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Plant Organs: Leaves

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Plant Organs: Leaves Chapter 8 LEARNING OBJECTIVE 1 Describe the major tissues of the leaf (epidermis, mesophyll, xylem, and phloem) Relate the structure of the leaf ... – PowerPoint PPT presentation

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Title: Plant Organs: Leaves


1
Plant Organs Leaves
  • Chapter 8

2
LEARNING OBJECTIVE 1
  • Describe the major tissues of the leaf
    (epidermis, mesophyll, xylem, and phloem)
  • Relate the structure of the leaf to its function
    of photosynthesis

3
Typical Leaf
4
Blade
Veins
Petiole
Axillary bud
Stipules
Stem
Fig. 8-1, p. 152
5
Animation Simple and Compound Leaves
CLICKTO PLAY
6
KEY TERMS
  • BLADE
  • Broad, flat part of a leaf
  • PETIOLE
  • Part of a leaf that attaches blade to stem

7
Leaf Morphology
8



Stepped Art
Fig. 8-2, p. 154
9
KEY TERMS
  • PHOTOSYNTHESIS
  • The biological process that includes the capture
    of light energy and its transformation into
    chemical energy of organic molecules (such as
    glucose), which are manufactured from carbon
    dioxide and water

10
Tissues in a Leaf Blade
11
Animation Leaf Organization
CLICKTO PLAY
12
Epidermis
  • The transparent epidermis allows light to
    penetrate into the mesophyll, where
    photosynthesis occurs

13
KEY TERMS
  • CUTICLE
  • Waxy covering over epidermis of aerial parts
    (leaves and stems) of a plant
  • Enables the plant to survive in the dry
    conditions of a terrestrial environment

14
Trichomes
15
KEY TERMS
  • STOMA
  • Small pores in epidermis of stem or leaf
  • Permit gas exchange for photosynthesis and
    transpiration
  • Flanked by guard cells
  • GUARD CELL
  • Two guard cells form a pore (stoma)

16
Stomata
  • Stomata typically open during the day, when
    photosynthesis takes place, and close at night

17
KEY TERMS
  • MESOPHYLL
  • Photosynthetic ground tissue in the interior of a
    leaf
  • Contains air spaces for rapid diffusion of carbon
    dioxide and water into, and oxygen out of,
    mesophyll cells

18
Vascular Bundle
  • Leaf veins have
  • xylem to conduct water and essential minerals to
    the leaf
  • phloem to conduct sugar produced by
    photosynthesis to rest of plant

19
KEY TERMS
  • BUNDLE SHEATH
  • One or more layers of nonvascular cells
    (parenchyma or sclerenchyma) surrounding the
    vascular bundle in a leaf

20
LEARNING OBJECTIVE 2
  • Contrast leaf structure in eudicots and monocots

21
Animation Monocot and Dicot Leaves
CLICKTO PLAY
22
Bundle Sheath Extensions
23
Upper epidermis
Bundle sheath extension
Bundle sheath
Midvein
Bundle sheath extension
Lower epidermis
Fig. 8-5, p. 157
24
Leaf Cross Sections
25
Leaf Cross Sections
26
Upper epidermis
Palisade mesophyll
Midvein
Lengthwise view of vein
Spongy mesophyll
Privet
Air space
Lower epidermis
Stoma
Xylem
Phloem
(a) Privet (Ligustrum vulgare), a eudicot, has a
mesophyll with distinct palisade and spongy
sections.
Fig. 8-6a, p. 158
27
Bundle sheath cells
Midvein
Mesophyll
Parallel vein
Upper epidermis
Lower epidermis
Phloem
Xylem
Fig. 8-6b, p. 158
28
Monocot and Eudicot Leaves
  • Monocot leaves
  • Usually narrow
  • Wrap around the stem in a sheath
  • Have parallel venation
  • Eudicot leaves
  • Usually have a broad, flattened blade
  • Have netted venation

29
Bulliform Cells
  • Large, thin-walled cells on upper epidermises of
    leaves of certain monocots (grasses)
  • Located on both sides of the midvein
  • May help leaf roll or fold inward during drought

30
Bulliform Cells
31
(a) A folded leaf blade. The inconspicuous bullifo
rm cells occur in the upper epidermis on both
sides of the midvein.
Bulliform cells
Midvein
Fig. 8-7a, p. 159
32
Bulliform cells
(b) An expanded leaf blade. A higher
magnification of the midvein region shows the
enlarged, turgid bulliform cells.
Mesophyll cell
Midvein
Fig. 8-7b, p. 159
33
LEARNING OBJECTIVE 3
  • Outline the physiological changes that accompany
    stomatal opening and closing

34
Variation in Guard Cells
35
Closed
Open
Guard cells
Subsidiary cells
(a) Guard cells of eudicots and many monocots are
bean shaped.
Fig. 8-8a, p. 160
36
Closed
Open
Subsidiary cells
Guard cells
(b) Some monocot guard cells (those of grasses,
reeds, and sedges) are narrow in the center and
thicker at each end.
Fig. 8-8b, p. 160
37
Fig. 8-8d, p. 160
38
Animation Stomata
CLICKTO PLAY
39
Stomatal Opening 1
  • 1. Blue light activates proton pumps
  • in guard-cell plasma membrane
  • 2. Protons (H) are pumped out of guard cells,
    forming a proton gradient
  • Charge and concentration difference on two sides
    of the guard-cell plasma membrane

