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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