Effects of Light Intensity on the Rate of Photosynthesis

Aim

To work out how light intensity can affect the rate of photosynthesis.

Hypothesis

I think that the further away the light source is the smaller the rate of photosynthesis is. This is because there is a further distance for the light to each the plant in order for it to photosynthesise. Although the closer the light source is, the more photosynthesis, the light source could also kill or damage the Elodea (type of pondweed) because it could become too hot and denature its cells. But because light intensity is also a limiting factor of photosynthesis, the rate of photosynthesis could go up and up and reach its maximum level. So, if it would be shown in a graph, the graph would show a line going up and up and eventually continuing as a straight line. The straight line is due to the limiting factors of light intensity (Carbon dioxide and concentration of Chlorophyll).

Glucose + Oxygen (+ light) Carbon dioxide + Water

Safety

Ð'* Don't place hands on bulb- damage to skin may occur.

Variables

Independent: distance of light bulb

Dependant: Amount of oxygen bubbles, distance of bulb away from pondweed and the amount of water.

Control: amount of water

Method

Ð'* Place some Elodea in a boiling tube.

Ð'* Place 7cmÐ'Ñ- of oxidised water in the boiling tube.

Ð'* Place boiling tube in test tube rack.

Ð'* Place the light source (bulb) 0cm away from the boiling tube and use a stop watch to time it for 1 minute.

Ð'* Count how many bubbles you see appearing in the water.

Ð'* Repeat experiment for other distances (10-50cm).

Conclusion

On my graph, I drew a best fit curve. The curve clearly shows that the further away the light bulb is from the Elodea, the less (average) oxygen bubbles there is and the less photosynthesis

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