Photosynthesis

Photosynthesis produces glucose using light

It uses energy to change carbon dioxide and water into glucose and oxygen.

It takes place in chloroplats in green plants which contain pigments called chlorophyll that abosorb llight.

Its endothermic meaning energy is transferred from the environment to the chloroplasts by light.

Carbon dioxide + water → glucose + oxygen

Factors that affect the rate of photosynthesis :

Light intensity:

Not enough light slows down the rate of photosynthesis

Light provides the energy needed for photosynthesis.

As light level increases the rate of photosynthesis increases steadily but only up to a certain level. Beyond this it wont make a difference. As light intensity increase the rate of photosynthesis will no longer increase. This is because temperature or CO2 level will be the limiting factor.

In a lab you can change the light intensity by moving a lamp closer to or further away from a plant.

Carbon dioxide

Carbon dioxide also slows down photosynthesis and one of the raw materials needed for photosynthesis.

The amount of CO2 will only increase with the rate of photosynthesis up to a certain point. After this, the graph flattens out showing that CO2 is no longer the limiting factor.

As long as light and CO2 are in a plentiful supply then the limiting factor must be temperature.

Temperature

If temperature is the limiting factor then its because its too low. It needs to be just right. This is because the enzymes work too slow at lower temperatures. If the plants get too hot then the enzymes it needs for photosynthesis will be damaged.

This happens at about 45 degrees.

Required practical activity 6: investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed.

Canadian pondweed can be used to measure the effect of light intensity on the rate of photosynthesis. The rate at which the pondweed produces oxygen corresponds to the rate at which its photosynthesising meaning the faster the rate of oxygen production the faster the rate of photosynthesis.

1. Place a source of white light a specific distance from the pondweed.

2. Leave the pondweed to photosunthesise for a set amount of time. As it photosynthesises the oxygen released will collect in the capillary tube.

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

4. Controlled variables are the temperature and time the pondweed is left to photosynthesis.

5. The experiment is repeated twice witih the light soruce at the same distance and the mean volume of O2 calculated.

6. Then the whole experimanet is repeated with the light source at different distances from the pondweed.