Download Human reproduction - NSW Department of Education

Science Stage 5
NEW SOUTH WALES
D E PA R T M E N T
OF EDUCATION
AND TRAINING
Human reproduction
Set 2: Reproducing
Number: 43938
Title: Human Reproduction
This publication is copyright New South Wales Department of Education and Training (DET), however it may contain
material from other sources which is not owned by DET. We would like to acknowledge the following people and
organisations whose material has been used:
Extract from Science Syllabus Years 7-10 © Board of Studies, NSW 2003
Outcomes pp iii-v
Photograph of baby walking with father © Julie Haeusler
Front Cover, Cover
Sets 1 and 2
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i
Reproducing
Contents
Lesson 7
Sexual reproduction .............................................. 1
Lesson 8
How life begins – sperm meets egg................... 11
Lesson 9
From fertilised egg to embryo............................ 21
Lesson 10
From embryo to foetus ........................................ 29
Lesson 11
From foetus to baby ............................................. 39
Lesson 12
Multiple births........................................................57
Checking your progress .......................................................................... 69
Suggested answers ................................................................................... 71
ii
What do you need ?
Here is a reminder of the items you need for this set. To save time,
it might be a good idea to get all these things ready before you start.
Items marked with a star, *, are optional.
Lesson 7
•
coloured pencil
Lesson 9
•
scissors
•
glue
Lesson 10
•
ruler
•
red and blue pencils
Lesson 11
•
square piece of plastic wrap (about 30 cm2)
•
1 piece of red wool and one piece of blue wool,
each about 12 cm long
•
coloured pencils
•
•
one or two cotton balls or a small piece of crumpled paper
•
sticky tape
scissors
1
Lesson 7
Sexual reproduction
So far in this unit, you have looked at the part of our life cycle where
we grow and develop from children into adults. We called this part
'growth and development'. But, as we all know, adults grow old and
eventually die.
For the human species to continue to survive, enough adults need to
produce offspring to replace those that die. Reproduction must
take place to complete the life cycle. (The prefix re- means again
and production is making. So reproduction is making again.)
Now we'll look at how humans reproduce and so complete the life cycle.
Shade in this part on our life cycle diagram below.
adult
child
baby
growth and
development
reproduction
adult female
adult male
pregnant
female
Humans produce offspring by a type of reproduction called
sexual reproduction. And so do most other animals, and many plants.
Human reproduction Set 2
2
What does sexual reproduction mean?
To make a baby, two parents are needed – a mother and a father.
A reproductive cell from the father (a sperm) must join with a
reproductive cell from the mother (an egg) before the baby can begin
to form.
Reproductive cells are often called sex cells. The eggs (ova) are
female sex cells and the sperm are male sex cells.
Can you see why we say humans reproduce by sexual reproduction?
Human reproduction is called sexual reproduction because
two different sex cells (a sperm and an egg) must join to produce
a new life.
Here is a diagram summarising sexual reproduction in humans.
Sexual reproduction in humans
female
male
egg
(female sex cell)
sperm
(male sex cell)
new cell
developing
baby
Human reproduction Set 2
aa
3
Compare the diagram of human reproduction with the following
diagram.
The animal in this picture lives in water and can only be seen clearly
under the microscope. I have drawn it much larger here to show you
how it reproduces by splitting into two halves.
aa
REPRODUCTION
one organism
two organisms
Many other tiny animals and plants reproduce in this way.
Is this sexual reproduction? Explain.
There are no sex cells joining to form the two new organisms.
The offspring have formed from one parent splitting into two.
So this is not sexual reproduction. (It is called asexual reproduction.
The prefix a- means not. So asexual means not sexual.)
Human reproduction Set 2
4
Cells that produce a new human being
We are made up of millions of tiny cells. Each of these cells has
a nucleus which is the control centre of the cell. The nucleus contains
chromosomes made of DNA that control everything that goes on
in a cell.
There are many different kinds of cells in our bodies, each doing
a special job. The function of the sex cells (the sperm and eggs)
is to start new lives.
Like all other cells in our bodies, sex cells have their own
special structure so they can perform their role.
What do sperm and ova look like?
Here are diagrams of human sex cells.
Compare the size and structure of the egg and the sperm.
Human egg cell (magnified 200 times)
nucleus – contains genetic information
yolk – contains stored food
Human sperm cell (magnified 3 000 times)
tail – lashes to and fro
helping the sperm to swim
head
nucleus – makes up most of
the head of the sperm,
and contains DNA
Which is smaller – a human egg cell or a human sperm cell?
Did you work out the answer from the magnification number?
A sperm is much smaller than an egg.
Human reproduction Set 2
5
Use the diagrams to answer the questions below.
The role of a sperm is to get to the egg so it can join with it
to form the first cell of a baby. How is a sperm suited to its role?
A sperm has a long tail to help it swim to the egg.
The egg cannot move on its own. Its role is to join with a sperm
and to supply the new cell with food during the first few days
of its development. How is an egg cell suited to its role?
An egg cell is very large so it can store a lot of food.
What important part of a cell can you see in both the sperm and the egg?
Both sex cells have a nucleus which contains DNA. (DNA contains the
plans or instructions for a living organism in a chemical code.)
Adult males produce sperm by the millions!
How many sperm are shown
in this diagram?
The easy way to count sperm
is to count heads (or tails).
There are ten sperm in this diagram.
Human reproduction Set 2
6
Chromosomes in sexual reproduction
DNA (deoxyribonucleic acid) is the chemical inside a cell's nucleus
that stores information about how the cell will grow and function.
The DNA is tightly twisted into rod-shaped structures called
chromosomes (CROWM-o zowms). Sections along each chromosome
are called genes (JEANS). Each gene is responsible for a characteristic
that the organism may develop.
Each human sex cell contains 23 chromosomes.
An egg has 22 chromosomes and 1 female sex chromosome called
an X chromosome.
A sperm also contains 22 chromosomes plus either an X chromosome
or a male sex chromosome called a Y chromosome.
Now complete these sentences.
When an
and sperm join, they form the first cell of
the new baby. This first cell contains
chromosomes
from the egg and
chromosomes from the sperm.
So the baby's first cell contains a total of
chromosomes.
The first cell will have an
chromosome from the egg
and either an X or a Y chromosome from the
.
Please turn to the answer pages to check your answers.
When an egg and a sperm join, the new cell that forms has a complete,
or double, set of chromosomes – half from the mother and half from
the father. It is this complete set of chromosomes that will control how
the first cell develops into a baby, then into a child, then into an adult.
This is why most children look something like each parent – DNA has
been passed on to them from both the mother and the father.
I have summarised this for you in the next diagram.
Human reproduction Set 2
7
egg
contains one set of DNA
from the mother
sperm
contains one set of DNA
from the father
new cell
has one complete,
or double, set of DNA
in its nucleus
baby
child
adolescent
adult
Human reproduction Set 2
8
Boy or girl?
We take it for granted that when a baby is born, it is either a boy or a girl.
There is a 50% chance it will be a boy and a 50% chance it's a girl.
Have you wondered why this happens?
All eggs contain
an X chromosome
+
22 chromosomes
X chromosome
23 chromosomes
A
Half of sperm contain
an X chromosome
+
22 chromosomes
X chromosome
Half of sperm contain
a Y chromosome
+
23 chromosomes
22 chromosomes
Y chromosome
23 chromosomes
B
C
What happens when an egg (A) joins with sperm B?
