Year 8 Reproduction Notes
2014 (Mr. Hung)
Name: ____________
Part A: Reproduction in Humans (Health Education)
Reproduction is the process by which new living things are produced to replace those
which die from disease, old age or are eaten by predators. Many animals (including
humans) and plants reproduce by sexual reproduction.
Vagina
Uterus (womb)
Sexual reproduction requires sex cells. Female animals produce eggs from the
ovaries, male animals produce sperm from the testes.
Egg cell
Sperm cell
sperm about to enter the ovum
.
To make a new individual, a male and female sex cell must fuse (join) together. This
is called fertilisation. In humans fertilisation occurs in the oviduct(egg tube).
Each month an ovary
releases an egg cell
into an oviduct.
The sperm cells swim
through the uterus
to the oviduct.
If they meet an egg The fertilised egg
cell, fertilisation will cell divides into a ball
occur.
of cells (an embryo).
The embryo travels
down the oviduct and
implants into the
uterus lining.
Year 8 Science - Reproduction: Summary Notes 2014 – Mr. Hung
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Part B: Two Main Types of reproduction
There are two types of reproduction: asexual and sexual.
Asexual
Sexual
Asexual reproduction
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one parent dividing in two to give new individuals.
is much quicker than sexual reproduction
produces individuals which are identical to the parent. This can be a disadvantage as
all individuals have the same weaknesses e.g. prone to the same illnesses.
Sexual reproduction
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involves two parents (one male, one female) producing sex cells which join together to
make a new individual
takes much longer than asexual reproduction
produces individuals which are different from one another
Asexual Reproduction
Number of organisms
One parent needed
involved
Sexual Reproduction
Two parents are required to mate
Cell division
Simple – mitosis – one to two with same
genetic material
Cells divide by Meiosis – one to 4 cells
called sex cells or gametes
Types
Budding, binary fission, vegetative
reproduction, fragmentation, spore formation
Advantages
Time Efficient; no need to search for mate,
requires less energy
Variation, Unique., organism is more
protected
Disadvantages
No variation - if the parent has a genetic
disease, offspring does too.
Requires two organisms, requires more
energy
involvement of sex
cells
no formation or fusion of gametes(sex cell)
formation or fusion of gametes(sex
cell) occurs - fertilisation
found in
lower organisms – bacteria, sponges
higher invertebrates and all vertebrates
Year 8 Science - Reproduction: Summary Notes 2014 – Mr. Hung
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Part C: Different types of Asexual Reproduction
Type
Binary fission
Budding
Spore
formation
Vegetative
reproduction or
Propagation
What is it?
simplest form of asexual reproduction parent organism divides into two parts that
are equal - daughter cell is identical to
parent
parent cell divides into two unequal parts
or a smaller body part is grown to become
an adult.
spores are released by parent organism,
spores germinate and grow to form new
individuals
a type of asexual reproduction found in
plants where new independent individuals
are formed without the production of
seeds or spores.
a new organism grows from a fragment of
the parent. Each fragment develops into a
mature, fully grown individual.
Fragmentation
Or
Regeneration
Parthenogenesis an unfertilized egg develops into a new
individual.
Cloning
the production of multiple, identical
offspring. A clone is an animal who is
genetically identical to its donor "parent
Examples
Bacteria and protozoans such as
Euglena, Amoeba, Paramecium.
Yeast, sponge and hydra
Bread mould, mosses and ferns
Onion, Strawberry, Carrot, Potato
Some flat worms (eg. Planarian),
some echinoderms like star fish
and sea anemones.
water fleas, aphids, stick insects,
some ants, bees and parasitic
wasps), some reptiles, amphibians
and fish
Lamb, cow, fish
Year 8 Science - Reproduction: Summary Notes 2014 – Mr. Hung
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Year 8 Science - Reproduction: Summary Notes 2014 – Mr. Hung
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Vegetative propagation involves artificial and natural means by which plants reproduce.
