How do plants, without musculature, move in such short periods of time to face the sunlight?

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How do plants, without musculature, move in such short periods of time to face the sunlight?

In: Biology

Generally “rapid” plant motion involves a shift in [turgor pressure](http://en.wikipedia.org/wiki/Turgor_pressure) – the solute concentrations in the plant’s vascular system change, causing individual cells to absorb more water and expand or release more water and shrink. Together, they can change the shape of the plant. This principle can be exploited further by a structure called a [pulvinus](http://en.wikipedia.org/wiki/Pulvinus) which acts a bit like a skeletal joint. Some animals similarly use liquid pressure to move, most famously spiders and other arthropods.

It’s called “tropic” movement. There’s a hormone in plants called “auxin” that causes their cells to expand when exposed to sunlight. The direction the light comes from determines how the expansion is expressed in the plant to achieve the best exposure to light.