21.2 What are the types of reproduction?
Asexual
• involves one parent
• involves no gametes
• offspring are genetically
the same as the parents
Sexual
•
•
•
•
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
single
chromosome
parent
bacterial
cell
1) Chromosome
replicates
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21.3 How do organisms reproduce
asexually?
Binary fission in bacteria
single
chromosome
parent
bacterial
cell
2) Cytoplasm divides
into 2 parts
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21.3 How do organisms reproduce
asexually?
Binary fission in bacteria
single
chromosome
parent
bacterial
cell
3) Two identical
daughter cells are
formed
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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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Vegetative propagation in flowering plants
Examples of storage organs :
Tuber
Bulb
Rhizome
Corm
• short swollen
• horizontally
• swollen
• short
underground
growing
underground
underground
stem
underground
stem
stem with
stem
layers of fleshy
e.g. Gladiolus
e.g. potato
‘scale leaves’ e.g. ginger
corm
tuber
rhizome
e.g. onion bulb
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Tuber
e.g. potato tuber
In winter
 aerial shoots die
 new tubers
remain dormant
In spring
 each bud grows
into a new plant
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Tuber
In summer
e.g. potato tuber
shoot
old tuber
dries out
new
tuber
formed
adventitious roots
 buds use the stored
food
 adventitious roots
and shoots develop
 new leaves carry out
photosynthesis
 excess food sent to
underground shoots
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Bulb
fleshy
scale leaf
e.g. onion bulb
dry scale leaf
bud
 bulb remains dormant under
unfavourable conditions
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Bulb
e.g. onion bulb
new flower
stalk
leaf
fleshy leaf
new
bulb
 bud develops into a
shoot using stored food
 green leaves
make food
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Rhizome
In spring
older parts
e.g. ginger rhizome
aerial
shoot
In summer
leaf
 food is passed from
the older parts to the
growing regions
 food made from
photosynthesis is
passed down to the
underground parts
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Corm
e.g. Gladiolus corm
In spring
bud
scale leaf
remains of last
year’s corm
 stored food is passed to
bud for growth
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Corm
e.g. Gladiolus corm
aerial
shoot
leaf
new
corm
new corm
old
corm
 excess food made is
passed down to new
corm
 a new corm is
developed
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Artificial vegetative propagation
 vegetative propagation carried out artificially
 produce desired varieties
 e.g. cuttings (插條法)
in African violet
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21.4 How do flowering plants reproduce
sexually?
 flowering plants reproduce sexually
by producing flowers
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Structure of a flower
stigma
style
carpel
anther
filament
petal
ovary
ovule
sepal
flower stalk
• attaches flower
to the main stem
stamen
nectary
receptacle
• sepals, petals,
stamens and carpels
are attached to this
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Structure of a flower
sepal
Sepals (萼片)
 the outermost ring
(calyx 花萼) of a
flower
 protect the inner parts
of the flower when it
is a bud
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Structure of a flower
Petals (花瓣)
petal
 the second ring
(corolla 花冠) of a
flower
 may be brightly
coloured to attract
insects
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Structure of a flower
Petals (花瓣)
insect guide petal
 may have nectaries
to produce nectar
which attracts
insects
 may have insect
guides to lead
insects towards the
nectaries
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Structure of a flower
Stamens (柱頭)  male reproductive organs
filament
supports
anther
anther
anther
when
anthers
ripen
pollen
sacs
consists of pollen sacs
pollen sacs
split open to
release pollen
grains
filament
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Structure of a flower
Carpels (心皮)
stigma
(柱頭)
style
(花柱)
 female reproductive parts
 the centre of a flower
 each consists of
– style (carries the stigma)
– stigma (receives pollen
grains)
– ovary (with ovules inside)
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Structure of a flower
Carpels (心皮)
ovary wall
stigma
style
integuments
ovule
female
gamete
ovary
micropyle
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Brief Revision
~ Word corner ~
Carpel
** Carp-  Fruit
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Structure of a flower
Flowers
Bisexual
(兩性)
 have both stamens
and carpels in one
flower
Unisexual
(單性)
 have either stamens
or carpels in one
flower
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Pollination
 transfer of pollen grains from anthers to stigmas
 male gametes fertilize the ovules
Pollination (傳粉作用)
insect-pollination
wind-pollination
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Wind-pollinated flowers
- pollinated by wind
The flowers are
structurally adapted to
pollination.
