In this portfolio activity, you will think about how to design, conduct, and evaluate an investigation to gather evidence that photosynthesis converts light energy to stored chemical energy by showing how leaves take in carbon dioxide and release oxygen at a measurable rate

Answer 1

Designing an investigation to gather evidence of photosynthesis as a process that converts light energy into stored chemical energy can be both engaging and informative. Here’s a structured approach to conducting and evaluating such an experiment, focusing on measuring the rate of photosynthesis through carbon dioxide uptake and oxygen release.

Objective

To demonstrate how leaves take in carbon dioxide and release oxygen during photosynthesis, and to measure these processes at different light intensities.

Materials

1. Plant specimens (e.g., Elodea or a similar aquatic plant)
2. Sodium bicarbonate (to supply carbon dioxide)
3. Water
4. Light source (e.g., lamp with adjustable intensity)
5. Graduated cylinder
6. Timer
7. Thermometer (to monitor temperature)
8. Ruler (if measuring plant height)
9. Data recording sheets

Procedure

Step 1: Prepare the Experiment

1. Setup: Fill a graduated cylinder with a known volume of water. Add a small amount of sodium bicarbonate to the water to ensure a consistent supply of carbon dioxide.
2. Plant Preparation: Cut a sprig of the chosen aquatic plant and place it upside down (cut end down) in the graduated cylinder filled with the sodium bicarbonate solution.

Step 2: Light Variation

1. Positioning Light Source: Place a light source at a fixed distance from the graduated cylinder. Adjust the distance to set different light intensities for different trials, for example:
   • Trial 1: 10 cm
   • Trial 2: 20 cm
   • Trial 3: 30 cm

Step 3: Conduct the Experiments

1. Allow Acclimatization: Let the plant acclimatize for about 5 minutes in the sodium bicarbonate solution before starting measurements.
2. Start the Timer: Begin timing and observe bubbles forming at the cut end of the plant, which indicates oxygen production.
3. Data Collection: Count the number of oxygen bubbles released in a set time period (e.g., 5 minutes) as an indicator of the rate of photosynthesis.
4. Repeat Trials: Repeat the experiment for each light intensity setting at least three times for accuracy.

Step 4: Data Recording

• Record the number of bubbles produced at each light intensity along with any environmental conditions such as temperature.

Data Analysis

1. Calculate Average Production: For each light intensity, calculate the average number of bubbles produced across trials.
2. Graph Results: Create a graph plotting light intensity (independent variable) against the average number of bubbles produced (dependent variable).

Evaluation

1. Interpreting Results: Analyze how changes in light intensity affect the rate of photosynthesis as indicated by the bubble count.
2. Identifying Trends: Look for patterns in the data – typically, you should observe that higher light intensities result in more oxygen production (more bubbles).
3. Discuss Limitations: Reflect on sources of error (e.g., inconsistent bubble counting, variations in plant health or size, control of temperature).
4. Suggest Improvements: Consider ways to refine the experiment, such as using a gas sensor for more precise measurements or controlling other variables like temperature and CO2 concentration.

Conclusion

This investigation effectively shows the relationship between light and the rate of photosynthesis in leaves through measurable outputs (oxygen production). By comparing how different light intensities impact this process, the experiment reinforces the concept of photosynthesis as a conversion of light energy into chemical energy.