What chromosomes will be in the first cell of the baby?
The baby's cell will contain 22 and X chromosomes from the mother (egg)
and 22 and X chromosomes from the father (sperm).
The baby's chromosomes will be 44 chromosomes and 2 X chromosomes.
2 X chromosomes are written as XX.
A cell that contains XX chromosomes develops into a girl.
Every body cell in a female has 44 chromosomes and XX sex chromosomes.
What happens when an egg (A) joins with sperm C?
What chromosomes will be in the first cell of the baby?
Look in the answer pages if you'd like to check your answer.
A cell that contains XY chromosomes develops into a boy.
Every body cell in a male has 44 chromosomes and XY sex chromosomes.
Which parent – the mother or the father –
is responsible for causing the sex of the baby?
__________________________________
The father is responsible (because a sperm can contain either an X chromosome
or a Y chromosome but an egg can contain an X chromosome only.)
Exercise 7
Now you are ready to complete send-in Exercise 7.
Human reproduction Set 2
9
Send-in page
Lesson 7:
Name
______________________________
Sexual reproduction
Exercise 7
Here are diagrams of two human cells.
Use these diagrams to answer the questions below.
A
B
Q
l.
(a) What is the name of the cell labelled A?
______________________
(b) What is the name of the cell labelled B?
______________________
(c) i.
2.
Name the part of the cells labelled Q.
____________________
ii. What chemical inside Q stores information?
_____________
iii. What structures are made of this chemical?
______________
iv. What are sections of these structures called?
_____________
Explain how each of the cells is suited to its role.
Cell A
_____________________________________________________________
Cell B
______________________________________________________________
Human reproduction Set 2
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3.
Use the diagram to the right
to explain why human reproduction
is an example of sexual reproduction.
4
(b) Explain how DNA his passed on from parents to offspring.
Human reproduction Set 2
11
Lesson 8
How life begins – sperm meets egg
In this lesson, we will look at how the sperm gets to the egg
to start a new life. But first, let’s check what you remember
about the making of eggs and sperm.
Where are sperm and eggs made?
Refer to the following diagrams as you complete the summary below.
Male reproductive organs
Female reproductive organs
fallopian
tube
ovary
vas
deferens
uterus
vagina
penis
testis
•
Eggs (or ova) develop in a woman’s
•
One egg (or one ovum) is released about every
•
Once an egg is released, it enters the
•
The release of an egg from the ovary is called
•
Sperm are produced in a man’s
•
Sperm leave a man’s body through the
Now turn to the answer pages to check your answers.
Human reproduction Set 2
.
.
.
.
.
.
12
How do sperm enter a woman’s body?
If a man and a woman want to have a baby, a sperm from the man
has to reach an egg while it is inside the woman’s fallopian tube.
The woman and the man bring the sperm and the egg together
by having sexual intercourse.
When a man is about to pass sperm to a woman, the couple move
close together. They become sexually aroused and the man’s penis
begins to change shape. At first the penis is soft and hangs downwards.
Soon it receives an extra flow of blood from the body causing it
to become stiff and stand upright (erect). This is called an erection.
The penis becomes erect so that the man can push it into
the woman’s vagina.
As the man moves his penis up and down inside the vagina,
the muscles around each vas deferens and testis start to contract (shorten).
This forces semen, containing millions of sperm cells, to spurt out
through the penis into the vagina. The release of semen from the penis
is called ejaculation (e-JACK-you-lay-shun). It is also often called
orgasm (OR-gaz-m), climax, or ‘coming’.
The placing of the penis inside the vagina and the passing of sperm
from a man to woman is called sexual intercourse. Other names often
used instead of sexual intercourse are copulation (COP-you-lay-shun),
‘making love’ and ‘having sex’.
Both men and women may give and receive pleasure during
sexual intercourse. People who are sexually mature are able
to have intercourse. However, all cultures and religions have
their own ideas of when people should be allowed to have intercourse
and when they should not. People need to look to their own values
and those of their family and culture before making up their minds
about sexual intercourse outside of marriage.
Human reproduction Set 2
13
How do sperm get to an egg?
What happens to the millions of sperm that are released
inside a woman’s vagina during sexual intercourse?
Let’s follow the journey of the sperm by looking at the next diagram
and the information about it written as points below.
egg just released from ovary
➀
➃
fallopian tube
➁
ovary
➄
uterus
sperm
➂
vagina
•
•
•
•
•
Many of the sperm don’t get through the narrow opening
of the uterus.
_______
Some sperm swim into the uterus but most get no further.
(They may run out of energy or be killed by warmth or
substances inside the uterus.)
_______
Some of the stronger sperm move up through the uterus
towards the fallopian tubes.
_______
Some of these take a wrong turning and swim up
the empty fallopian tube.
_______
Some of the sperm enter the fallopian tube which contains the egg.
They swim towards the egg helped by movements of their tails.
_______
On the line beside each point above, write the number from the diagram
which shows what is explained in that point.
Then check your answers in the answer pages.
So, of the millions of sperm that started out on the journey,
probably only a few hundred approach the egg.
Human reproduction Set 2
14
Fertilisation
What happens when the sperm meet an egg in the fallopian tube?
A few hundred sperm may reach the egg but only one enters
and joins with it.
Once the sperm and egg join, we say the egg has been fertilised.
This process is called fertilisation (FIR-till-eyes-ay-shun). In humans,
it is also called conception (con-SEP-shun). You can see some of
the stages of fertilisation in the next two pictures.
Here is the egg in the fallopian tube, surrounded by sperm.
1.
The nucleus of a sperm must join with the nucleus of the egg
for conception to occur.
What must a sperm do to reach the egg's nucleus?
2.
How many sperm have entered this egg?
Only one sperm has bored its way through the coating around the egg.
It is this sperm that will fertilise the egg.
As soon as one sperm has penetrated the egg, chemicals are produced
which stop other sperm from entering it.
Human reproduction Set 2
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Next, the nucleus in the head of the sperm must get to the egg's nucleus.
Can you see how this happens in the following diagram?
Write your answer in sentences.
nucleus of egg
nucleus of sperm swells up
and moves towards
nucleus of egg
tail of sperm
The head of the sperm breaks away from the tail and releases the sperm’s nucleus.
This nucleus swells up and moves towards the nucleus of the egg.
This is the moment of fertilisation.
The nucleus of the sperm and
the nucleus of the egg join together.
Human reproduction Set 2
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The two sex cells (egg and sperm)
become one new cell,
the fertilised egg.
It is the first cell of the baby.
This is how you and
everyone else began.
The fertilised egg is smaller
than a pinhead. But inside it,
in the nucleus, the genes on
the chromosomes contain all
the instructions and information
for a new human being to develop.
Contraception
Can a man and a woman have sexual intercourse without starting a baby?
Yes. A baby can only begin to form if they have intercourse
when there is an egg in the woman’s fallopian tube. The problem is
that you can’t know for sure whether an egg is there or not.
When people have sexual intercourse and don’t want to have a baby,
there are a number of ways that they can stop conception from happening.
These are called methods of contraception.
The prefix contra means against.
What do you think ception in the word contraception refers to?
ception is referring to conception, when a sperm fertilises an egg.
Contraception means against conception, or against fertilisation.
But not all methods of contraception prevent fertilisation!
You may learn more about contraception in your
Personal Development lessons.
Human reproduction Set 2
17
Mastery test 1
How life begins
Before you go on to look at how the fertilised egg develops,
check that you know the meaning of these terms:
conception, ejaculation, erection, fertilisation, sexual intercourse.
