Find out how light affects the rate of photosynthesis.

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Photosynthesis

Introduction

Photosynthesis is the process plants use to produce their own food, turning Carbon Dioxide and water into glucose and oxygen. This process can be explained using the formula:

Sunlight

6CO2+6H2O C6 H12 O6 +6O2

In this piece of coursework I am going to find out how light affects the rate of photosynthesis.

The energy from sunlight is absorbed into the plant by a green chemical called chlorophyll, which is found in chloroplasts in the plant's cells. Plants need a healthy supply of carbon dioxide and water to make photosynthesis possible, the water is drawn in by the roots, and the carbon dioxide is taken in by the leaf. The chlorophyll is able to split water in to hydrogen and oxygen, the 'light' reaction. The oxygen leaves the leaf and the hydrogen and carbon dioxide combine to make glucose, the 'dark' reaction.

The leaf is specially adapted for photosynthesis as shown in the cross section of the leaf (taken from www.bbc.co.uk/schools/gcsebitesize). One adaptation of the leaf is that the chloroplasts, which contain chlorophyll, are found in the palisade layer, close to the surface of the leaf, so they can absorb sunlight easily. Another adaptation of the leaf is that the cuticle and the epidermis are transparent to allow light to pass through to the palisade cells.

Preliminary work

We have completed some preliminary work to identify what is needed to ensure a fair test and get accurate results.

Firstly we did a trial experiment to help us decide what distances to use in the real experiment. We found that it was impossible to get the lamp any closer than 5 cm and the elodea stopped producing oxygen bubbles after 30 cm. We decided to use these distances - 6,9,12,15,18,21 and 24 cms; we chose those as they are within the 5- 30 cm boundaries and we can easily find a pattern. Now we know the distances we are going to use we can work out the light intensity for each distance, by using the formula- Light intensity =1/d2

6cm - Light intensity = 1/36 = 0.027 Lux

9cm - Light Intensity = 1/81 = 0.012 Lux

2cm - Light Intensity= 1/144 =0.0069 Lux

5cm - Light Intensity = 1/225 = 0.0041 Lux

8cm - Light Intensity = 1/324 = 0.0031 Lux

21cm - Light Intensity = 1/441 = 0.0023 Lux

24cm - Light Intensity = 1/576 = 0.0017 Lux

To make these numbers easier to graph we can divide by 1000 instead of 1 this changes the results to:

6cm - Light intensity = 1000/36 = 27 Lux
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9cm - Light Intensity = 1000/81 = 12 Lux

2cm - Light Intensity= 1000/144 =6.9 Lux

5cm - Light Intensity = 1000/225 = 4.1 Lux

8cm - Light Intensity = 1000/324 = 3.1 Lux

21cm - Light Intensity = 1000/441 = 2.3 Lux

24cm - Light Intensity = 1000/576 = 1.7 Lux

As part of this experiment we need to look at limiting factors and how to control them. There are a number of different limiting factors - temperature, light, Carbon Dioxide and water. After a lot of research we found that ...

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