Class 9 Science: Reproduction: How Life Continues — Chapter Question Set

(b) reproduction

(c) a single parent

(b) identical to the parent

(b) fleshy underground stems

(a) vegetative propagation

(a) cutting

(c) a twig of the rooted Plant A

(c) the buried middle part of a flexible twig

(a) the shoot tip (apical meristem)

(a) buds

(d) develops on the parent body and later separates

(a) hyphae

(c) a sac-like structure at the tip of hyphae

(d) moisture and nutrients

(a) mitosis

(c) clones

(b) Louis Pasteur

(d) half the chromosome number

(c) 46

(b) 23 chromosomes

(c) chromosomes

(a) 8

(d) stamen

(b) filament and anther

(c) anther

(c) stigma, style, ovary

(c) an egg cell (female gamete)

(c) pollination

(c) self-pollination

(d) cross-pollination

(c) light, small pollen produced in large numbers

(d) Vallisneria and Hydrilla

(d) are brightly coloured, fragrant and produce nectar

(b) pollen tube that grows through the style

(a) fertilisation

(a) zygote

(b) the ovary becomes the fruit and ovules become seeds

(d) fish and frogs

(d) reptiles, birds and mammals

(d) feeding stage that accumulates nutrition

(c) testes

(a) slightly cooler than normal body temperature

(d) vas deferens

(a) urethra

(a) seminal vesicles and prostate gland

(c) ovaries

(c) oviduct (fallopian tube)

(d) uterus

(c) cervix

(a) ovulation

(c) menstruation

(b) 3–7 days

(d) the ninth week

(c) the father's sperm (X or Y chromosome)

(a) in-vitro fertilisation (IVF)

reproduction

clones

pollination

fertilisation

seed; fruit

meiosis

budding

spores

pollen

cooler

ovulation

cervix

test tube

condoms

Copper-T

False

True

False (it halves the number)

True

False (it is the female part)

True

False (it occurs in the oviduct)

True

False (it is the reverse)

True

False (it contains 46)

True

False (it is strictly prohibited by law)

True

True

(a)

(c)

(a)

(d)

(a)

(a)

(a)

(d)

Reproduction is essential because it ensures the continuity of life and the survival of a species from one generation to the next. When an organism ages and dies, its kind continues to exist through the offspring it has produced; without reproduction, a species would eventually become extinct.

Vegetative propagation is a form of asexual reproduction in plants in which new plants arise from vegetative parts such as stems, roots or leaves, without seeds or gametes. Examples include potato and ginger, which multiply through their underground stems, and Bryophyllum, which produces plantlets on the margins of its leaves.

Offspring of asexual reproduction are called clones because they are produced through mitotic cell division, which preserves the chromosome number and genetic content exactly as in the single parent. As a result, every offspring is genetically identical to its parent, with no variation between them.

The four artificial methods of vegetative propagation are cutting, grafting, layering and tissue culture. Horticulturists use these methods to propagate desirable plant varieties quickly and uniformly, without waiting for seeds to form.

Mould spores and bacteria that spoil food need warmth and moisture to grow and reproduce. Refrigeration keeps food at a low temperature, which slows down or stops the reproduction of these microorganisms, thereby keeping the food fresh for a longer time.

In budding, a small, round outgrowth called a bud appears on the parent yeast cell. The bud gradually enlarges while the parent's nucleus divides, and one daughter nucleus moves into the bud. Finally, the bud separates from the parent cell and grows into an independent yeast organism — the diagram should show the parent cell, bud, and nucleus labelled.

A hydra has a tubular body with tentacles at one end. One or more bud outgrowths are seen on its body wall, formed by repeated mitotic cell division at a specific budding site. Each bud develops tentacles and a mouth, and later detaches to live independently — the labelled diagram should show the body, tentacles, and developing buds.

In asexual reproduction, a single parent produces offspring without gametes, and the offspring are genetically identical to the parent. In sexual reproduction, two parents each contribute specialised gametes, and the resulting offspring carry a mixture of characters from both parents, which introduces genetic variation.

Meiosis halves the chromosome number during gamete formation, so that when two gametes fuse at fertilisation, the zygote restores the species' fixed chromosome number. It also generates variation through recombination of genetic material, which is important for adaptation and evolution.

