Biological Science Classes VI-X for School Assistants and TET Paper 2A · Chapter 6

Reproduction and Adolescence

What to remember

Asexual reproduction needs one parent and gives identical offspring; sexual reproduction needs gametes from two parents and gives variation.
In flowering plants the ovule becomes the seed and the ovary becomes the fruit; in humans fertilisation is internal and the embryo grows in the uterus.
Adolescence is the change from childhood to adulthood, driven by hormones (testosterone in boys, oestrogen in girls) from puberty onwards.

Why living things reproduce

Reproduction keeps a species alive from one generation to the next. Each organism lives for a limited time, so new individuals must be formed. Reproduction also passes DNA from parent to offspring. There are two main modes: asexual and sexual.

Asexual reproduction

Only one parent takes part. No gametes are formed. The offspring are genetically identical to the parent (they are clones). It is fast, and one organism can give many offspring.

Binary fission: the parent divides into two equal parts. Example: Amoeba, bacteria, Paramecium.
Multiple fission: the nucleus divides many times and then the cell divides into many daughter cells. Example: Plasmodium (malaria parasite).
Budding: a small bud grows on the parent body, then separates. Example: Hydra, yeast.
Fragmentation: the body breaks into pieces and each piece grows into a new organism. Example: Spirogyra.
Spore formation: tiny spores with a hard coat grow into new individuals when conditions are good. Example: Rhizopus (bread mould), ferns, mosses.
Regeneration: a lost body part grows back, and in some animals a piece can form a whole animal. Example: Planaria, Hydra.
Vegetative propagation: new plants grow from roots, stems or leaves. Natural examples: potato (eyes on the tuber), ginger (rhizome), Bryophyllum (buds on leaf edges), sweet potato (root). Artificial methods: cutting (rose, sugarcane), layering (jasmine), grafting (mango, rose).

Tissue culture grows new plants from a small piece of tissue in a nutrient medium in the laboratory. It is a modern form of vegetative propagation.

Sexual reproduction in flowering plants

The flower is the reproductive organ of a plant.

Part	Function
Sepals (calyx)	Protect the bud
Petals (corolla)	Attract insects
Stamen (male): anther + filament	Anther makes pollen grains
Pistil or carpel (female): stigma, style, ovary	Ovary has ovules; stigma receives pollen

A flower with both stamens and pistil is bisexual (hibiscus, mustard). A flower with only one of them is unisexual (papaya, cucumber, maize).

Pollination is the transfer of pollen from the anther to the stigma. Self-pollination is within the same flower or plant. Cross-pollination is between two different plants and gives more variation. Agents: wind (maize, grasses), insects (bright flowers with nectar), water (Vallisneria), birds and bats.

Fertilisation: the pollen grain grows a pollen tube down the style to the ovule. The male gamete joins the egg to form the zygote. In flowering plants there is double fertilisation: one male gamete fuses with the egg and the other with the central cell, which forms the endosperm (food store).

After fertilisation: zygote becomes embryo; ovule becomes seed; ovary becomes fruit; other flower parts usually wither. A fruit that forms without fertilisation, and so has no seed, is called parthenocarpic (banana, seedless grapes).

Seed dispersal stops crowding and helps a plant reach new places.

Agent	Feature of seed or fruit	Example
Wind	Light, wings or hairs	Dandelion, drumstick tree, cotton
Water	Floats, fibrous or spongy coat	Coconut, lotus
Animals	Hooks or spines; or tasty fruit	Xanthium, mango, guava
Explosion	Fruit bursts when dry	Castor, balsam

Human reproductive system

Male: testes (in the scrotum, which keeps them slightly cooler than body temperature), sperm duct (vas deferens), urethra, penis, and glands (seminal vesicles, prostate). The testes make sperm and the hormone testosterone. Sperm have a head with the nucleus, a middle piece and a long tail for swimming.

