Required Practical 05: Photosynthesis

About this practical...

Provided you complete this at the right time of year, this is an excellent practical in which you will clearly see the link between light intensity and the rate of photosynthesis. Lots of links to good scientific method, such as control variables (ambient light level so complete on the same day etc) and using the same plant. The usually "invisible" process of photosynthesis comes to life. Don't forget to test the gas produced.


1. Set up the apparatus as shown by your teacher. You should have your plant specimen in a glass vessel, completely submerged under water.

2. Place your light source 1 m away from your plant and turn on the light.

3. Time 1 minute and count how many bubbles of oxygen leave your plant and float to the surface. Record the number of bubbles for that distance.

4. Move the lamp to be 80 cm away and repeat the above. Record how many bubbles are released in 1 minute.

5. Continue this until the lamp is 20 cm away.

6. If there is time, repeat each reading.

7. Use your completed table to calculate a mean then plot a graph of distance from the light source (x axis) against the mean number of bubbles per minute (y axis).

Any results that you need must be collected during this lesson. If you repeat this on another day, the plant will be different (deteriorated, grown or replaced with a different one) and the ambient light will also be different.

Safety & Managing Risks

Usual lab rules must be followed: loose hair tied back, goggles worn throughout the lesson, bags and stools tucked away and notify the teacher of any spills or breakages immediately. Take care of the proximity of water to the sources of electricity. For more detailed information, please consult CLEAPSS.

Technician notes:


Meter rules

Aquatic plants in boiling tubes with CO2 rich water

This page was updated on: 8th January 2022