Insect-pollinated flowers
- pollinated by insects
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Insect-pollinated flowers
scent
nectaries
Petal
• large
• brightly
coloured
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Insect-pollinated flowers
scent
Pollen grain
nectaries
• small in
number
• rough and
sticky/
with hooks
pollen grains
stick onto the
leg of the bee
• large and
heavy
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Insect-pollinated flowers
scent
nectaries
Stigma
• sticky
• inside the
flower
• firmly
attached to
style
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Insect-pollinated flowers
scent
nectaries
Anther
• inside the
flower where
insects will
brush
against it
• firmly
attached to
filament
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Wind-pollinated flowers
scent
Petal
nectaries
• small
• green or
dull-coloured
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Wind-pollinated flowers
scent
Pollen grain
nectaries
• large in number
• smooth and dry
• small and light
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Wind-pollinated flowers
scent
nectaries
Stigma
• large and feathery
• hand outside the
flower for picking
up pollen grains
from air
• loosely attached to
the style
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Wind-pollinated flowers
scent
Anther
nectaries
• hangs outside the
flower, exposed to
wind
• loosely attached to
filament so that
light wind can
shake it
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Fertilization
1 Pollen grains land
on the stigma of
the same species.
style
flower stalk
sepal
The growth of pollen tube and fertilization
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Fertilization
2 Sugary solution at the tip
of the stigma stimulates
the pollen grain to develop
a pollen tube.
style
flower stalk
sepal
The growth of pollen tube and fertilization
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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.
style
male
gamete
flower stalk
sepal
The growth of pollen tube and fertilization
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Fertilization
4 Pollen tube grows through
the micropyle.
The tip of the tube bursts to
release the male gamete
into the ovule.
style
ovule
ovary
male
gamete
flower stalk
sepal
micropyle
The growth of pollen tube and fertilization
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Fertilization
5 Male gamete fuses with
female gamete to form a
zygote.
style
ovule
ovary
male
gamete
flower stalk
sepal
micropyle
The growth of pollen tube and fertilization
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Fate of floral parts after fertilization
wither and
drop off
sepal
stamen
petal
A Bauhinia flower
after fertilization
remains of stigma
and style
integument
scar
seed
coat
ovary
wall
fruit
wall
ovule
seed
ovum
embryo
Fruit (pod) splits
open to two halves
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Fate of floral parts after fertilization
Fruit
consists of
fruit wall
protects
seed
helps
dispersal
made up of
seed
coat
protects
embryo
provides
food
food
store
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Structure of a mung bean
Micropyle (珠孔)
– a hole through
which embryo
absorbs water
Hilum (種臍)
Seed coat (種皮)
– protects the embryo
from damage and
against attack of
micro-organisms
– a scar;
formed when
the ovule
breaks from
the ovary wall
External appearance
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Structure of a mung bean
Cotyledons (子葉)
– as food stores
– provide food for
plumule and
radicle to
develop
Plumule (胚芽)
– develops into
shoot
Radicle (胚根)
– develops into
root
Embryo (胚胎)
Seed cut opened
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Advantages and disadvantages of sexual
reproduction in flowering plants
Advantages
1 offspring are genetically different from the
parents
 variations (變異) to adapt the environment
2 avoid overcrowding and competition
3 avoid transmission of diseases
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Advantages and disadvantages of sexual
reproduction in flowering plants
Disadvantages
1 slow way to produce new plants
2 external agents are needed for pollination
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