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Title: Plant Diversity


1
Plant Diversity
2
What is a Plant?
  • Plants are multicellular eukaryotes that have
    cell walls made of cellulose
  • They develop from multicellular embryos and carry
    out photosynthesis using the green pigments
    chlorophyll a and b
  • Plants are so different from animals that
    sometimes there is a tendency to think of them as
    not being alive
  • However, plants are alive, everywhere, and highly
    successful

3
The Plant Life Cycle
  • Plants have life cycles that are characterized by
    alternation of generations
  • In this life cycle, the haploid gametophyte phase
    alternates with the diploid sporophyte phase
  • A gametophyte is a haploid, or gamete-producing,
    phase of an organism
  • A sporophyte is a diploid, or spore-producing,
    phase of an organism

4
Alternation of Generations Life Cycle in Plants
5
What Plants Need to Survive
  • The lives of plants revolve around the need for
  • Sunlight
  • Water minerals
  • Gas exchange
  • Movement of water nutrients throughout the
    plant body

6
Evolution of Plants
  • The first plants evolved from an organism much
    like the multicellular green algae living today
  • However, the evolution of plants favored species
    that were more resistant to the drying rays of
    the sun

7
Overview of the Plant Kingdom
  • The great majority of plants alive today are
    angiosperms (the flowering plants)

Cone-bearing plants760 species
Ferns andtheir relatives11,000 species
Floweringplants235,000 species
Mosses andtheir relatives15,600 species
8
Figure 29.1 Some highlights of plant evolution
9
4 Main Groups of Land Plants
  • Bryophytes non-vascular plants
  • mosses, hornworts, and liverworts
  • Pteridophytes seedless vascular plants
  • Club moss, horsetails, ferns
  • Gymnosperms vascular seeded cone-bearers
  • Ginkgos, cycads, gnetophytes, conifers
  • Angiosperms vascular seeded flowering plants
  • Monocots dicots any plant, tree, or shrub
    that flowers or fruits

10
The Nonvascular Plants - Bryophytes
  • Mosses and their relatives are generally called
    Bryophytes (nonvascular plants)
  • THEY HAVE NO ROOTS, STEMS, OR LEAVES
  • They have a life cycle that depends on water for
    reproduction
  • They lack vascular tissue and therefore must grow
    low to the ground
  • Groups of Bryophytes include
  • Mosses
  • Liverworts
  • Hornworts

11
Mosses
  • The most common bryophytes are mosses
  • They grow abundantly in areas with water
  • They can tolerate cold climates well
  • They do not have true roots, stems, or leaves
    instead, they have rhizoids (long, thin cells)
    that anchor them to the ground

12
Liverworts
  • Liverworts are Bryophytes that produce gametes in
    structures that look like little green umbrellas
    during sexual reproduction
  • Liverworts can also reproduce asexually by means
    of gemmae (small cup-like spheres that contain
    haploid cells)

SEXUAL
ASEXUAL
13
Hornworts
  • Hornworts are generally found only in soil that
    is damp nearly year round
  • Their gametophytes look like those of liverworts

14
Life Cycle of Mosshttp//www.sumanasinc.com/webco
ntent/animations/content/moss.html
15
Evolution of Plants
BRYOPHYTES
16
Three variations on gametophyte/sporophyte
relationships
17
Evolution of Vascular Tissue
  • What happened to allow plants to grow taller than
    mosses?
  • Fossil evidence shows that these plants contained
    vascular tissue tissue that is specialized to
    conduct water and nutrients through the body of a
    plant

18
Vascular Tissue
  • The first vascular plants had a new type of cell
    that was specialized to conduct water
  • Tracheids are the cells found in xylem, a form of
    tissue that carries water upward from the roots
    to every part of a plant
  • Phloem transports solutions of nutrients and
    carbohydrates produced by photosynthesis
  • Lignin is a substance produced by plants that
    makes cell walls rigid
  • Both forms of vascular tissue, xylem and phloem,
    can move fluids throughout the plant body against
    the force of gravity

