Question 1

Which of the following best describes the relationship between photosynthesis and cellular respiration in the context of energy flow and chemical cycling in ecosystems, as shown in the first image?

Accepted Answer

Photosynthesis transforms light energy into chemical energy stored in organic molecules, which are then broken down by cellular respiration to produce ATP and release heat.

Question 2

In the chemical equation for photosynthesis $$6CO_2 + 6H_2O + light \ energy \rightarrow C_6H_{12}O_6$ + 6O_2$$, which molecule is oxidized and which is reduced?

Accepted Answer

$$H_2O is $$oxidized and $$CO_2 is $$reduced.

Question 3

Which structure in the chloroplast is the primary site of the light-dependent reactions, and what is its main function?

Accepted Answer

Thylakoid membrane; it houses the electron transport chain and produces ATP and NADPH.

Question 4

Why do plant cells require both mitochondria and chloroplasts?

Accepted Answer

Chloroplasts convert light energy to chemical energy during photosynthesis, while mitochondria generate ATP from organic molecules during cellular respiration.

Question 5

What is the primary role of chlorophyll a in the light reactions of photosynthesis?

Accepted Answer

To capture light energy and transfer excited electrons to the primary electron acceptor.

Question 6

If water ($$H_2O) is $$not available to the chloroplast, what would be the immediate effect on the light reactions?

Accepted Answer

Both ATP and NADPH production would decrease because electrons could not be supplied to Photosystem II.

Question 7

Which of the following best explains why the absorption spectrum of chlorophyll a and the action spectrum of photosynthesis both peak in the blue and red regions of the visible spectrum (see the fifth image)?

Accepted Answer

Photosynthesis is most efficient at wavelengths where chlorophyll a absorbs the most light, which are in the blue and red regions.

Question 8

What would be the effect on ATP and NADPH production if an herbicide blocked electron flow between Photosystem II and Photosystem I?

Accepted Answer

Both ATP and NADPH production would decrease because the electron transport chain would be interrupted.

Question 9

Which of the following is a direct input to the Calvin cycle, and what is its primary role?

Accepted Answer

NADPH; it donates high-energy electrons for the reduction of $$CO_2.$$

Question 10

A plant is exposed to increasing light intensity. What is the expected effect on the rate of the light reactions, and why does this effect plateau at high intensities?

Accepted Answer

The rate increases with light intensity until other factors (such as enzyme availability or $$CO_2$$ concentration) become limiting.

Question 11

Which of the following best describes the role of ATP synthase in the thylakoid membrane during the light reactions?

Accepted Answer

It synthesizes ATP from ADP and $$P_i$$ using the energy of the proton gradient across the thylakoid membrane.

Question 12

Why is the Calvin cycle considered an anabolic pathway?

Accepted Answer

It uses energy from ATP and NADPH to build sugars from $$CO_2.$$

Question 13

If a mutation caused Photosystem II to stop functioning but Photosystem I remained active, what would be the most likely outcome for the plant?

Accepted Answer

ATP and NADPH production would both decrease, severely limiting the Calvin cycle.

Question 14

Which environmental factor would most likely increase the rate of the Calvin cycle up to a certain point, and why?

Accepted Answer

Increasing $$CO_2$$ concentration, because it provides more substrate for carbon fixation.

Question 15

Which of the following best explains why treated weeds exposed to HerbiClear-27 show yellow leaves instead of complete die-off?

Accepted Answer

Interruptions in the light reactions reduce chlorophyll content, leading to less green pigment and yellowing of leaves.

Question 16

Which of the following is a correct sequence of events in the light reactions of photosynthesis?

Accepted Answer

Absorption of light by chlorophyll a → splitting of water → electron transport chain → ATP and NADPH production

Question 17

How does the structure of the thylakoid membrane facilitate its function in the light reactions?

Accepted Answer

Its large surface area and embedded proteins allow for efficient absorption of light and establishment of a proton gradient.

Question 18

Which of the following best describes the fate of oxygen produced during the light reactions?

Accepted Answer

It is released as a byproduct into the atmosphere.

Question 19

What would happen to the Calvin cycle if the supply of NADPH were interrupted?

Accepted Answer

The Calvin cycle would slow down or stop because NADPH is required for the reduction of $$CO_2.$$

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