Photosynthesis using algae wrapped in jelly balls

Photosynthesis can be a hard topic to demonstrate reliably in the lab, especially in winter. This fun and reliable practical makes investigating photosynthesis easy, with a technique that can be used with students from KS3 to post-16.

Algae can be considered as one-celled plants, and they usually live in water. You are going to use algae to look at the rate of photosynthesis. The algae are tiny and are difficult to work with directly in the water so the first part of the practical involves ‘immobilising’ the algae as algal balls. This effectively traps large numbers of algal cells in ‘jelly like’ balls so that we can keep them in one place and not lose them. We use sodium alginate to help make the jelly. Sodium alginate is not harmful to the algae.

When these algae are ‘wrapped up’ in the jelly balls they are excellent to use in experiments on photosynthesis. These algal balls are:

• cheap to grow and easy to make – you will be able to make hundreds in a very short time
• easy to get a standard quantity of plant material because each of the balls is approximately the same volume
• easy to keep alive for several weeks so you can keep them for future experiments

A kit, produced in collaboration with the NCBE, is available for this practical.

Further details to support those doing further investigations with this protocol with post-16 students are also available.