3 Cells and human reproduction
3
Cells and human reproduction
3.1
The basic unit of living things
1
The basic unit of living things is the cell.
2
A microscope can produce magnified images of small objects. It allows us to observe the
structure of cells in detail.
eyepiece
coarse adjustment knob
objective
fine adjustment knob
stage
arm
diaphragm
clip
mirror
base
3
Total magnification
of a microscope
4
=
Magnification of
eyepiece
×
Magnification of
objective
The image formed in the microscope is magnified and inverted.
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Both plant cells and animal cells have a cell membrane, cytoplasm and a nucleus.
6
Plant cells have a cell wall and a large vacuole but animal cells do not. Some cells of green
plants have chloroplasts.
nucleus
cytoplasm
chloroplast
vacuole
cell membrane
cell wall
 A typical plant cell
nucleus
cell membrane
cytoplasm
 A typical animal cell
Structure
Function
Cell membrane

Controls the movement of substances into and out of the cell
Cell wall

Protects, supports and gives shapes to the cell
Cytoplasm

Site for many chemical reactions of the cell to take place
Nucleus

Contains genetic materials which control the cell activities
Vacuole

Contains mainly water; stores dissolved minerals
Chloroplast


Present in green parts of a plant
Site for carrying out photosynthesis
7
Living things grow by increasing the number and size of cells.
8
New cells are formed by a process called cell division.
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3. 2
A new life is born
1
Asexual reproduction
Sexual reproduction

does not involve sex cells

involves the fusion of a male sex cell with
a female sex cell

genetic materials of each new individual
are exactly the same as the original cell

the new individual carries genetic
materials from both parents
2
Human sex cells:
Sperm (male sex cell)
Site of

production

Egg (female sex cell)
in the testes

in the ovaries
looks like a tadpole

looks like a sphere
protective layer
head
cell membrane
Shape
nucleus
cytoplasm
tail
nucleus
Size

smaller

larger
Movement

the tail beats to move

cannot move by itself
3
The male reproductive system:
Penis–carries semen to
the female reproductive
system during sexual
intercourse
Sperm duct–carries
sperms from the
testes to the urethra
Testis–produces
sperms and sex
hormones
Sex glands–produce
sex hormones and the
fluid in semen
Scrotum
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The female reproductive system:
Oviduct–carries
eggs to the uterus
Uterus–the place
where an embryo
develops during
pregnancy
Ovary–produces
eggs and sex
hormones
Vagina–receives the
penis during sexual
intercourse; acts as a
birth canal for the
delivery of the baby
5
The fusion of a sperm and an egg is called fertilization. The fertilized egg divides and
develops into an embryo.
6
The process of an embryo becoming embedded in the uterine lining is called implantation.
7
Development of embryo in the uterus:
Umbilical cord –
connects the embryo
to the placenta
Embryo
Amnion–secretes
amniotic fluid
Placenta
Amniotic fluid–
serves as a
cushion to protect
the embryo against
shock
Nutrients and oxygen pass from
the mother’s blood into the
embryo’s blood
Waste passes from the embryo’s
blood into the mother’s blood
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During labour, the muscles of the uterus contract strongly to push the foetus out through the
vagina. The placenta will leave the uterus after the birth of the baby.
Muscles of the uterus
Placenta
Umbilical cord
Е
9
We show some common characteristics of our parents because our body cells contain the
genetic materials from our parents.
Е
10
The two babies born by a mother from a single pregnancy are called twins.
Identical twins
Non-identical twins

developed from a single fertilized egg

developed from two fertilized eggs

have the same genetic materials

have different genetic materials

are of the same sex and look like each
other

may be of the same sex or different sexes;
may not look like each other
3.3
Puberty
1
In general, girls enter puberty earlier than boys.
2
At puberty, our body begins to secrete more sex hormones. This causes body changes that
show important male and female characteristics which are called secondary sexual
characteristics.
3
Boys at puberty may experience nocturnal emission.
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Menstruation and menstrual cycle:
Uterine lining breaks down.
Menstruation occurs.
Uterine lining continues to
thicken.
Uterine lining
thickens again.
An egg is usually released from an ovary
around the middle of the menstrual cycle.
5

During menstruation, the tissues of the uterine lining (including some blood) and the
unfertilized egg pass out of the vagina.

Menstruation lasts about 5 days.

The periodical thickening and breaking down of the uterine lining is called the
menstrual cycle.

A menstrual cycle lasts about 28 days.
At puberty, teenagers experience many body changes and psychological changes.
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3 .4
Becoming parents
1
The absence of menstruation is the most reliable sign of pregnancy.
2
A pregnant woman should have pre-natal examinations. She should take extra care to keep the
foetus and herself healthy.

What pregnant women should and should not do:
Do
eat food rich in protein,
calcium and iron
Don’t
drink alcohol
or smoke
do gentle exercises
take any medicines without the
advice from doctors
3
Parents have great responsibilities towards their children. We should get ready to take these
responsibilities before having a baby.
4
A couple can practise birth control to avoid pregnancy. This helps achieve their family
planning goals.
Method of birth control
Working principle

avoid having sex around the days when an
egg may be present in the oviduct

stop the releasing of eggs from the ovaries
Natural family
planning
avoid intercourse
menstruation
Contraceptive
pills
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
prevents sperms from entering the vagina

coated with spermicide

prevents sperms from entering the uterus

coated with spermicide

prevents sperms from entering the uterus

coated with spermicide

ties and cuts the oviducts by surgery

no eggs can meet the sperms

ties and cut the sperm ducts by surgery

no sperms in the semen
Male condom
Female condom
Diaphragm
Female
sterilization
Male
sterilization
Е
Е
5
6
Process of in vitro fertilization (IVF) :

eggs are fertilized outside the female body;

the fertilized egg developed into an embryo;

the embryo is put back into the wife’s uterus;

implantation takes place and the embryo continues to develop.
Abortion is the ending of a pregnancy by surgery or drugs.
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3 .5
Sexually transmitted diseases
Е
1
Sexually transmitted diseases (STDs) can be passed from one person to another through
sexual activities or blood contact.
Е
2
STDs spread quickly. People with many sex partners have a higher risk of catching STDs.
Е
3
Prevention of STDs :
a
having only one sex partner;
b
using condoms properly during sexual intercourse;
c
avoiding direct contact with contaminated needles;
d
handling blood and wounds carefully.
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