Primary Root Tissue, Root Hairs and the Plant Vascular Cylinder

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  • 0:05 Types of Roots
  • 1:03 Root Cap
  • 1:59 Epidermis and Root Hairs
  • 3:23 Primary Root Tissue
  • 4:41 Vascular Cylinder
  • 6:08 Lesson Summary
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Lesson Transcript
Instructor: Danielle Weber

Danielle teaches high school science and has an master's degree in science education.

Roots of plants can provide support, food and water. We will look at diagrams and photos to see the different parts of roots in order to explain these different functions.

Types of Roots

Roots serve many purposes for plants, including the storage of food and the intake of water. Before we look at the structure of roots, let's look at a few examples of roots.

While there are numerous classifications of roots, we will only look at a few. The first one is prop roots. These help brace plants against the elements, such as wind. Corn plants have prop roots as seen here.

Prop roots help brace plants.
Image of prop roots

Some plants, such as carrots, beets and turnips, have roots that are designed for food storage. These are generally the roots that you may eat.

You may eat roots designed for food storage.
Image of carrots, beets and turnips

The last type of root we will look at is designed for water storage. A classic example of this can be seen in pumpkins.

Pumpkins have roots for water storage.
Image of pumpkins

We know that different types of roots have different functions, but different parts of the root also have different functions. Let's now look at a few key components of most roots and relate the structure to the function. While doing this, we will look back at the diagram below of a root in order to better identify the layers. Let's start on the outside and work our way in.

Diagram of a root
image of root diagram

Root Cap

When at a construction site, people are required to wear hardhats in order to protect their heads. In roots, the root cap serves a similar purpose. This outer area of the bottom of the root protects other root tissues as the root continues to grow into the soil. The cells in the root cap are specialized for several different things. First, they can sense gravity, which is why roots grow down. Second, they secrete a slimy substance that helps roots move through the soil.

Directly behind the root cap is the root meristem, which is where cell division occurs. This means that when the root grows, the new cells come from the root meristem. We will look at this structure more another time.

Let's go back to our diagram and label the root cap. You can see that it is found at the bottom tip of the root and forms a protective barrier between the soil and the rest of the root. The small area in orange below is the root meristem where cell division for new growth occurs.

The root cap is at the very bottom of the root, and the area above that is the root meristem.
diagram of root cap and meristem

Epidermis and Root Hairs

We've talked about the epidermis when we looked at the structure of stems and leaves. Roots also have this protective outer layer known as the epidermis. Remember that 'dermis' means 'skin' and 'epi' means 'outer.' This means that the epidermis is literally the outer skin. While the root cap is found at the bottom of the root, the epidermis is found throughout the length of the root. At the bottom where the root cap protects the root, the epidermis is just inside that hard layer. A good way to relate the epidermis to something more familiar is to think of carrots and potatoes. When you peel carrots and potatoes, you are actually removing the epidermis.

The epidermis can produce root hairs, which are the main site of water and nutrient absorption. Root hairs allow for greater surface area so that plants can take in more vital substances. While root hairs are very important, they only live for a few days. This means that the epidermis must continually produce new root hairs. In some plants, there are even specific types of fungi and bacteria that help with absorption.

Let's go back to our diagram to label these parts. The epidermis is the outer protective layer throughout the length of the root. At the bottom, where we already have the root cap, the epidermis is just inside. Sticking out from the epidermis are a few root hairs. We don't need to label all of them, but do note that there are many root hairs.

Root hairs stick out from the epidermis.
Label of epidermis and root hairs

Primary Root Tissue

As previously mentioned, there are several functions of roots. These include anchoring and supporting the plant, absorbing and moving water and minerals and storing the products of photosynthesis. The primary root tissue is responsible for storing food, which is one of the products of photosynthesis. This layer is sometimes called the cortex. This layer is found after the epidermis and often makes up the bulk of the root. This is especially the case in some plants, such as carrots or radishes. After you peel a carrot, there is a great crunchy snack. The majority of what you are eating when snacking on carrots is the cortex.

The end of the cortex in a root is distinguished by the endodermis. We already know that 'dermis' means skin, so let's consider the prefix 'endo.' 'Endo' means 'inner,' so the endodermis is the inner skin. In roots, this structure contains fatty substances that block water. This means that water will not pass from the inner layers to the cortex and that water in the cortex will not move into the inner layers.

Let's go back and label these structures on our diagram. We can see that directly behind the epidermis is the cortex. This large food storage part of the root is surrounded on the inner side by the endodermis here.

The cortex is behind the epidermis.
Image of cortex and endodermis

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