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ECZ GRADE 10 - 12 BIOLOGY SUMMARISED
NOTES (FOR REPRODUCTION) WITH EXAM
QUESTIONS AND ANSWERS
ESKULU ZM
6/15/19
0
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G10 TO
G12 BIOLOGY
(REPRODUCTION) NOTES
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Content
Unit 10: reproduction ............................................................................................................ 2
1.1.1 What is Asexual reproduction? ..............................................................................................2
1.1.2 Asexual reproduction in fungi................................................................................................3
1.1.3 Comparison of sexual and asexual reproduction ....................................................................3
1.2.1 Structure of a typical flower ..................................................................................................4
1.2.2 Reproductive parts of a flower ..............................................................................................6
1.2.3 Formation of a flowering plant’s gametes ..............................................................................7
1.2.4. Pollination ...........................................................................................................................8
1.2.5. Fertilisation ....................................................................................................................... 11
1.2.6. Seed and fruit formation – process after fertilization .......................................................... 12
1.2.7. dispersal ............................................................................................................................ 13
1.2.8. Vegetative propagation (Asexual reproduction in flowering plants)..................................... 15
1.2.9. Artificial propagation ......................................................................................................... 18
1.2.10. Advantages and disadvantages of vegetative propagation ................................................ 20
1.3.1. Strcuture of human reproductive organs in female ............................................................. 21
10.3.2. Strcuture of human reproductive organs in male .............................................................. 22
10.3.3 Gametes of human beings ................................................................................................. 23
10.3.6 Process of fertilization in humans ...................................................................................... 24
10.3.7 pregnancy and development of embryo ............................................................................ 24
1.3.8. menstrual cycle.................................................................................................................. 27
1.3.9. Twins................................................................................................................................. 29
1.3.10. Birth Control .................................................................................................................... 29
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UNIT 10: REPRODUCTION
1.1 Asexual Reproduction
1.1.1 WHAT IS ASEXUAL REPRODUCTION?
 Asexual reproduction is the process resulting in the production of
genetically identical offspring from one parent.
 This method of reproduction does not involve gametes (sex cells).
 In the single-celled organisms such as bacteria, the cell simply divides into
two and each new cell becomes an independent organism.
 In more complex organisms, part of the body may grow and develop into a
separate individual. For example, a small piece of stem planted in the soil
may form roots and grow into a complete plant.
 Bacteria reproduce by cell division or binary fission. Any bacterial cell can
divide into two and each daughter cell becomes an independent bacterium.
 This kind of reproduction, without the formation of gametes (sex
cells), is asexual reproduction.
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1.1.2 ASEXUAL REPRODUCTION IN FUNGI
 Fungi have sexual and asexual methods of reproduction. In the
asexual method they produce single-celled, haploid spores.
 These are dispersed by air currents. They reach a suitable situation
and grow hyphae, which develop into a mycelium.
1.1.3 COMPARISON OF SEXUAL AND ASEXUAL REPRODUCTION
Items
Number of parent
Presence of sex cells
Fertilization
Genetically different
parent and offspring
Generation change
Sexual reproduction
Two parents
Male and female sex
cells (haploid gametes)
Fertilization forms a
diploid zygote
Offspring genetically
different from both
parents
Reproduction takes a
long time, hence
population increases
slowly
Asexual reproduction
One parent
No sex cell
No fertilization takes
place
Offspring genetically
identical to parent
(called clone)
Reproduction occurs
rapidly
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1.2 Sexual reproduction in plants
 In flowering plants, the reproductive organs are the flowers.
 Some plants bear both male and female flowers on the same plant.
These flowers are, therefore, both male and female, a condition
known as bisexual or hermaphrodite.
 In maize for instance, male and female flowers are on different
plants.
1.2.1 STRUCTURE OF A TYPICAL FLOWER
 Petals
o The colour and scent of the petals attract insects to the flower;
the insects may bring about pollination.
 Sepals
o Outside the petals is a ring of sepals. They are green and smaller
than the petals. They protect the flower when it is in the bud.
