Reproduction in plants

Types of reproduction

Reproduction: is a characteristic of living organisms which is essential for continuity of life due to production of new individuals.

Types of reproduction: Asexual reproduction. Sexual reproduction.

Asexual reproduction Definition: it is a type of reproduction which

involves only one parent and the off springs are identical to the parent.

Cell division: this type occurs by mitosis cell division. The new cell contains the same number of chromosomes as the main cell.

Sexual reproduction Definition: it is a type of reproduction which

involves male and female where their gametes fuse to form zygote which develops into a new individual.

Cell division: this type occurs by meiosis where gametes are produced containing half number of chromosomes

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Two parents are involved

Gametes (male, female cells)are formed

Meiotic cell division Zygote is formed from

fertilization . Slow Animals and flowering

plants.

One parent involved

No gametes are formed

Mitotic cell division Identical to the parent. Rapid Simple organisms,

some plants

Sexual reproduction in :Flowering Plants The flowering plant is good example of

sexual reproduction and the flower is the reproductive organ of the plant, the flower may contain both male and female organs and it is called bisexual.

Other flower may contain only female or male organ it is called unisexual.

Structure Function

Receptacle

:

Sepals:

Extended flower stem which carried

modified leaves

Small green leaves (calyx

It becomes fleshy and edible after fertilization.

Protect the flower while it is in the bud.

Petals: Large, colored scented leaves. When scented it attracts insects, they land on it

They have guide lines to lead insect of nectar gland.

Protects the reproductive organs.

Stamens: Male reproductive organ consist of:

Anther: has 4 pollen sacs contain pollen

grains.

Filament.

Pollen sacs produce pollen grains (male Gametes)

Carries the anther.

Carpels: Female reproductive organs consists of:

Stigma, style, ovary

Stigma: receive pollen grains and produce nutritive to help in

Germination

style: holds the stigma.

ovary: produces ovules which contains female gametes.

Nectary

glands

Present in the base of the ovarySecretes sugary liquid called nectar to attract insects which

help in pollination.

•PollinationPollination: it is the transfer of pollen grains from anther to stigma. Types of pollination: self pollination and cross pollination.

Self pollination Cross pollination

Transfer of pollen grains from a stigma

of same flower OR another flower but of

the same plant.

In this type of flowers:

1. Stamens are longer than carpels.

2. Male and female organs mature at the

same time.

3. The reproductive organs ripen before

opening of the flower.

Less variation in the outcome.

The hereditary diseases are frequency.

Transfer of pollens from anther flower to

stigma to stigma of another plant but of

the same species.

In this type of flowers:

1. Stamens are shorter than carpels.

2. Male and female organs mature at

different times.

3. The ripening occurs after the flower

opens.

4. Stigma secretes liquid to kill pollens of

the same flower.

More variation.

Diseases are less.

Methods of pollination:There are many agents that can cause pollination such as wind, insects, water, animals, and humans.

Insect pollinated flower Wind pollinated flower

Large petals Small petals or no petals at all

Strongly scented most of the time. No scent.

Have nectar glands at the base of the

flower

No nectar glands.

Anthers and stigma are inside the flower

and insect has to brush in to get nectar.

Anthers and stigma are dangling outside

flower.

Sticky pollen grains which stick to insect Smooth, light pollens can be carried by

wind or water.

Large quantities of pollens are made

because some of them may be eaten or

lost.

Very large quantities of pollen grains are

made because they may be blown and lost

Flowers appear in warm weather where

there are many active insects

Flowers appear at cold weather.

Difference between wind and insect pollinated flowers

• FertilizationFertilization: it is the union of pollen grain of the male and egg cell of the female producing the zygote.Steps of fertilization:•The pollen grain falls on the stigma which produces a sticky liquid for nutrition of the pollen helping its germination.•The pollen grain enlarges protruding a pollen tube from it, where the nucleus of the pollen which is the male gamete passes through this tube.•The pollen tube extends toward the ovule and reaches the micropyle.•The tip of the pollen tube will rupture then the nucleus of the male gamete fuses with the female gamete producing the zygote.

When all these steps are completed the flower undergoes many changes which are:•Sepals, petals, stamens, stigma and style with dry and drop off.•The zygote will develop into the embryo of the seed and the ovule will develop into the seed.•The ovary will get bigger to form the fruit which: •Covers and protects the seed.•Helps in dispersal.•Stores food. Dispersal of seeds and fruits:-Dispersal: the scattering or spreading of seeds and fruits away from the main plant.•Prevent overcrowding that increase the chance for diseases.•Prevent competition between plants for space, water and light.•Increase in the growth of plants in different areas.In the mean time the spreading may increase the hazards of growing unwanted plants between crops or growing plants which may unhealthy properties.

Types of dispersal:•Wind dispersal:•They have certain structures that increase the surface area and they are light to be easily carried by winds for a long distance.Examples of those plants:•Poppy plant: the stem is long and the ovary is dry having halls to allow the seeds out, by the action of the wind and they will be scattered around.•Parachute fruits as Dandelion: they have feathery hear which come out of the fruit and seed that flow in air to different areas. •Sycamore: it has a wing structure to prevent its falling on the ground and so it will be easily carried by wind to different areas.•Animal dispersal:Animal can help in dispersal by:•Carrying the seeds on their fur (hooked seeds like Burdock.)•Eating of the fruit containing the seeds which will be excreted by the animal(blackberry)

Male flower is used to pollinate the female flower

The flower is pollinated the petals are starting to wither

Melon fruit