NCERT Solutions for Class 9 Science Chapter 11 Reproduction How Life Continues (PDF) – 2027

A farmer uses an asexual (vegetative) method when the plant must be an exact copy of a chosen parent, and a sexual (seed) method when he wants seed that stores well, travels cheaply and carries new combinations of characters.

Sexual reproduction produces variation; asexual reproduction produces many offspring quickly.

• Complex animals and flowering plants live long, have relatively few offspring and face changing surroundings (new pests, diseases, rainfall). Sexual reproduction mixes the characters of two parents, so every offspring is a little different; some of them can cope with the change, and the species survives and adapts.
• Yeast and hydra are small, short-lived and live where food is plentiful. Budding needs no partner and no gametes — one parent simply divides by mitosis, and a yeast cell can form a bud within a couple of hours — so their numbers rise very fast while conditions are favourable.

(i) Yes. Gardeners prune the overgrown branches at the end of the growing season, and they take their cuttings from that pruned material.

(ii) and (iii) — record what you actually measure. A typical shoot cutting is about 15 – 20 cm long and carries 3 – 5 nodes, which means 2 – 4 internodes between them.

In about two to three weeks, roots appear from the buried nodes and new shoots push out of the nodes above the soil. Compost is mixed into the soil because it holds moisture and keeps the soil loose enough for young roots to push through.

Within two to three weeks the graft heals and the buds on the Plant B piece sprout. From then on the shoot, the leaves and the flowers are all of Plant B’s variety, while everything below the graft joint stays Plant A. If Plant B was a yellow rose, the plant now carries yellow roses on a wild-rose root system.

New leaves keep coming out on the buried twig, and after 10 – 15 days roots grow from the buried portion. Once those roots are established, the twig is cut off from the parent and becomes an independent plant — a clone of the parent tree.

Yes. Under the compound microscope you see oval yeast cells, and many of them carry a smaller round swelling attached at one end — the bud. Sometimes a bud already carries a bud of its own, so short chains of two, three or four cells are seen.

Yes — the yeast is multiplying, and each bud is a genetic duplicate of the parent cell. But note carefully how it duplicates: the parent does not split into two equal halves. It pushes out a small bud at one point on its wall.

They show that yeast reproduces asexually by budding.

• Each bud grows out of a single parent cell; no two cells fuse, so no gametes or fertilisation are involved.
• The bud is formed by mitosis, so it is genetically identical to the parent — the yeast cells in the tube are clones.
• Buds appear within 1 – 2 hours and every new cell can bud again, so the number of yeast cells rises rapidly when sugar and warmth are available.

Yes. Budding is only one of several. All of them share the same core — a single parent and cell division by mitosis — and differ only in how the parent body is divided up.

Almost everywhere — wherever there is moisture, warmth and something organic to feed on. The chapter itself points to several of these places.

• In the air. Spores drift on air currents. This is the source that seeded your bread in Activity 11.3.
• On cooked food left out. A day on the kitchen counter in warm weather is enough for a smell and fuzzy patches to appear.
• On damp walls. The black patches so often seen in the monsoon are fungal colonies.
• In soil and in manure heaps. Fungi there break down dead leaves, straw and dung — this is how compost forms.
• On rotting fruit and vegetables, on old leather and damp clothes, and on our own skin and inside our gut.

They come from microorganisms that already exist — spores and cells present in the air, dust, water or on surfaces settle on the food and multiply. They are never produced by the food itself. Louis Pasteur showed by experiment that new life always comes from pre-existing life: a nutrient broth kept away from the microbes in the air stays clear, but spoils once they can enter.

Yes. By the third day the surface carries cottony white or grey threads, and on them tiny dark pin-heads — black in Rhizopus, greenish-black in Aspergillus. As more days pass the patch spreads and darkens.