Female: a pair of ovaries, oviducts (fallopian tubes), uterus and vagina. The ovaries make eggs (ova) and the hormones oestrogen and progesterone. Fertilisation takes place in the oviduct. The uterus is the organ where the embryo grows.

Menstrual cycle: it repeats about every 28 days in a healthy adult woman. One egg is released from an ovary about the middle of the cycle (ovulation). The uterus lining becomes thick to receive a fertilised egg. If there is no fertilisation, the lining and some blood leave the body through the vagina; this is menstruation and lasts a few days. It begins at puberty (menarche) and stops permanently at menopause, usually between about 45 and 50 years. FSH and LH from the pituitary control the cycle.

Fertilisation and development: the sperm fuses with the egg to form the zygote. The zygote divides, forms a ball of cells and gets embedded in the uterus wall (implantation). The embryo becomes a foetus. The placenta is a disc-shaped tissue joined to the uterus wall. Through the umbilical cord it passes food and oxygen to the foetus and takes away waste. The foetus floats in amniotic fluid, which protects it from shocks. Pregnancy lasts about nine months. Birth is the delivery of the baby.

Identical and fraternal twins: identical twins form when one zygote splits into two and they are of the same sex. Fraternal twins form from two eggs fertilised by two sperm.

IVF ("test-tube baby"): the egg is fertilised outside the body and the early embryo is put into the uterus. So the baby does not grow in a test tube.

Reproduction in animals

Oviparous: lay eggs (birds, frogs, reptiles, insects). Viviparous: give birth to young ones (humans, cow, dog).
Fish and frogs have external fertilisation in water. Birds, reptiles and mammals have internal fertilisation.
Metamorphosis is a big change in body form after hatching. In the frog: egg, tadpole, young frog, adult frog. The hormone thyroxine controls it; iodine is needed to make thyroxine.
Insects: in complete metamorphosis (butterfly, housefly, mosquito) the stages are egg, larva, pupa and adult. In incomplete metamorphosis (cockroach, grasshopper) the stages are egg, nymph and adult; there is no pupa.

Adolescence

Adolescence is the period between childhood and adulthood, roughly the teen years. Puberty is the stage when the reproductive organs become mature. In girls it starts a little earlier than in boys. The hypothalamus and pituitary start the change by releasing hormones.

Boys (testosterone)	Girls (oestrogen)
Moustache and beard	Breast growth
Voice breaks (larynx enlarges, "Adam's apple")	Wider hips
Broader shoulders, more muscle	Menstruation begins
Sperm production starts	Eggs are released by ovaries

Common changes: fast growth in height, hair under the arms and in the pubic region, more sweat and oil glands (pimples), mood swings. These changes are normal.

Care in adolescence: balanced diet with iron and calcium, daily exercise, personal hygiene, enough sleep, and avoiding tobacco, alcohol and drugs. Teenagers need accurate information, trust and a calm talk with parents and teachers.

Reproductive health: a healthy reproductive system, free from disease and with safe and informed choices. Contraception prevents pregnancy: barrier methods (condom), copper-T (IUD), oral pills, and surgical methods (vasectomy in males, tubectomy in females). Sexually transmitted infections include gonorrhoea and syphilis (bacterial), and HIV/AIDS, hepatitis B and HPV infection (viral). A condom also reduces the spread of these infections. HIV spreads through unprotected sex, infected blood and needles, and from mother to child. It does not spread by touch, handshake, sharing food or mosquito bites.

Teaching angle: in Classes VIII-X, use charts, models and cut-out diagrams. Treat the topic with respect, give factual answers, and avoid giggling or shame. Use the Bryophyllum leaf, potato eyes and sprouting gram seeds as hands-on activities.

Common questions students ask

Is menstruation a disease? No. It is a normal body process and the girl should keep clean and may carry on with normal school work. Why do some children reach puberty earlier than others? The age differs from child to child because of heredity, nutrition and health. Why is the age of marriage important? A body needs time to become mature, so early pregnancy can harm the health of the mother and the baby. A teacher should answer such questions in simple words and tell students to speak to a trusted adult or doctor when they are worried.

