1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Plant Structure and Function Chapter 25 Table of Contents Section 1 The Vascular Plant Body Section 2 Transport in Plants

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 The Vascular Plant Body Objectives Identify the three kinds of tissues in a vascular plant’s body, and state the function of each. Compare the structures of different types of roots, stems, and leaves. Relate the structures of roots, stems, and leaves to their functions. Chapter 25

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Tissues In vascular plants, there are three types of tissues— dermal tissue, ground tissue, and vascular tissue. Vascular tissue forms strands that conduct water and nutrients throughout a vascular plant. Dermal tissue forms the protective outer layer of a plant. Ground tissue makes up much of the inside of the nonwoody parts of a plant, including roots, stems, and leaves. Section 1 The Vascular Plant Body Chapter 25

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Tissues, continued The leaves, stems, and roots of a vascular plant contain all three kinds of plant tissues. Section 1 The Vascular Plant Body Chapter 25

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Tissues, continued Dermal Tissue System In the nonwoody parts of a plant, dermal tissue forms a “skin” called the epidermis. The epidermis of most plants is made up of a single layer of flat cells. The dermal tissue on woody stems and roots consists of several layers of dead cells that are referred to as cork. Section 1 The Vascular Plant Body Chapter 25

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Dermal Tissue Systems in Plants Section 1 The Vascular Plant Body Chapter 25

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Tissues, continued Ground Tissue System Most ground tissue consists of thin-walled cells that remain alive and keep their nucleus after they mature. The ground tissue in leaves, which is packed with chloroplasts, is specialized for photosynthesis. The ground tissue in stems and roots functions mainly in the storage of water, sugar, and starch. Section 1 The Vascular Plant Body Chapter 25

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Ground Tissue Systems in Plants Section 1 The Vascular Plant Body Chapter 25

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Vascular Tissue Systems Xylem Xylem has thick-walled cells that conduct water and mineral nutrients from a plant’s roots through its stems to its leaves. The conducting cells in xylem must lose their cell membrane, nucleus, and cytoplasm before they can conduct water. Gnetophytes and flowering plants also have a second type of xylem cell, which makes up conducting strands called vessels. Section 1 The Vascular Plant Body Chapter 25

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure of Xylem Section 1 The Vascular Plant Body Chapter 25

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Vascular Tissue Systems, continued Phloem Phloem contains cells that conduct sugars and other nutrients throughout a plant’s body. The conducting cells of phloem have a cell wall, a cell membrane, and cytoplasm. The conducting strands in phloem are called sieve tubes. Pores in the walls between neighboring sieve- tube cells connect the cytoplasms and allow substances to pass freely from cell to cell. Section 1 The Vascular Plant Body Chapter 25

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure of Phloem Section 1 The Vascular Plant Body Chapter 25

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Roots Most plants are anchored to the spot where they grow by roots, which also absorb water and mineral nutrients. Many dicots, such as carrots and radishes, have a large central root from which much smaller roots branch. This type of root system is called a taproot system. In contrast, most monocots, such as grasses, have a highly branched, fibrous root system. Section 1 The Vascular Plant Body Chapter 25

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Types of Roots Section 1 The Vascular Plant Body Chapter 25

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Roots, continued The ground tissue surrounding the vascular tissue is called the cortex. An epidermis covers the end of a root, or root tip. The epidermal cells just behind a root tip often produce root hairs, which are slender projections of the cell membrane. A mass of cells called the root cap covers and protects the actively growing root tip. Section 1 The Vascular Plant Body Chapter 25

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Radish Root Structure Section 1 The Vascular Plant Body Chapter 25

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Dicot and Monocot Root Structures Section 1 The Vascular Plant Body Chapter 25

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Stems Nonwoody Stems A plant with stems that are flexible and usually green is called a herbaceous plant. The stems of herbaceous plants contain bundles of xylem and phloem called vascular bundles. The ground tissue outside the ring of vascular bundles is called the cortex. The ground tissue inside the ring is called the pith. Section 1 The Vascular Plant Body Chapter 25

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Stem Section 1 The Vascular Plant Body Chapter 25

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Dicot and Monocot Stem Structure Section 1 The Vascular Plant Body Chapter 25

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Stems, continued Woody Stems Trees and shrubs, such as pines, oaks, roses, and hollies, have woody stems. Woody stems are stiff and nongreen. The wood in the center of a mature stem or tree trunk is called heartwood. The xylem in heartwood, which can no longer conduct water, provides support. Sapwood, which lies outside the heartwood, contains vessel cells that can conduct water. Section 1 The Vascular Plant Body Chapter 25

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure of Stems Section 1 The Vascular Plant Body Chapter 25

23. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Leaves Most leaves have a flattened portion, called the blade, that is often attached to a stem by a stalk called the petiole. A leaf blade may be divided into two or more sections called leaflets. Leaves with an undivided blade are called simple leaves. Leaves with two or more leaflets are called compound leaves. Section 1 The Vascular Plant Body Chapter 25

24. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Leaf Section 1 The Vascular Plant Body Chapter 25

25. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Simple and Compound Leaves Section 1 The Vascular Plant Body Chapter 25

26. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Leaves, continued Both xylem and phloem are found in the veins of a leaf. Veins are extensions of vascular bundles that run from the tips of roots to the edges of leaves. In leaves, the ground tissue is called mesophyll. Mesophyll cells are packed with chloroplasts, where photosynthesis occurs. Most plants have leaves with two layers of mesophyll. Section 1 The Vascular Plant Body Chapter 25

27. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Structure of a Leaf Section 1 The Vascular Plant Body Chapter 25

28. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Transport in Plants Objectives Relate transpiration to the movement of water up a plant. Describe how guard cells regulate the rate of transpiration. Recognize several distinguishing features of sugar maple trees. Describe the process of translocation in a plant. Chapter 25

29. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Movement of Water Transpiration drives the movement of water through a plant: Step 1 When the stomata are open, water vapor diffuses out of a leaf. This loss of water vapor from a plant is called transpiration. Step 2 The loss of water creates a pull that draws water up through the xylem. Step 3 Water drawn into the roots from the soil by osmosis moves up the stem. Section 2 Transport in Plants Chapter 25

30. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Water Movement in Plants Section 2 Transport in Plants Chapter 25

31. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Movement of Water, continued Guard Cells and Transpiration A stoma is surrounded by a pair of guard cells that are shaped like two cupped hands. Guard cells that take in water bend away from each other, opening the stoma and allowing transpiration to proceed. When water leaves the guard cells, they shorten and move closer to each other, closing the stoma and stopping transpiration. Section 2 Transport in Plants Chapter 25

32. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Control of Stomatal Opening Section 2 Transport in Plants Chapter 25

33. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Movement of Organic Compounds Botanists use the term source to refer to a part of a plant that provides organic compounds for other parts of the plant. Botanists use the term sink to refer to a part of a plant that organic compounds are delivered to. The movement of organic compounds within a plant from a source to a sink is called translocation. Section 2 Transport in Plants Chapter 25

34. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Translocation Section 2 Transport in Plants Chapter 25

35. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Movement of Organic Compounds, continued The German botanist Ernst Münch proposed a model of translocation called the pressure-flow model: Step 1 Sugar from a source enters phloem cells by active transport. Step 2 When the sugar concentration in the phloem increases, water enters the sieve tubes in phloem from xylem by osmosis. Step 3 Pressure builds up inside the sieve-tube cells and pushes sugar through the sieve tubes. Step 4 Sugar moves from phloem cells into a sink by active transport. Section 2 Transport in Plants Chapter 25

36. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Pressure- Flow Model Section 2 Transport in Plants Chapter 25