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How do plants sense a change in the environment?
Question Date: 2005-10-25
Answer 1:

Plants, unlike animals, do not have ears, eyes, or tongues to help them feel and acquire information from their environment. But they do sense their environment in other ways and respond accordingly.

Scientists have shown that plants can detect various wavelengths and use colors to tell them what the environment is like. When a plant grows in the shadow of another, it will send a shoot straight up towards the light source. It has also been shown that plants know when it is day and when it is night. Leaf pores on plants open up to allow photosynthesis during the daytime and close at night to reduce water loss.

Plants also respond to ultraviolet light by producing a substance that is essentially a sunscreen so that they do not get sunburned. Plants can sense weather changes and temperatures as well.

Plants have specific regulators, plant hormones, minerals and ions that are involved in cell signaling and are important in environmental sensing. In fact, without these, the plants will not grow properly.

Here are some examples of plant signaling:
1. Plant shoots grow up and roots grow down because they are responding opposite to the force of gravity. Shoots grow in the opposite direction of gravity (up) while roots grow towards gravity (down). The root cap senses force of gravity, transforms that information into a signal regulated by hormones and ions that the growing region of the root can understand (scientists still don't know exactly what the signal is). This signaling results in one side of the root growing faster than the other, so the root curves downward.
2. Plants also respond to wind or touch. If plants are in a windy spot they build thicker and tougher wind resistant stems. They can also sense when insects are on them. This can cause them to produce a chemical defense system.

There is an easy experiment you can do at home to check out plant response to the environment:
Plant two sets of seeds in soil, water them and then allow them to grow for about a week. Keep one of the sets of seeds in the dark, and expose the other to light. Compare the effects of light and dark on the plant growth. You will see that the seeds that grew in the dark produced seedlings that were tall and yellow with weak stems. But the plants that had exposure to light grew green short and sturdy stems seed leaves that had expanded. So the light had caused the seedlings to undergo some very dramatic changes.

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