Science Form 3 Chapter 4 5q2q3q

SCIENCE FORM 3 CHAPTER 4: REPRODUCTION

2.1 UNDERSTANDING SEXUAL AND ASEXUAL REPRODUCTION

Reproduction is the process of producing new individuals from living organisms. Sexual reproduction - Production of new individuals by living organisms involving gametes

Asexual reproduction - Production of new individuals by living organisms without involving gametes

Reproduction


Sexual reproduction involves two parents, one male and one female. The male parent has two testes that produce sperms. The female parent has two ovaries that produce ova.


The fusion between the nucleus of a sperm and the nucleus of an ovum to produce a zygote is called fertilisation. Sperm + Ovum

Zygote

Embryo

Baby

Foetus

General process of sexual reproduction

2.1 UNDERSTANDING SEXUAL AND ASEXUAL REPRODUCTION Fertilisation

Internal fertilisation

External fertilisation

Fusion of the nucleus of a sperm and the nucleus of an ovum in the female body

Fusion of the nucleus of a sperm and the nucleus of an ovum outside the female body


Internal fertilisation by lions


External fertilisation by frogs


Video on external fertilisation:


Organisms produced from sexual reproduction show variation. Variation is the differences between individuals of the same species. Sexual reproduction is shown by vertebrates, most invertebrates and flowering plants.


In asexual reproduction, there is only one parent involved. No gametes are involved and no fertilisation takes place. New individuals produced asexually are genetically identical to their parent. There is no variation.

2.1 UNDERSTANDING SEXUAL AND ASEXUAL REPRODUCTION Asexual reproduction Binary fission

Division of a single parental cell into two daughter cells

Example: Amoeba

Budding

Process of forming a bud at the side of the organism’s body

Example: Hydra and yeast

Spore formation

Vegetative reproduction

Regeneration

Process of producing spores in the sporangium

Process of producing new plants from vegetative part of the parent plant, other than the flower

Ability of the fragments of some organisms to grow and develop into completely new individuals

Example: Moss and ferns

Example: Banana, ginger, Bryophyllum and onion

Example: Flatworms and starfish


Binary fission of Amoeba


Budding of Hydra


Sporangium

Spore formation of fern


Vegetative reproduction of Bryophyllum


Video on spore formation of fern:


Regeneration in starfish


Video on the regeneration of planaria:


Sexual reproduction

Asexual reproduction

Similarities - Both processes form new individuals Differences Two

Number of parents

One

Yes

Involvement of gametes

No

Yes

Fertilisation

No

2.1 UNDERSTANDING SEXUAL AND ASEXUAL REPRODUCTION Reproduction

Sexual reproduction

Binary fission

Spore formation

Asexual reproduction

Budding

Vegetative reproduction

Regeneration

4.2 MALE REPRODUCTIVE SYSTEM

Two sperm ducts

A pair of seminal vesicles

Scrotum

A pair of testes

Prostate gland

Urethra

Male reproductive system

Penis


Seminal vesicle

Prostate gland

Penis

Sperm duct

Testis Urethra The male reproductive system

Scrotum


Part

Description and function

Sex glands

These include seminal vesicle and prostate gland. Sex glands secrete fluid which contains nutrients for the sperms

Sperm duct

A tube which transports sperms from the testis to the urethra inside the body

Testis

Produces the male sperms and male sex hormones

Scrotum

A sac which hangs outside the body It holds and protects the testes

Urethra

A tube which runs through the penis It is a age that allows sperm to flow out of the body It is a age that allows urine from the bladder to be excreted to the outside of the body

Penis

Male sex organ which is made up of soft tissues and rich in blood vessels It transfers semen into the vagina of the female during copulation


Sperm is produced by the testis. Sperm is the smallest cell in the human body. It consists of several parts: (i) Head (ii) Neck (iii) Middle piece (iv) Tail


Nucleus Acrosome

Neck Mitochondria

Head

Middle piece

A human sperm

Tail


The head of the sperm contains the nucleus. The nucleus consists of genetic material to be transferred to offspring. The tail enables the sperm to swim in the semen inside the vagina, uterus and fallopian tube of the female reproductive system.


