Photosynthesis Investigation Worksheet

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Part 1: Build the Model

Reading: Photosynthesis is the process by which plants convert light energy into chemical energy stored in glucose. It occurs mainly in the chloroplasts of plant cells. The pigment chlorophyll absorbs light energy. During the light-dependent reactions, light energy is captured and water molecules are split, releasing oxygen. During the Calvin cycle, carbon dioxide is used to build glucose. Water and carbon dioxide are the reactants; light is the energy source; glucose and oxygen are the products.

The rate of photosynthesis can change when conditions change. Important factors include light intensity, carbon dioxide concentration, temperature, and the amount of water available. If one factor is too low, it may become a limiting factor and prevent photosynthesis from increasing further.

1. Complete the equation: ________ + ________ + light energy → ________ + ________.

2. Select the statement that best explains why a leaf disk floats.

Oxygen produced during photosynthesis collects in the disk and increases its buoyancy.

Carbon dioxide makes the disk heavier.

The disk absorbs water and sinks.

3. Draw and label a model of photosynthesis. Include the chloroplast, light energy, carbon dioxide, water, glucose, and oxygen. Use arrows to show inputs and outputs.

4. Match each term with its definition.

A. Reactant

B. Product

C. Chlorophyll

D. Limiting factor

1. A substance made during a chemical reaction

2. A condition that restricts the rate of a process

3. A substance used during a chemical reaction

4. A green pigment that absorbs light energy

Part 2: Investigate Light and Photosynthesis

Investigation question: How does light affect the rate of photosynthesis?

Safety: Wear goggles, do not taste any materials, keep liquids away from electrical equipment, stop if equipment is damaged or liquid spills, and wash your hands when finished.

Procedure: 1. Place equal spinach leaf disks in dilute sodium bicarbonate solution. 2. Use a straw or syringe to remove trapped air from the disks. 3. Divide equal numbers of fully submerged disks between a bright-light cup and a dark cup. 4. Count the floating disks at 0, 5, 10, and 15 minutes. 5. Record observations clearly. Floating disks provide indirect evidence of oxygen production.

5. Identify the variables in this investigation.

Independent variable: ________________________________________________

Dependent variable: _________________________________________________

One controlled variable: ______________________________________________

6. Record your group’s results.

Bright-light cup: 0 minutes ______ 5 minutes ______ 10 minutes ______ 15 minutes ______

Dark cup: 0 minutes ______ 5 minutes ______ 10 minutes ______ 15 minutes ______

7. Create a line graph of your results. Put time on the x-axis and number of floating disks on the y-axis. Include a key for bright light and darkness.

8. What pattern do you observe? Calculate the change in floating disks for each condition by subtracting the starting number from the ending number.

9. The explanation says, “Light supplies energy for photosynthesis, so greater oxygen production should occur when light is available.” Does your evidence support this explanation? Use one numerical result and identify one limitation of the investigation.

10. Suppose increasing light intensity causes the number of floating disks to increase at first, but then the number levels off. Explain why another factor may have become limiting.

Part 3: Explain and Reflect

11. Explain how photosynthesis and cellular respiration are connected in an ecosystem. Include at least one substance shared by the two processes.

12. CER Response: Make a claim about how light affects the rate of photosynthesis. Support your claim with evidence from your group’s data, and explain why the evidence supports your claim.

Claim:

Evidence and reasoning:

Answer Key

1. Carbon dioxide + water + light energy → glucose + oxygen.

2. Oxygen produced during photosynthesis collects in the disk and increases its buoyancy.

3. Diagram should show light entering the chloroplast; carbon dioxide and water entering; glucose and oxygen leaving.

4. A-3, B-1, C-4, D-2.

5. Independent variable: light condition or light availability. Dependent variable: number of floating disks or inferred oxygen production. Controls may include disk number and size, solution concentration, temperature, cup size, and time.

6-8. Answers depend on group data. Expected pattern: disks in bright light generally float sooner or in greater numbers than disks kept in darkness.

9. A strong response uses a numerical comparison, states whether the evidence supports the explanation, and identifies a limitation such as unequal disk size, temperature differences, incomplete air removal, or small sample size.

10. A different factor, such as carbon dioxide concentration, temperature, water availability, or chlorophyll capacity, may limit the rate even when more light is available.

11. Photosynthesis produces glucose and oxygen, which cellular respiration uses to release usable energy. Cellular respiration produces carbon dioxide and water, which photosynthesis can use.

12. Responses should include a clear claim, a specific data point or pattern, and reasoning connecting floating disks with oxygen production.

Teacher Notes and Literacy Alignment

Before materials are distributed, check that students can identify the independent and dependent variables and explain why disks must begin fully submerged. During the investigation, assess accurate sequencing, safety, role participation, counting, and data recording. Accept varied numerical results because groups may differ in disk size, light distance, or air removal.

RST.9-10.4: Students determine the meaning of technical terms such as reactant, product, chlorophyll, limiting factor, and buoyancy using context and the matching activity.

RST.9-10.5: Students analyze how the reading and numbered procedure organize information to explain and test a scientific question.

RST.9-10.7: Students translate written observations into a data record and line graph, then use quantitative evidence to evaluate an explanation.