40
KEY TERMS
  • PROTON GRADIENT
  • Difference in concentration of protons on the two
    sides of a cell membrane
  • Contains potential energy that can be used to
    form ATP or do work in the cell

41
Stomatal Opening 2
  • 3. Gradient drives facilitated diffusion of
    potassium ions into guard cells
  • 4. Chloride ions also enter guard cells through
    ion channels
  • Ions accumulate in vacuoles of guard cells
  • Solute concentration becomes greater than that of
    surrounding cells

42
KEY TERMS
  • FACILITATED DIFFUSION
  • Diffusion of materials from a region of higher
    concentration to a region of lower concentration
    through special passageways in the membrane

43
Stomatal Opening 3
  • 5. Water enters guard cells from surrounding
    epidermal cells by osmosis
  • Increased turgidity changes the shape of guard
    cells, causing stoma to open

44
Stomatal Opening
45
Blue light activates proton pumps.
Protons are pumped out of guard cells, forming
proton gradient.
Potassium ions enter guard cells
through voltage-activated ion channels.
Chloride ions also enter guard cells through
ion channels.
Water enters guard cells by osmosis,and stoma
opens.
1
4
5
3
2
Fig. 8-9, p. 162
46
Stomatal Closing
  • As evening approaches, sucrose concentration in
    guard cells declines
  • Sucrose is converted to starch (osmotically
    inactive)
  • Water leaves by osmosis, guard cells lose their
    turgidity, pore closes

47
Adaptations to Environment
48
Blade
Petiole
Fig. 8-10, p. 163
49
Guard cells of sunken stoma
Epidermis and cuticle
Resin duct
Endodermis
Xylem
Vascular bundle
Phloem
Mesophyll cell (photosynthetic parenchyma cell)
Fig. 8-11, p. 164
50
LEARNING OBJECTIVE 4
  • Discuss transpiration and its effects on the
    plant

51
KEY TERMS
  • TRANSPIRATION
  • Loss of water vapor from a plants aerial parts

52
Transpiration
  • Occurs primarily through stomata
  • Rate of transpiration is affected by
    environmental factors
  • temperature, wind, relative humidity
  • Both beneficial and harmful to the plant

53
Transpiration
54
75 Water recycled by transpiration and evaporatio
n
25 Water seeps into ground or runs off to
rivers, streams, and lakes
p. 165
55
Wilting
56
Guttation
57
LEARNING OBJECTIVE 5
  • Define leaf abscission
  • Explain why it occurs and what physiological and
    anatomical changes precede it

58
KEY TERMS
  • ABSCISSION
  • Normal (usually seasonal) falling off of leaves
    or other plant parts, such as fruits or flowers

59
Leaf Abscission
  • In temperate climates, most woody plants with
    broad leaves shed leaves in fall
  • Helps them survive low temperatures of winter
  • Involves physiological and anatomical changes

60
Processes of Abscission 1
  • As autumn approaches, plant reabsorbs sugar
  • essential minerals are transported out of leaves
  • Chlorophyll is broken down
  • red water-soluble pigments are synthesized and
    stored in vacuoles of leaf cells (in some
    species)

61
Processes of Abscission 2
  • A protective layer of cork cells develops on the
    stem side of the abscission zone
  • Area where leaf petiole detaches from stem,
    composed primarily of thin-walled parenchyma cells

62
Processes of Abscission 3
  • Enzymes dissolve middle lamella in abscission
    zone
  • (cement that holds primary cell walls of
    adjacent cells together)
  • After leaf detaches, protective layer of cork
    seals off the area, forming a leaf scar

63
Abscission Zone
64
Axillary bud
Bud scales
Petiole
Abscission zone
Stem
Fig. 8-14, p. 167
65
LEARNING OBJECTIVE 6
  • List at least five modified leaves, and give the
    function of each

66
KEY TERMS
  • BUD SCALE
  • Modified leaf that covers and protects delicate
    meristematic tissue of winter buds
  • SPINE
  • Leaf modified for protection, such as a cactus
    spine

67
KEY TERMS
  • BRACT
  • Modified leaf associated with a flower or
    inflorescence but not part of the flower itself
  • TENDRIL
  • Leaf or stem that is modified for holding on or
    attaching to objects
  • Supports weak stems

68
KEY TERMS
  • BULB
  • A rounded, fleshy, underground bud that consists
    of a short stem with fleshy leaves
  • Specialized for storage

69
Leaf Modifications
70
Fig. 8-15a, p. 168
71
Fig. 8-15b, p. 168
72
Fig. 8-15c, p. 168
73
Fig. 8-15d, p. 168
74
Fig. 8-15e, p. 168
75
Fig. 8-15f, p. 168
76
Epiphytes
  • Flowerpot Plant

77
Stem
Pot (modified leaf)
(a) The leaves of the flowerpot plant
(Dischidia rafflesiana) are modified to hold
water and organic material carried in by ants.
Fig. 8-16a, p. 169
78
Root
(b) A cutaway view of a pot removed from a plant
reveals the special root that absorbs water and
dissolved minerals inside the pot.
Fig. 8-16b, p. 169
79
Carnivorous Plants
  • Leaves modified to trap insects
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