1. Chapter 23
Roots, Stems and Leaves

2. Learning Targets 23.1
What are the principal organs and tissues of vascular plants?
How is meristematic tissue different from other plant tissues?
What specialized cells make up vascular tissue?

3. Specialized Tissues in Plants
Three main organs of plants:
ROOTS: underground organs that absorb water and minerals
Also anchor the plant and hold it upright
STEMS: supporting structures that connect roots and leaves
Carry water and nutrients
Holds leaves up to light
LEAVES: carry out photosynthesis
Capture light, flat so cover more surface area
Cuticle and adjustable pores protect leaves from water loss

4. Tissue Systems
Within the roots, stems and leaves are FOUR specialized tissue systems:
DERMAL TISSUE: forms the skin of a plant (is the outermost layer of cells)
VASCULAR TISSUE: like the plant’s bloodstream (transports water and nutrients throughout the plant)
GROUND TISSUE: cells between the dermal and vascular tissues
MERISTEMATIC TISSUE: found only in the tips of shoots and roots

5. Three tissues of plants
Leaf
Stem
Root
Three tissues of plants
Dermal tissue
Vascular tissue
Ground tissue

6. Dermal Tissue Outer covering of a plant Consists of:
Epidermis: outermost layer
Cuticle: thick, waxy layer that protects against water loss and injury (covers epidermis)
On under side of leaves, contains guard cells which regulate water loss and gas exchange

7. Dermal Tissue

8. Vascular Tissue Transport system: “bloodstream”
Consists of xylem and phloem
Xylem: water-conducting tissue
Transports water to leaves
Phloem: food-conducting tissue
Takes sugar to the roots

9. Ground Tissue Tissue that lies between dermal and vascular tissue
Consists of parenchyma, collenchyma and sclerenchyma

10. Ground Tissue Parenchyma: Collenchyma
Thin cell walls and large vacuoles
In leaves, these cells are packed with chloroplasts and are the site of photosynthesis
Collenchyma
Cells with strong, flexible walls that help to support larger plants
This is what makes up the stringy part of celery

11. Ground Tissue Sclerenchyma
Cells that have an extremely thick, ridged, cell wall that makes ground tissue tough and strong.

12. Meristematic Tissue
New growth is produced in cells that make up meristematic tissue
It is the ONLY plant tissue that produces new cells by mitosis!!
Best place to see this at the tip of a shoot/root where apical meristem is located

14. Learning Targets 23.2 What are the two main types of roots?
What are the main tissues in a mature root?
What are the different functions of roots?

15. Roots Functions: TWO MAIN TYPES OF ROOTS: Absorb water and nutrients
Anchor plant
TWO MAIN TYPES OF ROOTS:
Taproots: found mainly in dicots
EX: carrot, dandelions, beets, radishes, oak tree
Fibrous Roots: found mainly in monocots
EX: grass

16. ROOTS

17. Root Structure
Epidermis of root is covered with tiny projections called root hairs
Increase surface area of root to absorb more water
Roots grow in length as their apical meristem produces new cells near the root tip
The fragile new cells are covered by a tough root cap that protects the root as it forces its way through soil

19. Learning Targets 23.3 What are the three main functions of stems?
How do monocot and dicot stems differ?
How do primary growth and secondary growth occur in stems?

20. Stems
FUNCTIONS:
Produce Leaves, branches and flowers
Hold leaves up in the sunlight
Transport substances between roots and leaves
Composed of dermal, vascular and ground tissue (like the rest of the plant)

21. Stem Parts Nodes: where leaves are attached
Internodes: regions between the nodes
Buds: contain undeveloped tissue that can produce new stems and leaves

23. Monocot v. Dicot Stems
Moncots: vascular bundles are scattered throughout the stem

24. Monocot v. Dicot Stems
Dicots: vascular bundles are arranged in a cylinder

25. Primary Growth
For a plant’s entire life, new cells are produced at the tips of roots and shoots
This is called primary growth
They increase in length
It takes place in all seed plants

26. Secondary Growth
The pattern of growth in which stems increase in width is called secondary growth
In conifers and dicots, secondary growth takes place in lateral meristematic tissue called the vascular cambium and cork cabium

