Q: Which equation correctly represents the overall process of photosynthesis in plants?

$$6CO_2 + 12H_2O + \text{Light energy} \rightarrow C_6H_{12}O_6 + 6O_2 + 6H_2O$$

Question 1

Which of the following statements best explains why green light is the least effective in driving photosynthesis in most plants?

Accepted Answer

Green light is reflected and transmitted by chlorophyll, so it is not absorbed for photosynthesis.

Question 2

A scientist exposes a plant to light with a wavelength of 700 nm. Which photosystem will be most directly excited by this light, and what is the name of its special chlorophyll a molecule?

Accepted Answer

Photosystem I; P700

Question 3

Which of the following best describes the role of water in the light reactions of photosynthesis?

Accepted Answer

Water donates electrons to replace those lost by chlorophyll in Photosystem II, and is split to release O$$_2.$$

Question 4

A plant is treated with a chemical that makes the thylakoid membrane freely permeable to H$$^+$$ ions. What is the most likely effect on ATP synthesis during the light reactions?

Accepted Answer

ATP synthesis will decrease because the proton gradient will dissipate.

Question 5

Which equation correctly represents the overall process of photosynthesis in plants?

Accepted Answer

$$6CO_2 + 12H_2O + 	ext{Light energy} ightarrow C_6H_{12}O_6 + 6O_2 + 6H_2O$$

Question 6

Which adaptation allows CAM plants to survive in hot, arid environments?

Accepted Answer

They open their stomata at night to fix CO$$_2$$ into organic acids, which release CO$$_2$$ for the Calvin cycle during the day.

Question 7

A researcher compares the dry mass of a C$$_3$$ plant and a C$$_4$$ plant grown at increasing atmospheric CO$$_2$$ concentrations. The C$$_3$$ plant's mass increases, while the C$$_4$$ plant's mass decreases. What is the best explanation for this observation?

Accepted Answer

C$$_3$$ plants benefit from higher CO$$_2$$ because photorespiration is reduced, while C$$_4$$ plants are already adapted to concentrate CO$$_2$$ and do not benefit as much.

Question 8

Which of the following is a direct product of the Calvin cycle that can be used to synthesize glucose and other organic molecules?

Accepted Answer

Glyceraldehyde 3-phosphate (G3P)

Question 9

Photorespiration is considered a wasteful process in C$$_3$$ plants because:

Accepted Answer

It consumes ATP and releases CO$$_2$$ without producing sugar.

Question 10

Which of the following best describes the difference between cyclic and linear electron flow during the light reactions?

Accepted Answer

Cyclic electron flow involves only Photosystem I and produces ATP but not NADPH or O$$_2.$$

Question 11

A mutation prevents a plant from producing carotenoids. Which of the following consequences is most likely?

Accepted Answer

The plant will be more susceptible to damage from excessive light due to lack of photoprotection.

Question 12

Which of the following statements about the interdependence of the Calvin cycle and the light reactions is correct?

Accepted Answer

The light reactions produce ATP and NADPH, which are used by the Calvin cycle to fix carbon.

Question 13

Which of the following best explains why C$$_4$$ plants are more efficient than C$$_3$$ plants in hot, dry climates?

Accepted Answer

C$$_4$$ plants use PEP carboxylase to fix CO$$_2 in $$mesophyll cells, concentrating CO$$_2 in $$bundle-sheath cells and minimizing photorespiration.

Question 14

Which of the following is the correct sequence of events in the linear electron flow of the light reactions?

Accepted Answer

Excitation of P680, splitting of water, electron transport, excitation of P700, NADPH formation

Question 15

Which of the following best describes the role of ATP synthase in chloroplasts?

Accepted Answer

It uses the proton-motive force generated by the H$$^+$$ gradient across the thylakoid membrane to synthesize ATP from ADP and inorganic phosphate.

Question 16

A plant is genetically engineered to lack functional rubisco. Which process would be directly affected?

Accepted Answer

The fixation of CO$$_2 in $$the Calvin cycle

Question 17

Which of the following is a real-world application of photosynthetic research that addresses climate change?

Accepted Answer

Using photosynthetic algae near industrial plants to capture CO$$_2$$ emissions and produce biodiesel.

Question 18

Which of the following best explains why the oxygen released during photosynthesis comes from water and not from carbon dioxide?

Accepted Answer

Experiments using the isotope $$^{18}O $$showed that when water containing $$^{18}O $$was used, the oxygen gas released contained $$^{18}O.$$

Question 19

Which of the following is NOT a function of carotenoids in plants?

Accepted Answer

Serving as the primary pigment in the reaction center of photosystems

Question 20

Which of the following best describes the fate of G3P produced in the Calvin cycle?

Accepted Answer

One G3P exits the cycle to be used for biosynthesis, while the rest are recycled to regenerate RuBP.

Photosynthesis: Mechanisms, Adaptations, and Global Importance

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