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21.2 What are the types of reproduction?

AsexualAsexual SexualSexual• involves one parent• involves no gametes• offspring are genetically

the same as the parents

• usually involves 2 parents• involves gametes • involves fertilization• offspring are genetically

different from each of parents

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21.3 How do organisms reproduce asexually?

Binary fission in bacteria Binary fission in bacteria

1) Chromosome replicates

single chromosome

parent bacterial

cell

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2) Cytoplasm divides into 2 parts

single chromosome

parent bacterial

cell

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3) Two identical daughter cells are formed

single chromosome

parent bacterial

cell

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Vegetative propagation in flowering plants Vegetative propagation in flowering plants

vegetative parts (e.g. stems, roots & leaves) new plants

allows the plants to survive in poor conditions

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Examples of storage organs :Examples of storage organs :

Tuber Bulb Rhizome Corm

• swollen underground stem

e.g. potato 　　 tuber

• short underground stem with layers of fleshy ‘scale leaves’

e.g. onion bulb

• horizontally growing underground stem

e.g. ginger rhizome

• short swollen underground stem

e.g. Gladiolus corm

Vegetative propagation in flowering plants Vegetative propagation in flowering plants

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In winterIn winter

aerial shoots die

new tubers remain dormant

each bud grows into a new plant

In springIn spring

Tuber e.g. potato tuber

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shoot

adventitious roots

old tuber dries out

new tuber formed

In summerTuber

buds use the stored food

adventitious roots and shoots develop

new leaves carry out photosynthesis

excess food sent to underground shoots

e.g. potato tuber

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fleshy scale leaf

dry scale leaf

bud

Bulb

bulb remains dormant under unfavourable conditions

e.g. onion bulb

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new bulb

leaf fleshy leaf

new flower stalk

Bulb e.g. onion bulb

bud develops into a shoot using stored food

green leaves make food

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Rhizome

aerial shoot

leafolder parts

e.g. ginger rhizome

In springIn spring

food is passed from the older parts to the growing regions

food made from photosynthesis is passed down to the underground parts

In summerIn summer

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remains of last year’s corm

scale leaf

bud

Corm e.g. Gladiolus corm

In springIn spring

stored food is passed to bud for growth

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new corm

leaf

aerial shoot

old corm

new corm

excess food made is passed down to new corm

a new corm is developed

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Corm e.g. Gladiolus corm

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Artificial vegetative propagation Artificial vegetative propagation

vegetative propagation carried out artificially

produce desired varieties

e.g. cuttings (插條法 ) in African violet

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flowering plants reproduce sexually by producing flowers

21.4 How do flowering plants reproduce sexually?

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carpel

stigma

style

ovary

ovule

sepal

anther

filamentstamen

petal

nectary

receptacleflower stalk• attaches flower

to the main stem

• sepals, petals, stamens and carpels are attached to this

Structure of a flowerExtension

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Sepals Sepals ((萼片萼片 ))

the outermost ring (calyx 花萼 ) of a flower

protect the inner parts of the flower when it is a bud

sepalStructure of a flowerExtension

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may be brightly coloured to attract insects

the second ring (corolla 花冠 ) of a flower

petalPetals Petals ((花瓣花瓣 ))


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may have insect guides to lead insects towards the nectaries

may have nectaries to produce nectar which attracts insects

petalPetals Petals ((花瓣花瓣 ))

Structure of a flowerinsect guide

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male reproductive organs

filament anther

supports anther

consists of pollen sacs

anther

pollen sacs

filament

when anthers ripen

pollen sacs split open to release pollen grains

Structure of a flowerStamens Stamens ((柱頭柱頭 ))

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Carpels Carpels ((心皮心皮 )) female reproductive parts

each consists of – style (carries the stigma)

– stigma (receives pollen grains)

– ovary (with ovules inside)

stigma (柱頭 )

style (花柱 )

the centre of a flower


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stigma

style

ovary

ovary wall

ovule

integuments

female gamete

micropyle

Carpels Carpels ((心皮心皮 ))