Before becoming an adult, every adolescent has to undergo the puberty stage. It is the time when the reproductive system starts to produce gametes. Boys reach puberty at 12 to 14 years of age. During puberty, the testes start to produce gametes and male sex hormones.


The male sex hormones are responsible for the physical, physiological and emotional changes in males during puberty. Deepening of voice

Growth of hair on the armpits and pubic region

Muscle growth

Changes during puberty in a male

Pimples

4.3 FEMALE REPRODUCTIVE SYSTEM

Uterus Two fallopian tubes (oviducts)

A pair of ovaries

Vagina

Female reproductive system

Cervix


Fallopian tube Uterus

Ovary Cervix Vagina The female reproductive system

4.3 FEMALE REPRODUCTIVE SYSTEM Part

Description and function

Ovary

Female sex organ that produces ova and female sex hormones

Fallopian tube (oviduct)

A muscular tube where fertilisation takes place

Uterus

Pear-shaped with thick muscular walls Place where the foetus develops and grows Lining of uterine wall is rich in blood vessels

Cervix

Neck of the uterus. Widens during childbirth

Vagina

Muscular tube which opens to the outside of the female body as the vulva Place where the sperms are transferred during copulation


Girls reach puberty earlier than boys between the ages at 10 to 12. At puberty, the ovaries start to produce mature ova and also release female sex hormones. The female sex hormones are responsible for the physical, physiological and emotional changes in females during puberty.


Widening of hips

Hair growth on the armpits and pubic region

Breast development

Menstruation starts Changes during puberty in a female


The ovum is spherical in shape and is the largest cell in the human body. The nucleus contains genetic material which is ed from the mother to her child. The ovum is not able to move by itself.


Cell membrane

Nucleus

Cytoplasm

Jelly layer Structure of an ovum

4.4 MENSTRUAL CYCLE

Menstruation starts when a female reaches puberty. It refers to the shedding of the lining of uterine wall and blood flowing through the vagina. The menstrual cycle is influenced by female sex hormones and takes 28 days. The menstrual cycle is influenced by mental stress, physical activity, emotional changes and the nutrition of an individual.

4.4 MENSTRUAL CYCLE

Fertile phase/ ovulation phase

Repair phase

Premenstrual phase

Menstruation phase Phases of the menstrual cycle

4.4 MENSTRUAL CYCLE Lining of uterine wall thickens and rich in blood vessels to prepare for the implantation of embryo, if fertilisation is successful. If fertilisation is not successful, the next cycle begins

Menstrual cycle Lining of uterine wall and blood vessels break down. These are discharged as menstruation occurs

Menstruation phase (Day 1 - 5) Repair phase (Day 6 - 11) Fertile phase or ovulation phase (Day 12 - 16) Premenstrual phase (Day 17 - 28) An ovum is released around the 14th day. Lining of uterine wall and blood vessels continue to develop

Lining of uterine wall thickens and more blood vessels are formed

4.4 MENSTRUAL CYCLE

Women stop menstruating when they are about 50 years old. This is called menopause, the time which marks the end of their fertility.

4.5 FERTILISATION AND PREGNANCY

During copulation, millions of sperms are transferred into the vagina. The sperms swim through the cervix into the uterus and up the fallopian tube to meet the ovum. If the ovum is present in the fallopian tube, fertilisation takes place.


Fertilisation produces a zygote. The zygote divides into two, then into four, and so on. After six days, a ball of cells, now called an embryo, is formed.

Fusion of the nucleus of the sperm and the nucleus of an ovum


Zygote develops into an embryo, then into a foetus which resembles a human being. When implantation is successful, the woman is said to be pregnant. It takes nine months from the time the zygote is formed until the foetus is ready to be born.

4.5 FERTILISATION AND PREGNANCY One successful sperm penetrates the membrane of the ovum. Fusion of the sperm’s nucleus and the ovum’s nucleus occurs (fertilisation)

The zygote moves down the fallopian tube into the uterus

The zygote forms a ball of cells, the embryo One mature ovum is released by the ovary into the fallopian tube (ovulation)

After fertilisation, a zygote is formed. It then undergoes repeated cell division

The embryo is implanted inside the lining of uterine wall 7 -8 days after fertilisation (implantation)

Ovulation, fertilisation and implantation of embryo


The embryo which becomes the foetus grows inside the uterus in a sac surrounded by a membrane called amnion. The sac is filled with a liquid called amniotic fluid which acts like a cushion to absorb shock. A flexible tube called the umbilical cord connects the foetus to the placenta.