19
Seedless Vascular Plants - Pteridophytes
  • Seedless vascular plants include
  • club mosses
  • horsetails
  • ferns
  • These plants HAVE true roots, leaves, and stems
  • ROOTS underground organs that absorb water
    minerals
  • LEAVES photosynthetic organs
  • STEMS supporting structures that connect roots
    and leaves

20
Club Mosses
  • These are small plants that live in moist
    woodlands and near streambeds and marshes
  • Lycopodium is the most common club moss today
    it looks like a mini pine tree

21
Horsetails
  • The only living genus of horsetails is Equisetum
  • Its leaves are arranged in distinctive whorls at
    joints along the stem

22
Ferns
  • Ferns are members of the phylum Pterophyta
  • They have creeping or underground stems called
    rhizomes and large leaves called fronds
  • They are most abundant in wet habitats water is
    required for reproduction!

frond
rhizome
roots
23
The Life Cycle of a Fern
Sporangia release spores. Most fern
species produce a single type of spore that gives
rise to a bisexual gametophyte.
The fern spore develops into a
small, photosynthetic gametophyte.
3
2
Although this illustration shows an egg and
sperm from the same gametophyte, a variety of
mechanisms promote cross-fertilization between
gametophytes.
Key
Haploid (n)
Diploid (2n)
Antheridium
Young gametophyte
Spore
MEIOSIS
Sporangium
Sperm
Archegonium
Mature sporophyte
Egg
New sporophyte
Zygote
Sporangium
FERTILIZATION
Sorus
On the underside of the sporophytes reprodu
ctive leaves are spots called sori. Each sorus is
a cluster of sporangia.
6
Fern sperm use flagella to swim from the
antheridia to eggs in the archegonia.
4
Gametophyte
A zygote develops into a new sporophyte,
and the young plant grows out from an
archegonium of its parent, the gametophyte.
5
Fiddlehead
Figure 29.12
24
Fern Sori
25
Evolution of Plants
Seedless Vascular Plants
BRYOPHYTES
26
Seed Plants
  • Over millions of years, plants with the ability
    to forms seeds became the most dominant group of
    photosynthetic organisms on land
  • Seed plants are divided into 2 groups
  • Gymnosperms bear seed directly on cones
  • Conifers
  • Cycads
  • Ginkos
  • Gnetophytes
  • Angiosperms flowering plants that bear their
    seeds within a layer of tissue that protects the
    seed
  • Grasses
  • Flowering trees and shrubs
  • All flowers

27
Reproduction Free From Water
  • Adaptations that allow seed plants to reproduce
    without water include
  • flowers or cones
  • the transfer of sperm by pollination
  • the protection of embryos in seeds

28
Cones Flowers
  • The gametophytes of seed plants grow and mature
    within sporophyte structures called cones or
    flowers
  • Cones are the seed-bearing structures of
    gymnosperms
  • Flowers are the seed-bearing structures of
    angiosperms

29
Pollen
  • In seed plants, the entire male gametophyte is
    contained in a tiny structure called a pollen
    grain
  • The pollen grain is carried to the female
    gametophyte by wind, insects, birds, small
    animals, or bats
  • The transfer of pollen from the male gametophyte
    to the female gametophyte is called pollination

30
Seeds
  • A seed is an embryo of a plant that is encased in
    a protective covering and surrounded by a food
    supply
  • An embryo is the early developmental stage of the
    sporophyte plant
  • The seed coat surrounds and protects the embryo
    and keeps the contents of the seed from drying
    out
  • After fertilization, the zygote contained within
    a seed grows into a tiny plant the embryo

31
The Structure of a Seed
Section 22-4
B
Seed embryo of plant that is wrapped in a
protective covering and surrounded by a food
supply.
A
Presence of a seed allows for reproduction
free of water.
32
Gymnosperms Cone Bearers
  • Gymnosperms include
  • Gnetophytes
  • Cycads
  • Ginkoes
  • Conifers

33
Gnetophytes
  • Welwitschia, an inhabitant of the Namibian desert
    in southwestern Africa, is one of the most
    remarkable gnetophytes
  • it has 2 huge leathery leaves which can grow
    continuously and spread across the ground

34
Cycads
  • Cycads are members of the phylum Cycadophyta
  • They are palm-like plants that reproduce with
    large cones
  • They can be found in all tropical and subtropical
    zones around the world

