Sexual Reproduction in
Animals
Lesson 2 : Human
Reproduction (cont’d)
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Mrs Theresa Teo/2003
REVISION OF PREVIOUS LESSON
We went through
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the need for reproduction.
the male and female gametes in animals.
internal and external fertilisation
development of eggs internally and externally
the place where male and female gametes
are produced or stored in human beings.
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Let’s share our views about having
children – Activity 1
Discuss in your groups :
1. Would you like to have children?
2. How many children would you like?
3. At what age would you start considering
getting married?
4. Should people get married before they
have children? Why?
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Mrs Theresa Teo/2003
TODAY’S LESSON
By the end of the lesson, you should have
an understanding of how human beings are
reproduced or how children are produced.
Let’s look at the parts of the male and
female reproductive system again.
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Reproductive system - Male
/Cowper’s gland
epididymis
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Reproductive system –
Female
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Mrs Theresa Teo/2003
TODAY’S LESSON
We know that the male gamete is found in the
testes and the female gamete is found in the
ovaries.
The question is how do we get the sperm and the
egg to fuse together so that the egg can be
fertilised and what happens after the egg is
fertilised in human beings (in mammals).
This cannot happen at any age. It can only start
happening after the human being matures or
reaches puberty.
Physical maturity is one thing. Mental maturity is
another. What do you think?7
Mrs Theresa Teo/2003
Puberty (Physical maturity)
The age at which secondary sexual characteristics appear
and gametes (sex cells) begin to be produced or released
Some general changes in both girls and boys.
• Height increases
• Face changes
• Armpit hair and pubic hair start to grow
• Sex organ develops and is capable of releasing the sex
cells.
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Sex Cells
• Male Sex Cells
– Called sperms
– Produced by testes
– Produced until old
age
– Capable of moving
on their own
– Millions of sperms
released during
each ejaculation
• Female Sex Cells
– Called eggs/ova
– Produced by
ovaries
– Produced until
menopause
– Not capable of
moving themselves
– Only one is
released during
ovulation
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Human
Sperm
Contains mitochondria
which provides energy for
the sperm’s activity
Enables the sperm to swim
towards egg
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Human Egg
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Puberty
•Specific changes in the male
 Boys usually reach puberty at an average age of 13
years.
 Sex organ starts to produce sperms
 Shoulder and chest become broader
 Voice breaks and deepens
 Moustache and beard start to grow
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Mrs Theresa Teo/2003
Puberty
 Specific changes in the female
 When a baby girl is born, the ovaries already contain around 400 000
ova or eggs.
 Girls tend to mature two years earlier than boys (average age of 11)
 When she matures, a small fraction of these eggs mature (approx. 450)
and is released from alternate ovaries each month.
 Breasts develop
 Hips widen
 Undergoes the menstrual cycle
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MENSTRUAL CYCLE
1.
It is a cycle that mature girls go through.
2.
It is the sequence of changes which occurs in the wall of the
uterus in the course of 28 days (approx. once every month)
3.
The changes are controlled by hormones secreted by the ovary.
4.
3 main events occur in the cycle.
a.
The lining of the uterus wall thickens to prepare for the
coming of the embryo.
b.
Ovulation – the release of ovum from the ovary once
every month
c.
Menstruation – lining of uterus wall breaks down and
flows out of the vagina as blood.
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Menstruation happens only if the ovum (i.e the egg)
does not get fertilised by a sperm.
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Menstrual Cycle
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What if fertilisation does occur?
HOW DOES FERTILISATION OCCUR?
1.
There is mating .
2.
Sperms are introduced into the female through the
vagina.
3.
The sperms swim through the uterus to the oviduct
towards the egg.
4.
A sperm bumps into the egg.
5.
The sperm penetrates the egg membrane.
6.
The tail drops.
7.
The egg membrane thickens to prevent other sperms
from entering.
8.
Mrs Theresa Teo/2003
16 the egg nucleus.
The sperm nucleus fuses with
Fertilisation
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Fertilisation
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What happens after fertilisation?
1. The egg is now a zygote.
2. The zygote divides into hundreds of cells to become an
embryo as it passes further down the Fallopian tube or
oviduct on the way to the uterus.
3. The embryo then becomes embedded in the uterine wall
which is now thick and rich in blood vessels. This is
called implantation.
4. This embryo continues to divide and the blood, blood
vessels and heart are among the first features to develop.
5. A fluid-filled sac called the amniotic sac protects the
embryo.
6. The embryo gets nutrients, oxygen and antibodies from
the blood vessels in the lining of the uterus called the
placenta.
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What happens after fertilisation?
7. The embryo passes the urea and carbon dioxide back to
the mother.
8. The embryo is attached to the placenta by the umbilical
cord.
9. Eventually, the cells develop into different types of tissues
and organs.
10. When all the main parts of the body and the internal
organs are formed, it is called a foetus.
11. Growth and development continues till around the 40th
week when the muscles of the uterus start to contract and
the process of giving birth begins.
12. The amniotic sac breaks and the contractions increase in
intensity and frequency, and the baby is pushed through
the vagina and out of the female’s
body.
Mrs Theresa Teo/2003
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Foetus Development
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5 months
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9 months
Fetus Development
and Structure
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Birth of baby
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For you to ponder about
• physical maturity vs mental maturity
• Is mental maturity (i.e. are you ready to
have children mentally) important?
• What do you mean by being mentally
ready?
• What must you get ready before children
come along?
• JOT DOWN YOUR THOUGHTS ON YOUR
WORKSHEET. I’M INTERESTED TO KNOW.
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