Post on 06-Sep-2020
plant reproductionchapter 38
Alternation of Generations
MEIOSIS
Mature
gametophyte
(n)
FERTILIZATION
Haploid (n)
Diploid (2n)
Spore
dispersal
Sporangium
Sporangium
Mature
sporophyte
(2n)
Sorus
Fiddlehead
Spore
(n)Young
gametophyte
ARCHEGONIUM
Egg
ANTHERIDIUM
Sperm
New
sporophyte
Gametophyte
Zygote
(2n)
• 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.• flowers reproduce asexually, and then facilitate sexual reproduction
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.
FERTILIZATION
POLLINATION
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
StamenAnther
Filament
Microsporangium
(pollen sac)
Microsporocyte (2n)
4 microspores (n)
Each of 4
microspores (n)
Malegametophyte
Generative
cell (n)
MEIOSIS
Ragweed
pollen
grain
Nucleus oftube cell (n)
MITOSIS
20 µm
75 µm
pollen• pollen production
• each diploid cell produces 4 microspores.• 4 microspores —> 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
Surviving
megaspore (n)
3 antipodal cells (n)
2 polar nuclei (n)
1 egg (n)
2 synergids (n)
Fema
le ga
meto
ph
yte
Ovule
Embryo
sac
Integuments (2n)
MITOSIS
100 µ
m
embryo sac• female gametophyte.
• ovule • inner tissue = nucellus • 1-2 protective layers = integuments
• 1 diploid cell in nucellus produces 4 haploid cells• 3 mitotic divisions• polar nuclei, egg, synergids, antipodals
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
sex of plants
monoecious
dioecious
hermaphroditic(flowers perfect)
(staminate and carpellate flowers)
(staminate flowers) (carpellate flowers)
incomplete
complete
imperfectperfect(hermaphroditic)
monoecious
dioecious
Stigma
Pollen tube
2 sperm
Style
Ovary
Ovule
Micropyle
Ovule
Polar nuclei
Egg
Synergid
2 sperm
Endosperm
nucleus (3n)
(2 polar nuclei
plus 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
CotyledonsRadicle
Seed coat
Seed coat
Endosperm
(a) Common garden bean, a eudicot with thick cotyledons
CotyledonsEpicotyl
HypocotylRadicle
(b) Castor bean, a eudicot with thin cotyledons
(c) Maize, a monocot
Scutellum(cotyledon)
Pericarp fusedwith seed coat
EndospermEpicotylHypocotyl
Coleoptile
RadicleColeorhiza
fruits• aggregate fruits
• made up of multiple ovaries • multiple fruits
• made up of more than one flower • achene
• dry pericarp
seed dispersal• benefits
• reduced competition between offspring for resources• decreased relatedness to potential mates• reduced competition between parent and offspring
• agents of seed dispersal
• pollination • coevolution - animal pollinators
pollination • many flowers are wind pollinated
• Asexual reproduction• vegetative reproduction
• no fusion of gametes.• Stems, leaves and roots.
• Apomixis - like parthenogenesis • fragmentation - stems, leaves• Roots can produce aerial shoots