11. Short and Long Answer Questions: Reproduction: How Life Continues

Short Answer Type Questions

Ques 1: What is vegetative propagation? Give three examples of plants that reproduce by this method.

Ans: Vegetative propagation is a type of asexual reproduction in plants in which new plants arise from the vegetative parts (growing parts) of a parent plant, such as stems, roots, or leaves. It involves only one parent and produces genetically identical individuals. Three examples are: (i) Potato – new plants sprout from the underground stem (tuber); (ii) Ginger – new shoots grow from the underground rhizome; and (iii) Bryophyllum – tiny plantlets sprout from the notches along the leaf margins.

Ques 2: What is budding? Describe how it occurs in yeast and hydra.

Ans: Budding is a type of asexual reproduction in which a small outgrowth (bud) develops from the parent organism, grows larger, and eventually separates to live independently. In yeast, small round outgrowths emerge from the parent yeast cell; these buds enlarge and detach to form new yeast cells. In hydra, repeated cell division at a specific site on the parent body produces a bud that enlarges into a new individual. In hydra, several buds can often be seen growing on the parent body at the same time.

Ques 3: What is spore formation? How are spores adapted to survive in unfavourable conditions?

Ans: Spore formation is an asexual mode of reproduction seen in organisms like fungi (e.g., Rhizopus). Spores are produced in huge numbers in sac-like structures or on swollen vesicles along the fungal hyphae. Each spore is a tiny, lightweight, usually single-celled structure that can float easily through air currents. Spores are well-adapted to survive unfavourable conditions as they wait for warmth, moisture, and nutrients before germinating quickly into a new individual. This is why fungi grow rapidly on moist bread in warm, dark conditions.

Ques 4: Why is meiosis necessary for sexual reproduction? What would happen if gametes were formed by mitosis instead?

Ans: Meiosis is a special type of cell division that reduces the chromosome number of a parent cell (diploid) to half (haploid) in the resulting gametes. This is necessary because during fertilisation, the male and female gametes fuse to restore the original chromosome number. If gametes were formed by mitosis instead, each gamete would carry the full set of chromosomes. On fertilisation, the chromosome number of the offspring would double in every generation, making normal development impossible. Thus meiosis ensures that the chromosome number remains constant across generations.

Ques 5: Describe the structure of a flower and name the male and female reproductive parts.

Ans: A complete flower has four parts – sepals, petals, stamens, and pistil. The sepal is the outermost green whorl that protects the flower bud. The petals are coloured projections that attract pollinators. The stamen is the male reproductive part; it consists of a filament and an anther which produces pollen grains containing male gametes. The pistil is the female reproductive part; it has three subparts – the stigma (which receives pollen), the style (a thin connecting tube), and the ovary (which contains ovules, each with an egg cell).

Ques 6: Differentiate between self-pollination and cross-pollination with one example of each.

Ans: Self-pollination is the transfer of pollen grains from the anther to the stigma of the same flower or another flower on the same plant. Example: sweet pea (Pisum sativum). Cross-pollination is the transfer of pollen from the anther of a flower on one plant to the stigma of a flower on another plant of the same species. Example: sunflower, where bees and butterflies carry pollen from one plant to another. Cross-pollination promotes genetic variation, while self-pollination produces offspring genetically similar to the parent.

Ques 7: What is fertilisation in flowering plants? Describe the events that follow fertilisation up to fruit formation.

Ans: Fertilisation in flowering plants is the fusion of the male gamete (from the pollen grain) with the female gamete (egg cell in the ovule). After pollen reaches a compatible stigma, the pollen grain produces a pollen tube that grows down through the style into the ovary. The male gamete travels through this tube and fuses with the egg cell in the ovule to form a zygote. The zygote develops into an embryo. Meanwhile, the ovary enlarges and develops into a fruit, while the ovules develop into seeds inside the fruit.

Ques 8: What is gametogenesis? How do the sperm and egg differ in size, number, and motility?

Ans: The process of formation of gametes is called gametogenesis. It takes place in the testes (in males) and the ovaries (in females) through meiosis, which reduces the chromosome number to half. Sperm and egg differ significantly: sperm are very small in size while eggs are large; millions of sperm are produced but only a few eggs form; sperm have no stored nutrients while eggs contain nutrients; and sperm are actively motile (they swim using their long tail) while eggs are non-motile. This asymmetry is seen across most animals.

Ques 9: What is the menstrual cycle? Describe what happens during menstruation and why it occurs.

Ans: The menstrual cycle is the recurring cycle of ovulation, preparation of the uterus lining, and menstruation. It typically repeats every 21-35 days (often around 28 days) and begins at puberty (ages 10-14) and continues till menopause (around age 50). If an egg released during ovulation is not fertilised, it degenerates within about a day. The thickened inner lining of the uterus, which had been prepared to receive a zygote, is no longer needed and sheds along with some blood through the vagina. This shedding process is called menstruation and usually lasts 3 to 7 days.

Ques 10: What are Sexually Transmitted Infections (STIs)? Name any four STIs and state one method of preventing their transmission.

Ans: Sexually Transmitted Infections (STIs) are infections that can be transmitted from an infected person to an uninfected person through sexual activity involving close physical contact. Four STIs are: gonorrhoea, herpes, syphilis, and HIV (which can eventually lead to AIDS). Some of these, like HIV, are not curable yet. Using condoms during sexual activity is one effective method that can prevent the transmission of STIs and also help prevent unwanted pregnancy.

