Fourth Grade Biology
Historical experiments and studies on living things have shown scientists that amidst adversity or less than desirable situations, life finds a way of living or surviving. Whether it be developing a way in which they can reproduce within themselves, or for one gender to turn into another gender in order to aid reproduction, or simply adapting to the circumstances that they find themselves in, plants and animals have consistently shown that life finds ways to get the things needed for the survival and propagation of the species. Plants and animals that are able to adapt to whatever comes their way or to their local environment, even if it isn't their natural habitat have better chances of living longer and populating the earth.
Charles Darwin's Phototropism
In 1809 a Swiss botanist named Augustin Pyrame de Candolle noticed unequal growth among his plants. The plant seemed to be directing itself towards the light and caused one side to grow a bit better than the other. He did not know at the time that what was happening is a plant characteristic we now call phototropism, or the bending or orientation of a plant's growth towards a light source. (*Note: If you did the third grade science projects on plants in which you partially cover a box and keep a plant in the shade of the covering, you will be familiar with this principle.)
Decades after de Candolle, Charles Darwin noticed the same phenomenon happening to his canary grass. He experimented with the grass, seeing how it would react to two situations. When he completely covered the grass from light the tips of the grass did not move in any particular direction. However, if only the stems or blades were covered and the tips exposed to the sun, then the tips of the grass would still move towards the sun. To Darwin, this was an example of how plants find ways to survive.
In more modern times, scientists have discovered that plants exhibit this characteristic because of a growth hormone called auxin, the name of which was given by botanist Frits Went. Given a situation wherein there is equal distribution of light, the hormone is distributed to all parts of the plant allowing the plant to grow normally. However, in situations where there is unequal light, auxin is distributed unequally along the plant, specifically towards the darker side, making it grow faster and forcing the plant to bend towards the light.
There are two types of phototropism and they usually occur among plants and fungi. There is positive phototropism, which is when a plant bends towards the light source, and there is negative phototropism, which is when a plant bends away from the light source. Apart from phototropism, plants have other reactions or responses when it comes to light exposure. One reaction, etiolation, happens when the plant grows completely in the dark.
Take note that tropism is a characteristic not restricted to plants. There are several types of tropism or directional growth which occur in other living organisms.
Next Article: Fourth Grade Chemistry
