Range
I will have a range of 2-12 volts
Safety
To make the experiment safe I will dry any spilt water straight away to avoid anyone slipping over and will take great caution in making sure all water is at a safe distance from all elecricals.
Variables (faire test)
Variables that may affect the outcome of this experiment if not kept constant are as follows:
Plant
Throughout the whole experiment we will use the same piece of pondweed
It is important that we do this because the size and surface area of leaves on the weed may change on a different piece of weed and therefore may alter the result.
Temperature of water
I will make sure not to use hot water, as when temperature increases so does the rate of photosynthesis and so will ruin our results because it will interfere in our study of light. This wont be a problem at all if I just use ordinary cold/tepid tap water, as the water would need to be round 21ºC, which is the pondweeds optimum temperature in order to affect it. The tap water however will be less than this and will be warm enough for the plant to photosynthesise in but not hot enough to speed up the reaction.
Amount of co2 present
It is important to keep this factor constant because as CO2 increases so does the rate of photosynthesis. In order to keep this factor constant I wont have to do anything as there is a very small percentage in the air anyway (0.03%) so it wont affect the experiment, the most I can do is not respire too much on it as carbon dioxide is exhaled.
Time
I will use the same amount of time each time (1min) to count how many bubbles form.
The plant inside
This isn’t something that we can alter however it is still a variable. The amount of chloroplasts would in increases the rate of photosynthesis the more chloroplasts the more photosynthesis carried out, as chloroplasts contain chlorophyll a substance that traps light energy that is essential for photosynthesis.
Distance of the plant from the light source (light intensity)
I will make sure that the lamp is the same distance away from the plant throughout the experiment (about15cm away).
Diagram of equipment
Prediction
I predict that the the higher the voltage the more bubbles released. I say this because higher voltage means more light intensity and the more light there is the more the plant can photosynthesise. The rate of photosynthesis to the light intensity is inversely proportional
When the lamp is at its brightest it will give more light (energy) that the pondweed will need to photosynthesise at its optimum speed. Also the rate of photosynthesis will increase when light intensity is increased because the amount of energy absorbed by the chlorophyll increases, which makes the transfer of carbon dioxide into sugars also increase. The rate of oxygen also increases when the light intensity increases thus proving how the rate of photosynthesis increases when light does as oxygen is a product of it and the more produced, shows that more photosynthesis occurred.
The equation for photosynthesis is:
sunlight
Carbon dioxide + water ----------------------> glucose + oxygen
Chlorophyll
Table explaining light with photosynthoses
(This table is taken from Biology for you, Gareth Williams)
The table shows in bright conditions more C02 is taken in for photosynthesis through the stomata (small holes underside of leaf) and as the light decreases so does the amount of C02 entering and in complete darkness no photosynthesis occurs. Overall I predict that the light voltage 12 will make the most bubbles.
Results
Conclusion
By analyzing my results I can say that my prediction was correct. The results show that the amount of light intensity and oxygen go up in a directly proportional rate. I can tell this because as I increased the voltage (light intensity), the amount of bubbles increased also (oxygen). Indeed photosynthesis proved to produce more oxygen as light intensity increased, proving the equation below:
CO2 + H2O -> (light energy) -> CH2O + O2
When the light was on 2 volts no bubbles were formed I think this is because it didn’t have enough time to photosynthesise.
The greater the light intensity the more intense photosynthesis was. Photosynthetic rate was being limited by certain factors such as carbon dioxide and temperature. As light intensity increases further, these factors limit the rate of photosynthesis even more until photosynthesis is completely limited. This is when photosynthesis is being carried out at a constant rate.
The lamp that I used had a cover that directed the light energy. The light energy did not spread out as much as a plain light bulb with no cover or normal sunlight. This distribution of the light energy was more concentrated, probably changing the gradient of the graph.
Evaluation
Overall, I would state the experiment as a success since my predictions were supported by my results. I feel I could have improved the experiment by repeating it in order to gain accurate results
My results however couldn’t have been very accurate because the classroom that we worked in was a poor site for carrying out this experiment, we were working very close to a large window and on a bright day, the lights were switched on, and also there were other experiments (the same) going On in the same room this would change the concentration of oxygen and carbon-dioxide in the air. I would improve the experiment by turning off all the lights in the science lab so that the light intensity would be equal for every repeat. I would also control the amount of carbon dioxide in the water by preparing the solution pre hand in order to give the basin a proper mix.
To improve the experiment further I would have used a different type of light than the type we use (normal light), I would have used Blue light, and this light is easily absorbed by chlorophyll, and is the same type of light, which comes from the sun.
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