35
Ginkgoes
  • Today, the phylum Ginkgophyta contains only one
    living species, Ginkgo biloba (the maiden-hair
    tree)
  • Cultivated and protected in China by monks
  • The male species of this tree is often planted in
    urban settings in the US, where their resistance
    to air pollution make them popular shade trees
  • The female tree smells like vomit

36
Conifers
  • Conifers are by far the most common gymnosperms
  • The phylum Coniferophyta includes
  • Pines
  • Spruces
  • Firs
  • Cedars
  • Sequoias
  • Redwoods
  • Yews

37
Conifers
  • Conifers thrive in a wide variety of habitats
  • Mountains, sandy soil, cool, moist areas
  • Conifers have leaves that are long and thin
    which reduces the surface area from which water
    can be lost by evaporation
  • They also have a thick, waxy layer that covers
    their leaves again to reduce water loss
  • Most conifers are evergreens meaning they
    retain their leaves year round

38
The Life Cycle of a Pinehttp//bcs.whfreeman.com/
thelifewire/content/chp30/30020.html
39
Evolution of Plants
Gymnosperms
Seedless Vascular Plants
Bryophyta
40
Angiosperms Flowering Plants
  • Angiosperm means enclosed seed
  • Angiosperms have unique reproductive organs known
    as flowers
  • Flowers attract pollinators, which makes
    spreading seeds more efficient than the wind
    pollination of most gymnosperms
  • Flowers contain ovaries, which surround and
    protect the seeds
  • After pollination, the ovary develops into a
    fruit, which protects the seed and aids dispersal
  • Fruit is a thick wall of tissue and another
    reason why angiosperms are successful the fruit
    attracts herbivores which eat the fruit and
    then spread the seeds

41
The Angiosperm Life Cyclehttp//www.sumanasinc.co
m/webcontent/animations/content/angiosperm.html
Figure 30.10
42
Diversity of Angiosperms
  • Angiosperms are an incredibly diverse group that
    includes
  • Monocots and dicots
  • Woody and herbaceous plants
  • Annuals, biennials, and perennials

43
Monocots and Dicots
  • Monocots and dicots are named for the number of
    seed leaves, or cotyledons, in the plant embryo
  • Monocots have one seed leaf and dicots have two

44
Characteristics of Monocots Dicots
45
Woody Herbaceous Plants
  • Flowering plants can be subdivided into various
    groups according to the characteristics of their
    stems
  • Woody plants are made primarily of cells with
    thick walls that support the plant body
  • Trees
  • Shrubs
  • Vines
  • Herbaceous plants do not produce wood as they
    grow, but rather they have stems that are smooth
  • Dandelions
  • Zinnias
  • Petunias

46
Annuals, Biennials, Perennials
  • There are 3 categories of plant life spans
  • Annual flowering plants that complete a life
    cycle within one growing season
  • Marigolds, pansies, zinnias, cucumbers
  • Biennial flowering plants that complete their
    life cycle in 2 years
  • Primrose, parsley, celery
  • Perennial flowering plants that live for more
    than 2 years
  • Peonies, asparagus, grasses

47
Evolution of Plants
Vascular w/ Seeds Angiosperms
Vascular w/ Seeds Gymnosperms
Vascular Seedless Pterophyta
Non-Vascular Bryophytes
48
Roots, Stems, and Leaves
49
Structure of Seed Plants
  • The three principal organs of seed plants are
  • Roots
  • Absorb water and dissolved nutrients
  • Anchor plants to the ground
  • Hold plants upright
  • Stems
  • Supports body of plant
  • Transports nutrients
  • Leaves
  • Photosynthetic organs

50
Tissue Systems
  • Plants consist of four tissue systems
  • Meristematic tissue
  • Dermal tissue
  • Vascular tissue
  • Ground tissue

51
Meristematic Tissue
  • Is found only in the tips of shoots and roots
  • called apical meristem
  • Is the only plant tissue that produces new cells
    by mitosis
  • Is responsible for the growth that takes place
    throughout the life of the plant

