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