Plants respond to gravity and the presence of water, light and chemicals - and even to touch. But how do they do this with no brain or nervous system?
Botanists are not sure. Their best explanation is that they contain many of the same substances that in animal cells, such as nerves, signal changes in physical states, prompting a response.
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Scientists believe the secret to plant movement probably lies in their cell membranes. These contain pores that let charged particles - ions - in and out and are sensitive to mechanical force: pushing, pulling and stretching cause them to open or close. The flow of ions is connected to the flow of water in and out of cells (osmosis), leading cells to become more or less turgid, creating movement.
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In animals, which have an obvious body and silhouette, the senses tend to be integrated by a nervous system, often connected to a brain. Humans are particularly brainy, so we assume that plants thus must be insensate. But they simply nave a different kind of body form: sprawling, changeable ind capable of incredible growth and regeneration.
Their intelligence is more localised and widely distributed Even more remarkably, plants can learn, too. The touch-ne-not plant Mimosa pudica folds its leaves if something such as an insect) brushes against it, remembers when it as last touched and tailors its response accordingly.
And that's not all. Experiments have shown that plants ot only retain memories of stimuli such as environmental resses, they can pass the responses to their offspring. The 54 million question is: how do they do that without brains?