Required practical: Photosynthesis

Question 1

Step 1

Answer 1

Place a boiling tube with sodium hydrogen carbonate solution 10cm away from an LED light source

Question 2

Step 2

Answer 2

Place a piece of pondweed with the end cut at the top into the tube

Question 3

Step 3

Answer 3

Place a funnel and measuring cylinder at the top of the boiling tube

Question 4

Step 4

Answer 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

Question 5

Step 5

Answer 5

Repeat experiment 2 more times and calculate the mean volume of oxygen gas

Question 6

Step 6

Answer 6

Repeat whole experiment, but moving the tube 10cm back each time until it’s 40cm away

Question 7

Why use an LED light?

Answer 7

Normal light bulbs produces heat energy. This affects the rate of photosynthesis
We are trying to measure the affect of light energy on photosynthesis

Question 8

Why calculate volume of oxygen rather than bubbles propounded?

Answer 8

Bubbles may be too quick to count accurately

Some bubbles are different sizes

Question 9

The inverse square law

Answer 9

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

Question 10

Why does the inverse square law happen?

Answer 10

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

Question 11

Why do we use sodium hydrogen carbonate?

Answer 11

Releases carbon dioxide = needed for photosynthesis