Under the microscope, after staining with cotton blue, you see a mat of branched, thread-like hyphae with upright stalks rising from it, each stalk ending in a rounded structure packed with dark spores. Match what you have drawn against Fig. 11.8.

Yes to both. The thread-like structures are the hyphae, the round sac at the tip of an upright hypha is the sporangium, and the tiny round bodies packed inside it are the spores.

From spores that were already floating in the air of the room. They settled on the moist bread, found warmth and nutrients there, and germinated. Nothing was added to the box except bread, cotton, tissue and boiled water — so the air is the only possible source.

Yes — several are known. The best-studied are:

• Aspergillus tubingensis — a relative of the very Aspergillus in Fig. 11.8, isolated in 2017 from a rubbish dump in Islamabad. It grows on polyester polyurethane and breaks it down within about two months.
• Pestalotiopsis microspora — found in the Amazon rainforest. It can live on polyurethane as its only food, and remarkably it can do so even without oxygen, which is the condition deep inside a landfill.
• Aspergillus flavus and several Penicillium species — these attack polythene film, though slowly.

A very large number — because each chromosome pair separates independently of every other pair during meiosis. If there are n pairs, the number of different gametes is 2ⁿ.

Eight. One bead is picked from each of the three pairs, and each pair offers two choices.

Combination 1 in the list is the one drawn in Fig. 11.9 — blonde and straight hair with brown eyes.

2²³ = 8,388,608 — about 84 lakh different gametes from a single person. And that is only one parent.

Bright colours and fragrance attract pollinators such as bees, butterflies, moths and birds. Colour makes the flower visible from a distance; fragrance guides pollinators even at night or through dense leaves; nectar at the base of the petals rewards them. While the animal feeds, pollen sticks to its body and is carried to the stigma of another flower, so pollination — and then fertilisation and seed formation — can take place.

Yes — both are present in the bud and in the open flower, but they are arranged differently.

Yes. The sepals are the outermost whorl, and in the bud they completely enclose the petals, stamens and pistil.

• Against drying — the delicate parts inside are shielded from sun and wind until they are ready.
• Against rain — water would spoil pollen inside the anther before it can be shed.
• Against insects — chewing insects would reach the developing ovules if the bud were open.

After the flower blooms the sepals do not fall off in most flowers. They stay below the petals and hold the whole flower together on its stalk, supporting the parts from beneath.

No, not all flowers have both. A complete flower has four parts — sepals, petals, stamens and pistil — but many flowers are missing one or more of them.

• Grasses such as wheat, maize and rice have no showy petals at all; being wind-pollinated, they would gain nothing from them.
• In some flowers the sepals and petals are fused, or look alike and cannot be told apart.
• A papaya tree bears male flowers on one plant and female flowers on another — the male flowers have no pistil and the female flowers have no stamens.

The other two parts are the reproductive ones:

Work outward to inward, one whorl at a time, and put a Yes or No against each part. The book has already filled in column A for you — Sepal Yes, Petal Yes, Stamen No, Pistil Yes — which tells you at once that flower A is a female (pistillate) flower, such as a papaya or a pumpkin female flower.

Every visible character of a flower part points to the job it does. Read the structure and the function follows.

Both cuts show the same thing from two directions — a hollow chamber with small white ovules attached to the inner wall by short stalks.

• Longitudinal section (L.S.) — cut from the stigma down through the ovary. You see the ovary wall on both sides and a row of ovules standing along the inside, each on a short stalk. In a hibiscus or a pea the ovules are lined up one above the other.
• Transverse section (T.S.) — cut across the ovary. You see the ovary in cross-section, divided by partitions into chambers (locules), with ovules in each chamber. A tomato ovary shows two to four chambers; a mustard ovary shows two; a pea pod shows one.

The petals attract the pollinator. They make the flower conspicuous from a distance, and in many flowers they also carry the scent glands and hold the nectar at their base.