Sepals form the outermost whorl of a flower and protect the delicate inner reproductive parts while the flower is still a bud. Petals are brightly coloured and often scented; they attract pollinators such as insects and birds through their colour, fragrance and nectar, thereby helping in pollination.

The pistil has three parts: (i) the stigma, the sticky tip that receives pollen during pollination; (ii) the style, a tube that connects the stigma to the ovary and through which the pollen tube grows; and (iii) the ovary, which contains ovules, each housing an egg cell that develops into a seed after fertilisation.

In self-pollination, pollen from the anther lands on the stigma of the same flower or another flower of the same plant. In cross-pollination, pollen is transferred from a flower on one plant to the stigma of a flower on a different plant of the same type, which brings more variation in the offspring.

Such flowers are pollinated by night-time visitors such as moths. Since colours are hard to see in the dark, white or light-coloured petals make the flowers visible, and a strong fragrance guides the pollinators to the flower from a distance.

After fertilisation, the zygote develops into an embryo inside the ovule, the ovules develop into seeds, and the ovary enlarges and ripens into a fruit. The petals, sepals and stamens usually wither and fall away, as their role in pollination is complete.

In external fertilisation, the eggs and embryos are exposed to water currents and predators, so most of them do not survive. Producing a large number of eggs therefore improves the chance that at least some offspring will reach adulthood. In internal fertilisation, the embryo is protected inside the mother's body, so fewer eggs are needed.

The butterfly life cycle has four stages: egg → larva (caterpillar) → pupa → adult butterfly. The larva is the feeding stage that grows by eating organic matter, the pupa is the non-feeding transformation stage, and the adult finally emerges — the diagram should show these four labelled stages in order.

The scrotum is a sac-like structure located outside the abdominal cavity that holds the testes. It keeps the testes slightly cooler than the rest of the body, and this lower temperature is necessary for the production of healthy sperm.

(i) The vas deferens is a long tube that carries the sperm produced in the testes onward towards the urethra. (ii) The urethra serves as a common passage for both urine and sperm to leave the body, though the two never pass at the same time.

Ovulation is the release of a mature egg (ovum) from an ovary into the oviduct. In a typical 28-day menstrual cycle, it occurs around the 14th day, when the mature follicle in the ovary ruptures and releases the egg.

Prenatal sex determination is banned because it often leads to sex-selective abortion, especially of female foetuses, which disturbs the balance of the societal sex ratio. A balanced sex ratio is essential for a healthy society, so the law prevents misuse of prenatal tests.

Introduction: Vegetative propagation is reproduction from the vegetative, growing parts of a plant instead of seeds.
Key Points:
1. Natural examples — Potato and ginger sprout from fleshy underground stems; Bryophyllum leaves sprout plantlets.
2. Single parent trait — New plants are genetically identical because only one parent is involved.
3. Agricultural use — Cutting, grafting, layering and tissue culture let farmers mass-produce desirable crops.
Conclusion: Vegetative propagation makes large-scale cultivation of desirable, uniform crops quick and reliable.

Introduction: Simple organisms multiply rapidly through asexual methods needing a single parent.
Key Points:
1. Budding in yeast — Small buds emerge as outgrowths on the parent cell and separate to grow independently.
2. Budding in hydra — Repeated cell division at one site forms a bud that enlarges and detaches from the parent.
3. Spore formation in fungi — Rhizopus and Aspergillus form millions of lightweight spores inside sacs on hyphae.
Conclusion: These fast methods let populations grow quickly when conditions are favourable.

Introduction: Meiosis halves chromosomes and mixes them randomly while forming gametes.
Key Points:
1. Chromosome separation — Each pair separates so every gamete gets only one chromosome of each pair.
2. Random combinations — Picking one bead from each of three pairs gives eight combinations; 23 pairs give immense variety.
3. Variation importance — Unique combinations make children different from parents and siblings, aiding survival and evolution.
Conclusion: Random mixing during meiosis generates the variation on which adaptation depends.

Introduction: A complete flower has four whorls — sepals, petals, stamens and pistil.
Key Points:
1. Sepals — Green outermost whorl protecting the flower in the bud stage.
2. Petals — Coloured whorl attracting pollinators by colour, fragrance and nectar.
3. Stamen and pistil — Stamen (filament, anther) makes pollen; pistil (stigma, style, ovary) holds ovules with eggs.
Conclusion: The flower is the reproductive organ, with stamen and pistil as its male and female parts.

