Investigate one factor which will affect the rate of photosynthesis

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Rachel Wilkins

Investigate one factor which will affect the rate of photosynthesis

Introduction

Photosynthesis is the process by which plants make their own food.  For photosynthesis to occur the plants need sunlight energy, the energy is absorbed by a green pigment called chlorophyll which is found in the leaves of the plant. This energy then combines with water molecules from the soil, and carbon dioxide from the air.  After this, a type of sugar called glucose is produced which can be used for the plants energy and oxygen is made as a byproduct.  

The equation for photosynthesis is:

 6CO2      +      6H2O      ->      C6 H12 O6      +      6O2.  

Any acceleration in the process of photosynthesis will naturally result in the production of more organic compounds and consequently more plant growth.  

There are certain things that affect photosynthesis called limiting factors.  These are: light intensity, temperature, amount of carbon dioxide available and the amount of water available.  Light intensity speeds up photosynthesis because sunlight is needed for the chemical reaction to happen and if the concentration of light is greater, more of it can be used to make glucose and oxygen.  The reason is similar for how carbon dioxide and heat affect photosynthesis.  Heat speeds up photosynthesis because the enzymatic reactions require the enzymes to be at a warm temperature to work at their best, although not above 40 oc as this is when they are destroyed by the heat.

I am going to investigate light intensity in my experiment to find out how it affects the rate of photosynthesis.  I will measure the rate of photosynthesis by calculating the amount of oxygen produced, as this is one of the products of photosynthesis.  I will measure the amount of oxygen produced by using a piece of equipment called a micro burette.  Using this piece of equipment I will measure what the volume the bubbles of oxygen given off are.  

Prediction

I predict that by decreasing the light intensity the rate of photosynthesis will also decrease.  I base this prediction on my background knowledge as well as previous experiments I have performed.  In the spring and summer plants grow at a quicker rate than in winter and autumn.  I believe that this is because light and heat are in a more plentiful supply.  Farmers place their crops on an east-west axis to obtain maximum sunlight for salad crops in polytunnels.  Also, horticulturalists use artificial ‘daylight’ bulbs in polytunnels to make their plants grow at a faster rate.      

In a recent experiment I carried out observing how light affects photosynthesis I placed an ‘S’ shaped stencil over a leaf and left it overnight with plenty of light.  The next day when I tested the leaf for it was only present within the ‘S’ shape when the iodine was added because it was exposed to the light.  However the part that was not exposed to the light revealed no starch was present.  This proves light is needed for photosynthesis to take place effectively.  Using an I.T. program the results showed that the greater the light intensity the faster the rate of photosynthesis, and the more oxygen given off.  I could see this from the graph that was produced:

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(P.T.O for graph)

From the graph it is clear that the more the light intensity was decreased, the less O2 was produced.  However, I also know that if the light intensity was too great the chloroplasts would be damaged and therefore unable to perform photosynthesis.  

Controlling other factors

The amount of carbon dioxide, heat and water can also affect photosynthesis so these will need to be kept the same throughout the test to keep it fair and avoid anomalies and an inaccurate experiment and poor results. ...

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