16
Reproduction
21/08/2024 Statements from Cambridge IGCSE Chemistry syllabus 0610 (for exams in 2016 – 2018)
16.1 Asexual reproduction
• Define asexual reproduction as a process resulting in
the production of genetically identical offspring
from one parent
• Identify examples of asexual reproduction from
information provided
• Discuss the advantages and disadvantages of
asexual reproduction:
– to a population of a species in the wild
– to crop production
What is reproduction?
• to produce new organisms by
passing the DNA to the offsprings.
Two kinds of
Reproduction
1) Asexual Reproduction
= a single organism can reproduce
without the help of another
2) Sexual Reproduction
= requires two different sex cells
(haploid cells) from two different
individuals fusing together to
reproduce the first cell (diploid
cell) of a new organism
Two types of reproduction
Asexual Sexual
● involves one parent • usually involves 2 parents
• involves gametes
● involves no gamete (sex
• involves fertilization
cell) – fusion of the nuclei of male & female
● offspring are genetically gametes ⇒ zygote
identical to the parents – • offspring are genetically different from
mitotic cell division each of their parents
Types of asexual reproduction
Examples of asexual reproduction
Binary fission Budding Spore formation
Vegetative
Fragmentation
propagation
Fission: Asexual Reproduction
Fission: Cell division in prokaryotes that
forms two genetically identical cells
DNA is copied
The cell begins to grow longer,
pulling the two copies apart
The cell membrane pinches inward
in the middle of the cell
Cell splits to form two new uniform,
identical offspring
Examples: bacteria, Ecoli, pond critters
Budding: Asexual Reproduction
Budding: a new organism grows
by mitosis and cell division on
the body of its parent
The bud, or offspring is
identical to the parent
The bud, when large enough,
can break off of the parent
and live on its own
Offspring may remain
attached and form a colony
Examples: Yeast, Hydra, cactus
● produced in large numbers.
Spore
formation ● occurs in fungi
e.g. Mucor, Rhizopus
Spore
formation
• Hypha grows up
vertically and tip
swells with
cytoplasm
containing many
nuclei
(Sporangium)
• Tip release spore
Vegetative
propagation
Tuber Vegetative propagation of a potato plant
Vegetative
propagation
Tuber Vegetative propagation of a potato plant
In spring
In winter
The aerial shoots die but the 📋 Each bud can produce a
new tubers remain dormant. new independent plant.
tuber formed by shoot
last year’s plant
In summer
old tuber
new tubers
adventitious roots eye (a bud)
🗑 The buds use the food stored Excess food made
in the tuber to produce in the leaves is sent
adventitious roots and shoots. to the underground
shoots and stored.
Application of asexual reproduction
•It is the only means of reproduction for
seedless plants such as pineapples,
●seedless
vegetative propagation
grapes, oranges, roses,
sugarcane, potato, banana, etc.
done artificially
● can produce desired
•Plants raised through vegetative
varieties quickly
propagation are genetically similar. It
●preserves
method:the type ofofcharacters
taking that a
‘cuttings’
plant breeder desires to retain.
e.g. Coleus (stem),
African
•It is very violet
economical and(leaves)
easy method for
the multiplication of plants.
Asexual reproduction in plants
Advantages Disadvantages
A relatively quick way Overcrowding can occur which
to produce new plants causes competition for resources
Good characters of Disease of the parent plants can
the parent are passed easily be transmitted to the
to the offspring offspring
Offspring have no new features
No new features in offspring to
No external factors or
adapt to any changes in
other plants are
environmental conditions
needed for
reproduction Undesirable characters are
passed on to the offspring
Asexual Reproduction (review)
16.2 Sexual reproduction
• Define sexual reproduction as a process involving
the fusion of the nuclei of two gametes (sex cells)
to form a zygote and the production of offspring
that are genetically different from each other
• Define fertilisation as the fusion of gamete nuclei
• State that the nuclei of gametes are haploid and
that the nucleus of a zygote is diploid
• Discuss the advantages and disadvantages of
sexual reproduction:
– to a population of a species in the wild
– to crop production
Terms to know:
•Haploid: having a single set of
chromosomes in each cell.
•Diploid: having two sets of
chromosomes in each cell.
