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Honors Biology

Chapter 10Plant Reproduction

John Regan

Wendy Vermillion

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Insert Ch opening photo

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10.1 Sexual reproduction in flowering plants

• Alternation of generations– Flowering plants have 2 multicellular stages in their life cycle

• Diploid sporophyte stage alternates with the haploid gametophyte stage

• The sporophyte produces haploid spores by meiosis– spores develop into gameotphytes

• The gametophyte produces gametes by mitosis– after fertilization the cycle returns to the sporophyte

stage

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Alternation of generations in flowering plants

• Fig 10.1

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Sexual reproduction in flowering plants cont’d.

• Overview of plant life cycle– Flower- reproductive structure of angiosperms

– The diploid sporophyte is the predominant stage

• The sporophyte bears flowers; flowers produce 2 spore types

– Megaspore-develops into female gametophyte-embryo sac

– Microspore-develops into the male gametophyte-pollen grain

• Pollination-deposition of pollen onto female flower parts

– Pollen grain contains 2 sperm cells; pollen grain digests a tube that the sperm swim through to reach the embryo sac

– Embryo sac contains an ovum; fertilization occurs and an embryo develops

– Embryo sac develops into a seed which can be enclosed in a fruit- aids dispersal

– When seed germinates a new sporophyte develops

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Sexual reproduction in flowering plants cont’d.

• Flowers– Typical flower has 4 whorls of modified leaves attached to a

receptacle

1. Sepals-green leaflike structures that protect bud

2. Petals-attract pollinators

3. Stamens-male structures– consist of anthers and filaments

4. Carpel-female structure– consists of a stigma, style, and an ovary

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Anatomy of a flower

• Fig 10.2

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Sexual reproduction in flowering plants cont’d.

• Flowers, cont’d.– A complete flower has all parts-petals, sepals, stamens, and carpels

flower can have a single carpel or multiple

• Each carpel contains the ovules

– Bisexual (perfect) flowers- have both stamens and carpels– Unisexual (imperfect) flowers-have either stamens or carpels

• Dioecious plants- have either staminate or carpellate flowers on one plant

• Monoecious plants- have both staminate and carpellate flowers on the same plant

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Sexual reproduction in flowering plants cont’d.

• Production of the male gametophyte– Microspores produced in anthers– Microspore mother cell divides by meiosis to produce 4 haploid

microspores– In each, the haploid nucleus divides mitotically and then an

unequal cytokinesis occurs– the 2 cells are enclosed in a pollen grain; the larger is the tube

cell, the smaller is a sperm cell– The sperm cell divides again to form 2 sperm

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Life cycle of a flowering plant

• Fig 10.5

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Sexual reproduction in flowering plants cont’d.

• Pollination– Transfer of pollen from an anther to a receptive stigma of a

carpel– Pollen grain contains 2 cells- generative cell, tube cell

• Tube cell grows into pollen tube

• Generative cell ÷ into 2 sperm cells

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Sexual reproduction in flowering plants cont’d.

• Production of the female gametophyte– Embryo sac ÷3x into 8 nuclei as the functional nucleus divides 4

times by mitosis– One small cell becomes the egg

– Double fertilization- one sperm fertilizes the egg and it becomes the embryo(2n); the other fertilizes the central cell to form the triploid (3n) endoderm

– Endosperm becomes the food source for the embryo inside the seed

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Pollination

• Fig 10.6

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Development of a eudicot embryo

• Fig 10.7

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Growth and development cont’d.

• Development of the eudicot embryo, cont’d.– Embryo changes from a ball of cells to a heart-shape– Cotyledons-embryonic leaves appear– Embryo next becomes torpedo-shaped, and the root tip and

shoot tip become visible– Epicotyl-portion of embryo between the cotyledons that

contributes to shoot development– Hypocotyl-portion below the cotyledons that contributes to stem

development– Radicle-contributes to root development

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Growth and development cont’d.

• Monocots versus eudicots– Eudicots have 2 cotyledons, monocots have one– In monocots, the cotyledons do not store food

• cotyledon absorbs food from endosperm and passes it to the embryo

• In eudicots the cotyledons store the nutrients the embryo uses

– Endosperm disappears as the cotyledons take up the nutrients

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Growth and development cont’d.

• seed dispersal- the function of fruits is to disperse seeds– seed dispersal

• Attach to fur of animals or clothing Ex: burrs

• Passed in feces of bird or mammals Ex: berries

• Dispersed when buried or stored by animals Ex: acorns

• Wind-winged or plumed seeds Ex: maple seeds

• Float-coconut

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Growth and development cont’d.

• Germination of seeds– Germinate in response to specific environmental conditions– Requires both inhibitor and stimulator substances– Mechanical stimuli also may be required in some– Uptake of water causes seed coat to burst

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Common garden bean seed structure and germination

• Fig 10.9

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Growth and development cont’d.

• Eudicot versus monocot germination– Eudicots

• Cotyledons shrivel and degrade

• Epicotyl produces immature leaves- plumule

• young shoot is hook-shaped as it emerges through the soil

– Monocots• Cotyledon does not have a storage function

• Plumule and radicle are protected by sheaths called the coleoptile and the coleorhiza respectively

• Plumule and radicle burst through the sheaths when germination occurs

• Young shoot is straight, not hooked

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Corn kernal structure and germination

• Fig 10.10