Exam traps

Binary fission (equal halves, Amoeba) is not budding (unequal outgrowth, Hydra, yeast).
Fragmentation (Spirogyra, pieces) is not regeneration (growing back a lost part, Planaria).
Pollination (pollen reaches the stigma) is not fertilisation (gametes fuse).
Ovule becomes the seed; ovary becomes the fruit; the zygote becomes the embryo.
Testes make sperm and testosterone; ovaries make eggs, oestrogen and progesterone.
Fertilisation takes place in the oviduct; embryo grows in the uterus.
Oviparous (lays eggs) is not viviparous (gives birth).
Metamorphosis of the frog depends on thyroxine; insects with a pupa have complete metamorphosis.

One-liners

1. Hydra reproduces by budding.
2. Plasmodium divides by multiple fission.
3. Rhizopus reproduces by spores.
4. Bryophyllum forms new plants from leaf buds.
5. Double fertilisation is found in flowering plants.
6. Banana is parthenocarpic, so it has no seeds.
7. Testosterone is the male sex hormone.
8. Ovulation occurs about the middle of the menstrual cycle.
9. The placenta links the foetus to the mother through the umbilical cord.
10. Amniotic fluid protects the foetus.
11. Menopause is the permanent stop of menstruation.
12. Vasectomy and tubectomy are surgical methods of contraception.

