1. Plant Structures Roots, Stems, and Leaves
Chapter 23

2. 23-1 Specialized Tissues in Plants
Plants are as successful if not more successful than animals
Seed plants have three main structures:
Roots
Stems
Leaves
Linked together by various means

3. 23-1 Specialized Tissues in Plants
Roots
Absorbs water and nutrients
Anchor plant to the ground
Hold soil in place and prevent erosion
Protect from soil bacteria
Transport water and nutrients
Provide upright support

4. 23-1 Specialized Tissues in Plants
Stems
Support for the plant body
Carries nutrients throughout plant
Defense system to protect against predators and infection
Few millimeters to 100 meters

5. 23-1 Specialized Tissues in Plants
Leaves
Main photosynthetic systems
Suseptable to extreme drying
Sight of oxygen/carbon dioxide intake and release

6. 23-1 Specialized Tissues in Plants
Plant tissue systems
Exist within the root, stems, and leaves
Dermal tissue
Vascular tissue
Ground tissue

7. 23-1 Specialized Tissues in Plants
Dermal Tissue
Outer covering
Single layer of cells
Cuticle – waxy coating
Trichomes – Spiny projections on the leaf
Roots have dermal tissue
Root hairs
Guard Cells

8. 23-1 Specialized Tissues in Plants
Vascular Tissue
Transport System
Subsystems
Xylem
Phloem
Subsystems are used to carry fluids throughout plant

9. 23-1 Specialized Tissues in Plants
Xylem
Two types
Seed plants
Angiosperms
Tracheid – long narrow cells
Walls are connected to neighboring cells
Will eventually die
Vessel Element – wider that tracheids

10. 23-1 Specialized Tissues in Plants
Phloem
Sieve Tube Elements
Cells arranged end to end
Pump sugars and other foods
Companion Cells
Surround sieve tube elements
Support phloem cells

11. 23-1 Specialized Tissues in Plants
Ground Tissue
Cells between dermal and vascular tissue
Parenchyma
Thin cell walls, large vacuoules
Collenchyma
Strong, flexible cell walls
Sclerenchyma
Extremely thick, rigid cell walls

12. 23-1 Specialized Tissues in Plants
Plant Growth
Meristems – tissues responsible for growth
Undifferentiated cells
Apical Meristem
Produce growth increased length
Differentiation
Cells will assume roles in the plant
Flower Development
Starts in the meristem

13. 23-2 Roots Types of Roots Taproots Fibrous roots Found in dicots
Long, thick root
Hickory and oak trees
Fibrous roots
Found in monocots
No single root larger than any other
Many thin roots
Help prevent erosion

14. Root Structure and Growth
Outside layer = epidermis
Central cylinder = vascular tissue
Between these two = ground tissue
Roots important in water and mineral transport 14

15. 23-2 Roots Root Structure Epidermis – outside layer
Root hairs
Cortex – spongy layer of ground tissue inside epidermis
Endodermis – layer inside cortex
Vascular cylinder – central vascular system
Root Cap – the tip, cellular production

16. Root Growth Roots grow by producing new cells near the tip!
Root lubricates its path
New cells are added at the root cap
Behind the meristematic tissue, cells grow longer
These cells specialize and take on different functions (process of differentiation)

17. Root Functions Anchor a plant in the ground
Absorb water and dissolved nutrients from the soil
Water and nutrients do not just soak into the root from the soil
The plant requires energy to absorb water 17

18. 23-2 Roots Plant Nutrient Uptake Plant requirements
Soil includes sand, silt, clay, air, bits of decaying organic matter
Soil type determines plant type!
Plant requirements
- Oxygen, CO2
- Nitrogen - Magnesium
- Phosphorus - Calcium
- Postassium - Trace elements

19. Types of soil
Sandy soil is made up of mostly grains of sand. Water passes through this type of soil quickly.
Clay soil is mostly made of fine clay particles. Water poured on clay soil sinks slowly.
Loamy soil contains decaying plant and animal matter along with clay and sand.

20. Essential Nutrients
Nitrogen is important for leaf growth and color. A plant that lacks nitrogen will have yellow leaves.
Phosphorous is needed for roots, stems and flower growth as well as seeds. A plant lacking phosphorous will have stunted growth and few flowers.

21. Potassium is important in root, stem and flower development as well
Potassium is important in root, stem and flower development as well. It helps the plants live in the cold and fight disease. Plants with too little potassium have stunted roots. Potassium is sometimes called potash.
Calcium is needed for cell growth and for strong cell walls.
Magnesium is needed to make chlorophyll. Plants will die without chlorophyll.

22. Plants also need very small amounts of what are called trace elements
Plants also need very small amounts of what are called trace elements. The plant will not grow well if these trace elements are not present, but if there is too much of the trace elements in the soil they are poisonous to the plant.