Introduction: Pollination needs external agents called pollinators to carry pollen to the stigma.
Key Points:
1. Wind pollination — Wheat and maize make millions of light pollen grains; stigmas are long and feathery.
2. Water pollination — In Vallisneria and Hydrilla, water currents carry pollen between flowers.
3. Insect and bird pollination — Bright, fragrant, nectar-rich flowers with sticky pollen attract bees, butterflies and birds like sunbirds.
Conclusion: Each strategy matches the flower's design to its pollinator's behaviour.

Introduction: Fertilisation follows pollination and starts a new life in the ovule.
Key Points:
1. Pollen tube growth — On a compatible stigma, pollen forms a tube that grows down through the style.
2. Gamete fusion — The male gamete travels through the tube and fuses with the egg cell in the ovule, forming a zygote.
3. Post-fertilisation changes — The zygote becomes the embryo; the ovary enlarges into a fruit; ovules become seeds.
Conclusion: Seeds dispersed by wind, water or animals germinate into new plants when conditions are favourable.

Introduction: Animals ensure gametes meet either outside or inside the female's body.
Key Points:
1. External fertilisation — Fish and frogs release eggs and sperm into water where fertilisation occurs outside.
2. Internal fertilisation — In reptiles, birds and mammals, fertilisation takes place inside the female body.
3. Survival comparison — External fertilisation needs many eggs since many are destroyed; internal fertilisation protects embryos, raising survival.
Conclusion: Egg numbers and parental care reflect each fertilisation strategy.

Introduction: The male system produces sperm and transfers them to the female body.
Key Points:
1. Testes and scrotum — Paired testes in the scrotum make sperm, kept cooler than body temperature.
2. Transport ducts — Sperm travel through the vas deferens to the urethra, the common passage for urine and sperm.
3. Glands and sperm structure — Seminal vesicles and prostate add nourishing fluids; each sperm has a head with genetic material and a swimming tail.
Conclusion: The system both produces male gametes and delivers them in a nourishing fluid.

Introduction: The female system produces eggs, receives sperm and supports the developing baby.
Key Points:
1. Ovaries — Pair of organs producing eggs and releasing hormones; a girl is born with millions of immature eggs.
2. Oviducts and uterus — Fallopian tubes carry the egg and are the site of fertilisation; the uterus hosts the growing foetus.
3. Cervix and vagina — The uterus opens into the vagina through the narrow cervix.
Conclusion: Each organ supports one stage from egg release to embryo implantation and birth.

Introduction: The menstrual cycle prepares the uterus for pregnancy every 21–35 days, often about 28 days.
Key Points:
1. Menstruation (days 1–5) — The thick uterine lining sheds with blood when the previous egg was not fertilised.
2. Rebuilding and ovulation (days 6–14) — The lining rebuilds while an egg matures; the ovary releases the egg around day 14.
3. Thickening phase (days 15–28) — The lining grows thick and blood-rich; without fertilisation it breaks down and the cycle repeats.
Conclusion: The cycle starts at puberty (ages 10–14 in girls) and continues till menopause around age 50.

Introduction: Human reproduction proceeds from gamete fusion to a roughly nine-month pregnancy.
Key Points:
1. Fertilisation and implantation — Sperm meet the egg in the oviduct; the zygote divides and implants in the uterine lining, beginning pregnancy.
2. Development stages — The embryo forms major organs in the first trimester; from the ninth week it is a foetus that grows and moves.
3. Birth and care — Uterine contractions push the baby out through the birth canal; breastfeeding protects and nourishes the newborn.
Conclusion: Three trimesters of protection and nourishment inside the uterus end with childbirth and infant care.

Introduction: Human gametes differ greatly despite carrying equal genetic contributions.
Key Points:
1. Sperm — Millions of very small, actively motile cells with tails and no stored nutrients.
2. Egg — A few large, non-motile cells that store nutrients for the early embryo.
3. Biological reason — The egg invests nourishment for the zygote; the sperm invests in numbers and motility to reach the egg.
Conclusion: This asymmetry between gametes is seen across most animals.