 Stamens
o The stamens are the male reproductive organs of a flower. Each
stamen has a stalk called the filament, with an anther on the end.
o Each anther consists of four pollen sacs in which the pollen grains
are produced by cell division.
 Pollen
o Insect-pollinated flowers tend to produce smaller amounts of
pollen grains, which are often round and sticky, or covered in tiny
spikes to attach to the furry bodies of insects.
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o Wind-pollinated flowers tend to produce larger amounts of
smooth, light pollen grains which are easily carried by the wind.
 Carpels
o These are the female reproductive organs. Each carpel consists of
an ovary, bearing a style and a stigma.
o Inside the ovary there are one or more ovules. The ovule will
become a seed, and the whole ovary will become a fruit. A fruit is
the fertilised ovary of a flower.
o The stigma has a sticky surface and pollen grains will stick to it
during pollination. The style may be quite short.
 Receptacle
o The flower structures just described are all attached to the
expanded end of a flower stalk. This is called the receptacle and,
in a few cases after fertilisation, it becomes fleshy and edible (e.g.
apple and pear).
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1.2.2 REPRODUCTIVE PARTS OF A FLOWER
 A carpel (or pistil) consists of style, stigma and ovary. At the top end of
the style, there is the knob-like structure called stigma, which collects
grains.
 The stigma is usually sticky so the pollen grains will cling to it. At the
bottom end of the style, there is a swollen portion called ovary in which
the female gametes are enclosed. Ovary contains one or more tiny
bodies called ovules.
 Each ovule possesses a large cell called embryo sac, which contains the
egg cell (female gamete).
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 Integuments are the protective sheaths surrounding the nucleus in the
developing ovule of a flower. These structures consist of diploid cells
that will later give rise to the testa of a fertilized seed.
 The part next to the carpel is the stamen, which forms the male parts of
the flower. Each anther is made up of pollen sacs, which contain grains
of pollen (male gamete).
1.2.3 FORMATION OF A FLOWERING PLANT’S GAMETES
 Pollen grains in the anther - After meiosis, nuclei of four cells (called
microspore) each divide again by mitosis. Resulting cells (pollen grains)
each have two nuclei (one later divides again to form two male nuclei).
 Embryo sac in the ovule - After meiosis, only one cell (called megaspore)
remains in the ovule. The megaspore in one of six cells is female gamete, or
egg cell.
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1.2.4. POLLINATION
 The transfer of pollen from the anthers to the stigma is called pollination.
The anthers split open, exposing the microscopic pollen grains
(Figure below).
 The pollen grains are then carried away on the bodies of insects, or simply
blown by the wind, and may land on the stigma of another flower.
Insect pollination
 The bees that visit lupin flowers for instance, come to collect pollen, which
they take back to the hive for food.
 The pollen from the anthers has collects on to the underside of the bee.
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 The bee, with pollen grains sticking to its body, then flies to another flower.
 The stigma comes out and touches the insect’s body, picking up pollen
grains on its sticky surface.
 Lupin and wallflower are examples of insect-pollinated flowers.
Wind pollination
 Grasses, cereals and many trees are pollinated not by insects but by wind
currents.
 The flowers are often quite small, green and leaf-like.
 They produce no nectar.
 The pollen grains, being light and smooth, may be carried long distances by
the moving air and some of them will be trapped on the stigmas of other
flowers.
 In the grasses, at first, the feathery stigmas protrude from the flower, and
pollen grains floating in the air are trapped by them. Later, the anthers
hang outside the flower the pollen sacs split and the wind blows the pollen
away.
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 This sequence varies between species.
Cross-pollination vs self-pollination
 If the transfer of pollen is from a plant to another of a different genetic
makeup, the process is called cross-pollination.
 If the transfer occurs within the same plant or the same flower, it is called
self-pollination.
 Fertilization does not take place when pollination takes place between
different species.
Disadvantages of cross-pollination
i. It has difficulty to maintain a pure bread.
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ii. It can be less likely for pollen to fall on the stigma if separated by
geographical barriers (mountain, river, etc.)