•Mitosis: cell division, which produces
two genetically identical cells.
•Meiosis: reduction division, which
produces four haploid reproductive
cells.
Sexual Reproduction
A type of reproduction in which the genetic
materials from two different cells combine,
producing an offspring
The cells that combine are called sex cells
Female – egg
Male – sperm
Fertilization: an egg cell and a sperm cell join
together
A new cell is formed and is called a zygote
Advantages: Sexual
Reproduction
Diverse offspring: genetic variation
among offspring
Half of the DNA comes from mom
Half of the DNA comes from dad
Due to genetic variation, individuals
within a population have slight
differences
Plants – resist diseases
Traits can develop to resist harsh
environments that allows an
organism survive
Advantages: Sexual
Reproduction
Selective Breeding
Used to develop many
types of plants and animals
that have desirable traits
Agriculture/Farming: better
plants, larger animals
Desirable pets
Disadvantages: Sexual
Reproduction
Time and Energy
Organisms have to grow and develop
until they are old enough to produce
sex cells
Search and find a mate
Searching can expose individuals to
predators, diseases, or harsh
environmental conditions
16.3 Sexual reproduction in plants
• Identify and draw, using a hand lens if necessary,
the sepals, petals, stamens, filaments and anthers,
carpels, style, stigma, ovary and ovules, of an
insect-pollinated flower
• State the functions of the sepals, petals, anthers,
stigmas and ovaries
• Use a hand lens to identify and describe the
anthers and stigmas of a wind-pollinated flower
• Distinguish between the pollen grains of
insect-pollinated and wind-pollinated flowers
Flowers
Sexual reproduction in flowering plants
● flowering plants reproduce sexually by producing flowers
anther
stigma stamen
filament
style
carpel petal
ovary
ovule nectary
sepal receptacle
● sepals, petals,
flower stalk stamens and carpels
are attached to this
Structure of a flower
Making new plants
Let’s take a closer look at the different parts of this flower.
The stigma is The petals attract
sticky to keep hold insects.
of the pollen.
The anther is the
The style part that makes
supports the the pollen.
stigma and
connects it to The filament
the ovary. holds up the
anther.
The ovary is
where the ovules, The sepal leaves
or eggs, are. protect the flower
before it opens.
Structure of a flower
sepal
Sepals
● make up the outermost
ring (calyx) of a flower
● protect the inner parts of
the flower when it is a
bud
petal
Petals
● make up the second ring
(corolla) of a flower
● may be brightly-coloured
to attract insects
● nectaries may be present at
the base to produce nectar
which attracts insects
● may have insect guides to lead
insect guide
insects towards the nectaries
Stamens
● male reproductive organs
consists of 2-4 pollen
● filament anther sacs inside which pollen
grains are formed
supports
anther
when anthers ripen pollen sacs
anther
split open to
pollen release pollens
sacs which contain
male gametes
filament
Carpels
stigma style
● the centre of a flower
● female reproductive
parts
● each consists of
● stigma (receives pollen
grains)
● style (carries the stigma)
● ovary (with ovules inside)
Carpels
stigma
● ovules are protected by
integument which has a style
small hole (micropyle) ovary wall
● ovules contain the integuments
female gametes ovule female
gamete ovary
● each ovule is
attached to the micropyle
ovary wall by a
stalk Structure of a carpel
16.3 Sexual reproduction in plants
• Define pollination as the transfer of pollen grains from
the anther to the stigma
• Define self-pollination as the transfer of pollen grains
from the anther of a flower to the stigma of the same
flower or different flower on the same plant
• Define cross-pollination as transfer of pollen grains from
the anther of a flower to the stigma of a flower on a
different plant of the same species
• Discuss the implications to a species of self-pollination
and cross-pollination in terms of variation, capacity to
respond to changes in the environment and reliance on
pollinators
• Describe the structural adaptations of insect-pollinated
and wind-pollinated flowers
Pollination
● the transfer of pollen grains from anthers to stigmas
→ fertilization of male & female gametes in ovules
cross-pollination self-pollination
1
Pollination
2
wind-pollination insect-pollination
How does pollination take place?
