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INTRODUCTION TO REPRODUCTION
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ASEXUAL REPRODUCTION
Living things can reproduce in two different ways:
(1) Sexually through the union or mating of male and female; or
(2) Asexually which does not involve the union of male and female.
If you take a cutting of a plant and place it in soil, it will grow into a new plant. Gardeners often use this
method to grow new plants. Some plants develop new plantlets, such as runners (strawberries) or side
branches (busy lizzy).
Strawberry plant with runners
Potato plant with underground tubers
In other plants, storage organs can develop underground which grow into new plants. This is how potatoes
are formed. Mushrooms also reproduce asexually, by means of spores.
As only one parent is involved in asexual reproduction, all the offspring have exactly the same genes as
their parent. The offspring are identical and they are called clones.
SEXUAL REPRODUCTION
Sexual reproduction, which involves two parents, occurs in most living plants and animals. The offspring
that result from sexual reproduction are similar to the parents, but not identical.
Sexual reproduction always involves the joining of two sex cells called gametes in a process called
fertilisation. In humans, the gametes are the ovum and the sperm.
The male and female reproductive systems in human beings are completely different because they have
different functions.
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The function of the male reproductive system is
to make sperm and to get them as close as
possible to the ovum.
The function of the female reproductive system
is to make ova and to provide a safe place for
the baby to grow during pregnancy.
PUBERTY
Male and female reproductive systems don’t develop fully until the person reaches puberty. After puberty
girls produce ova, or eggs, and boys make sperm. Many body changes happen at puberty as a child
develops into a young adult.
Male sex hormones, which are made in the testes, control the changes that happen to boys. They grow
taller, grow hair on their body, their shoulders broaden and their voices break.
Female sex hormones, which are made in the ovaries, control the changes that happen to girls during
puberty. They grow taller, their hips widen, hair grows on their body and their breasts begin to develop.
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At puberty, girls start menstruating. During the menstrual cycle, a girl’s body goes through a sequence of
changes, including releasing an egg (around day 14). This process is called ovulation. The egg moves
through the fallopian tube towards the uterus. Near the time of ovulation the lining of the uterus
thickens. The uterus is then ready to receive and nourish the fertilised ovum. If the ovum is not fertilised
it dies and the lining of the uterus starts to break up. Within about two weeks the woman has her period.
Blood and dead cells pass out through the vagina. This is called menstruation. The 28-day cycle of
ovulation, lining growth and menstruation is called the menstrual cycle.
FERTILISATION AND BIRTH
The sperm cell carries half of the information needed for reproduction and the egg cell carries the other
half. To produce an offspring the sperm and egg have to meet. This means that the male and female have
to come together. This is called copulation.
When a sperm cell meets an egg cell, the head of the sperm fuses with the egg. The information in the
nucleus of the male's sperm can combine with the information in the nucleus of the female's egg to
produce an offspring. This important event is called fertilisation.
Fertilisation takes place within the fallopian tube. The uterus is the place where the foetus develops
during pregnancy.
After fertilisation, a ball of cells grows and develops first into an embryo and then into a foetus. The
placenta develops and helps to keep the foetus alive by exchanging substances between the mother and
the foetus. The foetus gets all its food and oxygen from the mother through the placenta and the
umbilical cord. For nine months it grows and develops inside the mother’s uterus. When it is time to be
born, the muscles in the wall of the uterus start to contract and push the foetus out. This is called labour.
The baby is pushed out head first through the vagina. Once the baby is outside the mother’s body it starts
to breathe by itself and the umbilical cord can be cut.
GENETICS
Genetics is the part of biology that tells us why we are the way we are. It tells us why we have inherited
certain characteristics from our parents, some of which we might be grateful for and some of which we
certainly aren't!
Some of the characteristics we inherit are easy to see, like eye colour. Others, like your blood group, are
not so obvious. The characteristics that are passed on to you by your parents are called ‘inherited
characteristics’.
Tongue rolling
Eye colour
Blood type
A complicated set of chemical instructions is needed to build a human body. Nearly every cell in your
body has these instructions. They are stored in the nucleus in 23 pairs of chromosomes.
Chromosomes are made of DNA and protein. Small sections of these chromosomes are called genes. You
have over 100,000 genes all together and each gene carries a chemical instruction for a different
characteristic.
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