To investigate the factors that affect the rate of photosynthesis.

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Amreen Khadri 11QWR

                                Key Stage 4 Biology Coursework

Aim: to investigate the factors that affect the rate of photosynthesis.

Planning

Photosynthesis equation:

  carbon dioxide + water     sunlight           glucose  +  oxygen

                        6CO2         6H2O       chlorophyll      C6H12O6     6O2

Photosynthesis is the process that produces ‘food’ in plants. The food it produces is glucose. Photosynthesis takes place in the leaves of green plants.

Plants need light, carbon dioxide, water and chlorophyll in order to photosynthesise. The leaf is where the food is made. It gets light usually from the sun. The carbon dioxide enters the leaf form the air around.  Water comes form the soil, up to the stem and into the leaf. The most important thing is the chlorophyll, which is found in the chloroplasts. The chlorophyll absorbs the energy from the sunlight and uses it to combine carbon dioxide and water to produce glucose. Oxygen is a waste product. Therefore these are all limiting factors.

The rate of photosynthesis is affected by a number of factors including light levels, temperature, availability of water, and availability of nutrients. If the conditions that the plant needs are improved the rate of photosynthesis should increase.

The maximum rate of photosynthesis will be constrained by a limiting factor. This factor will prevent the rate of photosynthesis from rising above a certain level even if other conditions needed for photosynthesis are improved. This limiting factor will control the maximum possible rate of the photosynthetic reaction.

The rate of photosynthesis can be measured by measuring the amount of oxygen given off. To do this you place the water plant in water under a funnel in a beaker full of water. Then place a test tube over the funnel and start counting the bubbles given off. The bubbles are oxygen bubbles. I know this from preliminary work because I tested the gas by putting a glowing splint into the test tube and it re-lit so this proves the gas is oxygen. The more oxygen bubbles there are, the faster the rate of reaction of photosynthesis.


The temperature, light intensity, the length of the pondweed and the amount of carbon dioxide (sodium hydrogen carbonate) are all possible variables in this investigation.

I am going to investigate the effect of light intensity on the rate of photosynthesis.

Equipment I am going to use:

 

lamp                           spatula

beaker                   blade

funnel                        white tile                

test tube                sodium hydrogen carbonate

heat filter                water

elodea                            thermometer

metre ruler                stop clock

I will set up the equipment as shown below:

Method:

  1. Fill beaker with water (500ml).

  2. Add one spatula of sodium hydrogen carbonate.

  3. Measure temperature of water. Should be 34 C. If not add some hot water

  4. Place lamp at required distance (closest first).

  5. Place heat filter in between lamp and beaker. Turn lamp on.

  6. Cut elodea to 5cm with a blade and a white tile and immediately put in funnel and  

       water. Make sure funnel is placed firmly at the bottom of the beaker with blue tack.

  1. Fill the test tube with tap water and place it over funnel making sure no water

       escapes from the test tube so no gas is already in there.

  1. Leave the water to equilibrate for 2 minutes.

  2. Count the oxygen bubbles given off over a period of one and a half minutes.  Measure time with stop clock..

Repeat step 9 but alter the distances of the lamp from the beaker and keeping everything else the same. Check temperature each time.

Some points I should note when carrying out the investigation

        The lamp should be at the same height for each experiment. It should be level with the syringe each time.

        The distance should be measured from the front of the lamp to the syringe. Although taking these steps will make the experiment more accurate, it's accuracy is still limited by several factors:

        Some of the oxygen will be used for respiration by the plant.

        Some of the oxygen will dissolve into the water.

Fair Test::

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I am going to make it a fair test by making sure the temperature is the same by using a heat filter to stop the water absorbing the heat. I will leave the thermometer in the beaker and check the temperature of the water is kept the same throughout the experiment (25°C). I will carry out the experiment in the dark so no other light will affect the temperature of the water. I will do this to ensure the temperature is kept the same for each of the distances of the lamp because increasing the temperature will also increase the ...

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