•Pollen grains brush against the insect, it flies
to another plant, the grains rub on the
stigma
•The grain of pollen grows a tube, which goes
down the style until it reaches the ovary
•The male part joins with the female part to
form a seed. This is called fertilisation.
•After fertilisation the petal drop off
because they are no longer needed
Fertilisation
•Pollen grains germinate
on the stigma, growing
down the style to reach
an ovule.
•Fertilised ovules
develop into seeds.
•Ovary becomes the
fruit.
Fertilisation
• Pollination ≠ Fertilisation
• The male gamete (the male nucleus) has to get to the egg cell
• The egg cell lies in an ovule in an ovary at the centre of the plant
• The pollen grain germinates on the stigma
• It grows a pollen tube down the style
• It male nuclei travel down the pollen tube to the ovule
Cross-pollination and self-pollination
Cross-pollination
● pollen grains are
transferred to a
different plant
Cross-pollination and self-pollination
Self-pollination
● pollen grains are
transferred within the same
plant
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 ● pollinated by wind
Insect pollination ● pollinated by insects
The flowers are structurally adapted to
pollination.
Wind-pollinated flowers Insect-pollinated flowers
Insect-pollinated flowers are adapted to attract
insects to them to enable transfer of pollen
Pollen has
barbs for
nectar and a hooking onto
scent present insect fur
Anthers positioned
to rub pollen onto
insects
Sticky stigma to
collect pollen Brightly coloured
petals
Flower Structure Pollination Fertilisation Seed Dispersal Germination Test
Wind-pollinated flowers are different in structure because
they do not have to attract insects to them but do need to be
exposed to the wind.
Pollen grains are very Anthers are exposed to the
small and light. They wind so that pollen can easily
occur in very large be blown away
numbers
Stigma are
feathery to catch
pollen carried on
wind
Petals are small and
green as there is no
No scent or nectary
need to attract insects
Flower Structure Pollination Fertilisation Seed Dispersal Germination Test
Comparison of insect and wind
pollinated flowers
Wind pollinated flowers Insect pollinated flowers
Flowers are small and do not have Flowers are large and have brightly
brightly coloured petals (if at all) coloured petals
Large amounts of small, very light Sticky pollen is produced in small
pollen grains produced. amounts.
Stigmas are long and feathery and Stigmas are positioned inside the flower
held outside of the flower so insects brush against them
Anthers are held outside of the Anthers are positioned inside the flower
flower by long filaments so that insects will brush against them.
Wind pollinated flowers do not Insect pollinated flowers produce
produce nectar nectar in nectaries.
Eg. the grasses, cereals Eg. orchids, foxgloves
Wind Pollinated Flowers
Feature Reason
small petals, often brown or dull no need to attract insects
green
no scent no need to attract insects
no nectar no need to attract insects
pollen produced in great because most does not reach
quantities another flower
pollen very light and smooth so it can be blown in the wind
anthers loosely attached and to release pollen into the
dangle out wind
stigma hangs outside the flower to catch the drifting pollen
stigma feathery or net like to catch the drifting pollen
Insect Pollinated Flowers
Feature Reason
large, brightly coloured petals to attract insects
often sweetly scented to attract insects
usually contain nectar to attract insects
moderate quantity of pollen less wastage than with wind
pollination
pollen often sticky or spiky to stick to insects
anthers firm and inside flower to brush against insects
stigma inside the flower so that the insect brushes against
it
stigma has sticky coating pollen sticks to it
16.3 Sexual reproduction in plants
• State that fertilisation occurs when a pollen
nucleus fuses with a nucleus in an ovule
• Describe the growth of the pollen tube and its
entry into the ovule followed by fertilisation
(details of production of endosperm and
development are not required)
• Investigate and state the environmental conditions
that affect germination of seeds, limited to the
requirement for water, oxygen and a suitable
temperature
Fertilisation
STIGMA
Understand that the
STYLE
growth of the pollen
tube followed by
fertilisation leads to
seed and fruit
formation OVARY
Fertilisation
The pollen grain lands
STIGMA
on the sticky stigma,
and produces a pollen
tube.