Advantages of self-pollination
i. It may transmit undesirable characteristics.
ii. It may lead to loss of resistance to pathogenic and deficiency diseases.
iii. It may sometimes produce sterile seeds
1.2.5. FERTILISATION
 Pollination is complete when pollen from an anther has landed on a stigma.
If the flower is to produce seeds, pollination has to be followed by a
process called fertilisation.
 In all living organisms, fertilisation happens when a male sex cell and a
female sex cell meet and join together.
 For fertilisation to occur, the nucleus of the male cell from the pollen grain
has to reach the female nucleus of the egg cell in the ovule, and fuse with
it.
 The pollen grain absorbs liquid from the stigma and a microscopic pollen
tube grows out of the grain.
 This tube grows down the style and into the ovary, where it enters a small
hole, the micropyle, in an ovule (figure below).
 The nucleus of the pollen grain travels down the pollen tube and enters the
ovule.
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 Here it combines with the nucleus of the egg cell. Each ovule in an ovary
needs to be fertilised by a separate pollen grain.
 Double fertilisation occurs between (i.) one male definitive nucleus and an
egg cell to become zygote, and (ii.) another male nucleus and two
definitive nuclei to become endospermic nucleus.
1.2.6. SEED AND FRUIT FORMATION – PROCESS AFTER FERTILIZATION
 After fertilisation, changes take place in the ovule and ovary that lead to
the fertilised ovule becoming a seed and the ovary becoming a fruit.
 The following four changes take place:
i.
The zygote develops into an embryonic plant with small root (radicle)
and shoot (plumule).
ii.
Other contents of the ovule develop into a food store for the young
plant when the seed germinates.
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iii.
The ovule wall becomes the seed coat or testa.
iv.
The ovary wall becomes the fruit coat; this can take many forms
depending on the type of fruit.
Refer to the figure below.
1.2.7. DISPERSAL
 Seeds can be dispersed by the wind, animals, water, chance, explosion or
other means.
Wind-dispersed seeds
 usually have a parachute or a wing to help them be carried away from the
parent plant by the wind.
Examples: dandelion, sycamore
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Animal-dispersed seeds
 Succulent fruits attract animals because they are brightly coloured, juicy
and nutritious. When eaten, the seed pass through animal’s faeces. The
faeces provides nutrients for the seedlings when the seeds germinate.
 Hooked fruits catch on to an animal’s fur as it brushes past the plant.
Eventually the seeds drop off.
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Water-dispersed seeds
 The fruit have water resistant layer and there is a spongy layer inside fruit.
They float on water.
Self-dispersed seeds
 The pericarp of the fruits dries in the sun and shrivels. The fruit wall shrinks
and sets up tension which leads to explosion.
 The seeds flick out therefore, being dispersed. E.g. lupin, peas etc.
1.2.8. VEGETATIVE PROPAGATION (ASEXUAL REPRODUCTION IN
FLOWERING PLANTS)
 Several asexual methods of reproduction in plants (also called ‘vegetative
propagation’) are described below.
 It usually results from the growth of a lateral bud on a stem which is under
the soil.
 The bud produces a complete plant with roots, stem and leaves. When the
old stem dies, the new plant is independent of the parent that produced it.
a. Stolons and rhizomes
 The flowering shoots of plants such as the strawberry very short and below
ground. The stems of shoots such as these are called rootstocks.
 After the main shoot has flowered, the lateral buds produce long shoots,
which grow horizontally over the ground (figure below). These shoots are
called stolons (or ‘runners’), and have only small leaves at their nodes and
very long internodes.
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b. Bulbs and corms
 Bulbs such as those of the daffodil and snowdrop are very short shoots.
 The leaves which encircle the stem are thick and fleshy with stored food.
The stored food is used by a rapidly growing terminal bud, which
produces a flowering stalk and a small number of leaves.
 Vegetative reproduction occurs when some of the food is sent to a
lateral bud as well as to the leaf bases.
 The lateral bud grows inside the parent bulb and, next year, will produce
an independent plant
 Corms are similar to bulbs but it is the stem, rather than the leaf bases,
which swells with stored food. Vegetative propagation takes place when
a lateral bud on the short, fat stem grows into an independent plant.
