2005-2006 AP Biology

Chapter 38.

Plant Reproduction

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Animal vs. Plant life cycle

multicellular2n

multicellularsporophyte

2n

multicellulargametophyte

1n

unicellulargametes

1n

spores2n

gametes1n

Animal Plant

alternation of generations

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diploid

Alternation of generations

haploid

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Alternation of generations

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Alternation of generations Fern sporophyte

leafy plant you are familiar with

Fern spores haploid cells that will sprout into

gametophyte

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Alternation of generations Fern gametophyte

small diploid plant which produces gametes

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Alternation of generations Archegonium

female gamete-producing structure produces a single egg cell in a

vase-shaped organ

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Alternation of generations Antheridia

male gamete-producing structure produces many sperm cells that are

released to the environment

flagella = swimming sperm

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Evolutionary trends Alternation of generations

dominant haploid plant bryophytes - mosses

dominant diploid plant pteridophytes - ferns gymnosperm - conifers angiosperm - flowering plants

Evolutionary advantage? reduction of gametophyte protects delicate

egg & embryo in protective sporophyte

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Moss sporophytes

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Reduction of gametophyte

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Gametophytes of seed plants

male gametophyte pollen in male cone

female gametophyte develops in female

cone

seed naked in cone

male gametophyte pollen in anthers of

flower

female gametophyte develops in ovaries

of flower

seed protected in ovary ovary wall can

develop into fruit

Gymnosperm Angiosperm

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Gymnosperm life cyclefemale

gametophytein cone

malegametophyte

in pollen

sporophytein seed

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Angiosperm life cycle

femalegametophyte

in ovary

malegametophyte

in pollen

sporophytein seed

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Flowers

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Flower Modified shoot

with 4 rings of modified leaves sepals petals stamens

male carpals

female

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pistil

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Male & female parts of flower

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Parts of flower Male

stamens = male reproductive organs stamens have stalks (filament) &

terminal anthers which carry pollen sacs

pollen sacs produce pollen pollen grain = gametophyte

sperm-producing structure

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Parts of flower Female

carpels = female reproductive organs ovary at the base slender neck = style within the ovary are 1 or more ovules within ovules are embryo sacs female gametophyte = embryo sac

egg-producing structure

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Fertilization Pollination

pollen released from anthers is carried by wind or animals to land on stigma

pollen grain produces a pollen tube pollen tube grows down style into ovary &

discharges 2 sperm into the embryo sac 1 sperm fertilizes egg = zygote zygote develops into embryo

ovule develops into a seed ovary develops into a fruit containing

1 or more seeds

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Preventing self-pollination Various mechanisms

stamens & carpels may mature at different times arranged so that animal pollinator won’t transfer

pollen from anthers to stigma of same flowerbiochemical self-incompatibility = block pollen

tube growth

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Preventing self-fertilization

This model involves the “S” allele Pollen (male) with same allele cannot

germinate on stigma (female) Matching alleles interact & inhibit RNA

production

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Biochemical mechanism Preventing self-fertilization

pollen produces signal → receptor → kinase → signal transduction path → effector protein produced → block pollen tube growth

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Fertilization in flowering plants

Double fertilization 2 sperm from pollen

1 sperm fertilizes egg = diploid zygote

1 sperm fuses with 2 polar nuclei to form 3n endosperm

endosperm = food tissue in seed

coconut milk grains

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Pollen tube growth

grow down style to ovule path for sperm nuclei

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Fertilization in flowering plants

Development of the new sporophyte

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Plant embryo

endosperm

cotyledons

embryo

seed coat

ovary wall

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Seed Anatomy Sporophyte in seed

Sets stage for structure of plant Roots Shoots Leaves

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Germination How does the dicot differ from the

monocot?

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Mobilization of nutrients Seed germination

1. seed imbibes water 2. gibberellin release signals aleurone layer 3. amylase is released which hydrolyzes starch 4. sugar is absorbed by embryo

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Fruit Fruit is a mature ovary

seeds develop from ovules wall of ovary thickens to form fruit fruits protect dormant seeds &

aid in their dispersal

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Fruit development

Pea (legume)

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Fruit development Peach (stone fruit or drupe)

1 flower : 1 carpel : 1 ovary : 1 seed

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Fruit development Apple (pome fruit)

1 flower : 5 carpels : many ovaries : many seeds

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Fruit development Citrus fruit (berry)

1 flower : many carpels : many ovaries : many seeds

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Fruit development Raspberry (aggregate fruit)

1 flower : many ovaries : many seeds

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Reproduction in angiosperm Sporophyte plant produces unique

reproductive structure = the flower male gametophyte = pollen grain

develop within anthers of flower female gametophyte = embryo sac

develop within ovaries of flower pollination by wind or animals brings pollen

grain to female gametophyte fertilization takes place within ovary

double fertilization = embryo & endosperm seeds contain sporophyte embryo

development of seeds in ovary ovary develops into fruit around the seed

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Coevolution of plants & animals Angiosperms & animals have shaped

one another’s evolution Natural selection reinforced the

interactions because they improved the reproductive success of both partners

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Seed dispersal Plants produce enormous numbers of seeds to

compensate for low survival rate a lot of genetic variation for natural selection to screen