Types of Vegetative Propagation
Types
What is it?
consists of fleshy layers of leaves that
Bulb
store food for the developing plant; there
are lateral (side) buds which may grow to
form new plants.
swollen underground stems that can
Stem Tuber
develop into new plants; a tuber has
leathery skin and lots of eyes
contain a solid mass of stem tissue, rather
Corm
than concentric rings of leaves; this
consists of one or more internodes with at
least one growing point.
Runner or Stolon some plants produce long side shoots that
develop roots, eventually forming a new
plant
these are underground stems that can
Rhizome
develop into new plants. They grow
sideways in the soil and have a shoot with
leaves.
Swollen roots are full of stored food
Root Tuber
Sucker
Cutting
Layering
Grafting
Tissue Culture
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a new stem grows from the base of an old
one or root, forming a new plant.
pieces of roots, stems, or leaves are cut
and develop into new plants
a portion of an aerial stem grows roots
while still attached to the parent plant and
then detaches as an independent plant.
a cutting from one plant, called the scion,
is attached to the main body of a rooted
plant, the stock
a technique used to grow plants from
pieces of plant tissue
Examples
Onion, garlic, lily, tulip,
Daffodil
potato, and turnips
Gladiolus, Taro, Freesia
Strawberry, some grasses,
spider plant.
Ginger, Asparagus, Bamboo,
Iris, Banana
Carrot and beetroot, sweet
potato and yam
Banana, Rose
African violet
purple and black raspberries,
trailing blackberries.
Grapes, seedless oranges
African Violet
Asexual reproduction in plants is called Vegetative Propagation.
In Vegetative Propagation, the roots, stems, or leaves can grow a new plant.
5 kinds of natural vegetative propagation:
1. Bulbs: a short underground stem surrounded by colourless leaves that store food and
protect the bulb.
2. Corms: contain a solid mass of stem tissue, rather than concentric rings of leaves; this
consists of one or more internodes with at least one growing point.
3. Tubers: a underground stem that stores the food created above ground. A tuber contains
“eyes” that will sprout a new plant. These eyes are also called buds.
4. Runners: the main stem of a plant grows straight up through the dirt and new plants grow
from it. Each runner has a bud at the end for the new plant.
Year 8 Science - Reproduction: Summary Notes 2014 – Mr. Hung
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5.
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Rhizomes: a thick underground stem that stores food. Rhizomes contain nodes that develop into new
plants.
3 kinds of artificial vegetative propagation:
1.
2.
3.
Cuttings: created by cutting a stem or leave from a plant and place into water. After a few days you
will be able place into soil.
Grafting: created by attaching a stem cutting of one plant to another plant and they begin to grow
together. Can only be done with plants that are related.
Layering: when the stem of plant does not hold the plant up, and drooped part touches the earth.
When this happens roots start to grow from the leaf/flower touch the earth. Can be either artificial or
natural.
Year 8 Science - Reproduction: Summary Notes 2014 – Mr. Hung
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Part D: Development in Other Animals
Some young are very different from their parents. Metamorphosis is a complicated
process that some animals undergo when they change from juveniles to adults.
Caterpillar
or larva
pupa
Adult
butterfly
Examples of animals that undergo this process are frogs, toads, midges, moths and
butterflies.
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Two kinds of metamorphosis are complete and incomplete.
A complete metamorphosis has four stages: egg, larva, pupa and adult, eg. Silkworm,
bettle and butterfly as well as Frog .
An incomplete metamorphosis has three stages: egg, nymph and adult eg. Cockroach.
Part E: Fertilisation is necessary for Sexual Reproduction
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In sexual reproduction, two parents donate genes to their young, resulting in
offspring with a mix of inherited genes.
These genes are donated through a process called fertilisation. Fertilisation is
defined as the moment when a sperm and egg join together and form a zygote
(fertilised egg), it consists of both genes (DNA) from mum and dad, will develop into
a new individual.
There are two mechanisms by which fertilisation can take place.
o External fertilisation - the eggs are fertilised outside of the body
o Internal fertilisation - the eggs are fertilised within the female reproductive
tract.
