Roots, Stems and Leaves

1
Chapter 23

• Roots, Stems and Leaves

2
Section 23-1

• Specialized Tissues in Plants

3
Seed Plant Structure

• Cells of seed plants are organized into different
  tissues and organs
• Roots, Stems, Leaves
• Linked by systems that run through the plant
• Transport nutrients, protection, coordinate plant
  activities

4
Roots

• Absorb water and nutrients
• Anchor plants in the ground
• Hold soil in place and prevent erosion
• Protection from soil bacteria, fungi

5
Stems

• Support for the plant body
• Hold up leaves and branches
• Transport system
• Lift water from roots, carry products of
  photosynthesis from leaves
• Defense system
• Protect against predators and disease

6
Leaves

• Main photosynthesis system
• Broad, flat shape
• Increase sunlight absorbed
• Must protect against water loss
• Adjustable pores conserve water during gas
  exchange

7
Plant Tissue Systems

• Roots, stems and leaves have specialized tissue
  systems
• Dermal tissue skin
• Outermost layer
• Vascular tissue bloodstream
• Transport water and nutrients
• Ground tissue everything else

8
Dermal Tissue

• Outer covering of a plant has a single layer of
  epidermal cells
• Thick waxy coating called the cuticle protect
  against water loss and injury
• Trichomes help the leaf (fuzzy)
• Root hair cells - help absorb water
• Guard cells under leaves, regulate water loss
  and gas exchange

9
Vascular Tissue

• Transports water and nutrients throughout the
  plant
• Xylem water conducting tissue
• Tracheids, vessel elements
• Phloem food conducting tissue
• Sieve tube elements, companion cells

10
Xylem

• Tracheids

• Vessel Elements

• All seed plants
• Long narrow
• Cell walls impermeable to water
• Connected to neighboring cells by openings in
  cell wall
• Mature and die before they conduct water

• Angiosperms
• Wider than tracheids
• Mature and die before they conduct water
• Arranged end to end on top of each other
• Form a continuous tube when cell walls at ends
  are lost

11
Phloem

• Sieve Tube Elements

• Companion Cells

• Main phloem cells
• End to end to form sieve tubes
• End walls have many small holes
• Lose nucleus and most organelles, the rest hug
  the inside of the cell wall

• Surround sieve tube elements
• Keep their nuclei and other organelles
• Support the phloem cells
• Aid in the movement of substances in and out of
  the phloem

12
Ground Tissue

• Cells between the dermal and vascular tissues
• Parenchyma thin cell walls
• Most ground tissue
• In leaves, full of chloroplasts
• Collenchyma strong, flexible cell walls
• Sclerenchyma extremely thick, rigid cell walls

13
Ground Tissue
Collenchyma
Parenchyma
Sclerenchyma
14
Plant Growth and Meristematic Tissue

• Most plant have an indeterminate type of growth
• Grow and produce new cells and the tips of roots
  and stems for as long as they live
• Meristems clusters of tissue responsible for
  indeterminate growth
• Meristematic Tissue produce new,
  undifferentiated cells

15
Plant Growth and Meristematic Tissue

• Apical Meristem at the end of each growing stem
  and root
• Undifferentiated cells that divide to produce
  increased length of roots and stems
• Meristematic tissue is the only plant tissue that
  produces new cells by mitosis

16
Differentiation

• Cells in the meristem mature into cells with
  specialized structures and functions
  differentiation
• Become dermal, ground and vascular tissue
• Highly specialized flowers produced in meristems
• Genes transform apical meristem into a floral
  meristem

17
Section 23-2

• Roots

18
Types of Roots

• Taproot

• Fibrous Roots

• Mainly in dicots
• Primary root grows long and thick
• Secondary roots are small
• Oak, hickory, carrots, dandelions, radishes

• Mainly in monocots
• No single root grows larger than the rest
• Highly branched roots help prevent erosion
• Grasses

19
Root Structure and Growth

• Outside layer epidermis
• Central cylinder vascular tissue
• Between these two ground tissue
• Water and mineral transport

20
Root Structure and Growth

• Root hairs cover surface of root
• Can get into small spaces, increase water
  absorption
• Cortex just inside the epidermis
• Spongy layer of ground tissue
• Endodermis surrounds vascular system
• Region called the vascular cylinder

