The aim of this investigation is to investigate how light intensity affects the rate of photosynthesis.

Amount of Sodium Hydrogen Carbonate – The amount of sodium hydrogen carbonate affects the rate of photosynthesis because it provides the carbon dioxide for the pondweed in the water.

Experimental Variable:

The variable I am going to do is light intensity and the distance between the light source and the pondweed.

Prediction:

I predict as the light source is moved further away from the pondweed, the rate of photosynthesis would decline.  This is because the light intensity of the light from the light source should decrease because the distance is getting larger and the plant would have less light to absorb.

Hypothesis:

Equipment:

The following equipment was used in the investigation:

• Beaker (600ml)
• Meter Ruler
• Thermometer
• Pond weed
• Tile
• Cutter
• Measuring Cylinder
• Lamp
• Test Tube
• Funnel
• Goggles
• Stop Watch
• Transparent Plastic
• Tweezers
• Sodium Hydrogen Carbonate (NaHcl)

Fair Test:

To obtain a fair test in the investigation I am going to have:

Same amount of time – The same amount of time so that the results are fair

Same water temperature – The temperature of the water stays the same or the molecules or enzymes do not de-nature. The temperature also affects the speed and movement of the enzymes and the number of bubbles will increase due to the increase in temperature.

Same Volume of water (400ml) and sodium hydrogen carbonate (100ml) – The amount of Sodium Hydrogen Carbonate affects the rate of photosynthesis so if there was a different amount of it the rate would be different as well.

Same light source – If a different light source was used each time the light source the light bulb might consume more watts because it is a different light bulb.  This will cause the rate of photosynthesis to change.

Same Venue – If I were in a different venue the light from the sun would be different, so this might affect the rate.

Same Pondweed – If the pondweed were larger there would be more surface area with chlorophyll to absorb more light therefore increasing the rate of photosynthesis.

Method:

1. Collect all the equipment needed
2. Fill beaker with490ml of water and 10 ml of sodium hydrogen carbonate (NaHcl)
3. Cut end of pond weed with cutter at a 45 degree angle
4. Set up equipment as shown in diagram on the next page
5. Move the lamp 15 cm from the beaker
6. Place transparent glass in front of the lamp
7. Wear safety goggles to protect from
8. Switch on lamp and start the stop watch
9. Start counting the bubbles for 2 minutes
10.  Record results in a appropriate table
11. Move lamp 5 cm more away from the beaker
12. Repeat steps 8 – 11 until lamp is 35 cm from the beaker
13. Repeat the experiment 3 times after finished the first one

Results:

18th February 2003

18th February 2003

20th February 2003

20th February 2003

Diagram above shows us that as the lamp is moved further away from the beaker the rate of which photosynthesis occurs slows down.

Conclusion:

In the results, it shows us that as the distance between the beaker and lamp was amplified the number of bubbles coming out every two minutes slowly declined.  This means as the lamp was moved further away the rate of which photosynthesis was occurring was decreasing.  This is because the light intensity was also being reduced as the lamp was moved further away, therefore there was less light for the pondweed to absorb.

In the 3rd and 4th test the results are lower than the 1st and 2nd ones because maybe when I was doing the experiment the time of the day was different and there was less light coming through the windows from the sun.  Or maybe I waited for a shorter time for the pondweed to heat up and there was less oxygen stored in the plant that hadn’t come out yet.

Evaluation:

I think the experiment was generally successful because the result that happened is what I predicted in my prediction.  

Few things affected my results though.  

Firstly the temperature was different, this may have happened because the room temperature was different because maybe the air-conditioner was on.  The temperature of the water collected could have been a different temperature.  It could have been both of these factors that affected the temperature of the water.  To improve my experiment I could have done the experiment in the same room with the same environment.

I didn’t measure the light intensity so it was not possible for me to know if the light intensity was different.  I should have u a light meter to measure the intensity of the light.

I cannot approximately tell if the rate of photosynthesis is actually changing because I only count the bubbles without noticing the sizes of them so if the rate of which the bubbles are increasing, it might not actually be increasing.  Just that they are smaller ones than before, therefore there are more.

There could have been human errors in counting the bubbles because I was counting large numbers of bubbles in a long period.