Test the prediction that the closer the lamp is to a piece of pondweed in a tube of water the less amount of oxygen will be produced.

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Photosynthesis Investigation

Aim-

Our aim in this investigation is to test the prediction that the closer the lamp is to a piece of pondweed in a tube of water the less amount of oxygen will be produced.

Scientific Knowledge:

The equation for photosynthesis:

Photosynthesis is a chemical reaction occurring in the leaves of green plants. Using the energy from sunlight, it changes carbon dioxide and water into glucose and oxygen.

Oxygen is a 'waste' product of photosynthesis.

Glucose can be converted to sucrose and carried to other parts of the plant in phloem vessels. Glucose can also be converted into starch and stored (the starch can later be turned back into glucose and used in respiration).

A cross section of a leaf

Photosynthesis happens in cells in the middle of the leaf. These cells contain tiny bodies called chloroplasts; these contain a

green chemical called chlorophyll.

Chlorophyll is used to convert light energy into chemical energy.

The intensity of light falling on the plant is inversely proportional to the distance, which is called the inverse square law.

Doubling the distance between the lamp and the plant reduces the light intensity received by the plant by one quarter.

Equation:

By trebling the distance between the lamp and the plant reduces the light intensity received by the plant by one ninth.

Equation:

The inverse square law can be presented as:

L is the light intensity where as d is the distance between the lamp and the plant. Graphs can be plotted of the amount of gas produced against . This law assumes that the plant is not affected by any light other than that whose distance is being altered.

Fair test:

I will make it a fair test by using the approximately the same size of the leaf, trying to cut out extra light for example the windows and experimenting the project at room temperature.

Variables-

Input variables - light intensity is to be varied by increasing and decreasing the distance from the light source to the plant

Output variables - volume of oxygen produced (rate of photosynthesis) is to be measured by finding the volume of oxygen produced in a minute, and thus finding the rate of photosynthesis
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Control variables -Light wavelength (colour) - light energy is absorbed by the pigment, chlorophyll, in the leaf. Chlorophyll easily absorbs blue light, in the 400-450 nm range, and also easily absorbs red light, in the 650-700 nm range. However it does not easily absorb green or yellow light, rather it reflects them, decreasing the amount of light absorbed, and therefore the rate of photosynthesis. This can easily be controlled, simply by using the same lamp throughout the experiment.

Rate Increasing CO2

Increasing Light

Carbon dioxide concentration - This can affect the rate of photosynthesis, since ...

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