Introduction: Contraceptive methods prevent unwanted pregnancies in different ways.
Key Points:
1. Barrier methods — Condoms and vaginal covers stop sperm from reaching the egg; condoms also prevent STIs.
2. Hormonal and IUD methods — Oral pills alter hormone-controlled egg release; IUDs like Copper-T placed in the uterus prevent pregnancy.
3. Surgical methods — Blocking the vas deferens or fallopian tubes permanently stops sperm and egg from meeting.
Conclusion: Each method has benefits and side effects, so informed choice matters.

Introduction: A baby's biological sex depends on the sex chromosomes it inherits.
Key Points:
1. Mother's contribution — Every egg carries one X chromosome, as females are XX.
2. Father's contribution — A sperm carries either X or Y, as males are XY.
3. Outcome — X + X gives a girl; X + Y gives a boy, so the father's sperm decides the sex.
Conclusion: Sex-selective abortion skews the sex ratio, so prenatal sex determination is banned by law in India.

Introduction: In-vitro fertilisation is a medical technique combining gametes outside the body.
Key Points:
1. Procedure — An egg and a sperm are fused in a laboratory dish and the embryo is implanted in the uterus.
2. Significance — It helps couples who cannot conceive naturally to have a baby.
3. Indian contribution — Subhash Mukhopadhyay pioneered India's first test tube baby, Kanupriya Agarwal (Durga), in 1978 in Kolkata.
Conclusion: Though called a "test tube baby", the process actually occurs in a culture dish.

(a) Pollinators transfer pollen from the anther to the stigma of apple flowers, enabling fertilisation, without which fruits and seeds cannot form.
(b) A suitable hypothesis is: "Adding managed beekeeping to an orchard increases pollination and therefore apple yield compared with natural pollinators alone."
(c) Orchard B yielded more because the managed bees ensured that a greater proportion of flowers were pollinated, raising fruit set and reducing fruit drop.
(d) Farmers can reduce pesticide use during the flowering season, plant flowering companion crops, and keep bee boxes in the orchards to protect pollinators.

(a) The muslin bags prevented insects from bringing pollen from other flowers, while still allowing the flower inside to develop normally.
(b) Its own stamens had been removed, and the bag stopped any external pollen from reaching the stigma, so no fertilisation occurred and no fruit formed.
(c) The activity proves that the transfer of pollen to the stigma is essential for fertilisation and fruit formation in flowers.
(d) Pea plants show predominantly self-pollination, since the covered flower with intact stamens still bore fruit.

(a) This is cross-pollination, because pollen moves from one plant to a different plant of the same type.
(b) Unlike self-pollination, where pollen stays within the same flower or plant, here the pollen travels between two separate individuals.
(c) It mixes characters from two parents and creates variation in the offspring, which helps the new plants adapt better to their environment.
(d) Maize is wind-pollinated, so most pollen is lost in transit; producing enormous quantities of light pollen raises the chance that some grains reach a stigma.

(a) A valid hypothesis is: "The germination of pollen grains depends on the concentration of sugar in the surrounding medium."
(b) The type of pollen used, the temperature, the amount of solution and the observation time must all be kept identical across the slides.
(c) A pollen tube emerges from the germinating pollen grain and grows down through the style toward the ovary.
(d) The pollen tube delivers the male gamete to the ovule, where it fuses with the egg cell to complete fertilisation.

(a) Tomato shows self-pollination, because the stamens surround and cover the stigma, so pollen naturally falls on the stigma of the same flower.
(b) Wheat also shows self-pollination; its flowers are small and inconspicuous with light pollen and do not depend on insect visits.
(c) Papaya must cross-pollinate because its male and female flowers grow on separate trees, so pollen has to come from another tree.
(d) Wheat is pollinated by the wind, which carries its light pollen grains to the stigmas.

(a) Ravi is entering adolescence, the period between childhood and adulthood when the body matures physically and sexually.
(b) The testes are the hormone-producing organs responsible; they release hormones that control sperm production and bring about the pubertal changes seen in boys.
(c) No — sexual and physical maturity arrive much earlier than emotional and social maturity, which take longer to develop.
(d) Emotional maturity means being able to handle one's feelings properly, communicate clearly and make thoughtful, balanced decisions.

