Question 1

Which of the following best describes the primary goal of the light-harvesting reactions in photosynthesis?

Accepted Answer

To trap sunlight energy and store it as chemical energy in ATP and NADPH

Question 2

Where do the light-harvesting reactions of photosynthesis occur within the chloroplast?

Accepted Answer

On the membranes of the thylakoids

Question 3

During the light-harvesting reactions, what is the initial electron donor that replenishes the lost electron in Photosystem II?

Accepted Answer

Water ($$H_2O)$$

Question 4

What is the fate of the oxygen produced during photolysis in the light reactions?

Accepted Answer

It is released into the atmosphere

Question 5

Which molecule acts as the final electron acceptor in the non-cyclic electron transport chain of the light reactions?

Accepted Answer

NADP$$^+$$

Question 6

What is the main function of the proton (H$$^+) $$gradient established across the thylakoid membrane during the light reactions?

Accepted Answer

To drive the synthesis of ATP via ATP synthase

Question 7

Which of the following equations correctly represents the photolysis of water during the light reactions?

Accepted Answer

$$2H_2O \rightarrow 4H^+ + 4e^- + O_2$

Question 8

Why is ATP considered a good source of energy but not a good long-term energy storage molecule?

Accepted Answer

ATP is unstable and cannot be stored efficiently over time

Question 9

Which process directly uses the energy from the movement of H$$^+$$ ions through ATP synthase?

Accepted Answer

Synthesis of ATP from ADP and inorganic phosphate ($$ADP + P_i \rightarrow ATP)$$

Question 10

In the electron transport chain of the light reactions, which molecule is reduced after accepting an electron from Photosystem II?

Accepted Answer

Phaeophyton (Pheophytin)

Question 11

What is the role of NADPH produced in the light reactions?

Accepted Answer

It provides high-energy electrons for the Calvin Cycle to reduce $$CO_2$$ and synthesize sugars

Question 12

Which analogy best describes the function of the H$$^+$$ gradient in the thylakoid membrane?

Accepted Answer

A dam storing water to generate electricity

Question 13

If a mutation prevented the formation of the proton gradient in the thylakoid membrane, which process would be directly affected?

Accepted Answer

ATP synthesis via ATP synthase

Question 14

Which of the following best explains why the light reactions are also called the 'electron transport chain'?

Accepted Answer

Because electrons are transferred through a series of carriers, releasing energy to pump H$$^+$$ and synthesize ATP

Question 15

Which of the following is NOT a product of the light-harvesting reactions?

Accepted Answer

Glucose

Question 16

A scientist isolates chloroplasts and exposes them to light but provides no $$CO_2. $$Which products will still be formed?

Accepted Answer

ATP, NADPH, and $$O_2$$

Question 17

Which step in the light reactions is directly responsible for the release of oxygen into the atmosphere?

Accepted Answer

Photolysis of water ($$2H_2O \rightarrow 4H^+ + 4e^- + O_2$)

Question 18

Which molecule acts as a mobile electron carrier between Photosystem II and the cytochrome complex?

Accepted Answer

Plastoquinone

Question 19

If the ATP synthase enzyme in the thylakoid membrane is inhibited, which of the following would most likely occur?

Accepted Answer

ATP production would decrease, affecting energy supply for the Calvin Cycle

Question 20

Which of the following best describes the flow of electrons during the light reactions?

Accepted Answer

Water $$\rightarrow$$ Photosystem II $$\rightarrow$$ Electron Transport Chain $$\rightarrow$$ Photosystem I $$\rightarrow$$ NADP$$^+$$

Photosynthesis: The Light-Harvesting Reactions (Part 2)

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