RowQ
The Vault
RowQ
The Vault
CBSE Class 9 Biology · 12 questions · 29 marks
No individual lives forever, yet species persist for millions of years — reproduction is the reason. This chapter looks at the two broad strategies life uses: making near-perfect copies of oneself quickly, or combining genetic material from two parents to produce offspring that are never quite identical to either. You will follow a pollen grain to an ovule, trace what happens after fertilisation, and see why the variation created by sexual reproduction is the raw material on which evolution works.
A small bulge appears on the side of a yeast cell, grows, and finally separates as a new individual. This mode of reproduction is called:
Answer
Budding is correct — an outgrowth or bud forms on the parent body, enlarges, and detaches to become a new organism, as seen in yeast and Hydra. Binary fission splits the parent into two equal halves, fragmentation breaks a filament into pieces, and spore formation releases spores from a sporangium.
After fertilisation in a flowering plant, the ovary of the flower develops into the:
Answer
Fruit is correct — the ovary wall ripens and becomes the fruit that encloses and protects the seeds. The ovule becomes the seed, the zygote develops into the embryo inside the seed, and the pollen tube is a temporary structure that degenerates after delivering the male gamete.
In the human female reproductive system, where does fertilisation of the egg normally take place?
Answer
Fallopian tube is correct — the sperm meets and fuses with the egg in the upper part of the oviduct, and the resulting zygote then travels down to the uterus to implant. The ovary only releases the egg, the uterus houses the developing embryo, and the cervix is the narrow opening of the uterus.
Which structure allows the developing human embryo to obtain oxygen and nutrients from the mother's blood?
Answer
Placenta is correct — this disc-shaped tissue contains villi that provide a large surface for glucose, oxygen and other nutrients to pass from the mother to the embryo and for wastes to pass back. The cervix is the uterine opening, the fallopian tube is where fertilisation occurs, and the amnion is the fluid-filled membrane that cushions the embryo.
Assertion (A): A field planted entirely from cuttings of one high-yielding banana plant can be wiped out by a single fungal disease. Reason (R): Plants produced by vegetative propagation are genetically identical to the parent and therefore share the same susceptibilities.
Answer
Both A and R are true and R is the correct explanation of A — vegetative propagation is a form of asexual reproduction, so every plant in such a field is a clone carrying the same genes. If the parent lacked resistance to a particular fungus, every offspring lacks it too, and the pathogen can spread through the entire crop unchecked. A sexually reproduced population, by contrast, contains variation, so at least some individuals are likely to survive.
State three differences between asexual and sexual reproduction.
Answer
First, asexual reproduction involves only one parent, while sexual reproduction normally involves two parents, one producing male gametes and the other female gametes. Second, asexual reproduction does not involve the formation or fusion of gametes, whereas sexual reproduction depends on fertilisation, the fusion of a male and a female gamete to form a zygote. Third, offspring produced asexually are genetically identical to the parent and show almost no variation, while offspring produced sexually inherit a mixture of characters from both parents and show considerable variation, which is important for evolution and adaptation. Asexual reproduction is also generally much faster and simpler.
What is pollination, and how does it differ from fertilisation?
Answer
Pollination is the transfer of pollen grains from the anther of a stamen to the stigma of a carpel, carried out by agents such as wind, water, insects or birds; it is a purely physical transfer and takes place before fertilisation. Fertilisation is the fusion of the male gamete released from the pollen tube with the egg cell inside the ovule, producing a zygote. In short, pollination merely brings the gametes close together, while fertilisation is the actual union of the two gametes.
Describe how Planaria and Spirogyra reproduce, and explain why these methods are not suitable for a complex animal such as a dog.
Answer
Planaria reproduces by regeneration: if its body is cut into pieces, each fragment contains specialised cells that can divide and differentiate, so each piece regrows the missing parts and becomes a complete worm. Spirogyra reproduces by fragmentation: its filament simply breaks into two or more pieces on maturing, and each piece grows into a new filament. These methods are not suitable for a dog because its body is made of many highly specialised organ systems arranged in a fixed pattern, and its cells have already differentiated and lost the ability to rebuild an entire organism. A fragment of a dog cannot reorganise itself into a functional heart, brain and digestive system, so complex animals must reproduce sexually instead.
Why is variation among offspring important for a species in the long run?
Answer
Variation means that individuals within a species differ slightly in their characters, so they do not all respond in the same way to changes in the environment such as a new disease, a rise in temperature or a shortage of food. If conditions change sharply, at least some variants are likely to possess features that let them survive and reproduce, so the species continues instead of being wiped out. Over many generations this selective survival of useful variations is the basis of adaptation and evolution.
