How different heights of light increases or decreases

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My aim is to carry out an experimental investigation that will observe how different heights of light increases or decreases the amount of starch produced in a leaf.


I predict that the further away the light is under a leaf the more amount of starch produced to increase. I believe this because the more light the leaf is enabled to the less amount of photosynthesis will take place, I believe this because the light energy will increase causing friction, and this friction will then turn into heat which will destroy any enzymes in the leaf which will slow down the starch production made in the leaf. Before starch the food substance is called glucose which will turn into starch and will be stored in the roots, stems and leaves, loathing the storage system. I also predict that the longer the light shines on the leaf the less starch will be produced because the temperature of the light will begin to transfer into heat and begin to kill the enzymes in the leaf , this will cause the production of starch to fall dramatically.

Dependent Variable:

The amount of starch produced is a dependent variable because it will vary to show that my hypothesis is correct. The amount of starch produced in a leaf because the starch varies due to the light intensity. This will indicate if there is any glucose in the leaf. The amount of starch produced within the leaf will tell me how much glucose is in the leaf is produced in different light intensities.

Independent Variable:

The light intensity is a dependent variable because the light intensity will be shone at different heights. This will help me to understand if the light shone at different heights will produce less starch or more starch. I strongly agree that this will prove my hypothesis

Controlled Variable:

Surface Area of leaf is a controlled variable because the leaf at this precise moment cannot grow in surface area because it is dead therefore it is controlled.

The room temperature is a controlled variable because I can control the amount of temperature the plant gets because 24hrs before the experiment the leaf was kept under light for 24hrs and the room in which the experiment was held was not open until around 24hrs.

Preliminary Work

In my preliminary experiment I conducted the same experiment. I had the choice of alternating my experiment, but instead I decided to keep everything the same, this way any mistakes that occurred will be corrected to make my real investigation more accurate in terms of results and equipment used. In my preliminary I noticed that the colour of leaf took longer to change when I put iodine on it. It came to my conclusion that the amount of iodine I put on the leaf was very small. On the specific day of my preliminary the room temperature was above average, this caused most of the enzymes to die; this made the slowed down the production of starch and caused my results to be anomalous. All these mistakes were corrected and altered in my real investigation.

Equipment List

3 Plants – this is the base of my experimental .The need to repeat my readings are crucial to ensure that I do not have any anomalous results; this will also help me to find an average result and make my results more professional.

Kettle – I will boil the kettle to an appropriate temperature which will kill any productions in the leaf.

3 Beakers – The beakers act as container and the beaker also helps me to measure the amount of water.

9 Test tubes – This will measure the amount of different substances on an accurate scale.

Ethanol – This will remove chlorophyll from the leaf and destroy the waxy layer (cuticle) on the leaf’s surface.

Petri dish – This will provide the surface area for the reaction to take place. I t also acts as a store to keep the leaf on.

Cold water

Iodine –This will react with starch to indicate the colour change in the leaf. The iodine will indicate whether there is starch present in the leaf.

Water – The water will be provided from the tap, this water will be boiled in the kettle. This hot water will also be used to sterilise all the apparatus after.

Stands –

3 Lights – to ensure that the lamps don’t become over used because this could lead to heat.

Clamp – The clamp will hold the lamp, this will make sure that the light is shone evenly on the leaf.

Forceps – This instrument will be used to pick up and move the leaf from A to B.

Safety Glasses – This protect my eye from any corrosive substances I may come across while doing my experiment.


Before I started my experiment all leafs were left untouched.

Step 1: Set up all apparatus needed. Previously the plant was left in a normal room temperature for 24 hours.

Step 2: Boil the water for the appropriate time. Pour 20 cm of water in a beaker, after this remove four leafs at random from a plant (preferably the greenest) then use forceps to hold the leaf and transfer it into the beaker containing 20 cm of hot water..

Step 3: Add approximately 5 cm of ethanol in each test tube and place each of the leaves in it. The ethanol will destroy the chlorophyll on the surface area of the leaf.

Step 4: Place each of the test tubes in a beaker filled with boiled water for 2 minutes

Step 5: After the 2 minutes remove each of the plants from the ethanol and thoroughly cleanse the leaf with cold water and forceps. This will prevent the leaf reacting with iodine that is going to be added.

Step 6: Spread each on a Petri dish and add the required amount of iodine needed to change the colour of the leaf.

My range of readings will be ranged from 10-30cm.

Background Theory

We can write the overall reaction of this process as:

6H2O + 6CO2 ———-> C6H12O6+ 6O2


Photosynthesis is the process which produces food for plants. This food is stored in the plant as glucose; this food is then converted into starch. Before this process happens plants need certain criteria for them to produce starch. The most important criteria are light energy from the sun.Chlorophyll is a green photosynthetic pigment found in plants.The chlorophyll absorbs the light energy from the sunlight combining with carbon dioxide and water to produce glucose.The glucose can them be used for various activies to help sustain the plant.The main prurpose is to use the glucose and convert it into starch which can then be used for food purposes.

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