Q: Which equation correctly summarizes the overall process of photosynthesis?

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

Question 1

Which of the following best describes the main function of the proton gradient generated during the light reactions of photosynthesis?

Accepted Answer

To drive the synthesis of ATP via ATP synthase

Question 2

Peter Mitchell was awarded the Nobel Prize for his chemiosmotic theory. According to this theory, what is the direct source of energy for ATP synthesis in chloroplasts?

Accepted Answer

The movement of protons (H+) down their concentration gradient through ATP synthase

Question 3

Which equation correctly summarizes the overall process of photosynthesis?

Accepted Answer

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

Question 4

Why do plants sometimes engage in cyclic electron flow during the light reactions?

Accepted Answer

To produce more ATP without generating excess NADPH

Question 5

Which enzyme catalyzes the first step of the Calvin cycle, and what is its substrate?

Accepted Answer

Rubisco; ribulose 1,5-bisphosphate (RuBP) and CO$$_2$$

Question 6

Photorespiration is considered wasteful for C3 plants because:

Accepted Answer

It results in the loss of fixed carbon as CO$$_2$$

Question 7

What is the main difference between C4 and CAM plants in their strategies to avoid photorespiration?

Accepted Answer

C4 plants use spatial separation, while CAM plants use temporal separation

Question 8

Which of the following statements about ATP synthase is correct?

Accepted Answer

It uses the energy from the proton motive force to convert ADP and $$P_i$$ into ATP

Question 9

If a plant's cyclic electron flow pathway is defective, what is the most likely consequence under high light conditions?

Accepted Answer

The plant will be more susceptible to damage from high light intensity

Question 10

How many molecules of ATP and NADPH are required to generate one molecule of glyceraldehyde-3-phosphate (G3P) in the Calvin cycle?

Accepted Answer

$$9$$ ATP and $$6$$ NADPH

Question 11

Which of the following best explains why stomata close on hot, dry days and how this affects photosynthesis?

Accepted Answer

To prevent water loss, but this also reduces CO$$_2$$ intake and increases photorespiration

Question 12

Which of the following is NOT a product of the linear electron flow in the light reactions of photosynthesis?

Accepted Answer

Glucose

Question 13

What is the role of water in the light reactions of photosynthesis?

Accepted Answer

It donates electrons to photosystem II, producing O$$_2 as a $$byproduct

Question 14

Which of the following best describes the fate of the 3-phosphoglycerate produced in the Calvin cycle?

Accepted Answer

It is reduced to glyceraldehyde-3-phosphate using ATP and NADPH

Question 15

Which process is responsible for the release of oxygen during photosynthesis?

Accepted Answer

The splitting of water molecules by photosystem II

Question 16

A plant is exposed to an environment with low CO$$_2$$ and high O$$_2. $$What is the most likely outcome?

Accepted Answer

Photorespiration will increase, reducing the efficiency of carbon fixation

Question 17

Which of the following statements about Rubisco is FALSE?

Accepted Answer

It is only active in the absence of oxygen

Question 18

In C4 plants, what is the advantage of spatial separation of carbon fixation and the Calvin cycle?

Accepted Answer

It minimizes photorespiration by concentrating CO$$_2 in $$bundle-sheath cells

Question 19

Which of the following best describes the relationship between the light reactions and the Calvin cycle?

Accepted Answer

The light reactions provide ATP and NADPH required for the Calvin cycle

Question 20

Which of the following is a correct statement about cyclic photophosphorylation?

Accepted Answer

It produces ATP but not NADPH or O$$_2$$

LEC 12: Photosynthesis: Light Reactions, Chemiosmosis, and the Calvin Cycle

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