Chapter 24: Plant Reproduction and response

Sections 1-2

Reproductive structures made of specialized leaves

Sepals (outermost) enclose bud before it opens, protect flower during development

Petals just inside sepals – colors, shape, numbers attract pollinators

Stamens – male leaves Stalk called filament Anther at the end – produces pollen grains

(male gametophyte Carpels – female leaves – shelter female

gametophytes and seeds Broad base forms ovary, containing one or

more ovules where female gametophytes produced

Narrow stalk called style with sticky stigma at the top to catch pollen

Sometimes called pistil

Alternation of generations – male/female gametophytes live within sporophyte

Male gametophytes (pollen grains) develop within anthers Meiosis produces 4 haploid cells, each

undergoing mitosis to produce 2 haploid nuclei per pollen grain

Surrounded by thick wall for protection

Female gametophytes develop within carpel Ovules (future seeds) protected by ovary

(future fruit) Single diploid cell goes through meiosis to

produce 4 haploid cells 3 disintegrate, one undergoes mitosis to

produce 8 nuclei Surrounded my embryo sac – within ovule

(female gametophyte) Cell walls form around 6 of the nuclei

Female gametophyte con’t One nucleus is the nucleus of the egg If fertilization occurs, egg with fuse with male

gamete Zygote grows into new sporophyte

Most angiosperms pollinated by animals Wind pollinated plants (oak trees) rely on

good weather, lots of pollen Animal pollinated plants have bright

flowers, sweet nectar Pollinator’s bodies adapted to reach

nectar Insect pollination a win-win

If a pollen grain lands on the stigma of the same species, pollen tube begins to grow

One cell within pollen grain becomes pollen tube, the other divides into 2 sperm cells (“generative” cell)

Pollen tube grows into style to ovule

Double fertilization takes place in embryo sac One sperm nucleus fuses with egg nucleus,

diploid zygote will grow into embryo Other sperm nucleus fuses with 2 polar nuclei

in embryo sac to form triploid cell (3n) This grows into endosperm – nourishes

seedling Saves resources

Asexual reproduction in flowering plants – produce identical offspring by mitosis

New plants can grow from roots, stems, leaves, plantlets (potatoes, strawberries, cacti)

Very quick, plants can take over favorable environments

No genetic recombination

Use cuttings - length of stem cut and planted in soil to encourage root formation

Use grafting - a piece of stem or a lateral bud is cut from the parent plant and attached to another plant

The term “fruit” refers to a matured angiosperm ovary, usually containing seeds

Nutrients support development of growing embryo

Ovary wall thickens – can be fleshy, tough/dry

Dispersal by animals through eating or carrying Have tough coating and can pass through the

digestive system, sprout in feces Dry fruits catch on fur

Dispersal by wind/water Lightweight fruits carried by wind (dandelion)

or float (coconut)

After they mature, some seeds remain dormant where the embryo is alive and not growing before they germinate

Germination is the resumption of growth Affected by temperature, moisture

Before germination, seeds absorb water, tissues swell, seed coat cracks open

Young root emerges first, then the shoot Cotyledons are the first leaves – store

nutrients and transfer them to growing embryo

Monocots – leaf usually remains underground, shoot protected by sheath

Dicots – no sheath – end of shoot bends into a hook, straightens in sun

Long distance dispersal

Germination only under ideal growth conditions