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Grade 7 Intermediate About 10 min Version 1 Awaiting review Premium

Stomata: the tiny pores in a leaf

The surface of a leaf is covered by a thin layer of epidermal cells, which fit together like a jigsaw. Scattered among them, especially on the underside, are tiny pores called stomata (one is a stoma). Each stoma lies between two bean-shaped guard cells. Unlike the other epidermal cells, guard cells contain chloroplasts. When the guard cells swell with water they curve apart and open the stoma; when they lose water they straighten and close it. Through open stomata, carbon dioxide enters for photosynthesis and oxygen and water vapour leave.

What you will learn

  • Identify stomata and guard cells under the microscope.
  • Explain how guard cells open and close a stoma.
  • Describe what passes through stomata.

Before you start

  • Know that leaves make food by photosynthesis.

Materials

  • Leaves with an easily peeled underside (such as Tradescantia, spinach or a fleshy leaf)

Equipment

  • Microscope, slide, cover slip, forceps, dropper

Procedure

  1. Peel a thin layer from the underside of a leaf and look at it under the microscope.
  2. Choose a part name card, find out what it does, and place it on the matching letter.