Question 1

Which of the following best describes the relationship between photosynthesis and cellular respiration in the context of energy flow 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 cycling diagram (second image), what is the primary role of decomposers such as fungi and bacteria?

Accepted Answer

They break down dead organisms and return chemicals to the soil, completing the chemical cycle.

Question 3

Which of the following equations correctly represents the overall process of photosynthesis?

Accepted Answer

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

Question 4

Based on the third image, what is the immediate source of electrons for Photosystem II (PSII) in the light reactions?

Accepted Answer

Water ($$H_2O)$$

Question 5

What is the main function of the thylakoid membrane in the light reactions of photosynthesis, as illustrated in the fourth image?

Accepted Answer

It houses the electron transport chain and ATP synthase, facilitating the formation of a proton gradient for ATP synthesis.

Question 6

According to the absorption spectrum graph (fifth image), which wavelengths of light are most effective for driving photosynthesis?

Accepted Answer

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

Question 7

If a plant is exposed only to green light, what would you expect to happen to its rate of photosynthesis based on the absorption spectra?

Accepted Answer

The rate would decrease because chlorophyll reflects green light, resulting in less energy absorption.

Question 8

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 sugar molecules from $$CO_2.$$

Question 9

What would happen to the production of ATP and NADPH in the light reactions if water were not available to the chloroplast?

Accepted Answer

Both ATP and NADPH production would decrease because water is the source of electrons for the electron transport chain.

Question 10

Which of the following is a direct input to the Calvin cycle, as shown in the sixth image?

Accepted Answer

Carbon dioxide ($$CO_2)$$

Question 11

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 disrupted.

Question 12

Why do plants require both chloroplasts and mitochondria to survive?

Accepted Answer

Chloroplasts capture light energy to produce sugars, while mitochondria break down sugars to generate ATP for cellular work.

Question 13

If the supply of NADPH to the Calvin cycle is interrupted, what is the most immediate consequence?

Accepted Answer

The reduction of 3-phosphoglycerate (3-PGA) to G3P will stop, halting sugar production.

Question 14

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

Accepted Answer

Increasing light intensity

Question 15

What is the role of ATP synthase in the light reactions of photosynthesis?

Accepted Answer

It uses the proton gradient across the thylakoid membrane to synthesize ATP from ADP and $$P_i.$$

Question 16

Which molecule is reduced during the light reactions of photosynthesis?

Accepted Answer

NADP$$^+$$

Question 17

How does the absorption of light by chlorophyll ultimately lead to the production of ATP?

Accepted Answer

Light absorption excites electrons, which move through the electron transport chain, creating a proton gradient that drives ATP synthesis via ATP synthase.

Question 18

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

Accepted Answer

Chlorophyll is degraded or not synthesized efficiently, reducing green pigment and revealing yellow pigments.

Question 19

If Photosystem II stopped 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.

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