AQA GCSE FOUNDATION Biology: Measuring Plant Responses to Light

Investigating Phototropism: How Plants Respond to Light

This tutorial guides you through an investigation into phototropism, the growth of plants in response to light. You will grow seedlings under different light conditions, measure their growth patterns, and analyze your results to understand how light affects plant growth and the role of plant hormones in this process.

Materials

• Seeds: Cress seeds or sunflower seeds work well.
• Petri dishes or seed trays: To germinate your seeds.
• Cotton wool or absorbent paper: For providing moisture to the seeds.
• Water: To keep the seeds moist.
• Light source: A lamp or window providing consistent light.
• Ruler or measuring tape: For measuring plant height and growth direction.
• Markers: To label your samples and record data.
• Notebook or spreadsheet: To record your observations and data.
• Optional: Cardboard box, scissors, masking tape, clear plastic wrap.

Procedure

1. Seed Germination:

• Step 1: Place a layer of cotton wool or absorbent paper in your petri dishes or seed trays.
• Step 2: Moisten the cotton wool or paper thoroughly with water.
• Step 3: Place a few seeds (about 5-10) on the moistened cotton wool or paper, ensuring they are evenly spaced.
• Step 4: Repeat this process for several petri dishes or seed trays, creating a control group and experimental groups.
• Step 5: Cover the dishes or trays with a lid or plastic wrap to maintain humidity.
• Step 6: Place the dishes or trays in a dark place at room temperature.
• Step 7: Observe the seeds daily. Once the seeds have sprouted and seedlings have emerged, you are ready to proceed.

2. Setting Up the Experiment:

• Step 1: Divide your seedlings into different groups.
  • Control group: Place these seedlings in a location with equal light exposure from all sides.
  • Experimental groups: Create different light conditions for these groups:
    • One-sided light: Place these seedlings in a location where they receive light from only one direction (e.g., a window).
    • Darkness: Place these seedlings in a completely dark location.
• Step 2: Label your groups clearly using markers to track the different conditions.
• Step 3: Ensure each group receives consistent light exposure (or lack thereof) for the duration of the experiment.

3. Data Collection:

• Step 1: Measure the initial height of each seedling in your groups. Record this data in your notebook or spreadsheet.
• Step 2: Make observations and record the growth direction of each seedling over time. This can be done by measuring the angle of bending towards the light source.
• Step 3: Measure the height of the seedlings at regular intervals (e.g., every 24 hours) and record this data.
• Step 4: Continue collecting data for a few days to observe the growth patterns.

4. Analysis and Interpretation:

• Step 1: Create a table or graph to visualize your data, comparing the height and growth direction of seedlings under different light conditions.
• Step 2: Analyze your results.
  • How do the heights of the seedlings in each group compare?
  • What are the differences in growth direction between the groups?
  • What conclusions can you draw about the effect of light on plant growth?
• Step 3: Research the role of auxin, a plant hormone involved in phototropism. How does it affect plant growth?
• Step 4: Discuss your findings and explain how they demonstrate the concept of phototropism.

5. Extensions and Further Exploration:

• Investigate the effect of different light intensities: Compare the growth of seedlings exposed to high light intensity versus low light intensity.
• Explore the effect of different light wavelengths: Investigate how different colors of light affect plant growth.
• Perform a control experiment: Grow seedlings in a dark environment and then expose them to light for a specific period to observe their response.

By completing this experiment and carefully analyzing your results, you will gain a deeper understanding of how plants respond to light and the essential role of plant hormones in this process. This knowledge is crucial for understanding plant growth and development and can be applied to various fields, including agriculture and horticulture.