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Unit B: Plant Anatomy Lesson 1: Understanding Root Anatomy 1 Vocabulary Apical meristem Epidermis Fibrous root system Primary root Root cap Root hairs Secondary roots Taproot system 2 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 A pot bound plant in need of transplanting Courtesy of Delmar Publishing This is why plants become pot-bound: the roots start growing out of the pot because it is too small 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 4 Courtesy of Wm. C. Brown Publishers 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 Cotyledon Radicle = Primary root; notice all the root hairs Courtesy of McGraw Hill B. Other roots branch out from the primary root; called secondary roots 5 C. The apical meristem, found at the root tip, is where new cells develop Vascular cylinder (xylem & phloem) Cortex (food storage) Epidermis It is covered by the root cap – protects it from damage as it passes through coarse soil particles Apical meristem Root Cap Courtesy of Dorling Kindersley, Inc. 6 Epidermis 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 Courtesy of Delmar Publishing 7 Regions of Cell Development Region of Maturation Region of Elongation Root Cap Region of Cell Division Apical meristem Notice that cell division occurs at the tip of the root Older cells are found farther away from the root tip 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 9 Examples of Taproots Carrot Beet Sweet potato 10 Courtesy of Wm. C. Brown Publishers 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 Fibrous root system of grass Courtesy of McGraw Hill Publishing These roots form a large network underground 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 14 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 17 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 18 Several legumes that have nitrogenfixing 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. 19 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? 20 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? 21