Photosynthesis in Action

Overview

Students investigate how light availability affects photosynthesis using a leaf-disk flotation assay. They follow a multistep procedure, record quantitative results in a table, interpret the evidence, and explain how the investigation addresses the question: “How does light affect the rate of photosynthesis?”

Learning intentions

Students will be able to:

• Follow a multistep scientific procedure, including safety instructions and special conditions.
• Identify the reactants, products, and energy source in photosynthesis.
• Translate written instructions and numerical observations into a data table.
• Analyze whether experimental evidence supports an explanation about photosynthesis.

Success criteria

• I can correctly complete the leaf-disk investigation and explain why each step matters.
• I can record the number of floating disks at set time intervals in a clear table.
• I can use evidence to describe how light affected photosynthesis.
• I can explain the purpose of the procedure and identify one limitation of the investigation.

Curriculum links

• Reading technical texts: following complex, multistep procedures and attending to exceptions.
• Reading technical texts: translating written and quantitative information into tables or other visual forms.
• Reading technical texts: analyzing an author’s purpose and the scientific question addressed.
• Reading technical texts: comparing experimental findings with an explanation or account in another source.

Lesson structure (45 minutes)

1. 0–5 min · Hook and prediction. Teacher opens the hook and prediction slide showing two identical leaves, one in bright light and one in darkness, and asks, “Which leaf will produce oxygen faster, and what evidence would convince you?” Students make an individual prediction and briefly justify it with prior knowledge.

2. 5–11 min · Build the model. Teacher uses the photosynthesis model slides to review that carbon dioxide and water are inputs, light provides energy, and glucose and oxygen are outputs; clarify that oxygen production will be inferred when leaf disks float. Students complete the photosynthesis equation and label the input, energy, and output components on the photosynthesis investigation worksheet.

3. 11–16 min · Procedure and safety check. Teacher displays the procedure and safety slides and models the steps: place equal leaf disks in bicarbonate solution, remove trapped air with a syringe, divide disks between light and dark conditions, and count floating disks at regular intervals. Emphasize the exception that disks must be fully submerged at the start and that students should stop if liquid spills or equipment is damaged. Students annotate the procedure, identify the independent and dependent variables, and answer a partner’s “What could make this test unfair?” question.

4. 16–30 min · Hands-on investigation. Teacher organizes 25 students into groups of four or five, distributes pre-cut spinach disks, two clear cups, dilute sodium bicarbonate solution, straws or syringes, timers, and a lamp or designated bright-light area; groups follow the numbered procedure on the investigation data sheet. Students assign roles, place disks in light and dark conditions, count floating disks at 0, 5, 10, and 15 minutes, and record results in the table. Groups do not taste materials, keep liquids away from electrical equipment, and wash hands after the activity.

5. 30–37 min · Represent and interpret data. Teacher uses the data-table and graphing slides to model converting observations into a completed table and a line graph with time on the x-axis and number of floating disks on the y-axis. Students calculate the change in floating disks, create a graph on the worksheet, and compare their group’s light and dark results with one neighboring group.

6. 37–42 min · Evidence discussion. Teacher presents a short explanatory statement on the evidence discussion slide: “Light supplies energy for photosynthesis, so greater oxygen production should occur when light is available.” Students use their data and the brief background paragraph on the worksheet to decide whether the findings support or contradict the statement, then write one limitation such as unequal disk size, temperature differences, or incomplete air removal.

7. 42–45 min · Exit response. Teacher displays the plenary slide and asks students to answer independently on the worksheet: “How did the procedure allow you to investigate the effect of light on photosynthesis? Use one numerical result and explain what floating disks represented.” Students submit the worksheet as they leave.

Resources

• the photosynthesis investigation slide deck
• the photosynthesis investigation worksheet
• Pre-cut spinach or other broad-leaf disks
• Clear cups, dilute sodium bicarbonate solution, and straws or plastic syringes
• Timer for each group
• Lamp or bright-light area and dark covering
• Goggles, paper towels, and hand-washing access
• Student pencils and colored pencils

Assessment

• Check students’ procedure annotations, variable identification, and safety responses before materials are distributed.
• Circulate during the investigation to assess accurate sequencing, role participation, measurement, and table completion.
• Use the graph, evidence paragraph, limitation, and exit response to assess whether students connect floating disks with oxygen production and interpret findings cautiously.

Differentiation

• Provide a numbered, illustrated procedure, a completed example data row, and sentence starters: “The evidence supports…” and “One limitation is…”
• Pair students strategically and assign accessible roles such as timer, materials manager, counter, recorder, or safety checker; provide printed large-format directions for students with visual or processing needs.
• Support English learners with a word bank containing reactant, product, energy, oxygen, variable, evidence, and limitation, plus a labeled equation.
• Extend advanced students by asking them to compare the slope of the light and dark results, evaluate reliability across groups, and propose one improved control or follow-up test.