Reproduction

• the process of producing offspring

• necessary for the continuation of a species

Reproduction

Asexual Sexual

Two types of reproduction

Asexual Sexual• involves one parent• involves no gamete (sex

cell) • offspring are genetically

identical to the parents – mitotic cell division

• usuallyusually involves 2 parents involves 2 parents• involves gametes involves gametes • involves fertilizationinvolves fertilization

– fusion of the nuclei of male & fusion of the nuclei of male & female gametes female gametes zygote zygote

• offspring are genetically different offspring are genetically different from each of their parentsfrom each of their parents

Two types of reproduction

Types of asexual reproduction

Examples of asexual reproduction

Vegetative Vegetative propagationpropagation

Spore Spore formationformationBuddingBuddingBinary Binary

fissionfission

FragmentationFragmentation

Binary fission

Binary fission

• division of unicellular organisms into equal halves e.g. Amoeba

Binary fission

nucleus nucleus divides equally into two by mitosis

cytoplasm constricts

two daughter Amoebae are

formed

Budding

• production of buds, which grow to new individuals

• e.g. yeast

Budding

vacuole

nucleus

a yeast cell

a bud is formed

nucleus divides into two

a nucleus remains in the parent cell

a nucleus moves into the bud

the new cell breaks off from the parent cell

Budding

Spore formation

• produced in large numbers.

• occurs in fungi e.g. Mucor, Rhizopus

 

• Fungi are saprophytes- causing rotting of dead organic matters

• Produce spores for reproduction and dispersal

Spore formation

Fragmentation

e.g. spirogyra

Fragmentation

Amazing power of regeneration in starfish

Fragmentation

Fragmentation

regeneration in flatworm

Vegetative propagation

• development of new plants from vegetative / food storage organs

• occurs in flowering plants e.g. potato, onion, ginger, Gladiolus

Vegetative propagation

development of new plants from vegetative / food storage organs

1. Bulb 2. tuber 3. rhizome 4. corm

Vegetative propagation

1 When conditions become unfavourable such as winter,

storage organ

bud

the aerial parts of the plant die and the storage organ stops growing underground.It survives through bad conditions for growth.

aerial parts

Vegetative propagation

2 When conditions are suitable for growth, a new plant

develops from a bud. The storage organ provides food for the development of the new plant.

Vegetative propagation

They absorb water and minerals.

The shoot grows up and develops leaves.

adventitious roots

aerial shoot

3 Adventitious roots are formed.

Vegetative propagation

4 The storage organ dries up as food is used up for growth.

leaf

Vegetative propagation

5 The plant can now survive on its own by food made from photosynthesis. Some food made from photosynthesis is passed to a new storage organ.

new storage organ

previous storage

organ

Vegetative propagation

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

Tuber Vegetative propagation of a potato plant

Vegetative propagation

Tuber Vegetative propagation of a potato plant

In winter

1 The aerial shoots die but the new tubers remain dormant.

2 Each bud can produce a new independent plant.

In spring

3 The buds use the food stored in the tuber to produce adventitious roots and shoots.

shoottuber formed by last year’s plant

adventitious roots

4 Excess food made in the leaves is sent to the underground shoots and stored.

old tuber

new tubers

eye (a bud)

In summer

Vegetative propagation

Tuber Vegetative propagation of a potato plant

Bulb

Vegetative propagation

onion bulb

Bulb

Vegetative propagation

Growth of an onion bulb

1 The bud remains dormant.

fleshy leaf

scale leaf

bud

stem

root

2 After dormancy, the bud develops. The fleshy leaves provide food for the development of the shoot. They become dry scale leaves after their food storage has been used up.

3 The leaves make and provide food for the growth of a new bud.

new bulb

leaf

fleshy leaf

new flower stalk

Rhizome

Vegetative propagation

Growth of a ginger rhizome

Rhizome

Vegetative propagation

Growth of a ginger rhizome

The food produced from photosynthesis passes downwards to the underground parts.

Rhizome

Vegetative propagation

Growth of a ginger rhizome

The food produced from photosynthesis passes downwards to the underground parts.