21
Root Structure and Growth

• Roots grow in length at the apical meristem
• Fragile new cells are covered by a tough root cap
• Protects the root as it forces its way through
  the soil
• Lubricates as it grows
• New cells are continually added as cells are
  scraped away

22
Root Structure and Growth

• Zone of Cell Division apical meristem
• Zone of Elongation behind the meristem
• Most of the root growth occurs here
• Zone of Maturation mature cells become
  specialized (differentiation)

23
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

24
Nutrients in Soil

• Soil is a complex mixture that varies at
  different depths and locations
• Sand, silt, clay, air, decaying tissue
• Sandy soil large particles, few nutrients
• Silt and clay soils fine particles, high in
  nutrients

25
Plant Nutrients

• Essential Nutrients

• Trace Elements

• Needed in larger amounts
• Nitrogen, phosphorus, potassium, magnesium,
  calcium
• Found in varying amounts in soil
• Drawn up by roots

• Required in small quantities
• Sulfur, iron, zinc, molybdenum, boron, copper,
  manganese, chlorine
• Large amounts of trace elements in the soil can
  be poisonous

26
Active Transport of Minerals

• Epidermal cell membranes contain active transport
  proteins
• Use ATP to pump mineral ions from the soil into
  the plant
• High concentrations of mineral ions in the plant
  cells causes water to enter by osmosis

27
Movement Into the Vascular Cylinder

• Water and nutrients move into the cortex then to
  the endodermis
• Endodermis encloses the vascular cylinder (down
  the entire root)
• Brick-shaped cells surrounded on all sides by a
  waterproof strip Casparian strip
• Prevent the backflow of water

28
Osmosis

• Water moves into the vascular cylinder by osmosis
• Water moves from a higher concentration to a
  lower concentration
• Stays trapped in the vascular cylinder due to the
  Casparian strip

29
Root Pressure

• The one way movement of water and minerals
  generates enough pressure to move them through
  the entire plant
• As roots fill with water, they dont expand, so
  water must go up
• Forces water from the vascular cylinder into the
  xylem

30
Section 23-3

• Stems

31
Stem Structure and Function

• 3 Important Functions
• Produce leaves, branched and flowers
• Hold the leaves up to the sunlight
• Transport substances between roots and leaves
• Xylem and phloem, aid in photosynthesis

32
Stem Structure and Function

• Contains dermal, vascular and ground tissue
• Nodes where leaves are attached
• Internode space between nodes
• Buds undeveloped tissue that can produce new
  stems and leaves

33
Monocot and Dicot Stems

• Monocot

• Dicot

• Vascular bundles scattered
• Phloem faces the outside of the stem
• Xylem faces the center
• Ground tissue uniform, mainly parenchyma

• Vascular bundles arranged in a cylinder
• Parenchyma cells inside the ring of vascular
  tissue pith
• Parenchyma cells outside the vascular ring
  cortex

34
Primary Growth of Stems

• Primary Growth growth that occurs at the end of
  roots and shoots
• Growth produced by the apical meristems
• Takes place in all seed plants

35
Secondary Growth of Stems

• Stems must increase in thickness as well as
  height secondary growth
• Takes place in lateral meristematic tissues of
  conifers and dicots
• Vascular Cambium produces vascular tissue
• Cork Cambium produces outer covering of stems

36
Formation of the Vascular Cambium

• Xylem and phloem arranged in a ring
• Vascular cambium is a thin layer that forms
  between the xylem and phloem of each vascular
  bundle
• Divisions in the vascular cambium produces new
  cells, thicker xylem and phloem

37
Formation of Wood

• wood is actually layers of xylem
• As stems thicken older xylem stops conducting
  water and forms heartwood
• Darkens with age
• Heartwood is surrounded by sapwood
• Lighter in color (still transporting fluid)

38
Formation of Wood

• Tree growth is seasonal
• Spring early wood (light colored layer)
• Later in the growing season late wood (darker
  layer)
• of rings trees age, thick rings means a good
  growing season, thin rings means less growth

