Reproduction in Flowering Plants

Types of reproduction

Asexual – the production of clones; no other plant necessary (« I can do it own my own, thanks! »)

Sexual – gametophytes formed; pollination is necessary

Asexual reproduction• Also called vegetative reproduction

• Asexual reproduction occurs in various ways:

- production of rhizomes (modified stems);

could be ‘eyes’ on potatoes

- from fragments of roots or shoots (e.g dandelions, quack grass)

Costs and benefits

Benefits?

- Advantageous traits will be passed on

- Less energy than sexual reproduction

- Faster

- Only one plant needed

- Young plantelets are more robust and survive better

One big cost…..

No diversity in genetic clones – if the environment changes quickly or if there is a disease or insect outbreak, the entire population will die….

Human uses of asexual plant reproduction

Gardeners, nurseries Reproducing copies of plants with desirable characteristics using methods such as:

1) Stem cutting – in water or soil where new roots will form

2) Grafting - branch from plant with desirable features is attached to stem of other plant (common

in orchards)

3) Tissue culture – piece of plant in test tube

with growth media

Sexual reproduction

The product of sexual reproduction (in flowering plants)

is a seed.

Seed function:

- to protect and nourish the embryo

- to move the embryo to a new location

Costs and benefits

Benefits:

- High level of genetic diversity

- Seeds are dispersed; less competition for resources

- Seeds can remains dormant for a long time

Cost?

- Lots of energy – specialized structures

Sexual reproduction

Similar in angiosperms and gymnosperms

- Meiosis forms gametophytes – pollen grain and ovule

- Pollen grain is carried to ovule (in the process of pollination) where fertilization occurs

- Embryo grows by mitosis

- Germination occurs

It starts with pollination

• Pollination happens by wind only in gymnosperms and both wind & animals in angiosperms (pollinators)

• Conifers have both male and female cones on the same tree

• Pollen grain must land close to an ovule on a female cone (most don’t), then fertilization occurs (can take about 13 months)

Angiosperm pollination

• Animal-pollinated flowers are very showy and colourful while wind-pollinated flowers can barely be noticeable (maple tree)

• Some plants can have both female and male parts (e.g. corn), can self-pollinate

• Some plants only have male or female flowers (must cross-pollinate)

From Pollen to Ovary

The pollen grain grows a pollen tube

pollen tube

ovary containing ovule

towards the ovary, which contains the ovule and egg cell (female gamete).

Fertilisation takes place when the ‘sperm’ nucleus from the pollen grain enters the egg cell. The resulting zygote eventually turns into a seed.

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pollen tube with pollen grain nucleus

ovuleEmbryo grows inside the ovule.

egg cell

Zygote to Embryo

The zygote will grow through the process of mitosis to form an embryo (The ovule is now called a seed and is covered by a protective seed coat.)

seed coat

food supply (cotyledon)

embryo

seed

Fruit Formation

• Some plants produce fruit containing seeds.

• Fruit: Mature ovary• Tissue surrounding the

embryo develops into fruit.

• When the fruit is fully developed it drops off the plant, or is carried away by an animal.

• When fruit decomposes it releases the seed and germination can occur.

Germination• A seed requires moisture (water) to germinate.• The as the embryo grows, the root and shoot

break through the seed coat.

• Nutrients stored in the cotyledon provide nourishment and support early development

Sexual reproduction in gymnosperms

Conifers (e.g pines and cedars) produce both male and female cones

Male gametophytes (haploid) produced and stored in pollen grain

Wind pollination gets pollen grain to female gametophyte (haploid) in ovule

One sperm nuclei fertilizes the egg after a pollen tube grows into ovule (13 months)

Sexual reproduction in angiosperms

Seeds are contained inside a fruit – a mature ovary

This fruit is an important part of the diet for many animals including humans.

Sexual structure is the flower…….

Parts of a flower

Reproductive PartsMale reproductive organs

(stamen):• Anther: produces pollen grains• Filament: supports anther

above female reproductive organs

Female reproductive organs (carpel):

• Stigma: sticky landing site for pollen grains

• Style: tube that leads down to ovary

• Ovary: contains ovules that develop into seeds

Reproductive Mechanisms

Pollen (male gamete) from one plant lands

stigmapollen

on the stigma of another plant. This is called pollination.

Monocot and dicot flowers

Monocot:

Petals and stamens are

always in multiples of three.

Dicot:

Petals and stamens are in

multiples of four or five.

Pollination and fertilization in angiosperms

Cross – pollination: by wind or animals between flowers of different plants of the same or closely related species(pollinators) – like?

Self-pollination: pollen transfer from flowers on the same plant

Sexual reproduction

size

Selective breeding in plants

colourtaste

texture

Selective breeding and cross-breeding are carried out on plants to produce flowers and crops with desirable characteristics…

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9A Plant-breeding techniques

Anne the plant breeder chooses two parent plants with useful characteristics.

One plant will be the female parent. Anne removes the anthers and covers the flower with a bag. Why?

She puts the bag over the flower again. Later she collects the seeds and grows them to produce the new plant.

female parent

anthers removed

collected pollen

The other plant is the male parent. Its anthers develop as normal.

Anne collects its pollen and brushes it onto the female plant.

Fruit formation

A fruit – a mature ovary that helps protect and disperse the seed

Fruit – can be sweet and fleshy (e.g. plums and strawberries) or dry like walnuts and wheat or vegetables (e.g. peppers, peas and squash)

Importance of seeds

Grain crops (like wheat) are staples around the world

Greenhouses

Seed collection for breeding

Survival of other species on earth

Comparing Plant and Human Reproductive Systems

Plant• Male and Female organs

• Male Gamete is pollen

• Female Gamete is egg produced in ovule

• Pollen nuclei fuses with egg nuclei (fertiliation)

• Diploid zygote

• Zygote grows into embryo

• Embryo grows inside protective seed coat

• Cotyledons provide nourishment

Human• Male or Female organs

• Male Gamete is sperm

• Female Gamete is egg produced in ovary

• Sperm nuclei fuses with egg nuclei (fertilization)

• Diploid zygote

• Zygote grows into embryo

• Embryo grows inside protective womb

• Placenta provides nourishment