Food passes upwards from the older parts to the growing regions.

lateral bud grows into daughter rhizome

Corm

Vegetative propagation

Gladiolus

Corm

Vegetative propagation

Growth of a Gladiolus corm

1 Food stored in the swollen stem is passed upwards to the bud for its growth.

remains of last year’s corm

scale leaf

bud

In spring

2 When the leaves are well developed, the food they made is passed down to the new corm.

3 A new corm is developed over the old one each year.

new cormleaf

aerial shoot

old cormnew corm

Corm

Vegetative propagation

Vegetative propagation

Artificial vegetative propagation• vegetative propagation

done artificially• can produce desired

varieties quickly• method: taking of ‘cuttings’

e.g. Coleus (stem),

African violet (leaves)

Artificial propagation by cutting

Artificial　Vegetative　reproduction

Importance　of　Vegetative　Propagation

It is the only means of reproduction for seedless plants such as pineapples, seedless grapes, oranges, roses, sugarcane, potato, banana, etc.

Plants raised through vegetative propagation are genetically similar. It preserves the type of characters that a plant breeder desires to retain.

It is very economical and easy method for the multiplication of plants.

Artificial propagation by grafting

Eg. Fruit trees

Ornamental plants

Bauhinia of HK

Grafting is a method of asexual plant propagation where the tissues of one plant are encouraged to fuse with those of another.

In most cases, one plant is selected for its roots, and this is called the stock or rootstock. The other plant is selected for its stems, leaves, flowers, or fruits and is called the scion.

Artificial　Vegetative　reproduction

To ensure a quick growth union, all cut surfaces are covered with a soft wax to prevent drying. The tissues of both the stock and the scion will fuse together and will make organic connection, getting nourishment from the stock, but producing fruits of scion retaining parental characters. Grafting is not possible is monocot plants since cambial activity is essential for the union of stocks and scion.

Grafting blends the properties of two plants. It is also used in the production of dwarf fruit trees for the home gardens. High quality roses are usually grafted on wild rose root stocks. Other plants where grafting has been performed successfully are rubber, apple, pear, mango and guava.

Grafting　peach　into　plum

This wild plum tree has now become half peach and half plum

These peach grafts were been successful and have already produced blossoms

Main grafting steps: Trimming bark after cutting a branch to

be grafted

Next: Budwood inserted into branch Completed bark graft which has been tied with tape and waxed with grafting wax

The ‘grafted’ Bauhinia appear in two segments:  the upper half is Bauhinia blakeana 洋紫荊　 and the lower half is Bauhinia purpurea 紅花羊蹄甲 .  When you look at the joint carefully, then you will notice that the bark textures on both halves are significantly different.  Also, the leaves on the branches and those near the foot vary a little bit.  When we see the ‘grafted’ Bauhinia, Bauhinia blakeana is just one of the tree names. Bauhinia purpurea is another one.  (Well, if the foot of this tree does have leaves and flowers, then it should be labeled with two names!)

What are the

ADVANTAGES and DISADVANTAGES

of Artificial Propagation ?

External agents?

Good characters?

Vegetative propagation

Advantages DisadvantagesSpeed?

Undesirable characters….

Offspring are identical…..

Diseases in parents…..

Vegetative propagation

Advantages DisadvantagesOvercrowding…..

No external agents or other plants are

needed

Good characters are passed to the

offspring

A relatively quick way to produce new plants

No external factors or other plants are

needed for reproduction Undesirable characters are

passed on to the offspring

Offspring have no new features No new features in offspring to

adapt to any changes in environmental conditions

Disease of the parent plants can easily be transmitted to the

offspring

Good characters of the parent are passed

to the offspring

Vegetative propagation

Advantages DisadvantagesA relatively quick way to produce new plants

Overcrowding can occur which causes competition for resources

Importance　of　Vegetative　Propagation

It is the only means of reproduction for seedless plants such as pineapples, seedless grapes, oranges, roses, sugarcane, potato, banana, etc.

Plants raised through vegetative propagation are genetically similar. It preserves the type of characters that a plant breeder desires to retain.

It is very economical and easy method for the multiplication of plants.