1.
What is fertilisation?
(A) the release of sperm from the penis
(B) the release of an egg from the ovary
(C) the loss of blood and cells from the vagina
(D) the joining of an egg and a sperm
2.
_____
Another word which means the same as fertilisation is:
(A) copulation
(B) conception
(C) erection
(D) ovulation.
3.
_____
The placing of the penis inside the vagina, usually with
the passing of sperm from a man to a woman is called:
(A) sexual intercourse
(B) ejaculation
(C) fertilisation
(D) ovulation.
4.
_____
Before the penis can fit inside the vagina,
it must become stiff and stand upright. This is called:
(A) ejaculation
(B) sexual intercourse
(C) an erection
(D) fertilisation.
_____
Check your answers in the answer pages.
Exercise 8
Please complete send-in Exercise 8
Human reproduction Set 2
18
Human reproduction Set 2
19
Send-in page
Name
______________________________
Lesson 8: How life begins – sperm meets egg
Exercise 8
1.
Briefly describe the journey of the sperm to the egg.
You may wish to write your answer as a list of steps or
as a creative story. Just remember, it must contain
all the scientific information, described accurately.
My journey to the egg
Question 2 is on the next page.
Human reproduction Set 2
20
2.
Here are diagrams showing fertilisation.
Figure S
Figure T
(a) Circle the sperm in Figure S that fertilises the ovum.
(b) Describe what has happened in each diagram.
In Figure S:
In Figure T:
Human reproduction Set 2
21
Lesson 9
From fertilised egg to embryo
In this lesson, you will look at how the fertilised egg grows
and develops into a ball of cells called the embryo (EM-bree-oh).
Once the egg is fertilised, the woman is said to be pregnant.
The period of time during which the baby develops inside the mother
is called gestation (jest-AY-shun). In humans, this is about 38 weeks,
or a bit over nine months.
Where does fertilisation take place?
Do you remember where fertilisation takes place?
Here is a diagram to remind you.
Use it to help you fill in the spaces below.
egg
sperm
fallopian tube
ovary
uterus
vagina
Fertilisation takes place in the tube called the
During fertilisation, a
.
joins with an egg.
The fertilised egg then travels towards the
A sperm joins with an egg in the fallopian tube. This fertilised egg
then moves down the fallopian tube towards the uterus.
Human reproduction Set 2
.
22
The journey of the fertilised egg
Now look at what happens to the fertilised egg on its journey
to the uterus. You can see this in the following diagrams.
1. Fertilised egg
2. Two cell stage
3. Four cell stage
4. Eight cell stage
What is the first thing that happens to the fertilised egg?
Firstly, the fertilised egg divides to become two cells.
These two cells divide to become
The four cells then divide to become
cells.
cells.
Two cells become four cells; four cells divide to become eight cells.
The cells keep on dividing until a ball of cells is formed.
This ball of cells moves slowly towards the uterus.
Human reproduction Set 2
23
What happens to the chromosomes as the ball of cells grows?
Here is a fertilised egg.
Which sex chromosomes will this cell contain
if it is going to develop into a boy?
+
44 chromosomes
2 sex chromosomes
46 chromosomes
For a boy, the cell will contain XY sex chromosomes.
(XX would produce a girl.)
When the first cell divides to form two cells, each new cell must contain
the same 46 chromosomes. This is because each cell needs all the genes
to develop the characteristics, or features, for that baby.
What must happen to the chromosomes before the first cell divides in two?
The chromosomes must be copied so that each cell receives an identical set of DNA.
So to go from one cell to two cells, the first cell reproduces itself.
The DNA in the second cell is identical to the DNA in the first cell.
From two cells to four cells, each cell reproduces. And so on.
When cells reproduce, it is called cell division.
Making sex cells from body cells is a special kind of cell division because
when a body cell in the ovaries or testes divides, it makes sex cells with
half the number of chromosomes. But the chromosomes in sex cells
are still identical copies of chromosomes in body cells.
Why is do you think it is important that chromosomes are copied exactly
each time a cell divides?
In a growing baby, the genes in each new cell need to be identical so that
the baby can grow and develop using the same information, or plans.
Then, all the parts of the baby will be able to work together.
When sex cells are being made, chromosomes must be copied exactly so that
genes from the parent can be passed on to offspring.
Human reproduction Set 2
24
Meanwhile, what’s happening inside the uterus?
To get ready for the fertilised egg, the uterus has been growing
a new lining thickened with blood. If the egg has been fertilised
by a sperm, the lining remains. It does not break down and
flow from the body as it does during menstruation.
The menstrual cycle stops while the baby develops.
So missing a period is often a sign that a woman is pregnant.
Why doesn't the mother menstruate?
What substances are responsible for controlling the menstrual cycle?
I hope you wrote hormones!
When a woman becomes pregnant,
the growing embryo causes progesterone
to be made. Raised levels of this hormone
stop ovulation.
Which glands in the body will be affected
by higher levels of progesterone?
hypothalumus
pituitary
gland
FSH
LH
progesterone
oestrogen
If you'd like to check your answer,
turn to the answer pages.
ovary
Increased amounts of progesterone also maintain the lining in the uterus.
High levels of progesterone continue throughout pregnancy so that
the woman does not menstruate. The progesterone levels only fall
after the baby is born. Then the woman can begin to menstruate again.
So the developing baby stops the woman from menstruating!
And it's all done with hormones.
Human reproduction Set 2
25
What happens to the growing ball of cells?
The developing baby, now a ball of cells, gets to the uterus about a week
after fertilisation. It sinks into the thick lining of the uterus and goes on
growing. At this stage, it is called an embryo.
Here is a diagram showing the main changes as the fertilised egg
develops into an embryo during the first two weeks.
Day 1
Fertilisation takes place when
a sperm joins with the egg
as it travels down the oviduct
fallopian
tube
About 3 days later,
the fertilised egg moves down
the fallopian tube into the uterus. About 5 days later,
The cells keep dividing.
the ball of cells
reaches the uterus.
egg moves
down the tube
•
egg is released
from ovary
About 12 days later,
the fertilised egg is inside
the lining of the uterus.
It is now called an embryo.
ovary
Did you notice that there was only one fallopian tube in the diagram?
I left out the other fallopian tube so that I could draw the diagram
much larger.
Also, it is unlikely that there would be anything happening
in the other fallopian tube anyway!
Do you agree with my last statement? Say why you agree or disagree.
Did you remember that an egg is usually released from each ovary in turn,
every 28 days? So it is unlikely that two eggs from different ovaries
would be fertilised at the same time. It would be 28 days after the egg
in the diagram was released that an egg from the other ovary was released.
However, there are exceptions to this and you will find out
about multiple births later.
Human reproduction Set 2
26
Try this mastery test before you complete this lesson's send-in exercise.
Mastery test 2
Cell growth and reproduction
Complete the following summary.
An egg and a sperm can
As the fertilised egg moves
to reproduce by cell division.
if they meet in a fallopian tube.
the uterus, it begins
Each time a cell divides, it
an identical copy of its DNA
so that all cells in the baby will be able to
together.
Thus, every cell in the developing baby has an
set
of 46 chromosomes.
Cell division is needed so that the fertilised egg can
into a baby. A special kind of
is needed when
sex cells are formed in ovaries and testes. This special cell division
is needed so that humans can reproduce by sexual
Please turn to the answer pages and check your answers.
