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Chapter 23
Main Ideas:
1. Like all plants, the life cycles of mosses, ferns, and conifers include alternation
of generations.
2. Flowers are the reproductive structures of anthophytes.
3. In anthophytes, seeds and fruits can develop from flowers after fertilization.
I. Reproduction in Plants
A. Asexual reproduction
1. vegetative reproductionnew plants grow from parts of an
existing plant
2. most plants can reproduce w/vegetative reproduction
B. Alternation of Generations
1. consists of a sporophyte stage & a gametophyte stage
2. all cells of a sporophyte are diploid
3. some cells can undergo meiosis to form haploid spores
4. some cells can undergo cell division to form haploid gametophytes
5. when a sperm fertilizes an egg, a diploid zygote is formed=sexual
reproduction & it’s the 1st cell of the sporophyte stage
6. zygote can undergo cell division & form an embryo sporophyte
7. if it matures, the cycle begins againbasic pattern for most plants
C. Life Cycle of Mosses
1. gametophyte stage is the dominant stage
2. haploid spore can germinate & form a protonemasmall green filament of cells
that develop into gametophytes(male & female)
3. if a film of water is present motile sperm(from antheridium)
travels/swims in a film of H2O to an egg(in archegonium)
a.chemotaxis–>movement of a cell/organism in response to a
particular chemical
4. fertilization occurs producing a diploid zygote
5. zygote divides forming a sporophytehas a stalk & a capsule
6. sporophyte remains attached to the gametophyteH2O &
nutrients
7. cells i/s the capsule undergo meiosisproduce haploid spores
8. capsule ruptures releasing spores & if a spore germinates the cycle begins
again.
C. Life Cycle of Ferns
1. sporophyte stage is the dominant stage
2. remember that sori are on the underside of fronds & sori are clusters of
sporangia
3. meiosis occurs in the sporangiahaploid spores
4. sporangia release the spores
5. spore germinates forming a prothallus–>heart-shaped gametophyte–>has
both antheridium & archegonium
6. again the sperm must swim through a film of water to reach the egg
7. fertilization occurs producing a diploid zygotewhich develops into a
sporophyte
8. initially sporophyte depends on the gametophyte for nutrients, but once the
sporophyte produces fronds it can photosynthesize
9. prothallus will die & the sporophyte will produce a rhizome & then roots &
fronds will develop
10. once sporangia appear on the fronds, the cycle can begin again
D. Life Cycle of Conifers
1. conifers are heterosporous–>produce 2 types of spores that dev into male &
female gametophytes
1. sporophyte stage is the dominant stage
2. most conifers have male & female cones on separate branches
3. female cones have 2 ovules at the base of ea scale of each cone w/I ea ovule
meiosis of a cell prod 4 megaspores
a. 3 megaspores disintegrate
b. remaining megaspore undergoes mitosis & becomes the female
gametophyte
c. ea gametophyte consists of 2-6 archegonia
d. ea. archegonia contains an egg
4. male cones also have sporangia that produce microspores
a. microspores become pollen grainsmale gametophyte
5. pollinationtransfer of pollen grains from the male to the female cone
a. pollen grains enter the female cone through the micropyle which is the
opening in the ovule
b. fertilization does not occur for at least 1 yrthe male & female
gametophytes mature during this time
c. as the gametes mature, the pollen grain releases a sperm nucleus through a
pollen tube to the egg(fertilization)
d. zygote forms & is dependent on the female gametophyte for nutrients
II. Flowers
A. Flower structure
1. petalscolorful structures at the top of a stem that can
both attract pollinators & provide them w/a landing platform
2. flower stempeduncle
3. sepalsleaflike & encircle peduncle below the petals; protect the flower bud
4. stameni/s petals & is the male reproductive structure
5. antherat tip of stamen & produces pollen(sperm)
6. pistilattached to top of the peduncle & is the female
reproductive structure
a. 3 parts: the stigma, style, & ovary
b. ovary is the bottom part of the pistil
7. if a flower has sepals, petals, stamens, & pistils=complete
B. Pollination mechanisms
1. self pollination & cross pollination
a. self pollinating plants can pollinate themselves/another flower on the same
plant
b. cross pollinated plants receive pollen from another plant
2. animal pollination
a. when animals move from plant-plant they carry pollen from 1
plant to another
b. plants have colors & scents that attract animals
3. wind pollination
a. plants that lack showy flowers/fragrant scents are us. wind
pollinated
b. these plants prod. large amts of lightweight pollen
C. Photoperiodism
1. the amount of light present effects both growth & flower production
2. photoperiodism–>the flowering response that’s influenced by the
number of hrs of uninterrupted darkness
a. the beginning of flower dev for ea plant species is a response to a range
in the number of hrs of darkness=its critical period
b. short-day plant-->flowers when exposed to a number of hrs of darkness
that is greater than its critical period
c. long-day plant-->flowers when the number of hrs of
darkness is less than its critical period
d. intermediate-day plant–>flowers as long as the number of
hrs of darkness is neither too great/too few
e. day-neutral plant-->flowers over a range in the number of
hrs of darkness
III. Flowering Plants
A. Life cycle
1. anthophytes–>most diverse & widespread grp of plants
a. unique b/c they have flowers
b. dominant sporophyte generation
2. gametophyte development
a. in anthophytes dev of male & female gametophytes begins in
an undeveloped flower
b. anthophytes are heterosporous–>pistil prod megaspores & the
stamens prod microspores
c. female gametophyte
1. a specialized cell i/s the ovule of the pistil’s ovary
undergoes meiosis–>prod 4 megaspores
2. 3 of the 4 megaspores disintegrate
3. the nucleus of the functional megaspore undergoes mitosis
4. result=large cell w/8 nuclei
5. the nuclei migrate3 to ea end of the cell & 2 in the middle
6. polar nuclei-->2 nuclei in the center of the ovule
7. 1 of the 3 nuclei closest to the micropyle becomes the egg
d. male gametophyte
1. forms in the anther as microspores are produced by meiosis in the
pollen sac
2. each microspore goes through mitosis & a thick wall surrounds the
nuclei-->immature male gametophyte(pollen grain)
3. within the male gametophyte are the tube nucleus & the
generative nucleus
4. when the gamete is mature the anther will split open
B. Results of Reproduction
1. embryo contained in a seed is the next sporophyte generation
2. seed development begins w/fertilization
3. endospermprovides nourishment for the embryo & is the result of cell divisions
4. the o/s layer of the ovule becomes the seed coatprotection
5. as seeds develop, ovary enlarges & becomes the fruit
6. seeds are fully formed at maturity, but still have to germinate
7. seeds will germinate only when conditions are favorable, some can wait long
periods
8. dormancy-->period of inactivity/no growth in a seed
9. germination-->the process when the embryo in the seed starts to grow
a. water & temperature play major roles in seed germination
b. 1st part of the embryo to appear is called the radicle
c. portion of the stem nearest seed-->hypocotyl