(a) Her next period is most likely to begin around 2nd April, which is 28 days after 5th March.
(b) Ovulation occurs around the 14th day of the cycle, when the ovary releases a mature egg that travels to the oviduct, where it may be fertilised.
(c) The human zygote carries 46 chromosomes — 23 from the sperm and 23 from the egg.
(d) Hygiene practices include using clean menstrual products and changing them every 4–6 hours, and washing hands before and after changing, along with keeping the genital area clean and dry.

(a) No, the claim is only approximately correct and cannot be generalised to every woman or every cycle.
(b) Cycle length varies from about 21 to 35 days among women, and the day of ovulation shifts with the length of each individual cycle rather than staying fixed.
(c) In a typical 28-day cycle, day 14 is the approximate mid-point at which the ovary releases the mature egg.
(d) During pregnancy, hormones maintain the uterine lining to nourish the growing embryo, so the lining is no longer shed and menstruation stops.

(a) Plant tissue culture is asexual reproduction, as new plants are produced from the cells of a single parent without gametes.
(b) The plantlets arise from one parent's cells by mitosis, so they are exact clones; the apical meristem used is generally free of viruses, making the plantlets virus-free.
(c) Cutting and grafting are two traditional vegetative propagation methods (layering is another used by farmers).
(d) Genetic uniformity means the entire crop is equally vulnerable — a single disease or pest could wipe out the whole field.

(a) Bright colour, fragrance and nectar attract birds and insects; these flowers also often have large, sticky pollen grains.
(b) Wheat is pollinated by the wind, which explains why no animal visitors are seen in the fields.
(c) Insect pollination is more efficient — far fewer pollen grains yield several times more seeds, meaning very little pollen is wasted compared with wind pollination.
(d) In wind pollination most pollen is simply lost in transit, so sheer numbers guarantee that at least some grains land on feathery stigmas and achieve fertilisation.

Introduction: Asexual reproduction needs one parent and produces genetically identical offspring rapidly.
Key Points:
1. Vegetative propagation — New plants grow from stems, leaves or buds, as in potato, ginger and Bryophyllum.
2. Budding — Buds form on the parent body by cell division, as in yeast and hydra.
3. Spore formation — Fungi like Rhizopus release millions of lightweight spores from sacs on hyphae.
4. Common basis (mitosis) — Cell division keeps the chromosome set identical, forming clones.
5. Advantage — The method is fast and quickly raises population size in favourable conditions.
Conclusion: Asexual reproduction trades variation for speed, multiplication and genetic uniformity.

Introduction: Scientists and horticulturists have adapted natural vegetative propagation into efficient farming techniques.
Key Points:
1. Cutting — Stem pieces with nodes are planted in compost-rich soil, as in sugarcane and money plant.
2. Grafting — A stem piece of one plant is inserted into a slit on a rooted plant and bound until it heals.
3. Layering — A flexible twig's middle is buried; after roots form in 10–15 days, it is separated as a new plant.
4. Tissue culture — Virus-free plantlets are mass-produced from shoot tips in laboratories.
5. Agricultural importance — Desirable high-yield varieties can be multiplied on a large, uniform scale.
Conclusion: These methods have significantly improved agricultural and horticultural practices.

Introduction: Sexual reproduction combines genetic material from two parents, generating variation.
Key Points:
1. Two parents contribute — Each parent provides genetic material, so offspring inherit a mix of characters.
2. Meiosis halves chromosomes — Diploid cells form haploid gametes, keeping the zygote's chromosome number constant.
3. Random segregation — Each pair's chromosomes separate randomly, so every gamete carries a unique set.
4. Immense combinations — Three character pairs give eight combinations; 23 pairs give astronomically many.
5. Survival value — Variation helps some individuals tolerate changing environments and drives evolution.
Conclusion: Complex animals and flowering plants use sexual reproduction because variation aids long-term survival.

Introduction: The flower is the reproductive organ of angiosperms, the most diverse plant group.
Key Points:
1. Sepals — The green outermost whorl that protects the flower bud before it opens.
2. Petals — Coloured, often fragrant whorl that attracts pollinators with nectar.
3. Stamen (male part) — Filament supports the anther, which produces pollen grains with male gametes.
4. Pistil (female part) — Sticky stigma receives pollen; the style connects it to the ovary.
5. Ovary and ovules — The ovary contains ovules, each holding an egg cell that becomes a seed after fertilisation.
Conclusion: A complete flower's four whorls protect, attract and perform the actual reproduction.

