How Does Light Affect the Rate of Photosynthesis?

Topics: Carbon dioxide, Oxygen, Photosynthesis Pages: 7 (1933 words) Published: October 8, 1999
Biology Investigation

Problem: How does light affect the rate of Photosynthesis?

The Plan

In my experiment I am going to see how light affects the rate of photosynthesis. To do this experiment I am going to set up the apparatus as shown in figure 1.

The apparatus I am going to use are the following: -

1 Tripod
1 300ml Beaker
1 Boiling Tube
1 Clamp Stand
1 Boss
1 Ring Binder
1 Lamp
1 1 Metre Ruler
1 Thermometer
1 Stop Clock

To do the experiment I will set up the apparatus first. I will firstly place the tripod on top of the base of the clamp stand and fill the 300ml beaker with 250ml of water to create the water bath. I will place the boss in the middle of the bar on the clamp stand and place the clamp in the boss. I would then fill the boiling tube 43ml of water, put the pondweed in it and place it in the clamp. I would place the ring binder around the clamp stand surrounding the water base. Finally, I would plug in the lamp and place it 10cm away from the pondweed.

I done a preliminary experiment to get an idea how to do the main and proper experiment and what would happen in the experiment. In the preliminary experiment we didn’t use the safeguards so it wasn’t fair experiment. We did this because it gave us the idea what problems we might face when we did the main experiment and gave us the idea how to do it.

The pondweed should create photosynthesis by the following equation: -

6CO2 + 6H2O6C6H12O6+ 6O2

Photosynthesis occurs when plants take in Carbon Dioxide from the surrounding air in its leaves and water from the nearby soil in its roots. The leaves then take light energy from the Sun, which is absorbed in the chlorophyll in the cells and passes it along for it to be used in photosynthesis. Glucose is produced and is converted into Starch to be stored. Oxygen is produced from the water and it is a waste product so it is released into the air. The plant uses Carbon Dioxide and water to create Carbohydrates. Glucose is a small, soluble molecule which is useless for a plant to use as energy but it converts it into Starch, which is a large and insoluble molecule, so it can be stored for to be converted back into Glucose.

I made this experiment as fair as possible. Firstly, I put Sodium Bicarbonate in the boiling tube to enrich the water with Carbon Dioxide so more Oxygen bubbles would be produced. I had kept the volume of the water in the 300ml beaker and in the boiling tube the same so the temperature could stay the same, as that would affect the rate of photosynthesis. I put a ring binder around the clamp stand so that ‘foreign’ light wouldn’t be collected by the pondweed and continue photosynthesis after I had switched of the lamp. I constantly checked the temperature of the boiling tube and the beaker so it wouldn’t affect the rate of photosynthesis. I used a thermometer to check the temperature and I used a water bath to regulate the temperature of the boiling tube. I continuously used the same pondweed in all of my experiments so that the amount of chlorophyll would stay the same and the amount of Oxygen produced would also stay the same.

I predict that the amount of oxygen produced by the pondweed should decrease as I increase the distance between the boiling tube and the lamp. The rate of photosynthesis should decrease as I decrease light intensity and it should increase as I increase the light intensity.

Obtaining Evidence

DistancePreliminary Attempt

This set of results is the preliminary attempt. The results are inaccurate because it wasn’t a fair test, as I didn’t use any safeguards. 22 has a star next to it because it is an anomaly. This is due to the fact that no safeguards were used and possibly the pondweed caught ‘foreign’ light.

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