Investigation on how light intensity affects the rate of Photosynthesis.

Essay by hashthedealerJunior High, 9th gradeA+, November 2003

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Introduction: Photosynthesis is the process by which green plants use the light energy to convert carbon dioxide and water into simple sugar called glucose, which provides a basic energy source for the plant. Photosynthesis occurs in leaves that contain specialized cell structures called chloroplasts. Chloroplasts contain molecules of a green pigment called chlorophyll, consisting largely of carbon and hydrogen. It gives green color and absorbs the necessary light for photosynthesis. Chloroplasts are found in palisade cells, they have a large surface area, which means there is more change of light hitting a chloroplast. Light is a very important factor when it comes to the process of photosynthesis, without light the reaction cannot be carried out and no glucose can be made. Light intensity is one of the factors that affect the rate of photosynthesis and that is what our experiment is based on:

Aim: In this experiment we shall investigate how the rate of photosynthesis (measured by the increased volume of oxygen) is affected by changes of light intensity in water plants.

Hypothesis: I predict that as the intensity of light increases, so will the rate of photosynthesis. Furthermore, I hypothesise that if the light intensity increases, the rate of photosynthesis will increase at a proportional rate.


Constant VariedMeasured

ShootLight intensityRate of photosynthesis

Number of lightsDistance between light and pondweedNumber of Bubbles

Water ------

Time between each result recording ------


- Beaker almost full of water

- Pondweed

- 60 watt Lamp

- Ruler

- Stopwatch

- Short-stemmed Funnel

- Test Tube

-paper clip

-pure CO2


1. First clip that end of the pondweed that was not cut.

2. Then place a short-stemmed funnel over some pondweed in a beaker of water. Add pure CO2 to the beaker of water.

3. Fill a test tube with water...