Unit 7 Plants

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 2 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