygen. Oak trees, cyanobacteria and phytoplankton all split water and release O2.

Q: Most oxidation reactions in microbial bioenergetics involve the

Correct answer: removal of electrons and hydrogensIn biological systems oxidation almost always means the removal of hydrogen atoms - each an electron with its proton - transferred to a carrier such as NAD+ or FAD. That is why the enzymes are called dehydrogenases. The older definition, addition of oxygen, describes only a minority of biological oxidations.

Q: Phosphate regulation has been observed in the production of

Correct answer: all of thesePhosphate represses secondary metabolism generally, and the effect has been demonstrated across quite different product classes - antibiotics, alkaloids and gibberellins alike. It is a general regulatory phenomenon rather than a peculiarity of one pathway.

31.

Complete oxidation of glucose in aerobic respiration can yield a net output of _____ATP.

A.40
B.6
C.38
D.2

Answer: C

Correct answer: 38

Complete aerobic oxidation yields about 38 ATP in the classical accounting: 4 from substrate-level phosphorylation, and the rest from reoxidising 10 NADH and 2 FADH₂ through the electron transport chain. Modern measurements put the real figure nearer 30, because the proton gradient also pays for transport across the membrane.

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32.

Psychrophiles would be expected to grow:

A.in hot springs
B.on the human body
C.at refrigeration temperatures
D.at low pH

Answer: C

Correct answer: at refrigeration temperatures

Psychrophiles are cold-loving, growing best below about 15°C and often at 0°C. Their enzymes and membranes are adapted to stay flexible in the cold, which is why they spoil refrigerated food while mesophiles cannot.

Discuss in Forum

33.

Radioisotopes are frequently used in the study of cells. Assume a culture of E. coli is grown in a culture medium containing radioactive sulphur. At the end of 48 hours, it is expected to find the radioactive label located in

A.DNA
B.enzymes
C.RNA
D.all of these

Answer: B

Correct answer: enzymes

Sulfur enters the cell chiefly as cysteine and methionine, so a ³⁵S label ends up in proteins, enzymes among them. Nucleic acids contain no sulfur at all, which is exactly what Hershey and Chase exploited when they used ³⁵S to label phage protein and ³²P to label its DNA.

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34.

Which enzyme is responsible for biological nitrogen fixation ?

A.Nitrate reductase
B.Nitrogenase
C.Nitrite oxidase
D.Urease

Answer: C

Correct answer: Nitrogenase

Nitrogenase reduces atmospheric N2 to ammonia, an energy-expensive reaction requiring around 16 ATP per molecule fixed. The enzyme is irreversibly inactivated by oxygen, which is why nitrogen-fixing cells protect it inside heterocysts or root nodules.

Discuss in Forum

35.

What is the end product of glycolysis ?

A.Lactic acid
B.Pyruvate
C.Acetyl-CoA
D.Citrate

Answer: B

Correct answer: Pyruvate

Glycolysis splits glucose into two molecules of pyruvate. What follows depends on conditions: pyruvate enters the Krebs cycle by way of acetyl-CoA when a terminal electron acceptor is available, and is reduced to fermentation products when one is not.

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36.

A cell exposed to a hypertonic environment will _____by osmosis:

A.gain water
B.lose water
C.neither gain nor lose water
D.burst

Answer: B

Correct answer: lose water

A hypertonic environment has the higher solute concentration outside, so water moves out of the cell, down its own gradient. In a walled bacterial or plant cell the membrane pulls away from the wall - plasmolysis. Bursting is what happens in a hypotonic solution.

Discuss in Forum

37.

The catabolic reaction, pentose-phosphate exists in

A.prokaryotic cells
B.eukaryotic cells
C.prokaryotic and eukaryotic cells both
D.none of these

Answer: C

Correct answer: prokaryotic and eukaryotic cells both

The pentose phosphate pathway is essentially universal, found in bacteria and in eukaryotes alike. Its products are needed everywhere: NADPH for biosynthesis and for defence against oxidative damage, and ribose-5-phosphate for nucleotides.

Discuss in Forum

38.

Which of the following does not produce oxygen as a product of photosynthesis?

A.Oak trees
B.Purple sulfur bacteria
C.Cyanobacteria
D.Phytoplankton

Answer: B

Correct answer: Purple sulfur bacteria

Purple sulfur bacteria are anoxygenic photosynthesisers: they use H₂S rather than water as the electron donor, so the by-product is elemental sulfur, not oxygen. Oak trees, cyanobacteria and phytoplankton all split water and release O₂.

Discuss in Forum

39.

Most oxidation reactions in microbial bioenergetics involve the

A.removal of electrons and hydrogens
B.addition of electrons and hydrogens
C.addition of oxygen
D.removal of oxygen

Answer: A

Correct answer: removal of electrons and hydrogens

In biological systems oxidation almost always means the removal of hydrogen atoms - each an electron with its proton - transferred to a carrier such as NAD⁺ or FAD. That is why the enzymes are called dehydrogenases. The older definition, addition of oxygen, describes only a minority of biological oxidations.

Discuss in Forum

40.

Phosphate regulation has been observed in the production of

A.alkaloids
B.antibiotics
C.gibberellins
D.all of these

Answer: D

Correct answer: all of these

Phosphate represses secondary metabolism generally, and the effect has been demonstrated across quite different product classes - antibiotics, alkaloids and gibberellins alike. It is a general regulatory phenomenon rather than a peculiarity of one pathway.

Discuss in Forum

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