23 2 Roots Slide 2 of 36

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2 Types of Roots Types of Roots What are the two main types of roots? 3 of 36

3 Types of Roots The two main types of roots are: taproots, which are found mainly in dicots, and fibrous roots, which are found mainly in monocots. 4 of 36

4 Types of Roots In some plants, the primary root grows long and thick. This primary root is called a taproot. A carrot is an example of a taproot. Taproot Fibrous Roots 5 of 36

5 Types of Roots Fibrous roots branch to such an extent that no single root grows larger than the rest. Fibrous roots are found in grasses. Fibrous Roots 6 of 36

6 Root Structure and Growth Root Structure and Growth Roots contain cells from dermal, vascular, and ground tissue. 7 of 36

7 Root Structure and Growth What are the main tissues in a mature root? 8 of 36

8 Root Structure and Growth A mature root has an outside layer, the epidermis, and a central cylinder of vascular tissue. Between these two tissues lies a large area of ground tissue. The root system plays a key role in water and mineral transport. 9 of 36

9 Root Structure and Growth The root s surface is covered with cellular projections called root hairs. Root hairs provide a large surface area through which water can enter the plant. Root hairs 10 of 36

10 Root Structure and Growth The epidermis protects the root and absorbs water. Epidermis 11 of 36

11 Root Structure and Growth Inside the epidermis is a layer of ground tissue called the cortex. Ground tissue (cortex) 12 of 36

12 Root Structure and Growth The cortex extends to another layer of cells, the endodermis. Endodermis The endodermis completely encloses the vascular cylinder. 13 of 36

13 Root Structure and Growth The vascular cylinder is the central region of a root that includes the xylem and phloem. Vascular cylinder Phloem Xylem 14 of 36

14 Root Structure and Growth Roots grow in length as their apical meristem produces new cells near the root tip. Apical meristem 15 of 36

15 Root Structure and Growth These new cells are covered by the root cap that protects the root as it forces its way through the soil. Apical meristem Root cap 16 of 36

16 What are the different functions of roots? 17 of 36

17 Roots anchor a plant in the ground and absorb water and dissolved nutrients from the soil. 18 of 36

18 Uptake of Plant Nutrients To grow, flower, and produce seeds, plants need a variety of inorganic nutrients in addition to carbon dioxide and water. 19 of 36

19 The most important nutrients plants need include: nitrogen phosphorus potassium magnesium calcium 20 of 36

20 Active Transport of Minerals The cell membranes of root hairs and other cells in the root epidermis contain active transport proteins. 21 of 36

21 Transport proteins use ATP to pump mineral ions from the soil into the plant. Root hairs 22 of 36

22 The high concentration of mineral ions in the plant cells causes water molecules to move into the plant by osmosis. 23 of 36

23 Movement Into the Vascular Cylinder Osmosis and active transport move water and minerals from the root epidermis into the cortex. The water and dissolved minerals pass the inner boundary of the cortex and enter the endodermis. 24 of 36

24 The endodermis is composed of many individual cells. Endodermis 25 of 36

25 Each cell is surrounded on four sides by a waterproof strip called a Casparian strip. Casparian strip Casparian strip 26 of 36

26 The Casparian strip prevents the backflow of water out of the vascular cylinder into the root cortex. 27 of 36

27 Water moves into the vascular cylinder by osmosis. Because water and minerals cannot pass through the Casparian strip, once they pass through the endodermis, they are trapped in the vascular cylinder. As a result, there is a one-way passage of materials into the vascular cylinder in plant roots. 28 of 36

28 Root Pressure As minerals are pumped into the vascular cylinder, more and more water follows by osmosis, producing a strong pressure. This root pressure forces water through the vascular cylinder and into the xylem. 29 of 36

29 As more water moves from the cortex into the vascular cylinder, more water in the xylem is forced upward through the root into the stem. Root pressure is the starting point for movement of water through the vascular system of the entire plant. 30 of 36