Photosynthesis: Required Practical Flashcards
Explain the required practical for Photosynthesis
- Place the beaker 10cm away from LED light.
- Add sodium hydrogen carbonate solution
- Add pondweed with the cut end at the top
- Using a stopwatch calculate the number of bubbles per minute and repeat twice and calculate the mean.
- Repeat again and but try at different lengths e.g. 10,20,30,40,50
Why is it best to use an LED light?
Because a normal bulb might give out too much heat and may change the temperature of the experiment.
If you do use a normal bulb what should you do?
Place a glass of water in front of it.
What do we add to the boiling tube?
Sodium hydrogen carbonate solution.
Why do we add sodium hydrogen carbonate solution?
We add it because it gives off carbon dioxide which is needed for photosynthesis.
Why do we leave the pondweed for 5min before counting bubbles?
To acclimatise to conditions in the tube.
Why do we count the number of bubbles twice or thrice?
To find the mean for the most accurate results.
What are the two problems with this practical?
- The bubbles may be to fast to count accurately
2. Not all bubbles are the same size.
How can we solve this problem?
By measuring the volume of the bubbles rather than the amount.
How do we do this?
By placing pondweed in a funnel and catching the bubbles in a measuring cylinder and measuring the volume.
What is the inverse square law?
When the light intensity is inversely proportionate to the square of the distance.
What does the inverse square law mean?
It means that as the distance from the light source increases the light intensity decreases.
Describe the inverse law in another way.
If you double the distance the light intensity will halve.
