Do all plants have phototropism?

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Most plants are phototropic, which means that they respond to a light stimulus and grow toward the light. The reason for this is that plants contain a hormone called auxin which reacts to light. If a plant, for example, has one side exposed to light while the other side is in the shade, the auxins will expand in the shade and cause the plant to grow toward the light. There is thus more growth in the shade.

There are two reasons why the side of plants that is in the shade grows faster than the side that is in the sun. In grass and smaller plants, the growth hormone becomes more concentrated on the shady side and this causes this side of the plant to grow more quickly. However, in other plants, such as sunflowers and radishes, there is a natural chemical that slows down the growth of the plant’s sunny side. In both cases, the plant turns towards the light and the part of the plant that is in the shade grows faster.

Phototropism is a very strong force; most plants need light in order to be able to grow through the process of photosynthesis. Plants will do everything they can to obtain that light, even if it means they have to grow almost parallel to the ground in order to take advantage of the light. Phototropism is known to take place throughout the life of a plant. But it is most pronounced and can be manipulated more efficiently when the plant is still young.

There are two kinds of phototropism- positive and negative. Positive phototropism is the way a plant grows towards the light. It enables the plant to position its leaves so that it will be able to receive the energy it needs to grow and reproduce. On the other hand, negative phototropism takes place when the plant’s roots grow away from the light. This is also an important process, because it allows the plant to find the nutrients, soil and water it needs and to anchor itself in the ground.

Phototropism was first discovered in 1809. The Swiss botanist, Augustin de Candolle, verified that it was light that caused plants to grow, rather than air, as was previously believed. 70 years later, Charles Darwin and his son, Francis, also studied plants and plant growth. The Darwins found that a stimulus and a response can occur in different parts of the plant. This led to the subsequent discovery of plant hormones called auxins. Auxins cause the cells of plants to elongate during the process of phototropism and the plants to bend towards the light. A Dutch botanist named Frits Went made this discovery and named the growth hormone auxin, from the Greek word which means “to increase”. It was only in the 1940s that the chemical properties of the auxin hormone were identified as indole-3-acetic acid.

Resource by A.Moore

I just moved to Michigan from South Carolina. This is my first winter here and so far it's freezing. I enjoy traveling, drawing, camping, writing, and doing community service in my spare time. I work for a education company and help them with their outreach to teachers and students. Hope everyone enjoys my articles.

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