End Show Slide 1 of 36 Copyright Pearson Prentice Hall Biology

End Show Slide 2 of 36 Copyright Pearson Prentice Hall 23–3 Stems

End Show 23–3 Stems Slide 3 of 36 Copyright Pearson Prentice Hall Stem Structure and Function What are the three main functions of stems?

End Show 23–3 Stems Slide 4 of 36 Copyright Pearson Prentice Hall Stem Structure and Function Stems have three important functions: they produce leaves, branches and flowers they hold leaves up to the sunlight they transport substances between roots and leaves

End Show 23–3 Stems Slide 5 of 36 Copyright Pearson Prentice Hall Stem Structure and Function Stems make up an essential part of the water and mineral transport systems of the plant. Xylem and phloem form continuous tubes from the roots through the stems to the leaves. This allows water and nutrients to be carried throughout the plant.

End Show 23–3 Stems Slide 6 of 36 Copyright Pearson Prentice Hall Stem Structure and Function Stems are surrounded by a layer of epidermal cells that have thick cell walls and a waxy protective coating.

End Show 23–3 Stems Slide 7 of 36 Copyright Pearson Prentice Hall Stem Structure and Function Leaves attach to the stem at structures called nodes. The regions of stem between the nodes are internodes. Small buds are found where leaves attach to nodes. Node Internode Bud Node

End Show 23–3 Stems Slide 8 of 36 Copyright Pearson Prentice Hall Stem Structure and Function Buds contain undeveloped tissue that can produce new stems and leaves. In larger plants, stems develop woody tissue that helps support leaves and flowers. Bud

End Show 23–3 Stems Slide 9 of 36 Copyright Pearson Prentice Hall Monocot and Dicot Stems The arrangemnet of tissues in a stem differs among seed plants. How do monocot and dicot stems differ?

End Show 23–3 Stems Slide 10 of 36 Copyright Pearson Prentice Hall Monocot and Dicot Stems In monocots, vascular bundles are scattered throughout the stem. In dicots and most gymnosperms, vascular bundles are arranged in a ringlike pattern.

End Show 23–3 Stems Slide 11 of 36 Copyright Pearson Prentice Hall Monocot and Dicot Stems Monocot Stems Monocot stems have a distinct epidermis, which encloses vascular bundles. Each vascular bundle contains xylem and phloem tissue.

End Show 23–3 Stems Slide 12 of 36 Copyright Pearson Prentice Hall Monocot and Dicot Stems Vascular bundles are scattered throughout the ground tissue. Ground tissue consists mainly of parenchyma cells. Monocot Vascular bundles Epidermis Ground tissue

End Show 23–3 Stems Slide 13 of 36 Copyright Pearson Prentice Hall Monocot and Dicot Stems Dicot Stems Dicot stems have vascular bundles arranged in a ringlike pattern. The parenchyma cells inside the vascular tissue are known as pith. Dicot Cortex Pith Vascular bundles Epidermis

End Show 23–3 Stems Slide 14 of 36 Copyright Pearson Prentice Hall Monocot and Dicot Stems The parenchyma cells outside of the vascular tissue form the cortex of the stem. Dicot Cortex Pith Vascular bundles Epidermis

End Show 23–3 Stems Slide 15 of 36 Copyright Pearson Prentice Hall Primary Growth in Stems How do primary growth and secondary growth occur in stems?

End Show 23–3 Stems Slide 16 of 36 Copyright Pearson Prentice Hall Primary Growth of Stems All seed plants undergo primary growth, which is an increase in length. For the entire life of the plant, new cells are produced at the tips of roots and shoots. Year 1Year 2Year 3 Primary growth Apical meristem Primary growth Leaf scar

End Show 23–3 Stems Slide 17 of 36 Copyright Pearson Prentice Hall Primary Growth of Stems Primary growth of stems is produced by cell divisions in the apical meristem. It takes place in all seed plants. Apical meristem

End Show 23–3 Stems Slide 18 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems The method of growth in which stems increase in width is called secondary growth. In conifers and dicots, secondary growth takes place in the vascular cambium and cork cambium.

End Show 23–3 Stems Slide 19 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems Vascular cambium produces vascular tissues and increases the thickness of stems over time. Cork cambium produces the outer covering of stems. The addition of new tissue in these cambium layers increases the thickness of the stem.

End Show 23–3 Stems Slide 20 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems Formation of the Vascular Cambium Once secondary growth begins, the vascular cambium appears as a thin layer between the xylem and phloem of each vascular bundle. Vascular cambium

End Show 23–3 Stems Slide 21 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems The vascular cambium divides to produce xylem cells toward the center of the stem and phloem cells toward the outside. Secondary xylem Secondary phloem

End Show 23–3 Stems Slide 22 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems These different tissues form the bark and wood of a mature stem.

End Show 23–3 Stems Slide 23 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems Formation of Wood Wood is actually layers of xylem. These cells build up year after year. Wood Bark

End Show 23–3 Stems Slide 24 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems As woody stems grow thicker, older xylem cells near the center of the stem no longer conduct water. This is called heartwood. Heartwood supports the tree. Xylem: Heartwood

End Show 23–3 Stems Slide 25 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems Heartwood is surrounded by sapwood. Sapwood is active in water and mineral transport. Xylem: Sapwood

End Show 23–3 Stems Slide 26 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems Formation of Bark On most trees, bark includes all of the tissues outside the vascular cambium — phloem, the cork cambium and cork. Bark

End Show 23–3 Stems Slide 27 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems The vascular cambium produces new xylem and phloem, which increase the width of the stem. Vascular cambium

End Show 23–3 Stems Slide 28 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems The phloem transports sugars produced by photosynthesis. Phloem

End Show 23–3 Stems Slide 29 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems The cork cambium produces a protective layer of cork. Cork cambium

End Show 23–3 Stems Slide 30 of 36 Copyright Pearson Prentice Hall Secondary Growth of Stems The cork contains old, nonfunctioning phloem that protects the tree. Cork

End Show - or - Continue to: Click to Launch: Slide 31 of 36 Copyright Pearson Prentice Hall 23–3

End Show Slide 32 of 36 Copyright Pearson Prentice Hall 23–3 Structures on a stem that can produce new stems and leaves are called a.nodes. b.internodes. c.buds. d.branches.

End Show Slide 33 of 36 Copyright Pearson Prentice Hall 23–3 The vascular bundles in a monocot stem a.form a cylinder, or ring. b.are scattered throughout the stem. c.form concentric rings. d.separate into xylem bundles and phloem bundles.

End Show Slide 34 of 36 Copyright Pearson Prentice Hall 23–3 The outermost layer of a tree that contains old, nonfunctioning phloem is a.bark. b.cork. c.pith. d.apical meristem.

End Show Slide 35 of 36 Copyright Pearson Prentice Hall 23–3 Xylem and phloem are contained in a.the epidermis. b.vascular bundles. c.the pith. d.cork cambium.

End Show Slide 36 of 36 Copyright Pearson Prentice Hall 23–3 In stems, secondary growth results in a.growth at the tips of roots. b.growth at the tips of shoots. c.an increase in the width of stems. d.an increase in the length of stems.

END OF SECTION