Required practical: Photosynthesis Flashcards
Step 1
Place a boiling tube with sodium hydrogen carbonate solution 10cm away from an LED light source
Step 2
Place a piece of pondweed with the end cut at the top into the tube
Step 3
Place a funnel and measuring cylinder at the top of the boiling tube
Step 4
Calculate the volume of gas produced (bubbles) in the measuring cylinder in a minute
Use a stop watch to time it for a minute
Step 5
Repeat experiment 2 more times and calculate the mean volume of oxygen gas
Step 6
Repeat whole experiment, but moving the tube 10cm back each time until it’s 40cm away
Why use an LED light?
Normal light bulbs produces heat energy. This affects the rate of photosynthesis
We are trying to measure the affect of light energy on photosynthesis
Why calculate volume of oxygen rather than bubbles propounded?
Bubbles may be too quick to count accurately
Some bubbles are different sizes
The inverse square law
If you plot these results on a graph then:
When you double the distance, the number of bubbles produced per minute falls by 4 times.
If at 10 cm away it produced 20cm³ of oxygen, then at 20 cm away it would produce 5cm³ of oxygen
Why does the inverse square law happen?
If the distance is doubled, the light intensity falls by 4 times.
Causes the volume of oxygen produced to decrease by 4 times because rate of photosynthesis falls
Why do we use sodium hydrogen carbonate?
Releases carbon dioxide = needed for photosynthesis