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~ Word corner ~

** Carp- Fruit

Carpel

Brief RevisionBrief Revision

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FlowersFlowers

Bisexual(兩性 )

Unisexual(單性 )

have both stamens and carpels in one flower

have either stamens or carpels in one flower


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transfer of pollen grains from anthers to stigmas male gametes fertilize the ovules

insect-pollination wind-pollination

Pollination

Pollination (傳粉作用 )

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Wind-pollinated flowersWind-pollinated flowers

- pollinated by wind

Insect-pollinated flowersInsect-pollinated flowers

- pollinated by insects

The flowers are structurally adapted to

pollination.

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scent

nectariesPetal

• large

• brightly coloured

Insect-pollinated flowers

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scent

nectariesPollen grain

• small in number

• rough and sticky/

with hooks

• large and heavy

pollen grains stick onto the leg of the bee


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scent

nectariesStigma

• sticky

• inside the flower

• firmly attached to style


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scent

nectariesAnther• inside the

flower where insects will brush against it

• firmly attached to filament


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Petal

• small

• green or dull-coloured

Wind-pollinated flowers

scent

nectaries

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Pollen grain

• large in number

• smooth and dry

• small and light


scent

nectaries

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Stigma• large and feathery

• hand outside the flower for picking up pollen grains from air

• loosely attached to the style


scent

nectaries

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Anther

• hangs outside the flower, exposed to wind

• loosely attached to filament so that light wind can shake it


scent

nectaries

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Home 35The growth of pollen tube and fertilizationThe growth of pollen tube and fertilization

flower stalk

sepal

style

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Fertilization1 Pollen grains land

on the stigma of the same species.

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flower stalk

sepal

style

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Fertilization

2 Sugary solution at the tip of the stigma stimulates the pollen grain to develop a pollen tube.

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flower stalk

sepal

style

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Fertilization3 Pollen tube grows down the

style and eventually into the ovary by secreting enzymes to digest tissues of the style. The male gamete moves towards the ovule.

male gamete

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flower stalk

sepal

style

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Fertilization

male gamete

4 Pollen tube grows through the micropyle.The tip of the tube bursts to release the male gamete into the ovule.

ovule

micropyle

ovary

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flower stalk

sepal

style

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Fertilization

male gamete

ovule

micropyle

ovary

5 Male gamete fuses with female gamete to form a zygote.

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A A Bauhinia Bauhinia flower flower after fertilizationafter fertilization

Fruit (pod) splits Fruit (pod) splits open to two halvesopen to two halves

scar

seed coat

fruit wall

seed

embryoovum

ovule

ovary wall

integument

remains of stigma and style

wither and drop off

sepalpetal

stamen

Fate of floral parts after fertilizationExtension

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consists of

food store

embryoseed coat

dispersalseed

Fruit

fruit wall

provides food

protects

made up of

helpsprotects

Fate of floral parts after fertilizationExtension

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Home 42External appearanceExternal appearance

Seed coat (種皮 )– protects the embryo

from damage and against attack of micro-organisms

Micropyle (珠孔 )

– a hole through which embryo absorbs water

Hilum (種臍 )– a scar;

formed when the ovule breaks from the ovary wall

Structure of a mung beanStructure of a mung beanExtension

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Home 43Seed cut openedSeed cut opened

Cotyledons (子葉 )

– as food stores– provide food for

plumule and radicle to develop

Embryo (胚胎 )

Structure of a mung beanStructure of a mung bean

Plumule (胚芽 )– develops into

shoot

Radicle (胚根 )– develops into

root

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Advantages and disadvantages of sexual reproduction in flowering plants

11 offspring are genetically different from the parents

variations (變異 ) to adapt the environment

22 avoid overcrowding and competition

33 avoid transmission of diseases

AdvantagesAdvantages

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Advantages and disadvantages of sexual reproduction in flowering plants

11 slow way to produce new plants

22 external agents are needed for pollination

DisadvantagesDisadvantages

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