Micro　propagation　by　tissue　culture

Tissue　culture

Application　of　tissue　culture

Application　of　tissue　culture

Micro propagation of plantsPlant tissue in very small amounts can produce hundreds or thousands of plants continuously. By using tissue culture methods, millions of plants with the same genetic characteristics can be obtained.

Improved cropIn crop improvement efforts, pure strains can take six to seven generations of self-pollination or crosses. Through tissue culture techniques, homozygous plants can be obtained in a short time by producing haploid plants through pollen culture, anther or ovaries followed by chromosome doubling.

Production of disease-free plants (virus)Tissue culture technology has contributed in a plant that is free from viruses. In plants that have been infected with the virus, the cells in the bud tip (meristem) is an area that is not infected with the virus. In this way virus-free plants can be obtained from the meristem.

Genetic transformationFor example, bacterial gene transfer (such as cry genes from Bacillus thuringiensis) into the plant cells )

20.3　Sexual　reproduction　in　flowering　plants

• flowering plants reproduce sexually by producing flowers

Structure of a flowerStructure of a flower

carpel

stigma

style

ovary

ovule

sepal

antherfilament

stamen

petal

nectary

receptacle

flower stalk• sepals, petals,

stamens and carpels are attached to this

Structure of a flowerStructure of a flower

Sepals

• make up the outermost ring (calyx) of a flower

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

sepal

Petals

• may be brightly-coloured to attract insects

• make up the second ring (corolla) of a flower

petal

• nectaries may be present at the base to produce nectar which attracts insects

• may have insect guides to lead insects towards the nectaries insect guide

Stamens

• male reproductive organs

• filament anther

supports anther

consists of 2-4 pollen sacs inside which pollen grains are formed

anther

pollen sacs

filament

when anthers ripen pollen sacs split open to release pollens which contain male gametes

Carpels

• the centre of a flower

• each consists of – stigma (receives pollen

grains)– style (carries the stigma)– ovary (with ovules inside)

stigma style

• female reproductive parts

Carpels

• ovules are protected by integument which has a small hole (micropyle)

• ovules contain the female gametes

stigma

style

ovary• each ovule is

attached to the ovary wall by a stalk

ovary wall

ovule

integuments

female gamete

micropyle

Structure of a carpelStructure of a carpel

PollinationPollination

Pollination

– the transfer of pollen grains from anthers to stigmas fertilization of male & female gametes in ovules

cross-pollination self-pollination

wind-pollination insect-pollination

1

2

Cross-pollination and self-pollination

– pollen grains are transferred to a different plant

Cross-pollination

Cross-pollination and self-pollination

– pollen grains are transferred within the same plant

Self-pollination

Inbreeding　(Self-pollination)

Advantages:

1.Preserves well-adapted genotypes

2.Insures seed set in the absence of pollinators

Disadvantages:

Decreases genetic variability

Outbreeding　(Cross-pollination)

Advantages:

1. Increases genetic variability

2. Strong evolutionary potential

3. Adaptation to changing conditions

4. Successful in long-term

Disadvantages:

1. Can destroy well-adapted genotypes (offspring are not guaranteed to be viable)

2. Relies on effective cross-pollination

Wind-pollination and insect-pollination

Wind pollination

Insect pollination

— pollinated by wind

— pollinated by insects

Wind-pollinated flowersWind-pollinated flowers Insect-pollinated flowersInsect-pollinated flowers

The flowers are structurally adapted to pollination.

Structural adaptation of wind-pollinated flowers

scentnectaries

pollen grain• large number• smooth and dry• light in weight

scentnectaries

stigma

• large• feathery• projects outside the

flower for picking up pollen grains from air

Structural adaptation of wind-pollinated flowers

scentnectaries

petal

• small• green or dull-

colouredstigma

pollen grain

Structural adaptation of wind-pollinated flowers

scentnectaries

anther

• hangs outside the flower, exposed to wind

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

petal

stigma

pollen grain

Structural adaptation of wind-pollinated flowers

scentnectaries

pollen grain• smaller

number• rough and

sticky/ with hooks• heavier

pollen grains of this flower stick onto the leg of the bee

Structural adaptation of insect-pollinated flowers

scentnectaries

stigma• smaller• sticky• remains inside

the flower

Structural adaptation of insect-pollinated flowers

pollen grain

scentnectaries

petal• larger• brightly-

coloured

stigma

Structural adaptation of insect-pollinated flowers

pollen grain

scentnectaries

anther

• inside the flower where insects will brush against it

• firmly attached to prevent from being torn away by insects

petal

stigma

Structural adaptation of insect-pollinated flowers

pollen grain

Outbreeder　or　Inbreeder?　