Exercise 9
Now complete send-in Exercise 9 on the next page.
Human reproduction Set 2
.
27
Send-in page
Lesson 9:
Name
______________________________
From fertilised egg to embryo
Exercise 9
On the bottom of this page, there are five diagrams showing what happens
when an egg is fertilised and begins to develop into an embryo.
The diagrams are not in order.
Cut out each diagram and paste it in the correct space on this page
to match its description.
2. One sperm enters
the egg.
3. The sperm’s nucleus
moves to the egg’s
nucleus and joins
with it.
1. Many sperm move
to the egg.
4. The fertilised egg
divides.
5. The cells keep
dividing.
More and more cells
are produced.
Human reproduction Set 2
28
Human reproduction Set 2
29
Lesson 10
From embryo to foetus
Let’s continue the story of how a baby grows and develops
during gestation. There are still 36 weeks to go!
Getting settled – implantation
Previously you saw that the embryo had burrowed into the lining of
the uterus by about the eighth or ninth day after fertilisation.
At this stage, it is still a tiny ball of cells only about 1 mm across.
The settling of the ball of cells into the uterus' lining is called
implantation (IM-plan-tay-shun).
thickened lining of uterus
developing embryo
implants in lining
of uterus
•
uterus wall
For the first few weeks, the embryo absorbs the food and oxygen
it needs directly from the lining of the uterus.
But as it grows, the embryo needs a better supply of food and oxygen.
It also needs a way to get rid of its wastes. The embryo begins
to develop a structure that will perform these functions for it
throughout gestation. This developing structure is called
the placenta (pla-SENT-ah).
(The placenta will also make the hormone, progesterone, to prevent
the mother from menstruating.)
Human reproduction Set 2
30
The placenta – the baby’s life support system
Soon after the embryo attaches itself to the wall of the uterus,
a mass of blood vessels grows around it. This will develop
into an organ called the placenta.
The next diagram shows the embryo about four weeks after fertilisation.
It looks nothing like a human being at this stage.
The human embryo, four weeks after fertilisation
developing
placenta
embryo
uterus
vagina
Notice how the embryo is surrounded by hundreds of tiny, root-like
blood vessels. These are all part of the developing placenta.
The diagram above is drawn to actual size. The woman's uterus is
shown at its normal size, about the size of a clenched fist.
What is the real size of the embryo about four weeks after fertilisation?
Find out by measuring the longest part of the embryo in the diagram.
longest part of embryo =
mm
Did you find the embryo was about 7 mm from top to bottom after four weeks?
Human reproduction Set 2
31
bag of
watery liquid
In this diagram, the embryo is shown
five times larger than actual size.
embryo
Even at this stage, the embryo has a beating heart and a nervous system.
And can you see that it is floating in a bag of liquid? This liquid is called
amniotic (AM-knee-ot-ick) fluid and the bag around it is the amniotic sac (sack).
The amniotic fluid acts like a cushion against any shock, such as
a bump or if the mother falls. The liquid also keeps the embryo
at the right temperature. The embryo grows and changes
inside the amniotic sac within the mother’s uterus, where it is warm
and well protected. The amniotic sac continues to grow with the
developing baby. It only breaks when the baby is about to be born.
Here is a diagram of the embryo five weeks after fertilisation.
This diagram is not drawn to scale.
Complete the diagram by adding these terms as labels:
amniotic fluid, amniotic sac, embryo, developing placenta, umbilical cord.
The human embryo, five weeks after fertilisation
Compare your diagram with the one in the answer pages.
Human reproduction Set 2
32
How does the placenta work?
Once the placenta is developed, it carries out its role of exchanging
substances between the mother and the embryo until the baby is born.
The placenta grows into a large, dense, flat organ attached to the wall
of the uterus.
The umbilical (um-BILL-i-kal) cord connects the placenta to the embryo.
The umbilical cord contains blood vessels which carry blood from
the embryo to the placenta, and from the placenta back to the embryo.
In the placenta, blood of the mother is close to the embryo’s blood
but they do not mix. They are just close enough so that substances
such as food, oxygen and wastes can pass from one to the other
through the thin walls of the blood vessels.
Here is a diagram, greatly magnified, representing part of the placenta.
You can see where the mother’s blood vessels and the embryo’s
blood vessels come close together.
How the placenta works
mother’s
blood
embryo’s
blood vessels
mother’s
blood vessels
substances pass
through here
embryo
umbilical cord
placenta
Use a red pencil to carefully follow the flow of blood from the embryo
through the umbilical cord to the placenta. (Watch out in the placenta!)
What substances pass from the mother’s blood to the embryo’s blood
in the placenta?
Food and oxygen pass from the mother’s blood into the embryo’s blood.
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What substances pass from the embryo's blood to the mother's blood
in the placenta?
Waste substances produced by the embryo pass from the embryo's blood
into the mother's blood. The mother's body is able to remove these wastes.
The embryo’s blood, carrying the oxygen and food essential for life,
then flows back along the umbilical cord to the embryo.
Use a blue pencil to follow this flow of blood from the placenta
through the umbilical cord to the embryo.
What is a foetus?
Eight weeks after fertilisation, the embryo is about 25 to 35 mm long.
You can see in the next diagram that it is now much more like a human.
Eight weeks after fertilisation
amniotic fluid
umbilical cord
placenta
Can you see the embryo’s well-developed ears, eyes, fingers and toes?
Its nose and mouth are hidden in this diagram but they are also
well developed.
From now on the baby is no longer called an embryo.
It is recognisable as a human being and is called a foetus (FEET-us).
Human reproduction Set 2
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Mastery test 3
From fertilisation to foetus
Here is a summary for you to complete.
Use the words and phrases in the list below to complete the sentences.
Use each term once only.
Terms: amniotic fluid, ball, conception, egg or ovum, embryo,
fallopian tube, fertilisation, foetus, food, placenta, protection,
umbilical, uterus, warmth.
•
A new life begins to form when a sperm enters an
This joining of sex cells is called
It takes place inside a
•
of cells and is called an
and
.
from its mother
cord.
Inside the uterus, the embryo is surrounded by a bag of
This provides
•
.
.
The embryo receives oxygen and
through the
•
, or
The fertilised egg then divides rapidly and moves down
into the
. Here, it sinks into the lining of the wall.
It is now a
•
.
and
.
.
Once all the main parts of the embryo have formed and
it looks like a baby, it is called a
.
Be sure to check your answers and make any corrections before you go on.
You are showing that you take responsibility for your own learning
when you do this. And that's good!
You are doing well if you get all the answers right for the mastery test.
If you do not, you need to revise the lesson.
Exercise 10
Now you are ready to complete the send-in exercises for this lesson.
Human reproduction Set 2
35
Send-in page
Name
Lesson 10:
______________________________
From embryo to foetus
Exercise 10
1.
(a) Label this diagram by writing the names of the parts
next to each pointer.
(b) Complete the table below by matching each part
you have labelled in the diagram with its function.
Part
Function
provides protection and
keeps the temperature constant
connects the developing baby
to the mother
provides substances essential for
the developing baby
grows and develops into a baby
Human reproduction Set 2
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2.
(a) Here is a diagram representing the embryo and the placenta,
greatly magnified. Complete the labels for the diagram.
X
Q
(b) Substances that are exchanged between the mother’s blood
and the embryo’s blood include oxygen, food and wastes.
i.
Which substances pass along the blood vessel labelled Q?
ii. Which substances are taken away from the placenta
in the blood vessels labelled X?