The placenta is formed from the tissue of the mother’s lining of uterine wall and the developing foetus. Nutrients and oxygen diffuse from the mother’s blood

Placenta

Carbon dioxide and waste products diffuse from the foetal blood

4.5 FERTILISATION AND PREGNANCY Structure

Description

Uterus

Has muscular walls Place where embryo implants itself and develops

Placenta

Made up of tissue from both mother and the foetus Place where exchange of nutrients, oxygen, carbon dioxide and waste products takes place between the mother’s blood and foetal blood

Umbilical cord

Tube which connects the foetus to the placenta

Amnion

Membrane which forms a sac that contains fluid

Foetus

Forms from an embryo

Amniotic fluid

Acts as a cushion and absorbs shock

Amnion

The foetus grows inside the uterus

4.5 FERTILISATION AND PREGNANCY Foetal capillaries

Maternal blood pool Maternal vein Maternal artery

Umbilical vein Umbilical cord

Umbilical arteries

Foetal portion of placenta

Maternal portion of placenta

A detailed structure of the placenta

4.6 IMPORTANCE OF PRENATAL CARE Nutrients

Sources

Functions

Carbohydrates and fats

Rice, bread, potatoes, butter, cheese

To supply energy for various daily activities of the mother

Protein

Chicken, beef, fish, beans, milk, cheese

For growth of new cells in the foetus

Folic acid

Broccoli, spinach, hazelnuts, groundnuts

For proper development of nervous system in the foetus

Vitamin C

Citrus fruit, tomatoes, guava, vegetables

For healthy skin of the foetus and mother

Calcium and phosphorus

Anchovies, cheese, milk

For formation of healthy bones in the foetus and maintenance of healthy bones and teeth of the mother

Iron

Liver, red meat, tuna fish

For formation of haemoglobin to prevent anaemia in the mother

Fibre

Cereals, vegetables, fruits

To prevent constipation in the mother

4.5 IMPORTANCE OF PRENATAL CARE

Spina bifida caused by deficiency of folic acid during pregnancy


Smoking cigarettes is bad for pregnant women: (i) Smaller babies (ii) Babies more likely to be born dead (iii) Babies who are mentally and physically retarded (iv) An abortion or babies born before full term


If a pregnant woman drinks excessive alcohol, the baby may suffer from Foetal Alcohol Syndrome. Alcohol may slow down the development of the foetus, and damage its brain, nervous system and heart. A pregnant woman should follow her doctor’s advice and only take drugs prescribed to her. There are drugs which may cause deformities in the foetus.


A baby with birth defects due to Foetal Alcohol Syndrome

4.7 IMPORTANCE OF RESEARCH IN HUMAN REPRODUCTION

Sterility is the inability to produce offspring. When married couples cannot have children, the male or female partner, or both may be sterile.

4.7 IMPORTANCE OF RESEARCH IN HUMAN REPRODUCTION Male The testes cannot produce sperm There is sperm production but low sperm count Low quality sperms produced

Female Ovaries cannot produce or release mature ova

Male is impotent. Sperms cannot be Blocked oviducts due to growth of transferred into the vagina tissues or infection Abnormal uterus or growth in the uterus prevents implantation of embryo Hormone imbalance or insufficient sex hormones produced

Hormone imbalance or insufficient sex hormones produced

Defective reproductive organs or organs infected with disease Health problems like high blood pressure and diabetes

4.7 IMPORTANCE OF RESEARCH IN HUMAN REPRODUCTION Ways to treat sterility

Drug treatment

- Stimulate the testes and ovaries to produce more sperms and ova - Men who are impotent can be treated with drugs

Surgery

- Blockages or growth inside the fallopian tube and uterus can be removed by surgery using a laparoscope

In vitro fertilisation (IVF)

