backnext home 1 21.2 what are the types of reproduction? asexualsexual involves one parent involves...
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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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21.3 How do organisms reproduce asexually?
Binary fission in bacteria Binary fission in bacteria
2) Cytoplasm divides into 2 parts
single chromosome
parent bacterial
cell
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21.3 How do organisms reproduce asexually?
Binary fission in bacteria Binary fission in bacteria
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 ))
Structure of a flowerExtension
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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
Structure of a flowerExtension
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stigma
style
ovary
ovary wall
ovule
integuments
female gamete
micropyle
Carpels Carpels ((心皮心皮 ))
Structure of a flowerExtension
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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
Structure of a flowerExtension
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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
Insect-pollinated flowers
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scent
nectariesStigma
• sticky
• inside the flower
• firmly attached to style
Insect-pollinated flowers
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scent
nectariesAnther• inside the
flower where insects will brush against it
• firmly attached to filament
Insect-pollinated flowers
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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
Wind-pollinated flowers
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
Wind-pollinated flowers
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
Wind-pollinated flowers
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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Home 36The growth of pollen tube and fertilizationThe growth of pollen tube and fertilization
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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Home 37The growth of pollen tube and fertilizationThe growth of pollen tube and fertilization
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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Home 38The growth of pollen tube and fertilizationThe growth of pollen tube and fertilization
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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Home 39The growth of pollen tube and fertilizationThe growth of pollen tube and fertilization
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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