39
Formation of Bark

• Bark all tissues outside the vascular cambium
• Phloem, cork cambium, cork
• As xylem grows, the phloem stretches
• Cork cambium produces new cork, thick waxy
  protective layer
• As a tree grows dead cork cracks and flakes off

40
Stem Adaptations

• Tuber underground stem that stores food potato
• Bulb central stem surrounded by short thick
  leaves amaryllis
• Corm looks like a bulb, thickened stem that
  stores food, surrounded by layers of thin leaves
  gladiolus
• Rhizome horizontal, underground stem ginger

41
Section 23-4

• Leaves

42
Leaf Structure

• Absorb light, carry out photosynthesis
• Blades thin flattened sections
• Petiole attaches blade to stem
• Composed of dermal tissue, vascular tissue and
  ground tissue

43
Leaf Structure

• Top and bottom covered by epidermis
• Covered by cuticle to form a waterproof barrier
• Vascular tissue connected directly to the
  vascular tissue in stems
• In the leaf blade, vascular tissue is surrounded
  by parenchyma and sclerenchyma cells

44
Leaf Functions - Photosynthesis

• The bulk of most leaves consists of specialized
  ground tissue called mesophyll
• Photosynthesis occurs in the mesophyll
• Carbohydrates produced move into the phloem and
  are carried throughout the plant

45
Leaf Functions - Photosynthesis

• Palisade mesophyll absorb light that enters the
  leaf
• Spongy mesophyll loose tissue with many air
  spaces
• Air spaces connect with the exterior through
  stomata
• Surrounded by guard cells that expand and
  contract to control gas exchange

46
Leaf Functions - Transpiration

• The surfaces of spongy mesophyll are kept moist
  so that gases can enter and leave the cells
  easily
• Water evaporates from these surfaces and is lost
  to the air
• The loss of water through the leaves is called
  transpiration

47
Leaf Functions Gas Exchange

• Leaves take in carbon dioxide and give off oxygen
  during photosynthesis
• When cells use food they take in oxygen and give
  off carbon dioxide
• Stomata cant be open all the time or plants
  would lose more water than they can draw up
  through roots

48
Leaf Functions Gas Exchange

• Guard cells are on the underside of leaves
• Control stomata, regulate movement of gases
• Water pressure high open
• Usually open during the day
• Water pressure low closed
• Usually closed at night

49
Leaf Adaptations

• Pitcher Plant leaf attracts and digests insects
• Cactus non-photosynthetic thorns,
  photosynthesis in stem
• Pine waxy epidermis, stomata sunken below the
  surface
• Rock Plant adapted for hot, dry areas round
  with few stomata

50
Section 23-5

• Transport in Plants

51
Water Transport

• Xylem tissue forms a continuous set of tubes that
  bring water from roots into stems and leaves
• Root pressure does not exert enough force to lift
  water high into trees
• A combination of root pressure, capillary action
  and transpiration is required

52
Capillary Action

• Water molecules stick to other water molecules
  cohesion
• Water molecules stick to other surfaces
  adhesion
• Capillary Action ability of water to rise in
  thin tubes
• Tracheids and vessels elements are hollow tube
  shaped cells

53
Transpiration

• Transpiration evaporation of water from leaves
• Major force of water transport in the topmost
  branches and leaves
• Water exiting leaves pulls replacement water up
  from roots
• Transpirational Pull

54
Controlling Transpiration

• The leafs gas exchange subsystem helps maintain
  homeostasis
• Lots of water high pressure in guard cells,
  stomata open
• Scarce water low pressure in guard cells,
  stomata closed

55
Transpiration and Wilting

• Osmotic pressure keeps leaves and stems stiff
• Wilting results from loss of water
• Plant cells bend inward when they lose pressure
• Pressure decreases and stomata close to conserve
  water

56
Nutrient Transport

• Water is pulled upward through xylem, but
  nutrients are pushed through phloem
• Phloem pumps sugars into fruit (leaves into stems
  into fruits)
• Pump food into roots for winter storage, move
  back into stem for growth in the spring

57
Movement from Source to Sink

• Source where sugar is produced by
  photosynthesis
• Sink where sugars are stored or used
• Nutrients can move in both directions between
  sink and source as needed (pressure-flow
  hypothesis)