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