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c. Tubers
 Potatoes are stem tubers. Lateral buds at the base of the potato shoot
produce underground shoots (rhizomes).
 These rhizomes swell up with stored starch and form tubers.
 The tubers have buds. If the tubers are left in the ground or
transplanted, the buds will produce shoots, using food stored in the
tuber.
 Hence, the potato plant can propagate vegetatively.
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1.2.9. ARTIFICIAL PROPAGATION
 Agriculture utilises vegetative propagation in order to produce fresh
stocks of plants.
 The methods of artificial propagation are by taking cuttings, by grafting
and budding.
a. Cuttings
 It is possible to produce new individuals from certain plants by
putting the cut end of a shoot into water or moist earth.
 Roots grow from the base of the stem into the soil while the shoot
continues to grow and produce leaves.
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b. Grafting
 Involves attaching part of one plant of
a. the same plant (autografting)
b. another plant of the same species (homografting)
c. a plant of different species (heterografting)
 The piece removed is called the scion, and that to which it is attached
is known as the stock.
c. Budding
 Is a type of grafting where a bud and its adjacent stem are the parts
grafted
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1.2.10. ADVANTAGES AND DISADVANTAGES OF VEGETATIVE
PROPAGATION
Advantages
It enables the plant population to
grow faster and increase yield
It can be selected for desirable
characteristics (taste, resistance to
disease etc.)
New plants can be produced even
when seed production falls
It is not dependent on pollinators for
reproduction
Disadvantages
The plants are usually overcrowded
and compete for space and nutrients
All are susceptible to the
environmental change
The identical daughter lack in genetic
variation, resulting in all susceptible to
the same diseases
The plant cannot widely disperse as
such they do not colonize new areas
1.3. Reproduction in human beings
 Fertilization and subsequent development of embryo of human beings take
place inside the body of the female like other mammals. Mammals are
viviparous and as such this reproductive behaviour is called viviparous.
 In order to be able to reproduce, the human should reach sexual maturity.
Secondary sexual characteristics of male and female human being at puberty.
At puberty, the pituitary secretes gonadotrophic hormone, which stimulates
testes to produce testosterone in male and stimulates the ovaries to produce
ostregon in female. These lead to the development of sexual characteristics in
humans.
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1.3.1. STRCUTURE OF HUMAN REPRODUCTIVE ORGANS IN FEMALE
Part
Cervix
Funnel of oviduct
Ovary
Oviduct
Urethra
Uterus
Vagina
Function
A ring of muscle, separating the vagina
from the uterus
directs an ovum (egg) from the ovary
into the oviduct
contains follicles in which ova (eggs)
are produced
carries an ovum to the uterus, with
propulsion provided by tiny cilia in the
wall; also the site of fertilisation
carries urine from the bladder
where the foetus develops
receives the male penis during sexual
intercourse; sperm are deposited here
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10.3.2. STRCUTURE OF HUMAN REPRODUCTIVE ORGANS IN MALE
Part
Epididymis
Penis
prostate gland
Scrotum
seminal vesicle
sperm duct
Testis
Urethra
Function
a mass of tubes in which sperm are
stored
can become firm, to insert into the
vagina of the female during sexual
intercourse in order to transfer sperm
adds fluid and nutrients to sperm to
form semen
a sac that holds the testes outside the
body, keeping them cooler than body
temperature
adds fluid and nutrients to sperm to
form semen
muscular tube that links the testis to
the urethra to allow the passage of
semen containing sperm
male gonad that produces sperm
passes semen containing sperm
through the penis; also carries urine
from the bladder
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10.3.3 GAMETES OF HUMAN BEINGS
Spermatogenesis – the production of sperm cells
 The lining of the sperm-producing tubules in the testis consists of rapidly
dividing cells.
 After a series of cell divisions, the cells grow long tails called flagellae
(singular: flagellum) and become sperm, which pass into the
epididymis.
 During copulation (sexual intercourse), the epididymis and sperm ducts
contract and force sperm out through the urethra.
 The prostate gland and seminal vesicle add fluid to the sperm. This fluid
plus the sperm it contains is called semen, and the ejection of sperm
through the penis is called ejaculation.