Practice questions

Which organism reproduces by budding?
1. Hydra
2. Planaria
3. Spirogyra
4. Amoeba
Answer
A. Hydra
Hydra and yeast form buds on the parent body.
Plasmodium reproduces by
1. binary fission
2. multiple fission
3. budding
4. fragmentation
Answer
B. multiple fission
The nucleus divides many times before the cell splits into many daughter cells.
Spirogyra mainly multiplies by
1. spore formation
2. budding
3. fragmentation
4. grafting
Answer
C. fragmentation
The filament breaks into pieces and each piece grows into a new filament.
Bread mould (Rhizopus) reproduces by
1. regeneration
2. spores
3. budding
4. binary fission
Answer
B. spores
Spores from sporangia grow into new mould in good conditions.
The part of a flower that makes pollen grains is the
1. anther
2. stigma
3. sepal
4. ovary
Answer
A. anther
The anther of the stamen produces pollen.
After fertilisation in a flowering plant, the ovule develops into the
1. fruit
2. petal
3. pollen grain
4. seed
Answer
D. seed
The ovule becomes the seed and the ovary becomes the fruit.
Transfer of pollen from an anther to a stigma is called
1. fertilisation
2. germination
3. pollination
4. dispersal
Answer
C. pollination
Pollination is only the transfer; the fusion of gametes is fertilisation.
Which plant part is used in vegetative propagation of Bryophyllum?
1. Root
2. Leaf
3. Flower
4. Seed
Answer
B. Leaf
Buds on the leaf margin grow into plantlets.
The male sex hormone is
1. progesterone
2. thyroxine
3. oestrogen
4. testosterone
Answer
D. testosterone
Testes secrete testosterone, which brings secondary male characters.
Fertilisation in humans normally takes place in the
1. oviduct
2. uterus
3. vagina
4. ovary
Answer
A. oviduct
The sperm meets the egg in the fallopian tube.
The structure that joins the foetus to the placenta is the
1. oviduct
2. amnion
3. umbilical cord
4. urethra
Answer
C. umbilical cord
The cord carries food and oxygen to the foetus and waste away.
The hormone that controls metamorphosis in a frog is
1. testosterone
2. adrenaline
3. thyroxine
4. insulin
Answer
C. thyroxine
Thyroxine from the thyroid causes the tadpole to change into a frog.
Which of the following is an oviparous animal?
1. Human
2. Frog
3. Cow
4. Dog
Answer
B. Frog
Frogs lay eggs; the others give birth to young ones.
The permanent stop of menstruation in women is called
1. puberty
2. ovulation
3. menarche
4. menopause
Answer
D. menopause
Menopause occurs at about 45 to 50 years of age.
Which method is a surgical method of contraception in males?
1. Vasectomy
2. Tubectomy
3. Copper-T
4. Oral pill
Answer
A. Vasectomy
In vasectomy the sperm ducts are cut and tied.
The voice of a boy becomes deeper in adolescence because the
1. lungs shrink
2. tongue grows
3. larynx enlarges
4. trachea closes
Answer
C. larynx enlarges
Testosterone enlarges the voice box (Adam's apple).
Which of the following is a sexually transmitted infection caused by a virus?
1. Gonorrhoea
2. HIV/AIDS
3. Syphilis
4. Cholera
Answer
B. HIV/AIDS
Syphilis and gonorrhoea are bacterial; HIV is a virus.
Seedless banana is an example of
1. parthenocarpy
2. double fertilisation
3. regeneration
4. budding
Answer
A. parthenocarpy
The fruit forms without fertilisation, so there are no seeds.
A farmer wants all plants in a field to have the same good fruit quality as the parent mango tree. The best method is
1. sowing seeds
2. cross-pollination
3. seed dispersal by birds
4. grafting
Answer
D. grafting
Vegetative propagation keeps the parent's characters; seeds give variation.
A student cuts a Planaria into two pieces and each piece grows into a full worm. This is
1. spore formation
2. budding
3. binary fission
4. regeneration
Answer
D. regeneration
Regeneration is the growth of lost body parts into a full individual.
Brightly coloured, scented flowers with nectar are most likely pollinated by
1. water
2. insects
3. wind
4. rain
Answer
B. insects
Colour and nectar attract insects; wind-pollinated flowers are small and dull.
Coconut fruits are well suited to dispersal by water because they have
1. light wings
2. an exploding pod
3. a fibrous floating husk
4. tiny hooks
Answer
C. a fibrous floating husk
The husk is fibrous and buoyant, so the fruit floats.
Why are testes found outside the body cavity in the scrotum?
1. Sperm formation needs a temperature a little lower than body temperature
2. They help in digestion of food
3. They must be near the kidneys
4. They need more oxygen from the air
Answer
A. Sperm formation needs a temperature a little lower than body temperature
The slightly cooler temperature is needed for sperm production.
Where does the embryo implant and grow in a woman?
1. Vagina
2. Ovary
3. Uterus
4. Oviduct
Answer
C. Uterus
After implantation in the uterus wall the placenta forms.
The menstrual cycle in a healthy adult woman is about
1. 28 days
2. 7 days
3. 14 days
4. 45 days
Answer
A. 28 days
Ovulation occurs about the middle of this cycle.
Which of the following lays eggs and has a pupa stage in its life cycle?
1. Frog
2. Butterfly
3. Fish
4. Cockroach
Answer
B. Butterfly
Butterfly has complete metamorphosis with egg, larva, pupa and adult.
A tadpole kept in water without iodine would most probably
1. lay eggs early
2. grow wings
3. turn into a fish
4. fail to turn into a frog
Answer
D. fail to turn into a frog
