Photosynthesis — Biology Practice Worksheet

Grades 7–10 Easy difficulty 10 problems

Photosynthesis is the process plants, algae, and some bacteria use to convert light energy into chemical energy stored in glucose. The overall equation is $6\mathrm{CO_2} + 6\mathrm{H_2O} \to \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2}$ , with light energy driving the reaction.

Photosynthesis happens in chloroplasts, the organelles that contain the green pigment chlorophyll. Chlorophyll absorbs mostly red and blue light and reflects green light, which is why plants look green.

The process has two stages. The light-dependent reactions occur in the thylakoid membranes: they capture light energy, split water, release oxygen, and make the energy carriers ATP and NADPH. The Calvin cycle then takes place in the stroma, using that energy to build glucose from carbon dioxide.

Photosynthesis and cellular respiration are nearly opposite processes. Photosynthesis stores energy in glucose and releases oxygen, while cellular respiration ( $\mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} \to 6\mathrm{CO_2} + 6\mathrm{H_2O}$ ) breaks glucose down to release usable energy for the cell.

Skills practiced

Writing and interpreting the overall photosynthesis equation
Identifying the roles of chloroplasts and chlorophyll
Distinguishing light-dependent reactions from the Calvin cycle
Comparing photosynthesis with cellular respiration
Tracing the inputs and outputs of matter and energy

Name: Date: Period:

Practice Worksheet: Photosynthesis

Instructions: Solve each problem carefully. Show all work clearly. Write your final answer in the space provided or on a separate sheet as directed.

1.Photosynthesis primarily takes place in which organelle of a plant cell?
1. A. Nucleus
2. B. Mitochondrion
3. C. Chloroplast
4. D. Ribosome

Photosynthesis — Practice Worksheet (continued)

2.Which of the following is a reactant (input) of photosynthesis?
1. A. Oxygen
2. B. Glucose
3. C. Water
4. D. Carbon dioxide

Photosynthesis — Practice Worksheet (continued)

3.What is the main pigment found in chloroplasts that absorbs light energy?
1. A. Carotene
2. B. Chlorophyll
3. C. Xanthophyll
4. D. Melanin

Photosynthesis — Practice Worksheet (continued)

4.The overall chemical equation for photosynthesis is: $6CO_2 + 6H_2O \xrightarrow{\text{light energy}} C_6H_{12}O_6 + 6O_2$ In this equation, what is the chemical formula for glucose?
5.Name the two main stages of photosynthesis.

Photosynthesis — Practice Worksheet (continued)

6.In which part of the chloroplast do the light-dependent reactions occur?
7.What gas is released as a byproduct of photosynthesis?

Photosynthesis — Practice Worksheet (continued)

8.Label the parts of the chloroplast in the diagram below. Write the correct term on each line. Blank 1: _____ Blank 2: _____ Blank 3: _____ Terms to use: Stroma, Thylakoid, Granum

Photosynthesis — Practice Worksheet (continued)

9.What is the primary purpose of photosynthesis for the plant?

Photosynthesis — Practice Worksheet (continued)

10.Which of the following best describes the role of light in photosynthesis?
1. A. It is a product of the reaction.
2. B. It provides the energy needed to convert carbon dioxide and water into glucose.
3. C. It is used to break down glucose into smaller molecules.
4. D. It has no role in photosynthesis.

Answer Key

1.

Chloroplasts contain chlorophyll and are the site where photosynthesis occurs.

Final answer: C) Chloroplast
2.

Both water (H $_2$ O) and carbon dioxide (CO $_2$ ) are reactants in photosynthesis. If only one answer is expected, the most commonly cited reactant is carbon dioxide.

Final answer: C) Water and D) Carbon dioxide
3.

Chlorophyll is the green pigment that absorbs light energy, primarily in the blue and red wavelengths.

Final answer: B) Chlorophyll
4.

Glucose is a six-carbon sugar with the formula C $_6$ H $_{12}$ O $_6$ .

Final answer: C $_6$ H $_{12}$ O $_6$

Answer Key (continued)

5.

The light-dependent reactions require light and occur in the thylakoid membranes, producing ATP and NADPH. The Calvin cycle does not require light directly and uses ATP and NADPH to fix carbon dioxide into glucose.

Final answer: The light-dependent reactions and the Calvin cycle (light-independent reactions).
6.

The light-dependent reactions take place in and across the thylakoid membranes inside the chloroplast.

Final answer: The thylakoid membranes (thylakoids)
7.

Oxygen is released as a byproduct when water molecules are split during the light-dependent reactions.

Final answer: Oxygen (O $_2$ )
8.

The thylakoid is the flattened sac where light reactions occur. A stack of thylakoids is called a granum. The stroma is the fluid-filled space surrounding the thylakoids where the Calvin cycle takes place.

Final answer: Blank 1: Thylakoid, Blank 2: Granum, Blank 3: Stroma

Answer Key (continued)

9.

Photosynthesis converts light energy into chemical energy stored in glucose, which the plant uses for cellular respiration and growth.

Final answer: To produce glucose (food/energy) for the plant.
10.

Light energy is absorbed by chlorophyll and converted into chemical energy (ATP and NADPH), which powers the synthesis of glucose.

Final answer: B) It provides the energy needed to convert carbon dioxide and water into glucose.

Common mistakes to avoid

Reversing the reactants and products of the equation
Thinking plants get most of their mass from the soil instead of from carbon dioxide
Believing plants only photosynthesize (they also perform cellular respiration)
Mixing up where each stage occurs (thylakoid vs. stroma)
Forgetting that the released oxygen comes from splitting water, not carbon dioxide

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Last updated: 2026

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