Plants lack a central nervous system. How do they know to drop leaves in full shade and to curve stems towards the current light source?

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    $\begingroup$ Welcome to the site. Please visit the help centerand take a tour. In particular pay attention to the homework page. You might want to investigate phototropism. $\endgroup$
    – bob1
    Oct 5, 2021 at 8:07
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    $\begingroup$ Plants are not sentient beings, and do not “know” anything. If you chose to post here please use scientific language. $\endgroup$
    – David
    Oct 6, 2021 at 19:24

1 Answer 1


The curving of stems towards light sources is called phototropism. It is a hormonal phenomena that responds to light. Just like human beings, plants have hormones in them.

The hormone that makes plant respond to light is auxin. It is a type of growth hormone, causing growth in the parts where it accumulates, and it does so in regions away from light. So, when a plant faces the light, auxin accumulates and causes growth of the side which is not facing the light. Thus, excessive and uneven growth leads to the plant to bend towards the the light.


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