- IVF is usually used for a woman with blocked fallopian tubes - Ova are removed from the woman’s ovaries and then fertilised by her husband’s sperms in a glass dish. The embryo is then implanted into the uterine wall where it develops into a foetus


Drug to increase the number of sperms

Drug to increase the number of ova

Drug to treat impotence


A laparoscope is used to perform minor surgery by ing it through small incision in the abdomen


In vitro fertilisation


Birth control method

Temporary contraceptive methods

Permanent contraceptive methods (sterilisation)

- Work based on three principles: Preventing ovulation, preventing fertilisation and preventing implantation of embryo

- Involves removal of one’s reproductive capability and requires surgery - Sterilisation is irreversible

4.7 IMPORTANCE OF RESEARCH IN HUMAN REPRODUCTION Principle of temporary contraceptive methods

Method

Description

Preventing ovulation

Contraceptive pills The ovaries are suppressed so that they do not produce and release ova

Preventing fertilisation

Natural method

Married couples avoid copulation during fertile period

Using a condom

Prevents sperms from entering the vagina

Using a diaphragm

Prevents the sperms from entering the uterus

Intrauterine contraceptive device (IUCD)

Small device made of plastic or copper wire of various sizes and shapes It is inserted by a doctor into the uterus of the female

Preventing implantation of embryo


Diaphragm

Contraceptive pills

Condom


Ovary

Cervix

Vagina

Uterus

IUCD

IUCD


Male sterilisation is called vasectomy. Surgery is carried out to cut off a section from each sperm duct and the two ends are then tied. This prevents the sperms from being transported to the urethra.


Sperm duct

Seminal vesicle Ejaculatory duct Prostate gland

Urethra

Sperm duct is cut and tied Testis

Scrotum Vasectomy


Female sterilisation is called ligation. Surgery is carried out to cut off the middle section of both fallopian tubes. The open ends are then tied to prevent the ovum from moving along the fallopian tubes to meet the sperms.

4.7 IMPORTANCE OF RESEARCH IN HUMAN REPRODUCTION Fallopian tubes

Middle section of the fallopian tube is cut off

Ovary Uterus

Cervix

Vagina

Ligation

4.8 SEXUAL REPRODUCTION SYSTEM OF FLOWERING PLANTS

In flowering plants, flowers form the reproductive system of the plant. They produce the male and female gametes for sexual reproduction. A typical flower consists of: (i) Sepals (ii) Petals (iii) Stamen (iv) Pistil


Stamen

Anther

Stigma

Pistil

Style Filament

Ovary

Sepal Petal

Receptacle Longitudinal section of a flower

4.8 SEXUAL REPRODUCTION SYSTEM OF FLOWERING PLANTS Structure

Function

Sepal

Protects the flower during the bud stage

Petal

Attracts insects and animals

Stamen

Male reproductive organ of a flower

Pistil

Female reproductive organ of a flower

The male reproductive organ of the flower is called the stamen. Each stamen consists of the filament and the anther. The filament is a long stem-like structure which holds and exposes the anther to facilitate pollination.


The anther produces the pollen grains which, in turn, produce the male gametes.

Pollen grains come in different sizes and shapes


The female reproductive organ of the flower is called the pistil. The pistil is made up of the stigma, style and ovary. The ovary is the enlarged part of the pistil. Within the ovary are the ovules which contain the female gamete. The slender, middle part of the pistil is the style. This is where the pollen tube grows down the ovary.


At the tip of the style is the stigma. The stigma traps the pollen grains on its sticky surface.

4.9 POLLINATION

Pollination is the process of transferring ripe pollen from the anther to the stigma. Pollination

Self-pollination

Cross-pollination

Transfer of pollen from the anther of a flower to the stigma of the same flower or to the stigma of another flower on the same plant

Transfer of pollen from the anther of a flower to the stigma of another flower on a different plant of the same species

4.9 POLLINATION

Cross-pollination Self-pollination

Self-pollination

Pollination

4.9 POLLINATION Self-pollination

Cross-pollination

Involves only one plant

Involves two plants of the same species

Requires one or two flowers from the same plant

Requires two flowers from different plants of the same species

If it involves one flower, both the anther and stigma must mature at the same time. If it involves two flowers, the anther and stigma can mature at different times

