Reproduction in Plants• define asexual reproduction as the process

resulting in the production of genetically identical offspring from one parent.

• define sexual reproduction as the process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring.

• state the functions of the sepals, petals, anthers and carpels.

• outline the process of pollination.• describe the growth of the pollen tube and its

entry into the ovule followed by fertilisation.

Sexual VS Asexual Reproduction

Sexual reproduction: process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring

Asexual reproduction: process resulting in the production of genetically identical offspring from one parent

Involves fusion of two gametes Does not involve fusion of gametes

Requires two parents Require only 1 parentVariation in offspring Offspring are identical

Asexual reproduction

Advantages:• Offspring produced are identical to parents,

hence higher chance of good characteristics of parents being passed to the offspring

• Only one parent is involved, hence do not depend on external agents, like wind or insect and able to reproduce rapidly

Disadvantage:• No genetic variations among offspring, hence less

adapted to changes in the environment

April 19, 2023Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 4

stigma

style

ovary

ovule

carpel

filament

anther

stamen

Sepal

ReceptaclePedicel

Petal

Parts of a Flower

Parts of a flower

Structure FunctionSepals - Protect the other parts of the flower in the

bud stageReceptacle - enlarged end of the flower stalkPedicel - Flower stalkPetals - are brightly coloured to attract insects for

pollination

- provide a platform for insects to land

April 19, 2023Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 6

Side view of a stamen

vascular bundle

Stamen with upper half of anther cut off

pollen sacs

pollen grains

anther lobes

pollen tube nucleus

generative nucleus

Pollen grains

Mature pollen grain

Parts of a Stamen

Filament Anther

Stamen

Stamen

Structure FunctionStamen - consists of an anther and a filamentFilament - holds the anther in a suitable position

to disperse the pollenAnthers - produces pollen grains.

- When it matures, it splits open to release the pollen grains.

Pollen grain - contain the male gametes

April 19, 2023Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 8

Carpel

The female part of a flower. All

the carpels together make up the pistil.

. A carpel consists of:

- an ovary;

- a style above the ovary; and

- one or more stigmas.

Side view of a carpel

ovary

stigma

style

Parts of a Carpel

Carpel

Structure FunctionStigma - It receives the pollen grains.

- The mature stigma secretes a sugary fluid that stimulates the pollen grains to germinate

Style - connects the stigma to the ovaryOvary - contains one or more ovules

Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte.

Ltd.

Pollination

• Pollination is the transfer of pollen grains from the anther to the stigma.

• Pollination is usually brought about by insects or wind.

• There are two types of pollination: a) Self-pollination b) Cross-pollination

Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte.

Ltd.

Self-Pollination

Self-pollination: Pollen grains are transferred to the stigma of the same flower, or a different flower of the same plant.

Features of plants that self-pollinate• Bisexual flowers with anthers and stigma maturing at the same time.• Stigma is found directly below the anthers.•Plants with closed bisexual flowers

anther

stigma

transfer of pollen grains

Self-pollinationAdvantages•Only one parent plant is required•Beneficial qualities are passed down from parent plants to offspring because offspring inherit the parents’ genes•Not dependent on external factors to pollinate•Less pollen is wasted

Disadvantages•Less varieties of offspring produced since they are genetically similar to the parents.

• Hence, reduces the chance of the species surviving changes in the environment

• may lead to the offspring becoming weaker, smaller and less resistant to diseases.

Cross-Pollination

Cross-pollination: Pollen grains are transferred to a flower in another plant of the same kind of species.

Features of cross-pollinated plants:• Have either male or female flowers.• Anthers and stigmas of bisexual flowers mature at different times.• Stigma of bisexual flowers may be located some distance away from the anthers .

anther

stigma

transfer of pollen grains

Plant A

Plant B

Cross-pollinationAdvantages•Offspring can inherit beneficial qualities from both parents.•More varieties of offspring are produced.

• This increases the chances of the offspring surviving changes in the environment.

•More viable seeds that are capable of surviving longer before germination are produced.

Disadvantages•Require two parent plants•Require external factors, like insects or wind•More pollen is wasted

Insect pollinated plants

Features ReasonsLarge petals To provide a landing platform for

insects to restBrightly-coloured; fragrant; presence of nectar

To attract the insects

Nectar guides To lead insects to the nectarPollen grains with rough surface

To cling on insects’ bodies

Stigmas are sticky To be able to retain pollen grains settling on them from insects

Wind pollinated plants

Features ReasonsProtruding, large, feathery stigma

To provide a large surface area to capture windborne pollen grains

Long filament with protruding anthers

To allow pollen grain to be carried away by wind

Pollen grains are light and smooth

To be carried away easily by the wind

Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte.

Ltd.

Comparisons between insect-pollinated and wind-pollinated flowers

Feature Insect-pollinated flowers Wind-pollinated flowers

Petalslarge with brightly-coloured petals

small and dull-coloured, without petals

Nectar Present. Absent.

Scent Fragrant and sweet-smelling Scent is absent.

Stigmassmall and compact and do not protrude out of flowers

Protruding, large and feathery

StamensNot pendulous and do not protrude out of flower

Long and pendulous filaments with protruding anthers

PollenFairly abundant. Pollen grains are larger with rough surfaces.

More abundant. Pollen grains are tiny with smooth surfaces.

Nectar guides

Present. Absent

Fertilisation

• One male gamete fuses with the ovum to form a zygote. The other male gamete fuses with the definitive nucleus to form an endosperm nucleus.

Fertilisation• When a pollen grain germinates on

the stigma, a pollen tube grows out of it.

• The pollen tube grows right through the style into the ovary.

• The pollen tube enters the ovule through an opening in the ovule wall called the micropyle.

• The tip of the pollen tube bursts, releasing the two male gametes into the ovule.

• One male gamete fuses with the ovum (female gamete) to form a diploid zygote.

• The other male gamete fuses with the definitive nucleus to form the endosperm nucleus.

style

ovary wall

ovule

funicle

placenta

ovum (egg)

definitive nucleus

micropyle

male gametes

germinating pollen grain

pollen tube

stigma

What happens after fertilisation?

• The ovule develops into the seed• The ovary develops into the fruit• The zygote develops into the embryo• When the seed germinates, embryo develop

in the new plant