What Affects the Rate of Photosynthesis?

The rate of photosynthesis depends on limiting factors, such as light intensity, carbon dioxide concentration, and temperature.

💡 Key Concept: The faster the reactants (CO₂, water, and light) are available, the faster the reaction occurs, up to a certain point.

Investigating the Rate of Photosynthesis (Required Practical)

Experiment: Measuring Oxygen Production

A common method to measure photosynthesis is using pondweed (e.g., Elodea) in water to count oxygen bubbles released.

Equipment Needed

✔ A beaker of water
✔ Pondweed (Elodea)
✔ Light source (lamp)
✔ Ruler (to measure distance)
✔ Stopwatch
✔ Sodium hydrogen carbonate (for extra CO₂)

Method

1. Place pondweed in a beaker of water.
2. Add sodium hydrogen carbonate (to provide CO₂).
3. Place a lamp at a measured distance from the plant.
4. Start a stopwatch and count the oxygen bubbles produced in 1 minute.
5. Repeat with the lamp at different distances.

Expected Results

✔ More light = faster photosynthesis (up to a point).
✔ More CO₂ = increased rate (until another factor becomes limiting).
✔ Higher temperature = faster reactions (until enzymes denature).

💡 Graph Analysis:

• Light intensity increases → photosynthesis increases (until another factor limits it).
• At high temperatures, enzymes denature, stopping photosynthesis.

How to Improve Accuracy in the Experiment

✔ Use a gas syringe instead of counting bubbles (more precise measurement).
✔ Keep temperature and CO₂ levels constant.
✔ Repeat the experiment and calculate an average.

💡 Why Is This Important? To ensure reliable and repeatable results.