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?

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 overall 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 absorb light energy and excite electrons for transfer through the electron transport chain.

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 Calvin cycle is considered an anabolic pathway?

Accepted Answer

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

Question 8

A herbicide blocks electron flow between Photosystem II and Photosystem I. What is the most likely effect on ATP and NADPH production?

Accepted Answer

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

Question 9

Which environmental factor would most likely increase the rate of the light reactions up to a certain point, after which the rate would plateau?

Accepted Answer

Increasing light intensity.

Question 10

Based on the absorption spectrum graph, which wavelengths of light are most effective for photosynthesis?

Accepted Answer

Blue (430-470 nm) and red (640-680 nm)

Question 11

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 3-PGA to G3P.

Question 12

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

Accepted Answer

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

Question 13

A plant is exposed to only green light. What is the most likely outcome for its rate of photosynthesis?

Accepted Answer

The rate of photosynthesis will decrease because chlorophyll reflects green light.

Question 14

Which of the following is a direct input to the Calvin cycle?

Accepted Answer

NADPH

Question 15

If Photosystem II stopped functioning but Photosystem I remained active, what would be the most immediate effect on the plant?

Accepted Answer

ATP production would decrease, and oxygen would not be produced.

Question 16

Which of the following best explains why treated weeds exposed to a herbicide that disrupts the light reactions show yellow leaves?

Accepted Answer

Interruptions in the light reactions reduce chlorophyll content, causing leaves to lose their green color.

Question 17

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 18

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

Accepted Answer

It provides a large surface area for the electron transport chain and ATP synthase, facilitating efficient light energy conversion.

Question 19

Which of the following best describes the role of the electron transport chain in the light reactions?

Accepted Answer

It transfers electrons from water to NADP$$^+$$, creating a proton gradient used to generate ATP.

Step-by-Step Study Guide for Photosynthesis and Cellular Respiration

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