Green cabomba, a pondweed with floating fan-like leaves, makes an attractive aquarium plant, but its value for the lab is in its oxygenating properties. Use the bubbles of oxygen given off by Cabomba to demonstrate oxygen evolution in the process of photosynthesis. Cabomba is no longer available in the UK, due to the recent invasive plant directive. We have trialled several alternatives and you can read our recommendations here.

Practicals

• Photosynthesis - Resource: Using Cabomba to demonstrate oxygen evolution in the process of photosynthesis

Teaching Topics

• Photosynthesis

Description

Green Cabomba, Cabomba caroliniana

An aquatic pondweed often used in home aquarium tanks as both an ornamental and oxygenating plant. Non-native to the UK.

Growing and sourcing

Obtaining: Green Cabomba pondwwed is easily available from aquarium shops or pet shops that have aquarium section, and specialist science suppliers such as Blades Biological. A care sheet can be downloaded from them too. Red Cabomba (Cabomba furcata) is also available, but is considerably less easy to keep in the lab.Be aware if purchasing Cabomba that it is very sensitive to extreme cold (sub-zero) conditions and prolonged exposure to such temperatures can cause the stem of the plant to lignifiy thus not allowing oxygen evolution from the cut stem. Whilst the plant may survive, it will not be suitable for use in practical experiments.

Care: Cabomba pondweed is best kept in a a constantly aerated tank (just use a simple aquarium pump) filled with tap water ocated near a window with another aquatic plant Elodea (ratio 6:1 of Cabomba to Elodea). In this ratio the plants survive happily together for months. If you don’t add Elodea in the ratio suggested, we find that the Cabomba breaks down rapidly over a week or so.

Note: Must be disposed of carefully. This plant must NOT be put into the domestic water–course, as it becomes an invasive pest. We recommend disposal in domestic waste or (preferably) by burning. Always dispose of non-native plants like Cabomba appropriately - be plant wise.

Curriculum Links   

GCSE

• AQA GCSE Science A C.1.7.2 - Suggested practical
• AQA GCSE Science B 3.3.1.2 - Suggested practical
• AQA Biology B2.3 - Suggested practical
• OCR GCSE Biology B4b - Suggested practical

A-level

• Edexcel AS/A2 3.1 Topic 5 - Opportunities for practicals
• AQA Biology AS/A2 3.4.3 - Opportunities for practicals
• Scottish Highers Unit 2 Metabolism - Photosynthesis experiments