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3.
The following diagrams show two stages in the development of a baby.
Diagram S
4–5 weeks
Diagram T
8 weeks
actual size
actual size
(a) i.
The process of
is needed for the
developing baby in Diagram S to grow into the one
in Diagram T.
ii. This process of making new cells is also needed for
adults to be able to
, making offspring.
(b) Compare Diagram S and Diagram T.
Apart from the increase in size, describe three other changes
in the developing baby between Week 4 and Week 8 of gestation.
i.
____________________________________________________________
ii.
____________________________________________________________
iii.
____________________________________________________________
(c) What do we call the developing baby when it is at the stage shown in:
i.
Diagram S?
_______________________________________________
ii. Diagram T?
_______________________________________________
Human reproduction Set 2
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Human reproduction Set 2
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Lesson 11
From foetus to baby
By the end of the fourth month of pregnancy, the baby is growing very rapidly
and there is less and less room in the uterus. The uterus stretches and
it is at this stage that the mother’s abdomen (belly) begins to bulge.
She can feel the baby moving about.
Two or three months before birth, the baby comes to rest, head downwards.
This is probably the position in which it will be born.
The foetus at four months
The foetus at six months
What do you notice about the size of the baby’s head compared with
the rest of the body?
Did you notice that the baby appears to be out of proportion?
Its head is large compared with the rest of its body.
Human reproduction Set 2
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During the last few months of pregnancy, the rest of the body
catches up a lot with the head because the baby’s body grows rapidly
and builds up fat under the skin.
The placenta is fully developed now and is shaped like a large saucer.
umbilical cord
placenta
Find and label the placenta of the six month old foetus on the
previous page.
There's a diagram in the answer pages if you'd like to check your answer.
At the end of nine months gestation is nearly over. The baby should
weigh about 3.5 kilograms and be about 55 centimetres long, on
average. In the beginning, it was a single cell. Now it is a fully
formed baby made of millions and millions of cells, all working
together in a coordinated way.
Human reproduction Set 2
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Mastery test 4
From fertilisation to birth
1.
A developing baby has different names, depending on
its stage of development.
Name the stages shown below.
2.
Label the diagram below using the following terms
placenta foetus umbilical cord
bladder
The female organs and the developing baby
Check all your answers now.
Human reproduction Set 2
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42
What has influenced the mother and baby?
Why does the baby develop as it does?
How are the processes of reproduction coordinated?
You'll find some answers for these questions in this section.
What influences how the baby develops?
Can you answer that question? Try!
Did you discuss DNA or chromosomes or genes in your answer?
These words refer to the way that information is stored in each cell –
information that produces the features of the baby and the adult it becomes.
Genes are very important in determining the characteristics of the baby.
But there are other things that can affect the way the baby develops too.
They are called environmental factors. Environmental factors are
things that happen to the baby while it is developing.
Let's consider some examples.
Alcohol
Alcohol can have a big effect on a developing baby.
If a mother drinks alcohol, the alcohol moves across the placenta
to the baby. Doctors are not sure of the effects on the developing baby
of small amounts of alcohol, but binge drinking (drinking more than
four alcoholic drinks in two hours) may cause brain damage and
changes in the appearance of the baby. Most doctors recommend
that mothers drink as little alcohol as possible during pregnancy.
Cigarettes
Mothers who smoke tend to have smaller babies and their babies are
more likely to be born prematurely (before they are fully developed).
Cigarettes contain substances that reduce the effectiveness of the placenta
so the baby is unable to develop at the normal rate. Doctors recommend
that women do not smoke when they are pregnant. They also suggest that
even breathing cigarette smoke can influence the baby's development.
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Diseases
If the mother has some infections, they can affect the way the baby develops.
For example, if the mother has german measles, or rubella, in the first
three months of a pregnancy, there is a high risk that the baby will be blind,
deaf or have brain damage. That is why it is important for children
to be immunised against rubella. Have you been immunised?
List three environmental factors that may influence how a baby develops.
___________________________
___________________________
___________________________
Now you can use the headings to check your answers!
Think! What are some other examples of environmental factors that
could affect a developing baby while it is inside its mother?
There are some suggestions in the answer pages.
How are reproductive processes coordinated?
Is everything done with hormones? You have learned about how
hormones coordinate menstruation and pregnancy. Hormonal
coordination is fairly slow, constant and affects the whole body at the
same time.
Are hormones the only coordination system in the body? No.
You probably remember that there is a nervous coordination system
in the body. It is made up of the nerves, spinal cord and brain.
Messages along nerves are electrical messages that travel very quickly
and usually involve only a few parts of the body at the same time.
They coordinate things like movements and the senses.
Do these coordination systems – the hormonal system and the
nervous system – always work separately from each other? No.
They can interact together to make the body function properly
and respond to changes.
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Interactions of coordination systems
For example, the mother's hormonal system works with her
nervous system during the process of birth. Hormones, such as
oxytocin (OX-ee-toe-sin) from the pituitary gland in the brain, prepare
the mother's uterus and cervix so that the baby can move out of her body.
The mother's nervous system enables her to use her muscles
to push the baby during birth so that the baby is born.
The production of milk by the mother's breasts is another example
of the interaction of the mother's hormonal and nervous systems.
The sight and sound of her hungry baby and the sucking of the baby
on her breast sends messages to the mother's brain through
her nervous system. These messages cause the pituitary gland
in her brain to release oxytocin.
Oxytocin causes ducts in the mother's breasts to squeeze milk
towards her nipples to feed her baby.
Mastery test 5
Influences on the mother and baby
Complete the following statements.
1.
The development of a baby depends on:
•
information stored in the DNA of the
on the baby's chromosomes
•
factors; for example, whether the mother
smokes, drinks alcohol, eats well, has an accident or has a
disease such as rubella during pregnancy.
2.
Most reproductive processes are coordinated by
.
They coordinate many changes throughout the body at the same time.
3.
Some reproductive processes are coordinated by an
of coordination systems. This means that coordination that happens
quickly and to specific parts using the
system
works together with the hormonal system to keep the body functioning.
Check your answers before you continue.
Exercise 11.1
Complete this send-in exercise now on page 53.
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Making a model of a developing baby
So far in this unit, you have looked at diagrams to find out
how a baby develops during pregnancy. Diagrams are very useful
because they save us reading lots of words to find out information.
But sometimes even diagrams aren’t enough to help us
understand something. We may need to build a model.
What is a model?
When you saw the word ‘model’, what did you think of?
Maybe it was model planes, cars or ornaments?
Or did you think of figures you make out of clay or plasticine?
‘Model’ usually means a three dimensional copy of a real object
or situation, much smaller than the real thing, and made to scale.
But sometimes a model represents something we can’t actually see;
for example, scientists often use models to show and explain
new ideas and even to help solve problems. Can you think of
a scientific model like this?
Did you think of the model of atoms in a gas, liquid, or solid?
Or the model of the atom? There are quite a few others in science.
A model needs to be as similar to the real thing as possible
if it is going to be useful.
Why make a model of a developing baby?
Your model will be three-dimensional, not just a flat diagram.
So it will be more like a real baby inside the mother. Also, as you
build your model, you have to put each part in its correct place.
While you are building, think about the benefits of the model for you.
Does it help you understand and remember how the parts of the
mother’s body and the baby fit together during a real pregnancy?
Think about the limitations too. What are the problems
with this model? What things doesn't it show well?
