Question 1

Which of the following best distinguishes oxygenic from anoxygenic phototrophy in terms of their environmental impact?

Accepted Answer

Oxygenic phototrophy produces $O_2$ as a byproduct, significantly increasing atmospheric oxygen, while anoxygenic phototrophy does not produce $O_2$.

Question 2

Which pigment is primarily responsible for the absorption of light energy in the reaction centers of phototrophic bacteria?

Accepted Answer

Chlorophylls and bacteriochlorophylls

Question 3

A researcher isolates a bacterium from a hot spring mat that is filamentous, uses organic acids as electron donors, and can utilize very long wavelengths of light (infrared). Which group does this organism most likely belong to?

Accepted Answer

Green nonsulfur bacteria (Chloroflexi)

Question 4

Which of the following statements about cyclic and non-cyclic electron flow in phototrophy is correct?

Accepted Answer

Cyclic electron flow generates ATP but not NAD(P)H, while non-cyclic electron flow generates both ATP and NAD(P)H.

Question 5

Which of the following is a unique feature of cyanobacteria among phototrophic bacteria?

Accepted Answer

They perform oxygenic photosynthesis using both PSI and PSII.

Question 6

A lake is found to have a dense layer of green, non-motile, strictly anaerobic bacteria that use $H_2S$ as an electron donor and possess chlorosomes. Which group do these bacteria most likely belong to?

Accepted Answer

Green sulfur bacteria (Chlorobi)

Question 7

Which of the following best describes the function of carotenoids in phototrophic bacteria?

Accepted Answer

They absorb light energy and protect cells from reactive oxygen species.

Question 8

In anoxygenic photosynthesis, what is the typical fate of electrons after they are excited by light in the reaction center?

Accepted Answer

They flow through an electron transport chain and return to the reaction center (cyclic electron flow).

Question 9

Which of the following equations correctly represents the overall reaction for oxygenic photosynthesis?

Accepted Answer

$6CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2$

Question 10

A marine microorganism is discovered that uses a rhodopsin-based pigment to generate a proton gradient in the absence of chlorophyll. What is the most likely function of this pigment?

Accepted Answer

It acts as a light-driven proton pump to generate ATP.

Question 11

Which of the following is a key difference between the electron donors used in oxygenic and anoxygenic phototrophy?

Accepted Answer

Oxygenic phototrophs use $H_2O$ as an electron donor, while anoxygenic phototrophs use compounds like $H_2S$, $Fe^{2+}$, or organic acids.

Question 12

Which structure is found in cyanobacteria and is analogous to the thylakoid membranes of chloroplasts in plants?

Accepted Answer

Thylakoids

Question 13

A purple sulfur bacterium is found in an anoxic zone with abundant $H_2S$ and light. Which of the following best describes its mode of phototrophy?

Accepted Answer

Anoxygenic photosynthesis using $H_2S$ as the electron donor

Question 14

Which of the following best explains why phycobilins are important for cyanobacteria in low-light environments?

Accepted Answer

Phycobilins increase light-harvesting efficiency by absorbing wavelengths not captured by chlorophyll.

Question 15

Which of the following is a correct statement about the Calvin Cycle in phototrophic microorganisms?

Accepted Answer

It is the major pathway for $CO_2$ fixation in oxygenic phototrophs.

Question 16

Which of the following best describes the role of the proton motive force (PMF) in phototrophic ATP synthesis?

Accepted Answer

PMF drives ATP synthesis via $F_{0}F_{1}$-type ATPase.

Question 17

A mutant cyanobacterium is unable to perform non-cyclic electron flow. Which of the following would most likely be affected?

Accepted Answer

The production of NADPH for carbon fixation

Question 18

Which of the following is a plausible reason why carotenoid expression is often regulated by light intensity in phototrophic bacteria?

Accepted Answer

To protect cells from photo-oxidative damage under high light conditions

Question 19

Which of the following best describes the evolutionary significance of cyanobacteria?

Accepted Answer

They are the ancestors of chloroplasts in plants and responsible for the rise of atmospheric oxygen.

Phototrophy: Principles, Physiology, and Diversity in Microorganisms

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