For fertilisation to occur during reproduction in species, three key requirements
must be met:
o male and female gametes are produced and mature at the same time
o gametes must meet a watery environment.
o Terrestrial organisms have overcome the problem of fertilisation in a dry
environment by using internal fertilisation, that is, fertilisation occurs within
the female body. Male gametes are transferred directly into the reproductive
tract of the female so the gametes remain in a moist environment.
Without internal fertilisation organisms could not colonise and live permanently in
terrestrial environments. Internal fertilisation means that terrestrial organisms are
able to complete the entire reproductive cycle without having to return to an aquatic
environment.
Year 8 Science - Reproduction: Summary Notes 2014 – Mr. Hung
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Differences between External and Internal Fertilisation
Internal Fertilisation
External Fertilisation
What is it?
Sperm meets the egg while the egg is still
inside the female body
Sperm (male) meets the egg (female)
while the egg is outside the female body
Conditions?
Need to have protection for the
developing egg
Usually happens in wet environment.
Male and female releases their gametes
(cells for reproduction) into their
surrounding
Advantages?
Usually result in production of large
number of offspring
Disadvantages?
Protection for the embryo ( the
developing young) as it develops within
the mother
Limited number of young
EXAMPLES
Mostly reptiles and mammals
Mostly amphibians and fish. However,
not for fish like guppies that give birth.
The presence of predators reduces the
survival of the eggs
PART F: SEXUAL REPRODUCTION IN FLOWERING PLANTS
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Sepals protect the flower when it is in bud.
Brightly coloured and scented petals attract
insects for cross-pollination.
The stamen is the male reproductive organ
and it consists of the filament and the
anther.
The filament supports the anther; pollen,
which contains the male sex cell, is produced
by the anther.
The female reproductive organ is the pistil
and this is divided into the stigma, the style
and the ovary.
The stigma receives the pollen – by wind or animals.
Pollen grains germinate on the stigma, growing a pollen tube downwards through the
style towards the ovary.
The ovary may contain several ovules, each of which produces an egg.
When a pollen tube enters an ovule a male nucleus fuses with the female ovum fertilisation takes place and produce a zygote.
Each zygote will develop into a seed.
More Information about Reproduction in Flowering plants:
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Pollination is the transfer of pollen from the anther of a stamen to the stigma.
Fertilisation is the fusion of two gametes; in flowering plants this will be one of the
male nuclei from the pollen grain and the ovum inside an ovule of the ovary.
Pollination can come from the same plant (self-pollination) or other plant (crosspollination)
Year 8 Science - Reproduction: Summary Notes 2014 – Mr. Hung
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Cross-pollination is preferable over self-pollination because it involves two different
parent plants and therefore results in greater variation in the offspring.
Differences between wind-pollinated flowers and insect-pollinated flowers
Insect Pollinated
Wind Pollinated
large, brightly coloured petals - to attract insects
small petals, often brown or dull green - no need to
attract insects
often sweetly scented - to attract insects
no scent - no need to attract insects
usually contain nectar - to attract insects
no nectar - no need to attract insects
moderate quantity of pollen - less wastage than with
wind pollination
pollen produced in great quantities - because most does
not reach another flower
pollen often sticky or spiky - to stick to insects
pollen very light and smooth - so it can be blown in the
wind and stops it clumping together
anthers firm and inside flower - to brush against
insects
anthers loosely attached and dangle out - to release
pollen into the wind
stigma inside the flower - so that the insect brushes
against it
stigma hangs outside the flower - to catch the drifting
pollen
stigma has sticky coating - pollen sticks to it
stigma feathery or net like - to catch the drifting pollen
Structure
Function
Sepals
Green; protect the unopened flower bud
Petals
may be brightly coloured to attract insects
Stamens
the male parts of the flower consisting of the anther held up on the filament
Pistil
The female parts of the flower consisting of the stigma, style and ovary
Anthers
produce male sex cells (pollen grains).
Stigma
the top of the female part of the flower which collects pollen grains
Ovary
produces the female sex cells (ovules)
Nectaries
produce sugary nectar which attracts insects
Pedicel
The flower stalk to support the flower
Year 8 Science - Reproduction: Summary Notes 2014 – Mr. Hung
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