Pondweed - Bio

Question 1

How to investigate the effect of light intensity on photosynthesis

Answer 1

1. take a boiling tube and place it 10cm away from the LED light source
2. Fill the tube up with sodium hydrogen carbonate solution
   3.Place a piece of pondweed into the boiling tube, with the cut end at the top
3. Leave it in the tube for 5 minutes
4. We should see bubbles of gas being produced from the cut end of the pondweed
5. Start a stopwatch and count the number of bubbles produced in 1 minute
6. Repeat this 2 more times and calculate a mean number of bubbles produced in 1 minute
7. Do the whole experiment again but now using different distances, 20cm, 30,40

Question 2

Why do we use an LED light source

Answer 2

as they do not release a lot of heat, too much heat would change the temperature of the experiment

Question 3

how would we need to change the experiment if we use a normal light bulb

Answer 3

we would need to place a beaker of water between the light and the boiling tube, this would absorb the heat produced by the bulb

Question 4

why do we use sodium hydrogen carbonate solution

Answer 4

because it releases carbon dioxide, which is needed for photosynthesis

Question 5

why do we leave the pondweed in the tube for 5 minutes

Answer 5

so it can adapt to the conditions in the boiling tube

Question 6

what gas do the bubbles produce

Answer 6

oxygen, which is produced by photosynthesis

Question 7

why might the speed of the bubbles cause a potential problem

Answer 7

the bubbles may be too fast to count accurately

Question 8

why might the size of the bubbles cause a problem

Answer 8

the bubbles might not be the same size, however, a large bubble counts the same as a small bubble

Question 9

how can we fix the problems

Answer 9

by measuring the volume of oxygen rather than counting bubbles
- this can be done by placing the pondweed under a funnel and catching the bubbles using a measuring cylinder, then we use the measuring cylinder to measure the volume of oxygen gas produced

Question 10

what results do we get from this experiment

Answer 10

as ewe increase the distance of the pondweed from the light source, the amount of bubbled per minute decrease

Question 11

what is the inverse square law

Answer 11

if we double the distance, the number of bubbles per minute falls down by 4x.

if we double the distance, the light intensity falls by four times

because we need light for photosynthesis, that also causes the number of oxygen bubbles to fall by 4 times