Measuring photosynthesis by oxygen evolution with Cabomba
This is a Science & Plants for Schools practical. Find more teaching resources and hands-on practicals for colleges and secondary schools at www.saps.org.uk
Join the free SAPS Associates scheme for new plant science teaching resources, latest research updates, tips and ideas from practising teachers, grant opportunities, and access to the SAPS Experts Panel.
In this experiment you are going to use the aquatic plant Cabomba to observe bubbles of oxygen which are released as the plant carries out photosynthesis.
These bubbles can be counted and the rate of bubbling can give you an indication of the rate of photosynthesis. If we alter the light intensity, does the rate of bubbling vary?
1. Cup your hand around the Cabomba sprig and gently flatten the fronds against the central stem.
2. Carefully lower the flattened Cabomba into measuring cylinder, apex lowermost, and hold the end of the stem against the glass with your finger (Figure 1).
[pic] [pic] [pic]
Figure 1 Figure 2 Figure 3
3. Fill the measuring cylinder with a 1% sodium hydrogen carbonate solution (Figure 2).
4. Cut the stem of the Cabomba sprig at an angle under the surface of the liquid. This cut end must remain in the liquid or an air lock may form. You should be able to observe bubbles of gas rising from the cut (Figure 3).
5. Place your Cabomba in front of a bright light source and let the plant equilibrate for five minutes. (You may want to place a flat sided container of water between the measuring cylinder and the lamp to prevent the water in the measuring cylinder heating up.) Count the bubbles produced in 30 seconds. Repeat the reading twice more and record your results in a table. Move the measuring cylinder so that it is different distances from the light source and let equilibrate again. Repeat the experiment until you have enough results to show a...