Draw on your knowledge of a typical flower to explain the sequence of events from pollination to seed formation.
Answer
A typical bisexual flower has four whorls: sepals, petals, stamens and one or more carpels. Each stamen has an anther that produces pollen grains carrying male gametes, and each carpel has a sticky stigma, a slender style, and a swollen ovary containing one or more ovules, each with an egg cell. The sequence begins with pollination. Pollen grains are carried from an anther to a stigma of the same species by wind, water, insects or birds. If pollen reaches a stigma of the same flower or the same plant, it is self-pollination; if it reaches a different plant of the same species, it is cross-pollination, which brings together genes from two individuals. Once a compatible pollen grain lands on the stigma, it absorbs moisture and germinates, growing a slender pollen tube. The tube pushes down through the style, guided towards an ovule, and enters it. Fertilisation follows: the male gamete carried in the pollen tube fuses with the egg cell inside the ovule, producing a single-celled zygote. This restores the full set of chromosomes and combines characters from both parents. After fertilisation the zygote divides repeatedly to form an embryo, which consists of a radicle, a plumule and cotyledons storing food. The ovule as a whole develops a protective seed coat and becomes the seed, while the ovary wall enlarges and ripens into the fruit that surrounds it. The sepals, petals, stamens, style and stigma have no further role and usually wither and fall off. When the fruit is dispersed and conditions are suitable, the seed germinates into a new plant.
Explain how the human male and female reproductive systems are each adapted to their functions, and describe what happens to the uterine lining when fertilisation does not occur.
Answer
The male reproductive system is adapted for producing and delivering large numbers of motile gametes. The testes lie in the scrotum outside the abdominal cavity, because sperm formation requires a temperature a little below normal body temperature. Besides sperm, the testes secrete testosterone, the hormone that brings about male secondary sexual characters at puberty. Sperm pass through the vas deferens, which joins the urethra, and along the way the seminal vesicles and prostate gland add secretions that nourish the sperm and make them easier to transport. The resulting fluid, semen, is delivered through the penis. The female reproductive system is adapted for producing a small number of large gametes and for nourishing an embryo internally. Each ovary produces eggs and secretes oestrogen and progesterone; from puberty, one mature egg is usually released roughly every 28 days. The funnel-shaped opening of the fallopian tube collects the released egg, and fertilisation takes place in the upper part of this tube. The zygote then travels to the uterus, a muscular, elastic organ whose lining has become thick and richly supplied with blood in preparation. The embryo implants in this lining, and a placenta develops, with villi that provide a large surface area through which glucose, oxygen and nutrients pass from the mother to the embryo, and carbon dioxide and nitrogenous wastes pass back to the mother's blood for disposal. If the egg is not fertilised, it survives only about a day. The thickened uterine lining is then no longer needed, so it breaks down along with its blood vessels and is shed slowly through the vagina over a few days. This monthly discharge of blood and tissue is called menstruation, and the cycle then begins again with the preparation of a fresh lining.
A horticulturist named Meera runs a nursery. She raises her prize-winning rose variety only from stem cuttings, because seedlings grown from rose seeds rarely produce flowers of the same colour. A visiting farmer, worried about a fungal blight sweeping through nearby nurseries, asks her whether her method is risky. Answer the following: (a) Name the method Meera is using and state whether it is sexual or asexual. (b) Explain scientifically why her seedlings differ in flower colour but her cuttings do not. (c) State one clear advantage of Meera's method for a commercial nursery. (d) Was the farmer's worry justified? Give a reason.
Answer
(a) Meera is using vegetative propagation by stem cuttings, which is a form of asexual reproduction because it involves a single parent and no fusion of gametes. (b) Seeds are the product of sexual reproduction, in which a male gamete from pollen fuses with an egg cell. The offspring therefore inherit a fresh combination of characters from two different parents, so flower colour and other traits vary. A stem cutting, by contrast, grows from ordinary body cells of one parent plant by cell division alone, so every new plant is a genetically identical clone with exactly the same flower colour. (c) The main commercial advantage is reliability and speed: Meera can produce large numbers of plants that are certain to carry her prize-winning flower colour, and cuttings usually flower much sooner than plants raised from seed. (d) Yes, the farmer's worry is justified. Because all her plants are genetically identical, none of them has any resistance the parent lacked. If the fungal blight can infect the parent variety, it can infect every plant in the nursery, and the entire stock could be lost at once. Maintaining a few plants of different varieties would reduce this risk.
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