Transcript Chapter 22: Introduction to Plants

Sections 1-4
 Organisms in Kingdom
Plantae are eukaryotes
that have cell walls
containing cellulose and
carry out photosynthesis
using chlorophyll a and b
 Sunlight –photosynthesis
 Leaves broad and flat, arranged on stem to maximize
light absorption
 Gas exchange –oxygen for cellular respiration, carbon
dioxide for photosynthesis
 Gases exchanged with atmosphere/soil without losing
too much water
 Water and minerals – structures limit water loss, faster
uptake of water from soil; some have specialized
tissues to carry water/nutrients
 Ancestors of land plants water-dwellers, similar to
green algae
 Simpler, have cell walls, identical photosynthetic
pigments, similar reproductive cycles to plants
 So genetically similar they should be plants
 First land plants had a water problem – grew close to
ground in damp places, dependent on water for life
cycle
 Several groups evolved – one line lead to mosses,
another to ferns, cone-bearing plants and flowering
plants
 Five major groups based on embryo formation,
specialized water-conducting tissues, seeds, and
flowers
 Alternation of generations – shifting between a diploid
(2n) phase and a haploid (n) phase
 Multicellular diploid called sporophyte produces
haploid spores by meiosis
 Spores grow into multicellular haploids called
gametophytes
 Gametophytes produce gametes – egg and sperm
 Zygote forms through fertilization, which develops
into new sporophyte
 Reduction in gametophyte size, increase in sporophyte
size
 “Algae” refers to any photosynthetic eukaryote other
than a land plant
 Classified in group of seedless plants
 Mostly aquatic (fresh and salt) or on land in
damp/moist areas
 Absorb moisture and nutrients directly from
surroundings – no specialized tissues
 Many alternate between haploid and diploid forms,
but not necessarily with each generation
 Example: Chlamydomonas
 Favorable conditions – haploid cell reproduces asexually
by mitosis
 Unfavorable conditions – switches to sexual
reproduction
 Cells fuse to form zygote (sporophyte) with thick
protective covering which will grow when conditions
improve, divide by meiosis into 4 haploids
 Green algae can form colonies
 Spirogyra form filaments
 Volvox form colonies of up to 5000 – shows some
specialization
 Mosses have protective
coating that makes them
resistant to drying,
rhizoids to anchor them
to soil and absorb water
and minerals
 Group including mosses, liverworts, and hornworts
 Specialized reproductive organs enclosed by
nonreproductive cells
 Higher degree of cell specialization
 Among first land plants
 Small because they do not make lignin, which is used
to harden cell walls, and do not have vascular tissues
 Alternation of generations
 Gametophyte dominant, sporophyte depends on it
 Produce sperm cells with flagella for swimming so
water must be present at some point in year
 When a moss spore lands in a moist place, it grows
into a gametophyte
 Forms rhizoids that grow into ground, shoots that
grow into air
 Gametes formed at tips of gametophyte
 Eggs produced in archegonia
 Sperm produced in antheridia
 Egg/sperm fuse to form diploid zygote – beginning of
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sporophyte stage
Sporophyte grows within gametophyte – dependent
Eventually grows out of gametophyte, develops stalk
ending in sporangium
Sporangium produces haploid spores by meiosis
Spores released
 Plants growing high above ground appeared ~ 420 mya
 Had vascular tissues – carry water and nutrients
more efficiently than bryophytes
 Vascular plants called tracheophytes because of
tracheids – water-conducting cells that are hollow,
tube-like, cell walls strengthened with lignin
 Tracheids arranges end to end make up xylem, the
tissue that carries water upwards from the roots – pits
between tracheids increase water movement
 Phloem is the other vascular tissue – transports
solutions of nutrients and photosynthetic products
 Three phyla, commonly known as club mosses,
horsetails, and ferns (most)
 Ferns have vascular tissues, strong roots, rhizomes
(stems underground), fronds
 Thrive with little light
 Wet environments
 Spores produced by the sporophyte grow into thin,
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heart-shaped haploid gametophytes (independent)
Sperm/eggs produced on gametophytes in antheridia
and archegonia
Sperm swim to eggs – water needed
Zygote develops into a new sporophyte plant
(dominant)
Haploid spores develop on the undersides of the
fronds in sporangia
 Seeds contain tiny living plant ready to sprout
 Plant embryo and a food supply – diploid, early stage
sporophyte
 Common ancestor for all modern seed plants
 Ability to survive on dry land – developed adaptations
 Cones and flowers
 Pollen
 Seeds
 In seed plants, male and female gametophytes
grow/mature within sporophyte – in cones or flowers
 Gymnosperms (naked seeds – cone-bearing plants)
bear seeds on scales of cones
 Angiosperms (flowering plants) bear seeds in flowers
within protective tissue
 Male gametophyte is contained in a pollen grain
 Carried to the female reproductive structure by wind
or animals
 The transfer of pollen from the male reproductive
structure to the female reproductive structure is called
pollination
 After fertilization, the zygote within seed grows into a
tiny plant (sporophyte embryo)
 A tough seed coat surrounds and protects the
embryo, keeps it from drying out
 The embryo begins to grow when conditions are right
 Uses nutrients from stored food supply until it can
carry out photosynthesis on its own
 Seeds exposed on scaled within cones
 Reproduction occurs in cones produced by mature
sporophyte
 Pollen cones (male) produce pollen grains (male
gametophyte)
 One haploid nucleus within pollen grain later divides to
produce 2 sperm nuclei
 Seed cones (female) produce female gametophytes
 Scales contain 2 ovules , where meiosis produces haploid
cells that develop into female gametophytes
 Each gametophyte contains multiple egg cells
 In spring, pollen cones release pollen grains which are
carried by wind
 Female cones secrete sticky substance to trap pollen
which is pulled inside the ovule
 Fertilization without open water
 Pollen grains landing near ovules split open, grow a
structure called a pollen tube containing 2 haploid
sperm nuclei
 Once the pollen tube reaches the female gametophyte,
one sperm nucleus disintegrates; the other fertilizes
the egg
 Zygote develops into embryo
 Seed encases embryo, dispersed by wind
 Angiosperms most abundant plants
 Most recent to evolve
 Develop flowers, which contain ovaries to surround
and protect seeds
 Flowers attract pollinators
 More efficient than relying on wind
 After pollination, ovary develops into a fruit,
containing at least one mature embryo
 Wall of fruit helps distribute seeds – animals eat, seeds
go through digestive system
 Increases range
 Used to be classified by numbers of leaves in their
embryos – cotyledons
 Monocots – one cotyledon
 Dicots – two cotyledons
 Now, monocots single group, dicots in several
 Differences in stems
 Woody plants are made of cells with thick cell walls
that support the plant body
 Herbaceous plants have stems that are smooth and
nonwoody