Iodine is needed to make thyroxine, which drives metamorphosis.
In which of the following do you find unisexual flowers?
1. Rose
2. Mustard
3. Papaya
4. Hibiscus
Answer
C. Papaya
Papaya has separate male and female flowers; hibiscus and mustard are bisexual.
Which of the following does NOT spread HIV?
1. Sharing a meal with an infected person
2. Mother to child during birth
3. Sharing needles
4. Unsafe blood transfusion
Answer
A. Sharing a meal with an infected person
HIV does not spread through food, touch or shared utensils.
Identical twins are formed when
1. one egg is fertilised by two sperms
2. one zygote splits into two
3. two eggs are fertilised by two sperms
4. an unfertilised egg divides
Answer
B. one zygote splits into two
They have the same genes and the same sex.
Which part of the pistil receives the pollen grains?
1. Ovary
2. Filament
3. Style
4. Stigma
Answer
D. Stigma
The stigma is the sticky tip of the pistil.
The 'test-tube baby' technique actually involves
1. growing the baby fully in a laboratory tube
2. fertilisation outside the body and transfer of the embryo to the uterus
3. fertilisation in the oviduct only
4. implanting a sperm in the ovary
Answer
B. fertilisation outside the body and transfer of the embryo to the uterus
IVF means in vitro fertilisation; development still takes place in the uterus.
Statements: 1. Budding produces offspring different in genes from the parent. 2. Spores are formed by gametes joining.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
D. Neither 1 nor 2
Budding gives clones, and spores are formed without fusion of gametes, so both are wrong.
Statements: 1. Zygote becomes seed. 2. Ovary becomes fruit after fertilisation.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
B. 2 only
The zygote becomes the embryo; the ovule becomes the seed.
Statements: 1. Sperm are made in the seminal vesicles. 2. Oestrogen is made by the ovaries.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
B. 2 only
Sperm are made in the testes; seminal vesicles add fluid.
Statements: 1. Pollination and fertilisation mean the same thing. 2. Wind-pollinated flowers are large and scented.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
D. Neither 1 nor 2
Pollination is only the transfer of pollen, and wind-pollinated flowers are small and dull.
Statements: 1. Frogs show external fertilisation. 2. Birds show internal fertilisation.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
C. Both 1 and 2
Frogs fertilise in water; birds fertilise inside the female body.
Statements: 1. Menopause marks the start of menstruation. 2. Menstruation starts at menarche.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
B. 2 only
Menopause is the end of menstruation, not the start.
Statements: 1. Placenta removes waste from the foetus. 2. Amniotic fluid protects the foetus from shock.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
C. Both 1 and 2
Both are correct functions.
Statements: 1. Copper-T is a barrier worn by the male. 2. Condoms can reduce the spread of STIs.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
B. 2 only
Copper-T is an IUD placed in the female uterus.
Statements: 1. Cockroach shows complete metamorphosis. 2. Housefly shows complete metamorphosis.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
B. 2 only
Cockroach has nymphs (incomplete); housefly has larva and pupa (complete).
Statements: 1. Voice change in boys is caused by oestrogen. 2. Hormones control changes in adolescence.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
B. 2 only
Testosterone, not oestrogen, causes voice change in boys.
Match: 1. Xanthium - hooks on fruit; 2. Castor - explosion of fruit. Which is correctly matched?
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
C. Both 1 and 2
Xanthium disperses by sticking to animals; castor fruit bursts open when dry.
Statements: 1. Regeneration is seen in Planaria. 2. Potato reproduces by eyes on the tuber.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
C. Both 1 and 2
Both are correct examples of regeneration and vegetative propagation.
Statements: 1. Sexual reproduction increases variation in a species. 2. Tissue culture is a sexual method.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2
Answer
A. 1 only
Tissue culture is a vegetative, asexual method.

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1.The bud in Hydra:
2.The egg is carried from the ovary to the uterus by
3.The female germ-cells or eggs are made in the:
4.Select the process responsible for stability of populations of species.
5.The ability of a fully differentiated organism to give rise to new individuals from their body parts is known as:
6.Sporangia blobs contain cells or spores that can eventually develop into new Rhizopus individuals. Such asexual reproduction is known as:
7.Spirogyra a multi-cellular organism simply breaks up into smaller pieces upon maturation and these pieces or fragments grow into new individuals. Such a mode of reproduction is known as:
8.Small changes in DNA copies during reproduction are important because they ________.
9.The sperms produced in the testes are transported via the ______.
10.The stage of Embryonic development in which all the organs of the child can be identified?

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