Unit B: Plant Anatomy

Lesson 1: Understanding Root Anatomy

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Vocabulary Apical meristem Epidermis Fibrous root system Primary root Root cap Root hairs Secondary roots Taproot system

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What Are the Functions of a Plant’s Roots?

A plant’s health is directly related to its roots Weak and diseased roots

decrease a plant’s health Roots need to continuously

grow in order to stay healthy This is why plants become

pot-bound: the roots start growing out of the pot because it is too small

A pot bound plant in need of transplanting

Courtesy of Delmar Publishing 3

Functions of a Root System 1. Absorb water and

minerals from the environment

2. Anchor the plant in the ground

3. Store food that has been made in the leaves by photosynthesis Can be used later by the

plant to grow and survive Taraxacum officinale – the common dandelion

Courtesy of Wm. C. Brown Publishers 4

What Are the Parts of a Root?

When a seed germinates, the first structure to appear is the root, or radicle A. It becomes the

primary root Usually the most

important root in some plants

B. Other roots branch out from the primary root; called secondary roots

Cotyledon Radicle = Primary root; notice all the root hairs

Courtesy of McGraw Hill 5

C. The apical meristem, found at the root tip, is where new cells develop It is covered by the root

cap – protects it from damage as it passes through coarse soil particles

Epidermis

Vascular cylinder (xylem & phloem)

Cortex (food storage)

Root Cap

Apical meristem

Courtesy of Dorling Kindersley, Inc. 6

D. The surface of the root is protected by skin cells called the epidermis

Where water and minerals enter the root by osmosis & diffusion

Can grow long, hair like projections called root hairs

They greatly increase the surface area of the root to allow more water intake

Epidermis

Courtesy of Delmar Publishing 7

Regions of Cell Development

Notice that cell division occurs at the tip of the root

Older cells are found farther away from the root tip

Root Cap

Region of Cell Division

Region of Elongation

Region of Maturation

Apical meristem Courtesy of McGraw

Hill Publishers 8

What Are the Two Types of Root Systems? Plant root systems are organized in two

basic ways; It has to do with primary and secondary roots A. A root system comprising one main

primary root and many secondary roots branching off the primary root is called a taproot system Their roots reach far into the ground; they

can be several feet long

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Examples of Taproots

Carrot Beet Sweet potato

Courtesy of Wm. C. Brown Publishers 10

Tap Root Systems Advantages Penetrate deeper into the soil

Obtain water from lower levels

Anchor the plant

Disadvantages Difficult to remove/harvest plants

Do not stabilize the soil well 11

B. A system which has no

dominant primary root but is made of many primary and secondary roots of similar size is called a fibrous root system Ex. Grasses, Magnolia,

Rhododendron, Euonymus

The roots are smaller, shorter and more compact; They usually never grow below the first 6-12 inches of soil

These roots form a large network underground

Fibrous root system of grass

Courtesy of McGraw Hill Publishing 12

Fibrous root system Advantages

Shallower, thus respond more quickly to fertilization/irrigation

Stabilize the soil better

Disadvantages

Less drought resistant

Tend to get exposed during cultivation 13

What Does a Healthy Root System Look Like? A healthy root system is white or nearly white

in color and smells fresh, or earthy

If roots are black, brown, or dark orange and smell rotten or sour, the root system is having some problems

Watering a plant properly is one of the most important ways to keep the root system healthy

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Healthy Roots Unhealthy Roots 15

If the plants are grown in pots, be sure that there are drainage holes in the bottom to allow excess water to drain Soak the pot until the growing medium is

saturated and water drips out of the drainage holes This encourages the roots to grow through

the entire pot Allow the pot to dry out slightly between

watering Watering too frequently is a common cause

of root death Medium that is kept wet has limited air

exchange; the root tissues die for lack of air 16

Recognize the economical importance of roots. Roots impact society in many different ways

The term root crops refers to any edible underground plant structure, but many root crops are actually stems, such as potato tubers

Edible roots include cassava, sweet potato, beet, carrot, rutabaga, turnip, parsnip, radish, yam and horseradish. Spices obtained from roots include and licorice. sassafras, angelica, sarsaparilla

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Sugar beet is an important source of sugar. The fish poison and insecticide rotenone is obtained from roots of Lonchocarpus spp.

Important medicines from roots are ginseng, aconite, ipecac, gentian and reserpine

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Several legumes that have nitrogen-fixing root nodules are used as green manure crops, which provide nitrogen fertilizer for other crops when plowed under.

Specialized bald cypress roots, termed knees, are sold as souvenirs, lamp bases and carved into folk art. Some people have used the flexible roots of white spruce for basketry.

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Summary What are the three functions of a root?

What is another name for a primary root?

In the tip of the root, what kinds of cells are the only ones that divide?

What is the epidermis and what is its function?

Where do root hairs grow from?

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Summary Why does a plant have to have numerous root

hairs instead of just two or three?

Pretend you are a water molecule and you need to get into the center of the root. What are all the layers you must go through before reaching the center?

Describe the functions of the xylem and phloem.

Where is food stored in the root?

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