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Upper Epidermis of a Leaf: Function & Definition

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  • 0:00 What Is an Epidermis?
  • 1:05 Special Features of…
  • 3:12 Lesson Summary
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Instructor: Terry Dunn

Terry has a master's degree in environmental communications and has taught in a variety of settings.

The epidermis of a plant is often overlooked, but it's an important barrier between the elements and the other tissues. Here you'll learn about the structure and functions of the upper epidermis of a leaf.

What Is an Epidermis?

Think for a moment about what leaves put up with. They're exposed to sun, rain, snow, cold temperatures, dry air, warm temperatures, and disease. They have to cope without being able to take shelter or run away. They're basically sitting ducks, and they need protection! Luckily, they have it.

Most plants are covered by a tightly packed, single layer of see-through cells, called the epidermis. The epidermis covers the outer surfaces of the leaves, stems, flowers, fruits, and roots of the plant, but it is chemically connected to cell layers below. Unlike some plant parts, there are no chloroplasts in most of the epidermis. Chloroplasts are the tiny parts within plant cells that help a plant photosynthesize. Instead, the epidermis is like a clear spray coating whose sole purpose is to protect the plant from the elements, while still letting the sun shine in. That's particularly important for a leaf because their main job is to photosynthesize.

This is what the upper epidermis of a leaf looks like through a microscope.

Special Features of the Epidermis

Despite being a one-layered sheet of cells, there's a surprising amount of variety within the epidermis of a leaf. There are even differences in the epidermis on the underside and upper side of a leaf. Usually, the outer walls of the epidermal cells are thickened for protection, and they may be covered with a waxy, waterproof coating called a cuticle. The cuticle prevents the plant from losing too much moisture, which is why you tend to see waxy plants in desert environments. The leaves of the desert creosote bush are covered with a waxy cuticle.

In reality, The epidermal layer of a leaf does not completely seal the surface. On the upper side, where the leaf is exposed to more sun and moisture loss, the seal is mostly continuous, but the underside is more like a punctured layer of protection. In the lower epidermis, there is a higher concentration of specialized features called stomata. They are essentially holes or stoma with two guard cells surrounding the holes. The guard cells are special epidermal cells that regulate the exchange of gases through the stoma. Interestingly, the guard cells do have chloroplasts so they help with photosynthesis as well.

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