Bioenergetics Practical

Question 1

Describe the process in which you can measure the rate of photosynthesis

Answer 1

1. We start by taking a boiling tube and placing it 10cm away from an led light source. (An led light source is used as these do not release much heat. Too much heat would change the temperature of the experiment.) 2. Now fill the boiling tube with 20cm^3 of sodium hydrogen carbonate solution (this releases carbon dioxide which is needed for photosynthesis) 3. Next we put a 10 cm piece of pondweed into the boiling tube with the cut end at the top. 4. We then leave this for a few minutes to acclimatise to the conditions in the boiling tube. 5. Start a stop watch and count the number of bubbles produced in one minute. 7. Do the whole experiment again from the start at 20cm, 30cm, 40cm. 8. Now repeat the experiment so you have a few readings for each distance.

Question 2

Describe the process in which you can measure the rate of photosynthesis if you only have a normal light bulb

Answer 2

If we do have to use a normal light bulb then we must place a glass beaker in front of the light so this will absorb any heat produced by the bulb so it does not interfere with our experiment.

Question 3

What are the two main problems with this practical? and how can we solve them?

Answer 3

1. The number of bubbles can be too fast to count accurately. 2. The bubbles are not always the same size and a large bubble would count the same as a small bubble.

We can solve these problems by placing the pond-weed under a funnel and catch the bubbles in a measuring cylinder. We can then use the measuring cylinder to measure the volume of the oxygen gas produced.