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Unit 7 Plants Ch. 23 Roots, Stems, & Leaves.

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Presentation on theme: "Unit 7 Plants Ch. 23 Roots, Stems, & Leaves."— Presentation transcript:

1 Unit 7 Plants Ch. 23 Roots, Stems, & Leaves

2 Seed Plant Structure 3 of the principal organs of seed plants are roots, stems, & leaves The root system of a plant absorbs water & dissolved nutrients

3 Seed Plant Structure A stem has a support system for the plant body, a transport system that carries nutrients, & a defense system that protects the plant against predators & disease Leaves are the plant’s main photosynthetic systems

4 Plant Tissue Systems Plants consist of 3 main tissue systems: dermal tissue, vascular tissue, & ground tissue

5 Dermal Tissue The outer covering of a plant, that consists of a single layer of epidermal cells The outer surfaces are often covered with thick waxy layer to protect against water loss & injury

6 Vascular Tissue Contains several types of specialized cells
Xylem consists of tracheids & vessel elements Phloem consists of sieve tube elements & companion cells

7 Vascular Tissue - Xylem
All seed plants have a type of xylem cell called a tracheid, cells that resist water pressure Vessel elements - wide cells that form hollow tubes, which water can move through freely

8 Vascular Tissue - Phloem
Sieve tube elements - main cells in phloem, form tubes through which materials, like sugars & other foods, are carried in a watery stream Companion cells - phloem cells that surround sieve tube elements, help movement of substances in & out of the phloem

9 Ground Tissue Cells that lie between dermal & vascular tissues
Consists mainly of parenchyma - cells that are packed with chloroplasts & are the site of most of a plant’s photosynthesis

10 Ground Tissue Collenchyma - cells that have strong, flexible cell walls that help support larger plants (makes up “strings” of a stalk of celery) Sclerenchyma - rigid cell walls that make ground tissue tough & strong

11 Plant Growth & Meristematic Tissue
Meristems - clusters of tissue that are responsible for continuing growth throughout a plant’s lifetime Meristematic tissue - undifferentiated cells, they have not yet become specialized for specific functions, such as transport

12 Plant Growth & Meristematic Tissue
Apical meristem - group of undifferentiated cells that divide to produce increased length of stems & roots

13 Plant Growth & Meristematic Tissue
Differentiation - cells develop into mature cells with specialized structures & functions As cells differentiate, they produce each of the tissue systems of the plant: dermal, ground, & vascular tissue

14 Types of Roots The 2 main types of roots are taproots, found mainly in dicots, & fibrous roots, found mainly in monocots Taproot - primary root Ex.) carrots, dandelions, beets, etc.

15 Types of Roots Fibrous roots - roots that branch to such an extent that no single root grows larger than the rest Ex.) grass

16 Root Structure & Growth
A mature root has an outsider layer, the epidermis, & a central cylinder of vascular tissue Between these tissues, lies a large area of ground tissue

17 Root Structure & Growth
Root hairs - tiny cellular projections that penetrate the spaces between soil particles & produce a large surface area through which water can enter the plant

18 Root Structure & Growth
Cortex - spongy layer of ground tissue just inside the epidermis Endodermis - another layer of cells that completely encloses the root’s vascular subsystem in a region called the vascular cylinder

19 Root Structure & Growth
Root cap - protects the root as it forces its way through the soil

20 Root Functions Roots anchor a plant in the ground & absorb water & dissolved nutrients from the soil


22 Stem Structure & Function
Stems have 3 important functions: they produce leaves, branches, & flowers; they hold leaves up to the sunlight; & they transport substances between roots & leaves

23 Stem Structure & Function
Nodes - where leaves are attached Internode - regions between the nodes Buds - contain undeveloped tissue that can produce new stems & leaves

24 Monocot & Dicot Stems In monocots, vascular bundles are scattered throughout the stem In dicots & most gymnosperms, vascular bundles are arranged in a cylinder

25 Monocot & Dicot Stems Vascular bundles - contains xylem & phloem tissue Pith - the parenchyma cells inside the ring of vascular tissue

26 Primary Growth of Stems
Primary growth - growth occurring only at the ends of a plant Its produced by cell divisions in the apical meristem, & takes place in all seed plants

27 Secondary Growth of Stems
Secondary growth - method of growth where stems increase in width In conifers & dicots, secondary growth takes place in lateral meristematic tissues called the vascular cambium & cork cambium

28 Secondary Growth of Stems
Vascular cambium - produces vascular tissues & increases the thickness of stems over time Cork cambium - produces the outer covering of stems

29 Formation of Wood Heartwood - older xylem near the center of the stem that no longer conducts water Sapwood - surrounds heartwood, active in fluid transport

30 Formation of Bark Bark - includes all of the tissues outside the vascular cambium, includes: phloem, the cork cambium, & cork


32 Leaf Structure The structure of a leaf is optimized for absorbing light & carrying out photosynthesis

33 Leaf Structure Blades - flattened section, attached to the stem by a thin stalk - petiole

34 Leaf Functions A leaf can be considered a system specialized for photosynthesis Subsystems of the leaf include tissues that bring gases, water, & nutrients to the cells that carry out photosynthesis

35 Leaf Functions Guard cells - specialized cells in the epidermis that control the opening & closing of stomata (air spaces) by responding to changes in water pressure

36 Leaf Functions Plants keep their stomata open just enough to allow photosynthesis to take place, but not so much that they lose an excessive amount of water


38 Leaf Functions Transpiration - the loss of water through its leaves

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