Petals also do other jobs: they form a landing platform for the insect, many carry nectar guides — lines or patches that point the visitor to the nectar and, in passing, to the anthers and stigma — and at night they close in some plants and protect the inner parts.

By an experiment that stops pollen from reaching the stigma of some flowers and then checks whether fruits form — as Activity 11.6 does on a pea plant.

1. Remove the stamens from some flower buds, so that they have no pollen of their own.
2. Cover them with muslin cloth bags, so that no pollen can arrive from outside (muslin still lets air and light through).
3. Keep controls — a bagged flower with its stamens, and a flower left open — to show that the bag itself does not stop fruiting.
4. Compare fruit formation. If fruits fail to form only where pollen could not reach the stigma, pollen transfer is essential.

Fruits form in every treatment except one — the bud whose stamens were removed and which was then bagged.

That the transfer of pollen grains from the anther to the stigma — pollination — is necessary before a fruit can form. Take the pollen away and no fruit appears; leave it, whether the flower is bagged or open, and a fruit does.

If pollination does not occur, fertilisation cannot take place, so no seeds and no fruits are formed.

The unpollinated flower simply withers and drops off the plant.

Measured as seeds formed per pollen grain released, wind pollination succeeds about once in 6,000 grains and insect pollination about once in 33 grains — insect pollination is roughly 180 times more efficient per grain.

Insect pollination is far more efficient than wind pollination.

• Pollen to seed ratio: about 6,000 : 1 for wind-pollinated grasses (7,50,000 grains ÷ 125 seeds, taking middle values) but only about 33 : 1 for the insect-pollinated sunflower (30,000 ÷ 900). Wind pollination needs about 180 times more pollen for each seed.
• Efficiency of pollination and seed formation: wind carries pollen in all directions, so most grains fall on soil, water or other plants and very few reach a stigma. Insects carry pollen directly from one flower to another of the same kind, so far more ovules become seeds (800 – 1,000 against 50 – 200).

Because even a very small chance of success, multiplied by a very large number of pollen grains, still gives enough seeds.

• Wind cannot be steered, so each grain has only a tiny chance of landing on a stigma of its own kind; releasing lakhs of grains makes sure that some do.
• Pollen grains are small, light and cheap to make, so the plant saves on petals, scent and nectar.
• Wind is always available, so the plant never depends on pollinators, which may decline.
• Such plants (wheat, maize, rice) grow close together in large numbers and have long, feathery stigmas that catch pollen from the air.

Fertilisation. The pollen tube is on its way to the ovule, and the moment the male gamete inside it fuses with the egg cell, fertilisation has taken place and a zygote is formed.

Both are adapted for dispersal by wind. Look at what Fig. 11.16 actually shows.

• (a) Madar (calotropis) seeds — flat brown seeds, each carrying a dense tuft of long, fine, silky white hairs at one end.
• (b) Dandelion seeds — a whole spherical white head; each seed hangs below a stalk that opens out at the top into a ring of feathery hairs, like a tiny parachute. In the picture some have already broken free and are floating away.

Cross-pollination. The pollen is moving from the anther of a flower on one plant to the stigma of a flower on a different plant of the same kind — which is the chapter’s definition of cross-pollination.

Because in external fertilisation the chance that any one egg is fertilised and grows up is very small, so the number of eggs must be large enough to make up for it.

• Eggs and sperm are released into water, where currents carry them apart, so many eggs are never fertilised.
• The eggs lie unprotected; many are destroyed by water currents or eaten by other animals.
• The young get no parental care, so few survive. (Table 11.4: a frog lays 5,000 – 50,000 eggs at a time with low survival; a bird lays 1 – 15 with moderate to high survival.)

Internal fertilisation. The gametes meet inside the female’s body, where they are shielded from everything that destroys them in open water.

The father — more precisely, which of his two kinds of sperm happens to fertilise the egg. The mother cannot influence it at all.

Ravi is entering puberty — the stage of adolescence at which the body becomes reproductively mature. All three changes he has noticed are classic signs of it.

