Essay by poo101High School, 10th grade November 2006

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Aim: To find the effect of light intensity on the rate of photosynthesis by using water weed

Equipment List:

* UV Lamp- Plants use UV light rays to photosynthesis so this type of lamp is needed.

* Stop Watch- A simple stop, start and reset stop watch is needed to time the experiment up to a minute.

* Water Weed (Plant) - I have chosen this aquatic plant because of it quality of showing bubbles when photosynthesising, thus letting us measure the rate when underwater.

* Metre Ruler- To simply measure distance between 0-100cm.

* Cold Water

* Test Tube

* Clamp

* Beaker


1. Setup the water weed in the first tube facing the lamp's direction.

2. Setup the lamp at the first designated distance away from the tube, setting the light intensity.

3. Try and close all curtains and put it in dull place avoiding light from elsewhere.

4. Make a table, with "number of bubbles per minute", against distance away from test tube (cm).

5. Pour in the water from the beaker to the beak of the test tube.

6. Turn on the lamp, and record the number of bubbles released by the plant for 1 minute in the table drawn

7. Change the light intensity, by changing the distance away from the water weed to the next designated distance away from water weed.

8. Repeat above steps, repeating each distance 3 times.

9. Calculate average of the recorded results after finishing experiment

Fair Testing and Variables:

Key Variable:

Light Intensity (shifting the distance away from the light source to the water weed)

Output variables - volume of oxygen produced (rate of photosynthesis) is to be measured by finding the volume of oxygen produced in a minute.

Controlled Variables:

Same Lamp

Amount Of water...