23. 23-2 Roots Active Transport in Plants Vascular Cylinder
Root hairs use ATP
Pump minerals from
soil
Causes water molecules
to follow by osmosis
Vascular Cylinder
Casparian Strip – waterproof strip surrounding endodermal cells: H20 retention

24. Osmosis and Root Pressure
Water moves into the vascular cylinder by osmosis (diffusion through semipermeable membrane)
Water and minerals can’t pass through the Casparian strip, so they’re trapped once inside the vascular cylinder!
Root Pressure
One-way movement creates pressure
Forces water up into the plant
If pressure didn’t build up, roots would swell up!

25. 23-3 Stems Stem Structure Essential part of transport system
Produce leaves, branches, and flowers
Hold leaves up to sunlight
Transport substance between roots and leaves
Essential part of transport system
Function in storage and photosynthesis
Like other plant parts, stems have vascular, dermal, and ground tissue!

26. 23-3 Stems Xylem and phloem – major tubule systems
Transport water and nutrients
Composed of 3 tissue layers
Contain nodes – attachment for leaves
Internodes – regions between the nodes
Buds – undeveloped tissue

27. 23-3 Stem Types Monocot – vascular bundles are scattered throughout
- Distinct epidermis
Dicot – vascular tissue arranged in a cylinder
- Pith – parenchyma cells inside the ring (ground tissue with thin cell wall, large vacuole)
Monocot – vascular bundles are scattered throughout
Distinct epidermis
Dicot – vascular tissue arranged in a cylinder
Pith – parenchyma cells inside the ring (ground tissue with thin cell wall, large vacuole)

28. 23-3 Stem Growth
Primary growth – new cells produced at the root tips and shoots
Increases the length
Secondary growth – increase in stem width
Vascular cambium – meristematic tissue that produces vascular tissue and increases thickness
Cork cambium – produces outer covering of stems

29. 23-3 Stems Formation of Vascular Cambium
Xylem and phloem bundles present in a ring
Secondary growth initiates production of a thin layer
The vascular cambium divides
Produces new xylem and phloem

30. 23-3 Stems Formation of wood Wood – layers of xylem
Produced year after year
Results from the older xylem not conducting water – heartwood
Becomes darker with age
Sapwood – surrounds
heartwood

31. Annual Rings
In spring, growth happens quickly, producing light-colored xylem cells with thin cell walls
At the end of the season, the cells become darker with thicker cell walls (late wood)
Each season, a ring with light and dark is produced
By counting rings in a tree, you can estimate age!

32. 23-3 Roots Formation of Bark
All the tissues outside the vascular cambium
Consists of outermost layers of dead cork
Water proof

33. 23-4 Leaves Main site of photosynthesis Consist of:
Blade – thin flattened section
Petiole – stalk that attaches stem to blade
Covered by epidermis and cuticle (waxy covering)
Create water proof barrier

34. 23-4 Leaves Leaf Functions
Photosynthesis – occurs in the mesophyll (specialized ground tissue in leaf)
Palisade mesophyll – absorb light
Spongy mesophyll – beneath palisade level

35. Stomata Stomata – pores in the underside of the leaf Singular: stoma
Guard Cells – epidermal cells surrounding the stomata, specialized to open and close

36. 23-4 Leaves Transpiration Loss of water through its leaves
Replaced by water drawn into the leaf through xylem

37. Gas Exchange Take in CO2 and release O2
Can do the opposite – when using food, take in oxygen and release CO2
Gas exchange takes place at the stomata
Not open all the time
Stomata is controlled by water pressure in guard cells

38. Gas Exchange & Homeostasis
Plants keep stomata open just enough to allow photosynthesis to occur, but not to lose too much water!
When water pressure is high, guard cells pulled away and stoma opens!
When water pressure is low, inner walls pull together and stoma closes!
Usually: stomata open in daytime, closed at night… why?

39. 23-5 Transport in Plants Water Transport
Active transport and root pressure
Cause water to move from soil to roots
Capillary action
Combined with active transport and root pressure, moves materials throughout the plant

40. 23-5 Transport in Plants Capillary Transport
Capillary transport results from both cohesive and adhesive forces
Water molecules attracted to one another
Water is also attracted to the xylem tubes in the plant
Causes water to move from roots to the stem and upward

41. 23-5 Transport in Plants Transpiration
Evaporation is the major moving force
As water is lost, osmotic pressure moves water out of vascular tissue
This pulls water up from the stem to the leaves
Affected by heat, humidity, and wind

42. 23-5 Transport in Plants Controlling Transpiration
Open the stomata – increase water loss
Close the stomata – decrease water loss

43. 23-5 Transport in Plants Transpiration and Wilting
Osmotic pressure – keeps plants semi-rigid
Wilting is a result of high transpiration rates
Loss of water causes a drop in osmotic pressure
Loss of rigidity
Conserves water

44. 23-5 Transport in Plants Nutrient Transport Source to Sink
Most nutrients are pushed through plant
Nutrient movement takes place in phloem
Source to Sink
Source – any cell that produces sugars
Sink – any cell where sugars are used
Pressure-flow Hypothesis