52
Dermal Tissue
  • The outer covering of a plant consists of dermal
    tissue that consists of a single layer of
    epidermal cells
  • The exposed outer surfaces of these cells are
    often covered with a thick, waxy layer called a
    cuticle that protects against water loss injury
  • The surfaces of some leaves also have trichomes
    tiny projections which help protect the leaf and
    also give it a fuzzy appearance
  • On the underside of the leaves, dermal tissue
    contains guard cells, which regulate water loss
    and gas exchange

53
Vascular Tissue
  • Plant vascular tissue includes xylem and phloem
  • Xylem water conducting tissue that consists of
    tracheids and vessel elements
  • Phloem food-conducting tissue that consists of
    sieve tube elements and companion cells

54
Ground Tissue
  • The cells that lie between dermal and vascular
    tissues make up the ground tissues in plants
  • In most plants, ground tissue consists of
    parenchyma (packed with chloroplasts) and may
    contain collenchyma or sclerenchyma (both of
    which function in plant support)

55
Types of Roots
  • The two main types of roots are
  • Taproots found mainly in dicots
  • This type of root grows long and thick
  • Fibrous roots found mainly in monocots
  • This type of root branches to such extent that no
    single roots grows larger than the rest

56
Root Structure
57
Root Structure
58
Root Growth
  • Roots grow in length as their apical meristem
    produces new cells near the root tip. These
    fragile new cells are protected by a tough root
    cap

59
Roots Functions
  • Roots anchor a plant in the ground and absorb
    water and dissolved nutrients from the soil
  • Most water minerals enter a plant through the
    tiny hairs on roots
  • Essential plant nutrients include
  • Nitrogen
  • Phosphorus
  • Potassium
  • Magnesium
  • Calcium

60
Stem Function
  • Stems have three important functions in plants
  • Production of leaves, branches, and flowers
  • Holding leaves up to sunlight
  • Transport substances between roots and leaves

61
Stem Structure
  • In most plants, stems contain distinct nodes,
    where leaves are attached, and internodes,
    regions between the nodes
  • Small buds are found where leaves attach to the
    nodes
  • Buds contain undeveloped tissue that can produce
    new stems and leaves

62
Monocot Dicot Stems
  • In monocots, vascular bundles are scattered
    throughout the stem
  • In dicots and most gymnosperms, vascular bundles
    are arranged in a cylinder

63
Formation of Bark
  • On most trees, bark includes all of the tissues
    outside the vascular cambium

64
Leaf Structure
  • The structure of a leaf is optimized for
    absorbing light and carrying out photosynthesis
  • Blades are flattened sections that collect
    sunlight
  • The petiole is a thin stalk that attaches the
    blade to the stem

blade
petiole
blade divided into many leaflets
single blade on petiole
65
Leaf Functions
  • Plants must take in all the materials needed for
    photosynthesis
  • Specialized cells on the underside of the leaf
    regulate this process
  • Leaves absorb light and carry out most of the
    photosynthesis in plants

6CO2 6H2O ? C6H12O6
6 O2 Carbon dioxide water
? sugar oxygen
66
Photosynthesis
  • Photosynthesis is the process whereby an organism
    use light energy to convert carbon dioxide and
    water into oxygen and high energy sugars

67
Leaf Function Photosynthesis
  • The bulk of most leaves are composed of mesophyll
    tissue
  • Mesophyll cells are packed with chloroplasts and
    carry out nearly all photosynthetic activity of
    the plant
  • The stomata are the pore-like openings that allow
    CO2 and O2 to diffuse in and out of the leaf
  • Each stomata consists of 2 guard cells, which
    control the opening and closing of stomata by
    responding to water pressure

68
Leaf Function Photosynthesis
69
Transpiration
  • Water is lost from leaves in a process called
    transpiration

70
Gas Exchange
  • Plants keep their stomata open just enough to
    allow photosynthesis to take place, but not so
    much that they lose an excess amount of water
  • Guard cells control the stomata and thus regulate
    the movement of gases into and out of the leaf
    tissues
  • In general, stomata are open during the daytime
    when photosynthesis is active and then close at
    night when open stomata would only lead to water
    loss

71
Water Transport
  • The combination of root pressure, capillary
    action, and transpiration provides enough force
    to move water through the xylem tissue of plants