The anther and stigma can mature at different times

Less variety in new plants

More variety in new plants

4.9 POLLINATION

For pollination to occur, pollinating agents are needed to transfer the pollen grains. Insects

Animals

Water

Wind Types of pollinating agents

4.9 POLLINATION

Wind-pollinated flowers have long filaments to expose the pollen to the wind. They produce plenty of light pollen. The stigma is feathery to trap the pollen carried by the wind. Anther

Stigma Wind-pollinated flower

4.9 POLLINATION

Insects, like bees and butterflies, are important pollinating agents. Insects are attracted by big, colourful and scented flowers. When the insect lands on another flower to collect food, the pollen may drop off and stick on the stigma of that flower.

4.9 POLLINATION

Insect-pollinated flowers produce sticky pollen. Their styles are short and the stigma has a sticky surface.

Insect -pollinated flower

4.9 POLLINATION

Animals, like birds and bats, pollinate flower when they suck nectar from the flowers. The pollen sticks to the beak or body of the animals. Flowers pollinated by animals are big, colourful, scented, and produce sticky pollen.

4.9 POLLINATION

Water is a pollinating agent for submerged water plants like Elodea and Hydrilla. The water carries the pollen from the anther to the stigma. Wind-pollinated flower Small, pale coloured, not scented, no nectar

Insect-pollinated flower Big, brightly coloured, scented, nectar present

Long filament with big anther at the Short filament and small anther at end, filament sways in the wind and the end pollen disperses Plenty of light pollen

Sticky pollen

Long style

Short style

Feathery stigma

Sticky stigma

4.9 POLLINATION

Cross-pollination results in the combination of genetic materials from two parent plant of the same species. Healthier plants which can adapt better to changes in the environment

Healthier seeds

New varieties of plants Advantages of crosspollination

New plants that are more resistant to pests and diseases

4.10 DEVELOPMENT OF FRUITS AND SEEDS IN PLANTS

4.11 GERMINATION OF SEEDS

After fertilisation, most of the flower parts wilt and die. The ovules inside the ovary develop into seeds. A seed is made up of an embryo and a seed coat (testa). In monocotyledonous seed, the endosperm acts as a food store. In dicotyledonous seed, the cotyledons act as a food store.


Testa

Seed structure: Dicotyledonous seed (left) and monocotyledonous seed (right)


Part Seed

Embryo

Structure

Function

Testa

Protects the seed

Hilum

Place where the seed is attached to the fruit

Micropyle

Small hole which allows air and water to enter the seed

Embryo

Consists of plumule, radicle and cotyledon

Plumule

Part of the embryo which develops into a new shoot

Radicle

Part of the embryo which develops into a new root

Cotyledon

Stores and provides food for the dicotyledonous seed


Germination is the process in which the embryo grows into a seedling. The conditions required for germination are the presence of water, air and suitable temperature. The embryo needs food for growth and obtains it from food store in the cotyledon (dicotyledonous seed) or the endosperm (monocotyledonous seed).


The plumule grows upwards to form a new shoot. The radicle grows downwards into the soil to form the root. Now, it is called a seedling. The seedling continues to absorb food from the food store until it forms green leaves to produce its own food by photosynthesis.


Germination of seed

4.12 VEGETATIVE REPRODUCTION IN FLOWERING PLANTS

Besides sexual reproduction, many flowering plants can reproduce vegetatively. Vegetative reproduction is a method of producing new plants from any vegetative part of the parent plant, other than the flower. Parts of the plants that can reproduce vegetatively are the root, stem and leaf.

4.12 VEGETATIVE REPRODUCTION IN FLOWERING PLANTS

The vegetative parts contain stored food and buds. The buds use the stored food and grow into a new plant. Soon it will produce its own food by photosynthesis.

4.12 VEGETATIVE REPRODUCTION IN FLOWERING PLANTS Vegetative parts

Examples of plants

Roots

Sweet potato

Carrot

Potato

Ginger

Stems Underground stem


Examples of plants

Stems Horizontal stem (runners)

Water lettuce

Strawberry

Vegetative Onionreproduction

Hyacinth

Stems Bulb


Examples of plants

Leaves

Bryophyllum

Begonia

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