STYLE
OVARY
Fertilisation
STIGMA
The pollen tube,
containing the male
STYLE
nuclei, grows down
through the style
OVARY
Fertilisation
STIGMA
STYLE
OVARY
The pollen tube
continues until it
reaches the embryo
sac of the ovule in the
ovary
Fertilisation
The fertilized egg
then divides by STIGMA
mitosis and grows into
a seed which will
become a new plant.
STYLE
The layers around the
ovule harden and
become the seed coat.
OVARY
The male nucleus in
the pollen tube fuses
EMBRYO SAC
with the egg nucleus
in the embryo sac.
EGG NUCLEUS
In some plants the ovary grows into a
fruit to help with seed dispersal.
Flower to Fruit
20.4 What happens to the floral
parts after fertilization?
wither and
drop off remains of stigma
and style scar
sepal stamen
integument seed
petal coat
ovary fruit
wall wall
ovule seed
ovum embryo
A Bauhinia flower Fruit(pod) splits
after fertilization open to two halves
Fruits and seeds
Fruit
consists of
protects helps
fruit wall seed plant dispersal
made up of
seed protects undeveloped provides food
coat plant embryo food store
Fruits and seeds
Structure of a mung bean seed
micropyle
● a hole through which
embryo absorbs water
before it germinates hilum
seed coat ● a scar on the
● surrounds the embryo surface of the
and protects it from coat; formed
damage and against when the ovule
attack of detaches from
micro-organisms such the ovary wall
as bacteria and fungiExternal appearance
Structure of a mung bean seed
plumule
● develops into
the shoot
radicle embryo
● develops into
the root
cotyledons
● act as food stores
● contain starch and
proteins to supply
food for the plumule
Embryo cut opened and radicle to develop
Dispersal of seeds and fruits
Why seeds and
fruits
have to be dispersed
to
distances far away
from parents ?
To colonize new areas
which are suitable for
To reduce seed germination and
overcrowding and survival of species.
competition for
materials.
Dispersal
wind dispersal animal dispersal
adaptive features of fruits and seeds
are
• small • brightly-coloured
• light • sweet, juicy and good to
• may have wings/feathery eat (succulent)
hair • may have hooks
Germination
Flower Structure Pollination Fruit Development Seed Dispersal Germination Test
Germination
What’s needed?
Water
- to hydrate
the
Oxygen
protoplasm, to - For aerobic
mobilise respiration to
enzymes, to supply energy
hydrolyse for growth
stored food
(starch)
Warmth – to enable
enzymes to work
The seed contains the embryo
plant and cotyledons (starch
stores) Testa Water enters the seed
through the micropyle
and activates enzymes.
Plumule
(embryo shoot)
The water also softens
the testa to allow it to
split.
Radicle
(embryo root)
Micropyle Cotyledon
Flower Structure Pollination Fruit Development Seed Dispersal Germination Test
Enzymes are used in seed
germination
Plumule
The enzymes break
starch down into
starch maltose and then
glucose. The glucose
is used in respiration
amylase
to provide energy for
secreted
embryo plant growth
ab
so
rbe
d maltose
Radicle
This is the first part to
grow out of the seed
as it needs to absorb
more water
Flower Structure Pollination Fruit Development Seed Dispersal Germination Test
Changes in dry mass of the
germinating seed:
Seed loses weight as it uses
up starch stores in the
cotyledons as the seedling
cannot photosynthesise yet
Dry mass/g
Weight increases as
the seedling can
photosynthesise and
Dry mass is the plant grows
mass of solid
matter with all
water removed
Days
Flower Structure Pollination Fruit Development Seed Dispersal Germination Test
Conditions required for germination
Pyrogallol (absorbs oxygen)
No light
Oxygen Oxygen Oxygen Oxygen
present present present present
No
oxygen
moist dry moist moist moist
4 oC Warm Warm Warm Warm
A B C D E
Flower Structure Pollination Fruit Development Seed Dispersal Germination Test
Seed germination
4
1 2
1.4. The
The
3. seed
The
leaves
first
germinates
are
leaves
now fully
begin
and the
photosynthesising
to first
uncurlgrowth
and is
and2. providing
The first
photosynthesise.
seen. allroots
The the and
stored
The shootisbegin
nourishment
food
food
store tothe
utilised.
that
in the grow.
seed
plant
is
Food stores in theused seedup.
needs.are still being used.