Oogenesis – production of an egg cell
 The egg cells (ova) are present in the ovary from the time of birth. No
more are formed during the lifetime.
 Between the ages of 10 and 14, some of the egg cells start to mature
and are released one at a time about every 4 weeks from alternate
ovaries.
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10.3.6 PROCESS OF FERTILIZATION IN HUMANS
 In human, fertilization takes place inside the body of the female just like in
other mammals. This type of fertilization is called internal fertilization.
10.3.7 PREGNANCY AND DEVELOPMENT OF EMBRYO
 The fertilised ovum (zygote) first divides into two cells. Each of these
divides again, so producing four cells. The cells continue to divide in this
way to produce a solid ball of cells.
 This early embryo travels down the oviduct to the uterus. Here it sinks into
the lining of the uterus, a process called implantation.
 When all the organs are formed, the embryo is called a foetus. One of the
first organs to form is the heart, which pumps blood around the body of the
embryo.
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 Inside the uterus the embryo becomes enclosed in a fluid-filled sac called
the amnion or water sac.
 Which protects it from damage and prevents unequal pressures from acting
on it.
 The fluid is called amniotic fluid.
 The oxygen and food needed to keep the embryo alive and growing are
obtained from the mother’s blood by means of a structure called the
placenta.
Placenta
 Some of the cells, instead of forming the organs of the embryo, grow into a
disc-like structure, the placenta.
 The placenta is attached to the embryo by a tube called the umbilical cord.
 The nervous system (brain, spinal cord and sense organs) start to develop
very quickly.
 Blood entering the placenta from the mother does not mix with the
embryo’s blood.
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Functions of placenta
 The blood vessels in the placenta are very close to the blood vessels in the
uterus so that oxygen, glucose, amino acids and salts can pass from the
mother’s blood to the embryo’s blood.
 So the blood flowing in the umbilical vein from the placenta carries food
and oxygen to be used by the living, growing tissues of the embryo.
 In a similar way, the carbon dioxide and urea in the embryo’s blood escape
from the vessels in the placenta and are carried away by the mother’s
blood in the uterus.
 In this way the embryo gets rid of its excretory products. There is no direct
communication between the mother’s blood system and that of the
embryo.
 The exchange of substances takes place across the thin walls of the blood
vessels.
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 In this way, the mother’s blood pressure cannot damage the delicate
vessels of the embryo and it is possible for the placenta to select the
substances allowed to pass into the embryo’s blood.
 The placenta can prevent some harmful substances in the mother’s blood
from reaching the embryo. It cannot prevent all of them, however: alcohol
and nicotine can pass to the developing foetus.
 If the mother is a heroin addict, the baby can be born addicted to the drug.
Some pathogens such as the rubella virus and HIV can pass across the
placenta.
1.3.8. MENSTRUAL CYCLE
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 At the start of the cycle, the lining of the uterus wall has broken down
(menstruation).
 As each follicle in the ovaries develops, the amount of oestrogens
produced by the ovary increases. The oestrogens act on the uterus and
cause its lining to become thicker and develop more blood vessels.
 These are changes that help an early embryo to implant.
 Two hormones, produced by the pituitary gland in brain, promote
ovulation. The hormones are follicle-stimulating hormone (FSH) and
luteinising hormone, or lutropin (LH).
 They act on a ripe follicle and stimulate maturation and release of the
ovum.
 Once the ovum has been released, the follicle that produced it develops
into a solid body called the corpus luteum. This produces a hormone
called progesterone, which affects the uterus lining in the same way as
the oestrogens, making it grow thicker and produce more blood vessels.
 If the ovum is fertilised, the corpus luteum continues to release
progesterone thus, the uterus stays suitable for implantation.
 If the ovum is not fertilised, the corpus luteum stops producing
progesterone.
 As a result, the thickened lining of the uterus breaks down and loses
blood, which escapes through the cervix and vagina.
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 Menopause occurs between the ages of 40 and 55. The ovaries cease to
release ova or produce hormones. Hence, menstrual periods stop.