On 2 April.

46 — the full human number, restored the instant the two gametes fuse.

Barrier devices — condoms, and vaginal covers (female condoms). These are the only contraceptive methods that also protect against sexually transmitted infections.

The chapter names the infections concerned: gonorrhoea, herpes, syphilis, genital warts and HIV (which can eventually lead to AIDS). It also makes the point that some of these are not curable yet — which is exactly why prevention matters so much more here than treatment.

The risk of every sexually transmitted infection remains, in full. The pill guards against pregnancy; it does not guard against infection.

The long dependence is the price humans pay for a large, slowly-built brain — and the learning that this makes possible is precisely what has made the species successful.

(ii) Cross-pollination. The anthers were removed before they matured, so self-pollination was impossible; pollen from another plant of the same species was then placed on the stigma, which is cross-pollination.

(iii) Pollination → (i) Pollen germination on stigma → (ii) Fertilisation → (iv) Formation of zygote.

(iv) A is false, but R is true.

A is false: fertilisation takes place in the oviduct; the zygote divides by mitosis while travelling to the uterus and implants in the uterine lining only after several days. R is true in the sense that the uterine lining is thickened and prepared in advance in every cycle.

Because there is only one parent and only one kind of cell division involved — mitosis, which copies the chromosome set exactly instead of reshuffling or halving it.

• Only one parent is involved, so no chromosomes come from anywhere else.
• There is no meiosis and no fertilisation, so the chromosomes are never halved, reshuffled or combined with another set.
• Mitosis copies every chromosome and gives each daughter cell the same set as the parent cell.

So the offspring are clones — as in budding yeast and hydra, spores of Rhizopus, potato tubers and stem cuttings.

Because menstruation is the shedding of a uterine lining that is no longer needed — and during pregnancy that lining is very much needed, so it is kept instead of being shed.

Compare the two situations side by side:

Night-blooming flowers are pollinated by moths and bats that fly in the dark. White or pale petals reflect most of the little light available at night (moonlight, starlight), so they stand out against the dark leaves, whereas brightly coloured petals look dark. Such flowers also give out a strong fragrance after sunset (raat ki rani, harsingar, jasmine), which guides pollinators to them.

Because they are clones. Every plant in the field carries the same genetic information, so a pathogen that can defeat one plant can defeat all of them.

1. No genetic variation. All the plants come from one parent by mitosis. If the parent cannot resist a disease, none of them can, so one disease can spread through the whole crop.
2. Diseases pass on through planting material. Cuttings, tubers and grafts carry any viruses, bacteria or fungi present in the parent into the new plants.

Sexually reproduced plants differ from one another, so some of them may resist a new disease and survive.

Genetic diversity would fall sharply, and after a few generations the population would be almost uniform.

In self-pollination both gametes come from the same plant, so no characters are brought in from another plant. Generation after generation the offspring become more and more alike. With little variation left, the plants cannot adapt to a new disease, pest or change in climate, and a single disease could destroy the whole population. Harmful characters that were hidden may also show up, making the plants weaker.

He should use vegetative propagation — above all tissue culture from the shoot tip, and, depending on the crop, cutting, grafting or layering. All of these are asexual, so all of them give clones.

Why they are effective: only mitosis from a single parent is involved, so every new plant is genetically identical to the parent (same yield, fruit and taste); the plants skip flowering, pollination and seed formation, so they grow and give a crop quickly; and tissue culture produces thousands of healthy plantlets from a small piece of tissue.

(i) Hypotheses that this set-up can test. Each must be a statement that the experiment could prove wrong.

1. Pollen grains need an external sugar supply to germinate. Prediction: little or no germination at 0% (plain water), germination at the higher concentrations.
2. The percentage of grains that germinate depends on the sugar concentration. Prediction: the count of germinated grains changes from slide to slide.
3. The length of the pollen tube depends on the sugar concentration. Prediction: tubes are measurably longer on some slides than others.
4. There is an optimum concentration, with germination falling on both sides of it. Prediction: the graph of germination against concentration rises, peaks and then falls.