72
Nutrient Transport
  • When nutrients are pumped into or removed from
    the phloem system, the change in concentration
    causes a movement of fluid in the same direction
  • As a result, phloem is able to move nutrients in
    either direction to meet the nutritional needs of
    the plant

source cells cells that produce sugars by
photosynthesis
sink cells cells that use or store sugars
73
Reproduction of Seed Plants
74
Alternation of Generations
  • All plants have a life cycle in which a diploid
    sporophyte generation alternates with a haploid
    gametophyte generation
  • Gametophyte plants produce male and female
    gametes (sperm and eggs)
  • When the gametes join, they form a zygote that
    begins the next sporophyte generation
  • The sporophyte is what we recognize as the plant
    and the gametophyte is hidden deep within tissues
    of the sporophyte plant (inside cones or flowers)

75
Alternation of Generations
  • An important trend in plant evolution is the
    reduction of the gametophyte and the increasing
    size of the sporophyte

76
Life Cycle of Gymnosperms
  • Reproduction in gymnosperms takes place in cones,
    which are produced by a mature sporophyte plant
  • Pollen cones are the male cones which produce the
    male gametophyte pollen (sperm)
  • Seed cones are the female cones which produce
    female gametophytes (eggs)
  • The gymnosperm life cycle takes 2 years to
    complete
  • It begins in the spring when the male cones
    release pollen carried by wind to fertilize the
    female eggs

77
Pollen Cones and Seed Cones
pollen cone (male)
seed cone (female)
78
Life Cycle of Gymnosperms
79
Angiosperm Anatomy
80
Structure of Flowers
  • Flowers are reproductive organs that are composed
    of four kinds of specialized leaves
  • Sepals
  • Petals
  • Stamens
  • Carples

81
Sepals and Petals
  • The outermost circle of floral parts contains the
    sepals, which in many plants are green and
    closely resemble ordinary leaves
  • Sepals enclose the bud before it opens and
    protect the flower while it is developing
  • Petals, often brightly colored, are used to
    attract insects and other pollinators

82
Stamens and Carpels
  • Within the ring of petals are the structures that
    produce male and female gametophytes
  • The male parts consist of an anther and a
    filament that together make up the stamen
  • The filament is a stalk that supports the anther,
    which produces pollen grains
  • The innermost floral parts are carpels, each of
    which forms an ovary (containing eggs)

83
Stamens Carpels
84
Life Cycle of Angiosperms
  • Reproduction in angiosperms takes place within
    the flower
  • Following pollination and fertilization, the
    seeds develop inside protective structures

85
Life Cycle of Angiosperms
86
Pollination
  • Most gymnosperms and some angiosperms are wind
    pollinated, whereas most angiosperms are
    pollinated by animals

87
Seed and Fruit Development
  • As angiosperms seeds mature, the ovary walls
    thicken to form a fruit that encloses the
    developing seed
  • A fruit is a ripened ovary that contains
    angiosperm seeds

88
Seed Dispersal
  • Seeds dispersed by animals are typically
    contained in fleshy, nutritious fruits
  • Seeds dispersed by wind or water are typically
    lightweight, allowing them to be carried in the
    air or to float on the surface of the water

89
Seed Dormancy
  • Many seeds enter a period of dormancy when they
    first mature during which the embryo is alive but
    not growing
  • Environmental factors such as temperature and
    moisture can cause a seed to end dormancy
  • Seed dormancy can allow seeds to germinate under
    ideal growth conditions (most seeds germinate in
    spring)

90
Seed Germination
  • Seed germination is the early growth stage of the
    plant embryo

91
Plant Responses Adaptations
92
Patterns of Plant Growth
  • All plants follow a highly regulated pattern of
    growth that continues throughout the life of the
    plant
  • This pattern of growth leads to distinct shapes
  • The secrets of plant growth are found in
    meristems regions of tissue that can produce
    cells that later develop into specialized tissue
  • Meristems are found only at the tips of growing
    stems and roots

93
Plant Hormones
  • A hormone is a substance that is produced in one
    part of an organism and affects another part of
    the same individual
  • Plant hormones are chemical substances that
    control a plants patterns of growth and
    development, and the plants responses to
    environmental conditions
  • The portion of an organism affected by a
    particular hormone is known as its target cell
  • Hormones are produced in apical meristems, young
    leaves, roots, and in growing flowers or fruits

