Photosynthesis Investigation

Photosynthesis Investigation
Investigate the affect of light on the rate of photosynthesis of a piece of pondweed I am going to investigate how light will affect the rate of photosynthesis of pondweed. I predict that as the light becomes less intense, I do this by moving the light away from the pondweed, the rate of photosynthesis will decrease. The formula for photosynthesis is: 6CO2 + 6H2O C6O12H6 + 6O2 Carbon Dioxide + Water Glucose + Oxygen There are 3 major factors that limit the rate of photosynthesis, these are: ? Temperature ? Amount of Carbon Dioxide ? Light Intensity The only factor that we are able to measure successfully in school is the affect of light on the rate of photosynthesis, so we have to believe that the level will remain the same. This is very unlikely to happen so we could end up with a few rouge results. As the plant is moved closer to the light source.
The light intensity increases so the rate of photosynthesis should increase. [image] [image]As the plant is moved further away from the light the light intensity decreases and therefore the rate of photosynthesis should also decrease. Because oxygen is a product of photosynthesis we will measure the amount of bubbles against time. This is very inaccurate as no two bubbles will contain the same amount of oxygen, but it should give us some idea of what is happening. This is why we are using pondweed, as it will allow to estimate how much oxygen is being given off. The bubbles will be visible, as the pondweed is underwater. Water Pondweed Oxygen Bubbles Equipment: ? 1 piece of pondweed ? 1 250ml Pyrex beaker ? 1 stop clock ? 1 ruler ? 1 60 watt light bulb ? 1 stand ? 1 boss clamp ? a pair of scissors ? 175ml tap water To be set up as shown below: ? Attach the bulb to the boss clamp and then attach that to the stand then plug the light in and turn it on. ? Cut a piece of pondweed and make a clean diagonal cut at one end so all the oxygen bubbles can escape. Leave the plant in the same position throughout the experiment. ? Put the pondweed into the Pyrex beaker and fill the beaker with about 175ml of tap water (it must cover the plant). ? Make sure that the plant is the correct distance from the light. The experiment: ? The light bulb needs to be 5cm away from the beaker then give the pondweed 5 minutes to acclimatise to the light intensity. After the plant has acclimatised start the stop clock and begin to count how many bubbles reach the surface do this for 120 seconds and record the result. ? Do this for 5cm, 10cm, 15cm, 20cm and finally 25cm. ? Repeat this 2 or 3 times to obtain an average. Conclusion and Evaluation From this experiment I can confirm that as the source of light becomes stronger the rate of photosynthesis will increase. This conclusion proves my prediction correct. The pondweed photosynthesises less when the light levels are weaker. However the rate of decrease isn?t constant as shown below. 5 cm ? 93.5 Difference = 46.5 10cm ? 47 2nd Difference = 24.5 Difference = 22 15cm ? 25 2nd Difference = 12 Difference = 10 20cm ? 15 2nd Difference = -0.5 Difference = 10.5 25cm ? 4.5 As you can see there are no connections. Some of the reasons may have been the temperature, we no that a light bulb gives out heat so this heat would have messed up the results. The amount of light coming into the room probably changed along with the amount of carbon dioxide in the room. I thought the experiment was reasonably successful. There are some things I could have done to receive better results. I.e. taking readings from 5cms to 50cms that way I should get a smoother curve on my graphs. I could take more reading and give the plant longer to acclimatise. I would like to do the test in a stable environment, in which I could control the amount of carbon dioxide and temperature. So it will be at the same level every time.

Photosynthesis Investigation 9.1 of 10 on the basis of 1180 Review.