Human reproduction Set 2
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Now it’s time to start making your model
You may take up to 30 minutes to complete this activity.
Try not to spend any more time on it than this.
You will need:
•
the cut-outs from this booklet
•
a square piece of plastic wrap (about 30 cm2)
•
1 piece of red wool and one piece of blue wool, each about 12 cm long.
If you do not have wool, use string and colour it with pens or textas
*
coloured pencils
*
•
one or two cotton balls or a small piece of crumpled paper
•
sticky tape.
scissors
What to do:
Follow the instructions below to make your model.
To make a model of part of the mother
1.
If you’d like to colour the uterus in the model , do it now.
Use a red pencil and colour between the parallel curved lines
that outline each shaded ‘space where baby grows’.
2.
Cut around the thick, black outlines of the two pieces of the mother.
3.
Snip your scissors into the ‘space where baby grows’ in each piece.
Cut out all the shaded area in each piece.
4.
Cut a slit about 1 cm long along each of the dashed lines labelled ‘cut’.
5.
Fold along the dotted line near the label, placenta.
Fold one piece forwards and the other backwards.
6.
In this step, you will join the two pieces to make a three dimensional
shape. Squeeze the top and bottom of the front view of the mother
gently together so that you can slide the piece into the hole in
the side view of the mother. The slit at the top of the front view
fits into the slit near the top of the side view. The slit at the bottom
of the front view fits into the slit near the bottom of the side view.
When you look down onto the top of your model of the mother,
the two pieces are joined together making a cross shape.
Use small pieces of sticky tape at the top and bottom of your model
to keep it in shape if it tends to ‘fold up’ and become flat.
Human reproduction Set 2
47
space where baby grows
Cut out the shapes below and use them to make your model of a mother.
cut
cut
cut
fo
ld
front view bottom
cut
space where baby grows
side view bottom
p
l
a
cen
ta
Human reproduction Set 2
cut
48
Human reproduction Set 2
49
fold
fold
You will need this shape for your model of a developing baby.
You will need this shape for your model of a placenta.
fold
fold
fold
cover
this
fold
Human reproduction Set 2
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Human reproduction Set 2
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To make a model of the developing baby and umbilical cord
1.
If you’d like to colour the model of the baby, do it now. Use a
mauve or purply pink pencil to shade the baby.
2.
Cut around the thick, black outline of the baby.
3.
Fold the shape along the dotted line in the middle to make
two ‘sides’ of the baby.
4.
Put the ends of the red and blue pieces of wool (string) together
and twist them a couple of times to make a cord.
Use a small piece of sticky tape to fix one end of the cord ‘inside’
the baby near its tummy button.
5.
Wrap the arm around the baby by folding it on the dotted line.
Use a small piece of sticky tape to hold the arm in place.
If you’d like to make your baby more three dimensional,
push one or two cotton wool balls or some crumpled paper
inside the baby.
6.
Spread the plastic wrap out flat. Place the baby in the centre and
position the cord so that it points to a corner of the plastic wrap.
Fold the plastic wrap over the baby and twist it around the cord.
This makes a bag around the baby and covers all the cord with
a twisted layer of plastic.
To make a model of the placenta
1.
If you’d like to colour the model of the placenta, do it now. Use a deep
or purply red pencil to shade the paper shape.
2.
Cut around the thick, black outline of the shape and cut along the line
into the centre of larger circle. Make a hole in the centre of smaller circle.
3.
Move the cut line in larger circle around to cover the shaded area,
making a shallow cone. Use sticky tape to secure the cone.
4.
Put the free end of the plastic-covered cord attached to the baby
through the hole in the smaller circle. Use sticky tape on the back
of the circle to attach the end of the cord to the circle.
5.
Fold along the dotted line between the cone and the circle, making
a 'lid' for the cone. Fold the rectangular flaps at the edges of the circle
onto the cone and secure them with sticky tape.
To complete the model
Position the model of the baby inside the space in the model of the mother.
The baby’s head should point downwards. Fold the cord backwards and
forwards so that it fits into the space too. Use sticky tape to attach the
conical end of the model of the placenta to the placenta tabs on the side view
of the model of the mother.
Human reproduction Set 2
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Mastery test 6
Just before birth
1.
In the model you have just made, what was presented by:
(a) the wool?
___________________________________________________________________________
(b) the plastic wrap around the baby?
2.
______________________________________
What did you notice about the size of the foetus and the space
inside the mother?
Please check your answers before you continue.
Are models useful?
Now that you have completed your model, evaluate its usefulness.
Answer these questions aloud, to yourself (or to a friend if you can).
•
What are the benefits of your model?
For example, how does it help you to understand more about pregnancy?
•
Consider its limitations.
What important things doesn't the model show?
Does it show anything that isn't correct?
•
Can you think of any ways to improve the model?
How and why?
Exercise 11.2
Now you should be able to answer the questions in send-in Exercise 11.2.
Human reproduction Set 2
53
Send-in page
Name
______________________________
Lesson 11: From foetus to baby
Exercise 11.1
1.
Write at least three 'rules' that a pregnant friend should follow
so that environmental factors do not harm her developing baby.
(Write more 'rules' if you can.)
•
_____________________________________________________________________________________________
•
_____________________________________________________________________________________________
•
_____________________________________________________________________________________________
•
_____________________________________________________________________________________________
•
_____________________________________________________________________________________________
Question 2 is on the next page.
Human reproduction Set 2
54
2.
Describe an example of how the hormonal coordination system
and the nervous coordination system interact (work together).
You might like to use birth or breastfeeding as your example.
Use the questions below to guide your answer.
(a) Outline the situation involved. (What is the body doing?)
(b) What is the role of hormones in this situation?
(c) What is the role of nerves or the brain in this situation?
Human reproduction Set 2
55
Send-in page
Name
______________________________
Lesson 11: From foetus to baby (continued)
Lesson 11.2
1.
Label the diagram below by drawing a line to join each label
with the matching part of the diagram.
mother
uterus
amniotic fluid
amniotic sac
umbilical cord
foetus
placenta
vagina
Human reproduction Set 2
56
2.
Did your model help you to understand how the parts of the
mother’s body and the baby fit together during pregnancy?
Explain your answer.
3.
What was incorrect or unexplained by the model?
Try to give at least two answers.
4.
Do you think that making models could be useful in other areas
of science? Explain.
Human reproduction Set 2
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Lesson 12
Multiple births
Usually only one baby is born at a time. But sometimes,
a mother can give birth to two or more babies at the one time.
When this happens, the birth is called a multiple birth.
Multiple means more than one, or many.
When two babies are born at the one time, they are called twins.
In humans, about one birth in every hundred is of twins.
Three babies born at the one time are called triplets.
Four babies born at the one time are called quadruplets or quads.
The birth of triplets or quads does not happen very often.
Twins
As you probably know, there are different kinds of twins.
One kind of twin
The two girls in this drawing were born at the one time.
So they are twins.
Can you see many differences
between the two girls?
These two girls are very similar.
And, of course, they are the same
sex.
When twins look the same,
they are called identical twins.
Human reproduction Set 2
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Another kind of twin
The two girls in the next drawing
were born at the same time so
they are also twins.
Do these girls look the same?
Are they identical twins?
The girls do not look the same.
They are not identical.
When twins do not look the same, they are called non-identical twins.
Another name for non-identical twins is fraternal twins.
What about this boy and girl?
They have the same parents and
they were born on the same day,
so they are twins.
What kind of twins are they?