27. WOOD WOOD is actually layers of XYLEM
Heartwood: older xylem in center of wood, that no longer conducts water
Darkens with age as it accumulates impurities
Sapwood: surrounds heartwood, active in transport

28. WOOD Growth Rings Indicate age of tree and environmental conditions
Thick rings indicate the growing season experienced adequate moisture
Thin rings indicate there was less water (draught)

29. Wood
Bark
Cork
Contains old, nonfunctioning xylem that helps support the tree
Contains active xylem that transports water and minerals
Produces new xylem and phloem, which increase the width of the stem
Transports sugars produced by photosynthesis
Produces protective layer of cork
Contains old, nonfunctioning phloem that protects the tree
Xylem: Heartwood
Cork Cambium
Phloem
Vascular Cambium
Xylem: Sapwood

30. Learning Targets 23.4
How does the structure of a leaf enable it to carry out photosynthesis?
How does gas exchange take place in a leaf?

31. Leaves Main organs of photosynthesis
Makes food for plants (glucose: C6H12O2)
Structure is optimized for absorbing light and carrying out photosynthesis
Blades: thin, flattened to increase surface area to absorb sunlight
Attached to stem by petiole
Epidermis: outer layer
Cuticle: waxy, protective layer
Protects tissues and limits water loss

32. Leaves

33. Simple and Compound Leaves

34. Leaf Structure/Function
Photosynthesis
Most of photosynthesis carried out in MESOPHYLL layer
Packed with chloroplasts
Palisade Mesophyll: column-shaped cells just under epidermis
Absorb most of light coming into leaf

35. Leaf Structure/Function
Cuticle
Veins
Epidermis
Palisade mesophyll
Xylem
Vein
Phloem
Spongy mesophyll
Epidermis
Stoma
Guard cells

36. Leaf Structure/Function
Spongy Mesophyll: loose tissue layer beneath palisade with air spaces between cells
Air spaces connect with outside through STOMATA

37. Leaf Structure/Function
Cuticle
Veins
Epidermis
Palisade mesophyll
Xylem
Vein
Phloem
Spongy mesophyll
Epidermis
Stoma
Guard cells

38. Leaf Structure/Function
STOMATA: pores in underside of leaf that let carbon dioxide and oxygen diffuse in and out of the leaf
Each stoma consists of two GUARD CELLS
Guard Cells: cells in the epidermis that control the opening and closing of the stomata by responding to water pressure changes

39. Single stomata
Multiple stomata

40. Leaf Structure/Function
Gas Exchange
Leaves take in CO2 and give off O2 during photosynthesis
Plant leaves allow gas exchange by opening their stomata
If kept open all the time, there would be large amounts of water loss due to transpiration
Plants keep stomata open just enough to allow photosynthesis to take place, not long enough to lose too much water

41. Leaf Structure/Function
Guard cells regulate opening/closing of the stomata
If water pressure is high, they open the stomata
If water pressure is low, they close the stoma

42. Stomata/Guard Cells Stoma Open Stoma Closed Guard cells Guard cells
Inner cell wall
Inner cell wall
Stoma
Stoma Open
Stoma Closed

43. Leaf Structure/Function
Cuticle
Veins
Epidermis
Palisade mesophyll
Xylem
Vein
Phloem
Spongy mesophyll
Epidermis
Stoma
Guard cells

44. Learning Targets 23.5 How is water transported throughout a plant?
How are the products of photosynthesis transported throughout the plan?

45. Water Transport
Combo of root pressure, capillary action and transpiration provides force to move water through the xylem
Root Pressure: pressure created by water entering the tissues of a root that pushes water upward in a plant stem
Capillary Action: tendency of water to rise in a THIN tube
Water is attracted to the walls of the tube and to other water molecules

46. Water Transport Transpiration: loss of water through plant leaves
When water is lost through transpiration the leaf “pulls” water upward from the roots
Moves water from HIGH to LOW pressure

47. Water Movement Evaporation of water molecules out of leaves.
Pull of water molecules upward from the roots.