B4 The Rate of Photosynthesis cont.... (page 52)

Question 1

Look at graph 1 on page 52, Explain what it shows?

Answer 1

It shows how the rate of photosynthesis is affected by light intensity and temperature. At the start, both of the lines show that the light intensity increases the rate of photosynthesis increases steadily, but the lines level off when the light is no longer the limiting factor. The line at 25°C levels off at a higher point than the one at 15

Question 2

Look at Graph 2 on page 52, explain what this shows?

Answer 2

It shows how the rate of Photosynthesis is affected by light intensity and CO2 consentration. Both lines level off when light is no longer the limiting factor. The line at the Higher CO2 concentration of 0.4%. levels off at a higher point, then the one at 0.04%. This means CO2 concentration must have been the limiting factor at 0.04%. The limiting factor here isn’t temperature because it’s the same for both lines (25°C).

Question 3

What do Oxygen Production show the rate of?

Answer 3

Photosynthesis

Question 4

What can Canadian Pondweed be used to measure?

Answer 4

The effect of light intensity of the rate of photosyntnesis. the rate at which the pondweed produces oxygen corresponds to the rate at which its photosynthesising - the faster the rate of oxygen production the faster the rate of photosynthesis.

Question 5

Explain the process of Canadian Pondweed measureing the effect of light intensity on the rate of photosynthesis?

Answer 5

1) A sourse of white light is placed at a specific distance from the pondweed

2) The pondweed is left to photosynthesise for a set amount of time - as it photosynthesises, the oxygen released will collect in the capillary tube (see diagram pg 52).

3) At the end of the experiment, the syringe is used to draw the gas bubble in the tube up alongside a ruler and the length of the gas bubble is measured. This is proportional to the volume of O2 produced.

4) For this experiment, any variables that could affect the results should be controlled, e.g. the temperature and time the pondweed is left to photosynthesise.

5) The experiment is repeated twice with the light source at the same distance and the mean volume of O2 is produced is calculated

6) Then the whole experiment is repeated with the light source at different distances from the pondweed. (you can compare the results at different light intensities by giving the rate as the length of the bubble per unit time eg. cm/min)

The apparatus above can be altered to measure the effect of temperature of CO2 on photosynthesis. E.g. The test tube of pondweed can be put into a water bath at a set temperature, or measured amount of sodium hydrogencarbonate can be dissolved in water (which gives off CO2). The experiment can be repeated with different temperature of water/concentration of sodium hydrogencarbonate