C1.3.7 The effects of limiting factors on the rate of photosynthesis Notes

Experimental Methods to Test Effects of CO₂, Light, and Temperature on Photosynthesis

1. The rate of photosynthesis can be affected by several environmental factors.
2. These include light intensity, carbon dioxide concentration, and temperature.
3. When any of these factors are in short supply, it can limit the rate at which photosynthesis occurs, even if the other factors are abundant.
4. To understand how carbon dioxide concentration, light intensity, and temperature affect photosynthesis, we can manipulate these variables in controlled experiments.

1. Investigating the Effect of Light Intensity on Photosynthesis

Hypothesis

As light intensity increases, the rate of photosynthesis will increase up to a certain point, after which it will plateau, as other factors become limiting.

Experimental Setup

1. Materials: Aquatic plant/alga specimen (e.g., Elodea or Cabomba), light source (adjustable), water bath (to regulate temperature), and CO₂ source (such as sodium bicarbonate).
2. Method:
   1. Place a piece of the plant in a beaker with water containing dissolved CO₂ (via sodium bicarbonate).
   2. Adjust the light intensity by varying the distance of the light source from the plant (or use a dimmer switch if available).
   3. Measure the rate of photosynthesis by counting the number of oxygen bubbles released by the plant (or by measuring the volume of oxygen produced over time).
   4. Record the results at different light intensities.

Expected Outcome

1. As light intensity increases, the rate of photosynthesis will initially increase due to more energy being available for the light-dependent reactions.
2. However, beyond a certain intensity (saturation point), the rate of photosynthesis will level off, as other factors (like CO₂ or temperature) become limiting.

2. Investigating the Effect of Carbon Dioxide (CO₂) Concentration on Photosynthesis

Hypothesis

As the concentration of CO₂ increases, the rate of photosynthesis will increase, up to a point, after which the rate will plateau.

Experimental Setup

1. Materials: Aquatic plant/alga specimen (e.g., Elodea), CO₂ source (e.g., sodium bicarbonate), water bath, and light source.
2. Method:
   1. Place the plant in a beaker with water containing varying concentrations of CO₂ (adjust using different amounts of sodium bicarbonate).
   2. Ensure constant light intensity and temperature.
   3. Measure the rate of photosynthesis by counting the number of oxygen bubbles produced or by measuring the oxygen produced using an oxygen probe.
   4. Vary CO₂ concentrations and record the results.

Expected Outcome

1. As the concentration of CO₂ increases, the rate of photosynthesis should increase because the enzyme RuBisCO can fix more carbon during the Calvin cycle.
2. However, after a certain concentration, the rate will plateau as the enzymes become saturated with CO₂.

Varying Carbon Dioxide Concentration

1. Remove Dissolved Gases: Boil water to eliminate dissolved gases, including carbon dioxide. Cool the water before use.
2. Oxygenate the Water: Pour the water between containers to reintroduce oxygen without adding carbon dioxide.
3. Control Carbon Dioxide Levels: Add sodium hydrogen carbonate (NaHCO₃) incrementally to adjust carbon dioxide concentration.
4. Measure Photosynthesis: Use aquatic plants like Elodea or Cabomba to observe oxygen bubble production as a proxy for the photosynthesis rate.

3. Investigating the Effect of Temperature on Photosynthesis

Hypothesis

1. The rate of photosynthesis will increase as temperature rises, up to an optimal point.
2. Beyond this optimal temperature, the rate will decrease due to the denaturation of enzymes involved in photosynthesis.

Experimental Setup

1. Materials: Aquatic plant (e.g., Elodea), light source, water bath to control temperature, and CO₂ source.
2. Method:
   1. Place the plant in water with a fixed concentration of CO₂.
   2. Set the water bath to different temperatures (e.g., 10°C, 20°C, 30°C, 40°C, etc.).
   3. Keep the light intensity constant.
   4. Measure the rate of photosynthesis by counting the number of oxygen bubbles produced or using an oxygen sensor.

Expected Outcome

1. As temperature increases, the rate of photosynthesis will rise due to increased molecular motion and enzyme activity.
2. However, once the temperature exceeds the optimum temperature (usually around 30-40°C for most plants), enzyme denaturation will occur, causing a decline in the rate of photosynthesis.

Repeated Testing and Refinement

1. Scientific hypotheses require repeated testing to ensure reliability.
2. Experiments should be repeated multiple times to confirm results and identify any anomalies.