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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Lesson Transcript
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.

Expert Contributor
Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

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


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.

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Additional Activities

Stomata of Plants: Word Scramble Activity

In this activity, you will check your knowledge regarding the function and structure of the stomata.


For this activity, study the scrambled letters and try to unscramble or rearrange the letters to form a word or phrase that fits the given clues. To do this, you must right-click and print this page. With a pencil and an eraser, neatly write your answers in the appropriate blank spaces.

Scrambled Words

  2. AOTSM
  3. ARBNCO ODIXEID (two words)
  7. AWMR MSAETTRPEUER (two words)
  10. XEYONG


  1. _____ is the process by which plants convert energy from light into chemical energy.
  2. A _____ is one of the tiny pores in the leaves through which gases and water vapor pass.
  3. A plant cannot photosynthesize if there is an insufficient amount of _____ in the air.
  4. The specialized cells that _____ the stomata are used to control gas exchange.
  5. The shape of guard cells is dictated by the amount of water and _____ present within.
  6. Photosynthesis only occurs during the day when there is an abundance of _____.
  7. Opening of stomata at _____ indicates more evaporation will take place.
  8. A _____ plant will close its stomata to avoid water loss.
  9. Sunlight and _____ are a few of the factors that affect these guard cells.
  10. _____ is always a by-product of any photosynthetic process.

Answer Key

  2. STOMA
  10. OXYGEN

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