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Stomata of Plants: Function, Definition & Structure

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  • 0:01 Stomata Definition
  • 0:41 Function
  • 1:54 Structure
  • 2:49 Lesson Summary
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Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Did you know that plants 'breathe' through their leaves? Tiny openings called stomata allow plants to exchange gases necessary for cellular processes, such as photosynthesis.

Stomata: Definition

Take a deep breath in and then let it out. Breathing to you is a very natural function that you usually do without even thinking about it. When you breathe, you are taking in oxygen and releasing carbon dioxide. Taking in oxygen is very important because it allows your cells to do things, like make energy from the food you eat.

Plants 'breathe' too, but they do it through tiny openings in leaves called stomata (singular: stoma). Stomata open and close to allow the intake of carbon dioxide and the release of oxygen. It's very important that they do this because this is the very oxygen that we ourselves need to breathe!

Stoma of a plant
plant stoma

Function

The gas exchange that occurs when stomata are open facilitates photosynthesis. Photosynthesis is the process by which plants convert sunlight into usable energy. During photosynthesis, carbon dioxide is taken in from the atmosphere through the stomata and oxygen is released as a waste product. Both photosynthesis and the gas exchange that powers it are essential to the plant's survival.

An unfortunate side effect of the stomata opening is that it allows for water loss. Unlike you and me, plants do not need to sweat to cool off and prefer to keep their water inside; however, because the gas exchange of photosynthesis is so vital, some water loss through stomata is necessary. This process of plant water loss is called transpiration.

Although transpiration cannot be avoided, plants can minimize their water loss by controlling how wide their stomata are open, as well as what time of day they are open. Opening stomata when the surrounding air is more humid means that less water will evaporate from the plant leaves, but opening them when temperatures are warmer means more evaporation will occur. Likewise, if a plant is already dehydrated, it may close its stomata to prevent further water loss.

Structure

A stoma is the opening on a plant leaf, but there are specialized cells surrounding each stoma that control how open or closed it is. These specialized cells are called guard cells, and they are triggered by a number of factors, such as sunlight, humidity, temperature, and internal plant chemistry.

The way that guard cells regulate stoma is by changing their shape. The guard cell shape depends on how much water and potassium are present in the cells. Like a set of inflatable doors, they can make the stomata open wider or close up.

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