Bioenergetics: Photosynthesis RP

Question 1

What is photosynthesis?

Answer 1

The process by which plants synthesise glucose using light energy from the sun

Question 2

Describe how you would investigate the effect of light intensity on the rate of photosynthesis since an aquatic plant.

Answer 2

1. Place cut pondweed in a boiling tube (containing sodium hydrogen carbonate solution) at a fixed distance from a light source.
2. Count the number of bubbles produced in one minute using a stopwatch.
3. Repeat several times at different distances/light intensities and calculate a mean for each distance.
4. Plot a graph of light intensity (x) against rate of photosynthesis (bubbles per minute, y)

Question 3

Why is it best to use an LED light source rather than a lamp?

Answer 3

A lamp will emit more hear energy which may change the temperature of the experiment and affect the rate of photosynthesis.

Question 4

What is the relationship between the distance from a light source and light intensity?

Answer 4

Inverse square law:
light intensity ∝ 1/distance²

Question 5

How can the measurement of oxygen production be made more accurate?

Answer 5

Place the pondweed under a funnel with an inverted measuring cylinder over the spout.

Question 6

Why is sodium hydrogen carbonate solution used during this experiment?

Answer 6

It realeases CO₂, which is used by the pondweed during photosynthesis.

Question 7

Why can the number of bubbles produced be used to calculate the rate of photosynthesis?

Answer 7

Oxygen bubbles are formed as a product during photosynthesis.
The number of bubbles produced in a given time is proportional to the rate of photosynthesis.

Question 8

How could the method be improved to increase the validity of the results?

Answer 8

1. Control the concentration of CO₂.
2. Control the distance oil the bulb from the pondweed.
3. Control the species of pondweed.
4. Give pondweed time to equilibrate .
5. Repeat and calculate a mean.