Science: Photosynthesis: Light Reactions and Calvin Cycle Worksheet

Question 1

State the main purpose of the light reactions in photosynthesis.

Accepted Answer

The main purpose of the light reactions is to capture light energy and convert it into chemical energy stored in ATP and NADPH.

Question 2

Identify the main purpose of the Calvin cycle.

Accepted Answer

The main purpose of the Calvin cycle is to use ATP and NADPH to fix carbon dioxide into higher-energy carbon compounds that can be used to build sugars.

Question 3

In which part of the chloroplast do the light reactions occur, and in which part does the Calvin cycle occur?

Accepted Answer

The light reactions occur in the thylakoid membranes of the chloroplast, while the Calvin cycle occurs in the stroma.

Question 4

Write the reactants and products of the light reactions.

Accepted Answer

The light reactions use light energy, water, ADP, and NADP+ as reactants and produce oxygen, ATP, and NADPH as products.

Question 5

Explain why water is split during the light reactions.

Accepted Answer

Water is split during the light reactions to provide electrons and hydrogen ions needed for the electron transport chain and the formation of NADPH, and this process also releases oxygen as a byproduct.

Question 6

What is the role of chlorophyll in the light reactions?

Accepted Answer

Chlorophyll absorbs light energy and excites electrons to higher energy levels, allowing those electrons to enter the electron transport chain.

Question 7

Describe how ATP is formed during the light reactions.

Accepted Answer

ATP is formed when energy from moving electrons is used to pump hydrogen ions across the thylakoid membrane, and the flow of those ions back through ATP synthase drives the phosphorylation of ADP to ATP.

Question 8

What molecule provides the carbon atoms used to build sugars in the Calvin cycle, and how does it enter the cycle?

Accepted Answer

Carbon dioxide provides the carbon atoms used to build sugars, and it enters the Calvin cycle through carbon fixation when it is attached to RuBP by the enzyme rubisco.

Question 9

Name the two energy-rich molecules made in the light reactions that are used in the Calvin cycle, and describe what they provide.

Accepted Answer

The two energy-rich molecules are ATP and NADPH. ATP provides energy for reactions in the Calvin cycle, and NADPH provides high-energy electrons for reducing carbon compounds.

Question 10

A plant is placed in bright light but has no available carbon dioxide. Predict what will happen to the Calvin cycle and explain why.

Accepted Answer

The Calvin cycle will slow greatly or stop because carbon dioxide is required for carbon fixation, and without it the cycle cannot build the carbon compounds needed to make sugars.

Question 11

Compare the light reactions and the Calvin cycle by giving one major difference in their inputs and one major difference in their outputs.

Accepted Answer

One major difference in inputs is that the light reactions require light and water, while the Calvin cycle requires carbon dioxide, ATP, and NADPH. One major difference in outputs is that the light reactions produce oxygen, ATP, and NADPH, while the Calvin cycle produces carbohydrate precursors and returns ADP and NADP+.

Question 12

A student says, "Plants get all their energy directly from glucose, so light is only needed at the end of photosynthesis." Explain what is incorrect about this statement.

Accepted Answer

This statement is incorrect because light is needed at the beginning of photosynthesis to power the light reactions, which produce ATP and NADPH. Those molecules are then used by the Calvin cycle to build glucose and other carbohydrates from carbon dioxide.

Science: Photosynthesis: Light Reactions and Calvin Cycle

Science: Photosynthesis: Light Reactions and Calvin Cycle

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