The cells, there’s a surprising amount of

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.

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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.But, things sometimes get fuzzy where there is an epidermis. In many plants, the epidermal cells on stems and leaves produce a hair-like fuzz called trichomes, which may protect the plant from cold, wind, sun, or moisture loss. Some plants go a step further with their trichomes. Plants like stinging nettles, thistles, and some sticky plants secrete substances from their trichomes to protect themselves.

You may not have wanted to eat a nettle or thistle leaf to begin with, but you will certainly steer clear after you’ve brushed by and felt their stinging chemicals. And in a real deviation from the average leaf, insectivorous plants, like Venus fly traps, secrete a substance from their upper epidermis that can digest insects. For organisms that can’t take shelter or run away, it turns out plants do pretty well for themselves.

Lesson Summary

The epidermis of a plant is the single, clear layer of cells that cover the roots, stems, flowers, fruits, and leaves. It acts like a protective covering from the sun, temperature changes, and moisture changes in the environment.

Often a waxy coating, called a cuticle, adds an extra layer of protection.The upper and lower sides of a leaf are different. The epidermis and cuticle on the upper surface is more continuous, while the underside has more stomata, allowing gases to be exchanged between the plant and the air on the side that is less exposed. The hole in the stomata is the stoma, and it’s surrounded by two guard cells.

The guard cells contain chloroplasts, but other epidermal cells usually don’t.Some epidermal cells are specialized and grow hair-like structures, called trichomes, on the plant stems and leaves. Some plants secrete sticky, stinging and, in rare case, digestive substances from the trichomes of the upper epidermal cells.

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