These twins are of different sexes
so they must be non-identical,
or fraternal, twins.
Non-identical twins are as much as alike, and as different,
as any brothers and sisters. They just happen to have been born
at the same time.
Human reproduction Set 2
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A third type of twin
There is one more type of twin. But these twins are very rare.
They are called Siamese twins, after a famous twin pair who came
from Siam. (Siam was the earlier name for Thailand.)
Siamese twins are joined at birth. Doctors usually try to separate
Siamese twins just after they are born. This may be possible if they
are only joined by skin. However, they sometimes share organs,
such as the heart. This makes it very difficult to separate them
and only one twin may survive the operation.
How do twins form?
You have seen that there are different kinds of twins so
you probably realise that they must form in different ways.
Can you think of a way that twins could form?
To work it out, you need to remember how a baby usually forms.
So let’s do a little revision first.
•
A baby starts life as a single, fertilised egg.
This fertilised egg is formed when one sperm joins with one egg.
•
One egg is usually released from one of a woman’s ovaries
each month.
•
If sexual intercourse takes place at about the time an egg is
released from the ovary, the egg may be fertilised by a sperm
and a new life begins.
So how do twins form?
Make a prediction.
Read on to see if your idea is right.
Human reproduction Set 2
60
One way twins can form – two eggs instead of one
Did you know that sometimes two eggs are released from a woman’s ovaries
at the same time, one from each ovary?
Here is a diagram showing this.
egg
egg just released
from ovary
What could happen if two eggs were released at
the time of sexual intercourse?
Both eggs could be fertilised.
How many fertilised eggs would then travel towards the uterus?
Two fertilised eggs would then move towards the uterus.
How many babies could then grow and develop in the uterus?
Two babies could grow and develop in the uterus.
They would be twins because they would be born at the one time.
Human reproduction Set 2
61
➁
This diagram shows how twins
could form in this way.
Notice that the same steps occur
in each fallopian tube.
➀
What is the number on the diagram
showing:
fertilisation?
____
implantation?
____
ovulation?
____
➂
➃
The numbers, in order, are 2, 4 and 1.
Here is a diagram of these twins
developing inside their mother.
Interpret these diagrams to answer the following questions.
How many eggs were released to form these twins?
How many eggs were fertilised?
_________________________
______________________________________________________
Do these twins share a placenta or do they have separate placentas?
These twins have formed from two different eggs fertilised by two different sperm.
They have separate placentas.
Human reproduction Set 2
62
Do you think these twins will grow and develop to look the same
or different?
To help you make your prediction, let’s first recall what you have learned
so far in this unit about the growth and development of a fertilised egg.
•
Every sperm and egg has a set of chromosomes, made from DNA,
in its nucleus.
•
Genes on these chromosomes control how the fertilised egg
will develop into a baby, then into a child, then into an adult.
In this way, our genes control how we grow and change
throughout our lives.
•
All the sperm and all the eggs made by a baby’s parents
have similar DNA, but the genes on the chromosomes are not
exactly the same. For example, all the mother’s eggs and all the
father’s sperm have DNA that controls how a baby’s hair grows.
But the genes about hair may be different in each egg and sperm.
So the baby’s hair might turn out to be black, blonde, or brown;
straight or curly; or somewhere in between these.
Do the foetuses have exactly the same chromosomes?
______________________
So do you now think these twins will be the same, or different?
Here is my prediction. Is your prediction the same as mine?
The foetuses will not grow and develop to look exactly the same.
Why do I think this? These foetuses formed from two different eggs
and two different sperm. So their chromosomes are not exactly the
same.
So what kind of twins have formed?
________________________________________________
Could these twins be of different sexes?
___________________________________________
Non-identical twins (fraternal twins) have formed. They will look different
as they grow and develop. Non-identical twins can be of different sexes.
Did you predict that these twins will be different?
Well done if you did. If you did not, then you need to revise the
first part of this lesson before you go on to learn more about twins.
Human reproduction Set 2
63
Another way that twins form
This diagram shows another way
that twins are formed.
Write sentences to describe
what you can see happening
in this diagram.
There is an answer in the answer pages.
Here is a diagram of these twins
developing inside their mother.
Interpret these diagrams to answer the following questions.
How many eggs were released to form these twins?
How many eggs were fertilised?
_________________________
______________________________________________________
Do these twins share a placenta or do they have separate placentas?
These twins were formed from one egg fertilised by one sperm.
They share the same placenta.
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64
How can two embryos form from one fertilised egg?
Look back at the diagram at the top of the previous page.
You can see that the fertilised egg has moved down the fallopian tube
and has developed into a tiny ball of cells.
What happens to the ball of cells just as it sinks into the wall
of the uterus?
The ball of cells splits into two. Each part then develops into a separate embryo.
Do the two embryos have the same genes?
_______________________________________
Will the twins look alike as they grow and develop?
Will they be of the same sex?
________________________
___________________________________________________________
The embryos have formed from the same egg and the same sperm.
They have exactly the same genes so they have the same set of DNA
instructions from their growth and development. This means they will grow
and develop into twins that look the same. And they must be the same sex.
So, what kind of twins have formed in the diagrams?
Did you say that they are identical twins? You are doing well if you did.
Look back at the photograph of the identical twins.
Can you see any differences between them? Even though they
have identical genes, they have not grown and developed in exactly
the same way. Why are they able to develop differently?
Did you remember that there are two things that determine what you look like –
your genes and environmental factors? These twins must have been affected by
different environmental factors and that is why they look slightly different from
each other.
Human reproduction Set 2
65
Now try this Mastery test to see if you understand how twins form.
Mastery test 7
Twins
1.
Complete the sentences by filling in the spaces.
(a) Identical twins are formed from
egg and
sperm.
(b) Non-identical twins are formed from
and
2.
eggs
sperm.
Decide if the following sentences are true or false.
(T) or (F)
(a) Identical twins can be of different sexes.
___________
(b) Non-identical twins develop when
one fertilised egg splits into two.
___________
(c) Non-identical twins look as different as
brothers and sisters born at different times.
___________
(d) Non-identical twins do not look alike because
they have different sets of chromosomes.
___________
Check your answers in the answer pages.
Exercise 12.
Now you are ready to complete send-in Exercise 12.
Human reproduction Set 2
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Human reproduction Set 2
67
Send-in page
Lesson 12:
Name
______________________________
Multiple births
Exercise 12
1.
Here are three sets of twins.
Leon and Sue
George and Con
Helena and Maria
Which pair must be non-identical twins? Why?
Human reproduction Set 2
68
2.
The following diagrams (V and W) show the two main ways
that twins can form.
V
W
George and Con had DNA tests
and were surprised to find out
that they were not identical twins.
(a) Why could a DNA test show that they were non-identical?
(b) Which diagram, V or W, shows how George and Con formed?
(c) In your own words, describe how George and Con formed.
Use information in the diagram you chose to help you.