Introduction: Pollination is the transfer of pollen grains from the anther to the stigma of a flower.
Key Points:
1. Self-pollination — Pollen reaches the stigma of the same flower or same plant.
2. Cross-pollination — Pollen from one plant reaches a flower of another plant of the same type.
3. Wind and water agents — Grasses have light pollen and feathery stigmas; Vallisneria uses water currents.
4. Insect and bird agents — Bees, butterflies and sunbirds visit coloured, fragrant, nectar-rich flowers.
5. Necessity of pollination — Without it, fertilisation, fruit and seed formation cannot occur.
Conclusion: Nature provides plants with strategies matching pollinators to ensure reproductive success.

Introduction: After pollination, a chain of events produces fruits and seeds, continuing the species.
Key Points:
1. Pollen germination — On a compatible stigma, the pollen grain puts out a pollen tube through the style.
2. Fertilisation — The male gamete travels to the ovule and fuses with the egg, forming a zygote.
3. Seed and fruit formation — The zygote becomes the embryo; ovules become seeds and the ovary becomes a fruit.
4. Seed dispersal — Wind, water and animals spread seeds to new locations.
5. Germination — With favourable water, air and temperature, the seed grows into a new plant.
Conclusion: Sexual reproduction thus produces both new plants and variation for adaptation.

Introduction: The male reproductive system produces sperm and delivers them to the female body.
Key Points:
1. Testes in scrotum — Paired organs making sperm; the cooler scrotal temperature is essential for sperm formation.
2. Hormone production — Testes also make the hormone controlling sperm production and pubertal changes in boys.
3. Duct system — The vas deferens carries sperm to the urethra, the shared passage for urine and sperm.
4. Gland contributions — Seminal vesicles and prostate add fluids that nourish sperm and help movement.
5. Sperm structure — A head with genetic material and a long tail for swimming towards the egg.
Conclusion: Gametogenesis in males produces millions of tiny, active, motile sperm.

Introduction: The female system produces eggs, supports fertilisation and nurtures the developing baby.
Key Points:
1. Ovaries — Produce eggs and hormones; at birth a girl already has millions of immature eggs.
2. Oviducts and uterus — Fallopian tubes carry eggs and host fertilisation; the uterus holds the developing foetus.
3. Ovulation — From puberty, usually one egg is released each month, around day 14 of the cycle.
4. Uterine preparation — The uterine lining thickens with blood vessels to receive a possible zygote.
5. Menstruation — If no fertilisation occurs, the lining sheds with blood for 3–7 days and the cycle repeats.
Conclusion: The coordinated cycle continues from puberty (ages 10–14) until menopause around age 50.

Introduction: Sexual maturity arrives earlier than emotional maturity, so responsible choices are essential.
Key Points:
1. STI risk — Close contact can transmit infections like gonorrhoea, herpes, syphilis, warts and HIV; some are incurable.
2. Barrier protection — Condoms prevent both unplanned pregnancy and STI transmission.
3. Other contraceptives — Oral pills alter egg release; IUDs like Copper-T sit in the uterus; both have possible side effects.
4. Surgical methods — Blocking the vas deferens or fallopian tubes permanently prevents sperm meeting egg.
5. Safe practices — Medical termination (abortion) is legal in early pregnancy; sex-selective abortion is banned in India.
Conclusion: Informed, thoughtful decisions protect health and support healthy relationships.

Introduction: Human development spans about nine months of pregnancy divided into three trimesters.
Key Points:
1. Fertilisation and implantation — Sperm meets egg in the oviduct; the zygote divides and implants in the uterine lining.
2. First trimester — The embryo forms major organs; from the ninth week it is termed a foetus.
3. Second and third trimesters — The foetus grows stronger, the mother feels movements, and the baby prepares for birth.
4. Childbirth — Strong uterine contractions push the baby through the birth canal; surgery helps when needed.
5. Mother and newborn care — Breastfeeding, warmth, timely vaccination and maternal nutrition and rest are essential.
Conclusion: The health of the mother and the baby are closely connected and need proper care and support.