Photosynthesis practical Flashcards
- Take a…
boiling tube and place it 10 cm from an LED light source
If a normal light bulb is used…
a beaker filled with water must be placed between the boiling tube and the light to trap the heat.
- Fill the boiling tube with…
sodium hydrogen carbonate solution. This releases carbon dioxide needed for photosynthesis.
- Put a piece of…
pondweed into the boiling tube with the cut at the top, allowing carbon dioxide to escape.
- Leave the boiling tube with pondweed for…
5 minutes to acclimatise to the conditions.
- Oxygen bubbles are…
produced by photosynthesis.
- Start stop-watch and count…
the number of bubbles produced per minute.
- Repeat the counting of bubbles per minute…
two times and calculate the mean.
- Repeat the experiment…
again from the start at 20cm, 30cm and 40cm.
Problems
- number of bubbles can be too fast to count
- bubbles are not always the same size
Solution
Measure the volume of oxygen produced.
How to measure the volume of oxygen produced?
Place pondweed under a funnel and catch the bubbles in a measuring cylinder. Use the measuring cylinder to measure the volume of oxygen produced per minute.
Inverse-square law
If we double the distance, the number of bubbles per minute falls by a factor of 4.
If we double the distance the light intensity…
falls by 4 times.