(ii) Parameters that must be kept the same — everything except the one factor being tested.

Tomato and wheat are self-pollinated; papaya must be cross-pollinated. Each prompt is a structural clue that settles the question by itself.

(i) The hypotheses. Each is a testable statement about cause and effect.

1. The fall in apple yield is caused mainly by a shortage of pollinators, not only by climate change.
2. Adding a managed honeybee colony to an orchard will raise fruit setting, because more flowers get pollinated.
3. Better-pollinated flowers give better-fertilised, well-seeded fruits, which the tree holds on to — so fruit drop will fall.
4. Mixed farming with beekeeping raises the total income, since the farmer harvests honey as well as a larger apple crop.

(ii) The parameters.

(iii) Comparing the data (values read from Fig. 11.24):

(iv) Inference. Keeping bee colonies raised fruit setting (26% → 40%) and sharply reduced fruit drop (35% → 8%), so Place B kept about twice as many fruits as Place A. A shortage of pollinators is a major cause of falling apple yields, and beekeeping in orchards is a practical remedy that also gives honey.

The claim is not correct. Day 14 is a fair average for a 28-day cycle, but the word “always” makes the statement false.

Reason 1 — cycle length differs from person to person. The cycle typically repeats every 21 – 35 days. Ovulation usually happens about 14 days before the next period, so it falls around day 7 in a 21-day cycle and around day 21 in a 35-day cycle; day 14 fits only a 28-day cycle.

Reason 2 — even in the same person the cycle varies. Its length can change from month to month with illness, stress, travel or change in weight, and cycles are often irregular in the first years after periods begin. Some cycles release no egg at all.

“The Seed Village Programme trains farmers to produce and store quality seed in their own village, so that good seed is available locally at a low price. Saving indigenous seeds matters because they are adapted to our own soil and climate, they can be saved and re-sown every year, and they hold resistance genes that we may need in the future. Losing them would leave us dependent on a few uniform varieties, and a single new disease could then affect the whole crop.”

In IVF, an egg and a sperm are joined outside the body in a laboratory dish, and the early embryo is placed in the mother’s uterus. It helps couples when the oviducts are blocked, the sperm count is low or eggs are not released regularly. Its drawbacks are high cost, hormone injections, emotional stress, no guarantee of success and a higher chance of twins. In 1978, Subhash Mukhopadhyay of Kolkata pioneered India’s first test tube baby, Kanupriya Agarwal (Durga).

Sample survey findings:

(iii) How a hybrid is made: the stamens are removed from flowers of one parent before they mature, the flowers are covered with a bag, and pollen from the chosen second parent is dusted on the stigma by hand (artificial hybridisation).

Sample answer for (v): Asexual methods — cuttings, tubers, grafting, tissue culture — quickly give many plants identical to a chosen variety, as in sugarcane, potato, banana and mango. Sexual methods give seeds that store and travel easily, and crossing two parents produces new varieties with higher yield and disease resistance, as in wheat, rice and pulses. Farmers use both.

Sample findings — (i) pollination strategies and pollinators of different crops:

(ii) Why pollinators are declining, and what can be done.

The point of the exercise, stated first: the fruit is the ripened ovary and the seeds are the ripened ovules. So whatever arrangement you find inside the fruit must already have been present in the ovary of the flower — only much smaller. Cutting the fruit is a way of seeing the ovary enlarged.

It depends on how the cell divides. An amoeba splits into two nearly equal daughter cells, so no older parent cell is left behind and no ageing is seen. A budding yeast cell, however, keeps most of its damaged material and gives the small bud a fresh start, so the mother cell does age — it can produce only about 20 – 30 buds and then dies.