Essay by maxipaddleHigh School, 12th gradeA+, January 2004

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For my science experiment I will be testing if phototropism affects pea plants. The purpose of this is to see how much the growth of the plant is affected by sunlight. Many years ago the scientist Charles Darwin discovered what today we called phototropism. I intend to create my own small experiment except this time I will be using artificial light instead of natural light (the sun).

The definition of tropism is "a growth movement whose direction is determined by the direction from which the stimulus strikes the plant" and "photo" means relating to light. There for, Phototropism is when a plant grows towards a light source. This is caused by a hormone. A hormone is any of various similar substances found in plants and insects that regulate development. The hormone that causes the plant to grow towards the light is called auxin. Auxin makes the cells divide and the plant to grow.

The plant pumps more auxin to the side with the most shade causing the plant to be larger on one side, making the plant bend in the other direction.

The first scientist to ever experiment with phototropism was Charles Darwin. He was born in 1809 and died 1882. In his lifetime he wrote the famous book. On the Origin of Species. In 1880 Charles Darwin and his son Francis Darwin discovered that phototropism would not occur unless most of the plant was shaded. When they shaded the top of the plant phototropism did not occur so the plant stood up straight. However, when they put black sand up to the plants tip the plant would grow towards the light. The Darwins concluded that somehow the tip was causing more growth for the shaded area than the area with light.

Another scientist by the name Boysen Jensen held...