alternation of generations plant n reproduction meiosis
TRANSCRIPT
plant reproduction
chapter 40
• Alternation of Generations
Haploid (n)
Diploid (2n)
MEIOSISSpore
dispersal
Sporangium
SporangiumMature
sporophyte(2n)
Sorus
Fiddlehead
Spore(n)
Younggametophyte
Maturegametophyte
(n)Archegonium
Egg
Antheridium
Sperm
FERTILIZATION
Newsporophyte
Gametophyte
Zygote(2n)
• Alternation of Generations• Sporophyte - diploid (2n) --> meiosis --> haploid spores• Gametophyte - haploid (n) --> mitosis --> haploid gametes
• fertilization restores diploid
• angiosperms• sporophyte larger and nutritionally independent
• produces spores by meiosis.• gametophyte gives rise to gametes by
mitosis.• pollen grain is the male gametophyte
• Sexual Reproduction? - the flower• produce gametophytes, attract gametophytes, and develop
seeds.• most plants reproduce sexually all reproduce asexually.
FERTILIZATION
Mitosis: division of the nucleus resulting in an exact copy of the
originalMeiosis: reduction in the number of
chromosomes.Gametogenesis: Formation of
sperm and eggs.Fertilization: fusion of sperm and
egg.
flowers• floral anatomy
• arranged in whorls or circles of structures:• Sepals, petals,
stamens, and carpels.
• receptacle• calyx • corolla Sepal
Petal
Receptacle
calyx
corolla
flowers• stamens
• filament and an anther• Each pollen grain
contains two cells; • germinative• vegetative
Stamen Anther
Filament
Microsporangium(pollen sac)
Microsporocyte (2n)
4 microspores (n)
Each of 4microspores (n)
Malegametophyte
Generativecell (n)
MEIOSIS
Ragweedpollengrain
Nucleus oftube cell (n)
MITOSIS
20 µm
75 µm
pollen• pollen production
• each diploid cell produces 4 microspores.
• 4 microspores divide mitotically to form 4 pollen grains • generative cell - sperm nuclei• vegetative cell - pollen tube
• surrounding pollen grain • outer layer - sporopollenin• inner layer - pectin surround
flowers• carpels (pistils) -
• style and stigma• ovary
• contains 1+ ovules.• ovule produces/contains
embryo sac.• embryo sac -
• 2 polar nuclei and 1 egg.
Stigma Carpel
Style
Ovary
Receptacle
Ovule
Megasporangium (2n)
Megasporocyte (2n)
Integuments (2n)
Micropyle
MEIOSIS
Survivingmegaspore (n)
3 antipodal cells (n)
2 polar nuclei (n)
1 egg (n)
2 synergids (n)
Female
gametophyte
Ovule
Embryosac
Integuments (2n)
MITOSIS
100
µm
embryo sac• Producing the female
gametophyte.• ovule
• inner tissue = nucellus • 1-2 protective layers =
integuments• 1 diploid cell in nucellus produces
4 haploid cells• polar nuclei - 2 nuclei remain in
the center of the large cell • mature structure
• female gametophyte or megagametophyte or embryo sac.
floral structure• Variations
• Arrangement of floral parts: spiral or whorled.
• Floral whorls:• Complete
• carpels and stamens:• Perfect• Imperfect
• carpellate or staminate• Sex of the plants:
• Hermaphroditic• monoecious• dioecious
• "Oikos" = house
Stigma
Pollen tube
2 sperm
Style
Ovary
Ovule
Micropyle
Ovule
Polar nuclei
Egg
Synergid
2 sperm
Endospermnucleus (3n)
(2 polar nucleiplus sperm)
Zygote (2n)(egg plus sperm)
Egg
Pollen grain
Polar nuclei
fertilization• fertilization
• Some can self-fertilize• Other cannot self-fertilize -- self-
incompatible• Fertilization
• pollen tube• generative cell divides to form
2 sperm nuclei• endosperm• ovule --> seed• ovary --> fruit
seed development• Endosperm
• 3N nucleus • mitosis
• large multinucleate cell.• cells develop cell wall
• endosperm becomes solid.• mature embryo
• cotyledons • radicle• hypocotyl• epicotyl• plumules
Epicotyl
Hypocotyl
Cotyledons
Radicle
Seed coat
Seed coat
Endosperm
(a) Common garden bean, a eudicot with thick cotyledons
Cotyledons
Epicotyl
Hypocotyl
Radicle
(b) Castor bean, a eudicot with thin cotyledons
(c) Maize, a monocot
Scutellum(cotyledon)
Pericarp fusedwith seed coat
EndospermEpicotyl
Hypocotyl
Coleoptile
RadicleColeorhiza
• Fruits • e.g. apples, oranges,, peaches,
watermelon, cucumber, tomato, peppers
• aggregate fruits • made up of multiple ovaries
• multiple fruits • made up of more than one
flower
• Seed dispersal -- • reduced competition between offspring for resources• decreased relatedness to potential mates• reduced competition between parent and offspring
• agents of seed dispersal --• could eat the fruit (fish, mammals, birds, etc...)• seeds may be transported long distances after being ingested. • seeds may hitch a ride on an organism
pollination• pollination
• coevolution - animal pollinators