Often one can tell just by looking at a flower whether it cross-pollinates or self-pollinates.

OUTBREEDER INBREEDER

self-incompatibility

Size of flowers

colors

nectaries

scent

nectar guides

anthers position

Number of pollen grains

style position

Outbreeder　or　Inbreeder?　

Often one can tell just by looking at a flower whether it cross-pollinates or self-pollinates.

OUTBREEDER INBREEDER

self-incompatible self-compatible

large flowers small flowers

bright colors mono-colored

nectaries present nectaries absent

scented flowers unscented flowers

nectar guides present nectar guides absent

anthers far from stigma anthers close to stigma

many pollen grains fewer pollen grains

style not included in flower style included in flower

FertilizationFertilization

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

1 Pollen grains land on the stigma of the same species.

flower stalk

sepal

style

FertilizationFertilization

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

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

style

flower stalk

sepal

FertilizationFertilization

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

3 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

style

flower stalk

sepal

FertilizationFertilization

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

4 After growing into the ovary, the tube grows through the micropyle of the ovule andthe tip of the tube bursts to release the male gamete into the ovule.

ovule male gamete

micropyle

ovary

style

flower stalk

sepal

FertilizationFertilization

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

5 The male gamete enters the ovule and fuses with the female gamete to form a zygote.

ovule male gamete

micropyle

ovary

style

flower stalk

sepal

20.4What　happens　to　the　floral　parts　after　fertilization?

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

consists of

Fruits and seedsFruits and seeds

food store

undeveloped plant embryo

seed coat

plant dispersalseed

Fruit

fruit wall

provides food

protects

made up of

helpsprotects

Fruits and seedsFruits and seeds

Structure of a mung bean seed

External appearanceExternal appearance

seed coat– surrounds the embryo

and protects it from damage and against attack of micro-organisms such as bacteria and fungi

micropyle– a hole through which

embryo absorbs water before it germinates hilum

– a scar on the surface of the coat; formed when the ovule detaches from the ovary wall

Structure of a mung bean seed

Embryo cut openedEmbryo cut opened

plumule– develops into

the shoot

radicle– develops into

the root

cotyledons– act as food stores– contain starch and

proteins to supply food for the plumule and radicle to develop

embryo

Dispersal of seeds and fruitsDispersal of seeds and fruits

Why seeds and fruits have to be dispersed to

distances far away from parents ?

To reduce overcrowding and

competition for materials.

To reduce overcrowding and

competition for materials.

To colonize new areas which are suitable for seed germination and

survival of species.

To colonize new areas which are suitable for seed germination and

survival of species.

DispersalDispersal

wind dispersal animal dispersal

adaptive features of fruits and seeds are

• small• light• may have wings/feathery hair

• brightly-coloured• sweet, juicy and good to eat

• may have hooks

Concept Concept diagram

Reproduction

can becan be

asexual reproduction

sexual reproduction

Concept Concept diagram

asexual reproduction

can be bycan be by

binary fission

buddingvegetative

propagationspore

formation

stem tuber

bulb rhizome corm cutting

by the formation of by the formation of artificially artificially achieved byachieved by

Concept Concept diagram

in flowering in flowering plantsplants

male gamete

flower

copulation or IVF

fertilization

sexual reproduction

formsforms

female gamete

in mammalsin mammals

pollination

fertilization

involvesinvolves byby

fusion is fusion is calledcalled andand

afterafter

forfor

Concept Concept diagram

copulation or IVF

fertilization

producesproduces

fertilization forfor

formsforms

zygotefruit

containscontains

menstruation pregnancy

if if fertilization fertilization occursoccurs

if no if no fertilization fertilization occursoccurs

menstrual cycle

contraceptive methods

seeds

embryo

new organism

protectprotect

develops develops intointo

finally finally intointo

repeats repeats inin

prevented prevented byby