94
Tropisms
  • The responses of plants to environmental stimuli
    are called tropisms
  • Gravitropism response to gravity
  • Phototropism response to sunlight
  • Thigmotropism response to touch

95
Phototropism
  • Phototropism is the tendency of a plant to grow
    toward a source of light

96
Auxins and Phototropism
  • Auxins are produced in the apical meristem and
    are transported downward into the rest of the
    plant
  • They stimulate cell elongation and regulate cell
    growth this is what causes a plant to grow in a
    direction toward sunlight
  • They are also responsible for gravitropism the
    tendency of a plant to grow in a direction in
    response to the force of gravity

97
Auxins Phototropism
A higher concentration of auxins accumulate in
shaded parts of the stem, causing the plant to
bend toward the sunlight
98
Auxins and Branching
  • Apical dominance is a phenomenon in which the
    closer a bud is to the tip of a stem, the more
    its growth is inhibited
  • As a stem grows in length, it produces lateral
    buds an area on the side of a stem that gives
    rise to side branches
  • If you want your plants to be fuller instead of
    taller, you can clip off the top of the plant
    thus removing the auxins and change the overall
    shape of the plant

99
Auxins and Apical Dominance
Section 25-1
Apical meristem
Lateral buds
Auxins produced in the apical meristeminhibit
the growth of lateral buds.
Apical meristem removed
Without the inhibiting effect of auxinsfrom the
apicial meristem, lateral budsproduce many
branches.
100
Cytokinins
  • Cytokinins are plant hormones that are produced
    in growing roots and in developing fruits and
    seeds
  • In plants, cytokinins stimulate cell division and
    the growth of lateral buds, and cause dormant
    seeds to sprout
  • Thy often produce effects opposite to auxins

101
Gibberellins
  • Plants can produce more than 60 similar compounds
    known as gibberellins growth promoting
    substances
  • Gibberellins produce dramatic increases in size,
    particularly in stems and fruit
  • They are responsible for the rapid early growth
    of many plants

102
Ethylene
  • In response to auxins, fruit tissues release
    small amounts of the hormone ethylene
  • Ethylene then stimulates fruits to ripen
  • Commercial fruits are often picked before they
    ripen and then given a controlled dose of
    ethylene just before delivery to the store to
    produce a ripe color quickly

103
Photoperiodism
  • Photoperiodism in plants is responsible for the
    timing of seasonal activities such as flowering
    and growth
  • Short-day plants a plant that flowers when
    daylight is short
  • Long-day plants a plant that flowers when days
    are long

104
Effect of Photoperiod on Flowering
105
Winter Dormancy
  • Dormancy is the period during which an organisms
    growth and activity decrease or stop
  • As cold weather approaches, deciduous plants turn
    off photosynthetic pathways, transport materials
    from leaves to roots, and seal leaves off from
    the rest of the plant
  • During winter, the continued presence of leaves
    would only be costly in terms of water loss

106
Adaptations of Aquatic Plants
  • To take in sufficient oxygen, many aquatic plants
    have tissues with large air-filled spaces through
    which oxygen can diffuse
  • The reproductive adaptations of aquatic plants
    include seeds that can float in water and delay
    germination until after periods of flooding

107
Adaptations of Desert Plants
  • Xerophytes, or desert plants, have evolved
    adaptations including extensive roots, reduced
    leaves, and thick stems that can store water
  • The seeds of most desert plants can remain
    dormant for years and germinate only when
    sufficient moisture is available

108
Nutritional Specialists
  • Plants that have specialized features for
    obtaining nutrients include
  • Carnivorous plants digest insects
  • Venus flytrap
  • Parasitic plants grow into tissues of their
    host plants
  • Mistletoe
  • Epiphytes grow directly on the bodies of other
    plants but are non-parasitic
  • Spanish moss

109
Chemical Defenses
  • Many plants defend themselves against insect
    attack by manufacturing compounds that have
    powerful effects on animals
  • Foxglove is poisonous when eaten
  • Nicotine is a natural insecticide
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