Investigating the affect light intensity has on photosynthesis

Authors Avatar

Biology Coursework

Investigating the affect light intensity has on photosynthesis

Plan

        All living organisms need food. They need it as a source of raw materials to build new cells and tissues as they grow. They also need food as a source of energy. Food is a ‘fuel’, which drives essential living processes and brings about chemical changes. Animals take in food, digest it, and use the products to build their tissues or to produce energy, but plants, apart from a few insect-eating species, do not appear to take in food. This is because plants find food sources in water and the air. This is known as photosynthesis.

        Chlorophyll is a green substance found in the chloroplasts of plant cells. It absorbs sunlight and makes the energy from sunlight available for chemical reactions. Thus, chlorophyll converts light energy to chemical energy. Therefore photosynthesis is the building-up of food compounds from carbon dioxide and water by green plants using energy from sunlight, which is absorbed by chlorophyll. The products of photosynthesis are glucose and oxygen. There are many factors, which affect the rate of photosynthesis, including light intensity, temperature and carbon dioxide concentration. The maximum rate of photosynthesis will be constrained by a limiting factor.

The chemical equation for photosynthesis is:

        

I am going to investigate what affect, if any, light intensity has on the amount of oxygen gas produced during photosynthesis. I am going to use an electric lamp as my source of light and Canadian pondweed as, when placed in water, it gives off bubbles of gas from the cut end.

In my experiments it is important that only one condition is altered. For example, the method of keeping light from a leaf also cuts off its carbon dioxide supply. It would be impossible to decide whether it was the lack of light or the lack of carbon dioxide, which stopped the production of sugar. To make sure that no more than one condition is altered in my experiments I will set up a control in an identical situation but in darkness. I predict that the pondweed will not photosynthesis at all in darkness. To ensure a fair test I will use the same species and general size of the pondweed each time. I will also use the same set up of apparatus in each experiment and keep the water at the same temperature as a rise in temperature increases the rate at which carbon dioxide combines with hydrogen to produce carbohydrates. It is important to use the same lamp in each experiment as light wavelength (colour) can affect the rate of photosynthesis. Chlorophyll easily absorbs red and blue light but does not easily absorb green or yellow light; rather it reflects them, decreasing the amount of light absorbed, and therefore the rate of photosynthesis.

Join now!

I am going to repeat my experiment three times so that I will be able to draw to a reliable conclusion. In each experiment I am going to investigate 5 different distances between the lamp and the rest of the apparatus. My chosen distances are 5cm, 10cm, 20cm, 30cm and 40cm. I will count the number of bubbles given off at each distance for 1minute. Between the changes in distance I will allow a settling period of 3minutes for the pondweed to adjust itself to the change in light intensity.

I predict that the greater the intensity of light ...

This is a preview of the whole essay