Re: What is Phototropism?

Tropism refers to obtaining nutrition or food. The Prefix indicates what 
the nutrition is related to or caused by. Photo- refers to the fact that 
this nutrition is related to light. Phototropism is commonly seen in plants 
as the tend to grow toward the sunlight. The reason for this is through the 
hormone auxin which is stimulated by darkness and causes growth. That 
sounds like the opposite of the way it should be, but it is not. If growth 
is stimulated on the dark side of the plant and no growth occurs on the 
lighted side of the plant then the plant will bend toward the light. This 
response allows the plant to gather the maximum amount of sunlight in order 
produce food for survival.

Autotrophs are organisms that produce their own nutrition. Auto- meaning on 
its own. Plants, some bacteria, and some protists are also autotrophs.

Heterotrophs are organisms that get their nutrition from an outside source. 
Hetero- meaning different. The kingdoms Fungi and Animalia participate in 
this tropism exclusively. Eubacteria have some members that are 
heterotrophic as well as Fungi-like and Animal-like Protists.

There are many other types of tropisms and all are related to obtaining 
food in some form or another. The two above are general catagories with 
Phototropism being specific.

Hope this helped.

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Admin note:

David Hershey adds the following:

Tropism is very different from trophic. A tropism is a growth response to
an environmental stimulus in which the direction of the stimulus
determines the direction of growth. In phototropism the stimulus is light.
In gravitropism the stimulus is gravity. In thigmotropism the stimulus is
touch.

Reference

Salisbury, F.B. and Ross, C.W. 1985. Plant Physiology. Belmont, CA:
Wadsworth.