Reference
1.3.9. TWINS
 If both ova are fertilised, they may form twin embryos. Because the twins
come from two separate ova, each fertilised by a different sperm, it is
possible to have a boy and a girl.
 Twins formed in this way are called fraternal twins. They are no more alike
than other brothers or sisters.
 When a single fertilised egg, during an early stage of cell division, forms two
separate embryos they must be the same sex, because only one sperm
fertilised the ovum.
 These ‘one-egg’ twins are identical twins because, unlike fraternal twins,
they will closely resemble each other in every respect.
1.3.10. BIRTH CONTROL
Natural methods
 Abstinence
 Monitoring body temperature: By knowing exactly when ovulation
occurred, intercourse could be avoided for 3–4 days before and 1 day after
ovulation.
 Cervical mucus: Women can learn to detect these changes and so calculate
their fertile period.
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Artificial methods
 Barrier methods
o Sheath or condom: Placed on the erect penis before sexual
intercourse. This traps the sperm and prevents them from reaching
the uterus. It also prevents the transmission of sexually transmitted
infections (STIs).
o Diaphragm: A thin rubber disc, placed in the vagina before
intercourse, covers the cervix and stops sperm entering the uterus. It
does not prevent STIs.
o Femidom: This is a female condom. Semen is trapped inside the
femidom. A femidom reduces the risk of infection by STIs.
 Chemical methods
o Spermicides: are chemicals which, though harmless to the tissues,
can kill or immobilise sperm.
o Intra-uterine device (IUD): A small T-shaped plastic and copper
device, also known as a coil, can be inserted by a doctor or nurse into
the wall of the uterus, where it probably prevents implantation of a
fertilised ovum. It is about 98% effective but there is a small risk of
developing uterine infections, and it does not protect against STIs.
o Intra-uterine system (IUS): This is similar to an IUD; is T-shaped and
releases the hormone progesterone slowly over a long period of time
(up to 5 years). The hormone prevents ovulation. An IUS does not
protect against STIs.
o Contraceptive pill: There are many varieties of contraceptive pill in
which the percentage of oestrogen- and progesterone-like chemicals
vary. They are 99% effective, but increase the risk of breast cancer.
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1.3.11. SEXUALLY TRANSMITTED DISEASES:
 Sexually transmitted diseases or STD’s for short are caused by viruses or
bacterium passing from one partner or another during sexual
intercourse. The most spread STD’s are gonorrhoea and HIV (also known
as AIDS).
 Gonorrhoea is caused by a bacterium that lives and breeds in damp
conditions at 37oC. It lives in the reproductive system of the carrier
person. The bacteria could be easily transferred to the partner during
sexual intercourse.
 Symptoms of gonorrhea in men are very clear. They include spores on
the penis, discharges and painful urination. In women however, the
symptoms are less noticeable because women’s reproductive organs are
inside her body.
 They include discharges which the woman won’t be able to differentiate
between and the normal vaginal discharges. If a pregnant woman
catches the disease, it is likely that the baby will catch it two during
giving birth. The disease is easily cured by a course of antibiotics and
could be prevented by means of birth control and not having sexual
intercourse with more than one person.
 AIDS is a disease caused by the HIV (human immunodeficiency virus).
The virus lives in most of body fluids such as blood and reproductive
tract. It could be easily transmitted to the other partner during sexual
intercourse because their reproductive tracts come in contact.
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 The virus lives in breeds in lymphocytes (white blood cells). The virus
could live for years in the body before it starts showing symptoms of the
disease.
 AIDS is short for Acquired Immune Deficiency Syndrome. The disease
prevents white blood cells from killing bacteria and viruses, so one or
more weak viral or bacterial infections are enough to kill the patient.
 There is no cure for AIDS till now, it is best to prevent it from spreading
by not having sexual intercourse with an infected person.
 AIDS could also be spread by blood, so it is best prevent your blood
mixing the blood of an infected person or share unsterilized, needles
that have been used by an infected person to inject drugs into yourself.
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QUESTIONS
1.
3.
2.
4.
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5.
8.
6.
9.
7.
answers:
1. B
2. D 3. C
4. D 5. B
6. A 7. B
8. B
9. A
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