Human reproduction Set 2
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69
Checking your progress
At the end of this set
you should be able to:
You are making good progress if you can:
•
–
describe sexual
reproduction
–
–
–
explain why human reproduction is
an example of sexual reproduction
interpret diagrams of human sex cells
explain how human sex cells are suited
to their roles
explain why children look something like
each of their parents
•
describe what
happens during
fertilisation
–
–
describe the journey of the sperm to the egg
interpret diagrams of fertilisation
•
describe how
a fertilised egg
develops into
a baby
–
identify cell division as an essential process
for growth and reproduction
sequence changes in fertilised eggs
define the terms: embryo, foetus
identify some parts of the developing
foetus and state the functions of those parts
identify changes over time in the
developing baby
outline how the baby's DNA (genes and
chromosomes) influence its development
list some substances that are transferred
between the mother and developing baby
at the placenta
follow written instructions to make a model
of a developing baby
evaluate the model of a developing baby
identify environmental factors that may
affect how a baby develops
–
–
–
–
–
–
–
–
–
–
describe a situation in which hormonal and
nervous coordination systems interact
–
interpret diagrams showing
how twins form
explain in your own words why identical
twins are very similar whereas fraternal
twins can be different from each other
–
Human reproduction Set 2
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Human reproduction Set 2
71
Suggested answers
Lesson 7
page 6
Sexual reproduction
Chromosomes n sexual reproduction
When an egg or ovum and sperm join, they form the first cell
of the new baby. This first cell contains 23 chromosomes from the egg
and 23 chromosomes from the sperm. So the baby's first cell contains
a total of 46 chromosomes. The first cell will have an X chromosome
from the egg and either an X or a Y chromosome from the sperm.
page 8
Boy or girl?
What happens when an egg (A) joins with sperm C?
What chromosomes will be in the first cell of the baby?
The baby's cell will contain 22 and X chromosomes from the mother (egg)
and 22 and Y chromosomes from the father (sperm).
The baby's chromosomes will be 44 chromosomes and XY chromosomes.
Lesson 8
page 11
How life begins – sperm meets egg
Where are sperm and eggs made?
•
Eggs (or ova) develop in a woman’s ovaries.
•
One egg (or one ovum) is released about every month or 28 days or
menstrual cycle.
•
Once an egg is released, it enters the fallopian tube.
•
The release of an egg from the ovary is called ovulation.
•
Sperm are produced in a man’s testes.
•
Sperm leave a man’s body through the urethra or penis.
Human reproduction Set 2
72
page 13
How do sperm get to an egg?
•
•
•
•
•
page 17
Many of the sperm don’t get through the narrow opening
of the uterus.
3
Some sperm swim into the uterus but most get no further.
(They may run out of energy or be killed by warmth or
substances inside the uterus.)
5
Some of the stronger sperm move up through the uterus
towards the fallopian tubes.
2
Some of these take a wrong turning and swim up
the empty fallopian tube.
4
Some of the sperm enter the fallopian tube which contains the egg.
They swim towards the egg helped by movements of their tails.
1
Mastery test 1 – How life begins
1.
What is fertilisation?
(D) the joining of an egg and a sperm
2.
Another word which means the same as fertilisation is:
(B) conception.
3.
The placing of the penis inside the vagina, usually with
the passing of sperm from a man to a woman is called:
(A) sexual intercourse.
4.
Before the penis can fit inside the vagina,
it must become stiff and stand upright. This is called:
(C) an erection.
Human reproduction Set 2
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Lesson 9
page 24
From fertilised egg to embryo
Why doesn't the mother menstruate?
The hypothalamus and the pituitary gland are influenced by this hormone.
(There are arrows to these glands labelled 'progesterone' in the diagram.)
page 26
Mastery test 2 – Cell growth and reproduction
Here is the completed summary.
An egg and a sperm can join or fuse if they meet in a fallopian tube.
As the fertilised egg moves towards the uterus, it begins to reproduce
by cell division.
Each time a cell divides, it makes or forms an identical copy of its DNA
so that all cells in the baby will be able to work or function together. Thus,
every cell in the developing baby has an identical set of 46 chromosomes.
Cell division is needed so that the fertilised egg can grow or develop
into a baby. A special kind of cell division is needed when sex cells
are formed in ovaries and testes. This special cell division is needed
so that humans can reproduce by sexual reproduction.
Lesson 10
page 31
From embryo to foetus
The placenta – the baby's life support system
Here is the labelled diagram.
amniotic sac
embryo
umbilical cord
amniotic fluid
placenta
Human reproduction Set 2
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page 34
Mastery test 3 – From fertilisation to foetus
Here is the completed summary.
Lesson 11
page 40
•
A new life begins to form when a sperm enters an egg or ovum.
This joining of sex cells is called fertilisation, or conception.
It takes place inside a fallopian tube.
•
The fertilised egg then divides rapidly and moves down
into the uterus. Here, it sinks into the lining of the wall.
It is now a ball of cells and is called an embryo.
•
The embryo receives oxygen and food from its mother through
the placenta and umbilical cord.
•
Inside the uterus, the embryo is surrounded by a bag of amniotic fluid.
This provides protection and warmth.
•
Once all the main parts of the embryo have formed and
it looks like a baby, it is called a foetus.
From foetus to baby
The placenta is labelled on the diagram below.
placenta
Human reproduction Set 2
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page 41
Mastery test 4 – From fertilisation to birth
1.
The stages are:
baby (if it is born)
2.
embryo
foetus
You should have added five labels to your diagram. Each label needs
a straight (ruled) line connecting it with a part of the diagram.
placenta
foetus
umbilical cord
bladder
urethra
page 43
What influences how the baby develops?
Some other examples of environmental factors are: the food that the mother
eats (or doesn't eat) during pregnancy; drugs the mother may take;
any falls or accidents the mother has that could injure the developing baby
inside her.
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page 44
Mastery test 5 – Influences on the mother and baby
1.
page 54
The development of a baby depends on:
•
information stored in the DNA of the genes
on the baby's chromosomes
•
Environmental factors; for example, whether the mother smokes,
drinks alcohol, eats well, has an accident or has a disease such
as rubella during pregnancy.
2.
Most reproductive processes are coordinated by hormones.
3.
Some reproductive processes are coordinated by an interaction of
coordination systems. This means that coordination that happens quickly
and to specific parts using the nervous system works together with
the hormonal system to keep the body functioning.
Mastery test 6 – Just before birth
1.
(a) The wool represents blood vessels in the umbilical cord.
(b) The plastic wrap around the baby represents the amniotic sac.
2.
The baby only just fits into the space inside the mother. It is a very tight fit!
Lesson 12 Multiple births
page 63 Another way that twins form
Here is an example of a suitable answer.
One egg from the ovary is fertilised by one sperm. The fertilised cell grows
and divides by cell division into a ball of cells. This ball splits in two and
each half develops into a separate embryo.
page 65
Mastery test 7– Twins
1.
(a) Identical twins are formed from one egg and one sperm.
(b) Non-identical twins are formed from two eggs and two sperm.
2.
(a) F
(b) F
(c) T
(d) T
Human reproduction Set 2
Unit evaluation
Name
_______________________________
Teacher _______________________________
We need your input! Can you please complete this short
evaluation to provide us with information about this unit.
This information will help us to improve the design of these
materials for future publications.
1
Did you find the information in the unit clear and easy to
understand?
_______________________________________________________
_______________________________________________________
2
_______________________________________________________
What sort of learning activity did you enjoy the most? Why?
_______________________________________________________
3
_______________________________________________________
Name any sections you feel need better explanation (if any).
_______________________________________________________
4
_______________________________________________________
Were you able to complete each part in around 5 hours? If not
which parts took you a longer or shorter time?
_______________________________________________________
5
_______________________________________________________
Do you have access to the appropriate resources? This could
include a computer, the Internet, equipment and people to
provide information and assist with the learning.
_______________________________________________________
Human reproduction
Centre for Learning Innovation
NSW Department of Education and Training
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