Ques 11: Why do animals with external fertilisation generally produce a very large number of eggs? Give two examples of such animals.

Ans: In external fertilisation, the female releases eggs into the water and the male releases sperm over them. Since fertilisation occurs in an open environment, a very large number of eggs are destroyed by water currents or eaten by other animals before fertilisation or hatching can occur. To ensure the survival of at least some offspring and continuation of the species, animals with external fertilisation produce thousands of eggs at a time. Two examples are: (i) Fish – produce 100s to 1000s of eggs at a time; (ii) Frog – produces 5,000 to 50,000 eggs at a time.

Ques 12: How does variation arise in sexual reproduction? Why is variation important for the survival of a species?

Ans: During meiosis, the chromosomes of each pair in the parent cell separate randomly so that each gamete receives only one chromosome from each pair. Since there are 23 pairs of chromosomes in humans, this random assortment produces an enormous number of possible gamete combinations (at least $2^{23}$ combinations from 23 pairs alone). When two such gametes fuse during fertilisation, the offspring receives a unique combination of chromosomes from both parents, creating variation. This variation is important because it helps some individuals adapt better to changing environments; over many generations, such differences contribute to evolution and the long-term survival of the species.

Long Answer Type Questions

Ques 1: Describe the methods of vegetative propagation used in agriculture. How have these methods been adapted by scientists and farmers to improve crop production?

Ans: Vegetative propagation is asexual reproduction in plants that produces genetically identical offspring from the vegetative parts of a parent plant. Scientists and horticulturists have adapted this natural process into several agricultural methods:

Cutting: A stem cutting (with nodes and internodes) is taken from a parent plant, inserted into soil mixed with compost at about 45°-60° and watered regularly. New roots and shoots develop from the cutting. It is used for propagating plants like sugarcane, money plant, and rose.
Grafting: A healthy rooted plant (Plant A, the rootstock) has a slit cut in its stem. A cutting from another plant (Plant B, the scion) is inserted into this slit and wrapped to heal. Plant B grows along with Plant A, combining the desirable traits of both. This is widely used for growing high-yield fruits like mangoes and roses.
Layering: A flexible twig of a tree (such as lemon) is bent and the middle part is buried in soil. After 10-15 days, roots develop from the buried portion; the twig is then cut from the parent and planted separately. This is used in lemon and jasmine plants.
Tissue culture: Plantlets are grown from the shoot tip (apical meristem) of a plant in a laboratory on artificial nutrient media. This technique produces large numbers of healthy, virus-free plantlets quickly. It has revolutionised farming practices – for example, in banana farming where mass-produced healthy plantlets from meristems ensure high yields and eliminate virus-infected plants.

These methods enable farmers to cultivate desirable crops on a large scale efficiently, improve agricultural yields, and maintain the desired characteristics of parent plants.

Ques 2: Describe the process of pollination in flowering plants. Explain how different pollinators are adapted to carry out pollination, with examples.

Ans: Pollination is the transfer of pollen grains from the anther to the stigma of a flower. It is essential for fertilisation and seed/fruit formation. Pollination depends on external agents called pollinators. Different pollinators have different adaptations:

Wind pollination: Seen in plants like wheat, maize, and rice. These plants produce pollen grains that are light, small, and produced in very large numbers (5,00,000 to 10,00,000 per flower) so that at least some reach the stigma. The stigma is long and feathery to trap airborne pollen effectively.
Water pollination: Seen in aquatic plants like Vallisneria and Hydrilla, where water currents carry the pollen from one flower to another.
Insect pollination: Seen in sunflower, hibiscus, and marigold, which are pollinated by bees and butterflies. These flowers are brightly coloured, produce nectar, and give off fragrance to attract insects. Their pollen grains are large, sticky, or spiny to attach to the insect’s body, and the stigma is also sticky to receive them. Insect-pollinated plants produce fewer pollen grains (20,000-40,000 per flower) but form more seeds (800-1,000 per flower) due to the high efficiency of pollination.
Bird pollination: Some flowers, like those of the coral tree and hibiscus, are pollinated by birds such as the Indian white-eye and sunbirds. These flowers tend to be large, bright, and tubular to accommodate the bird’s beak.

This diversity of pollination strategies ensures reproductive success for different plant species across varied environments.

Ques 3: Describe the male and female reproductive systems in humans, naming their main parts and stating their functions.

Ans: Male Reproductive System:

Testes: Two oval-shaped organs present in a pouch of skin called the scrotum. They produce sperm through gametogenesis and also produce hormones (like testosterone) that control sperm production and cause physical changes in boys during puberty. The scrotum keeps the testes slightly cooler than body temperature, which is necessary for sperm formation.
Vas deferens: A long tube through which sperm travel from the testes; it ultimately opens into the urethra.
Seminal vesicles and prostate gland: These glands add fluids to nourish the sperm and keep them active and motile.
Urethra: A common passage for both urine and sperm.

Female Reproductive System:

Ovaries: A pair of organs that produce egg cells (female gametes) through gametogenesis and release hormones that regulate the menstrual cycle and cause physical changes during puberty.
Oviducts (Fallopian tubes): Connect each ovary to the uterus. The egg travels from the ovary through the oviduct, where fertilisation by a sperm may occur.
Uterus: A bag-like structure where the fertilised egg (zygote) implants, and the foetus grows and develops during pregnancy.
Cervix and vagina: The cervix is a narrow passage connecting the uterus to the vagina. During childbirth, the baby passes out through the vagina (birth canal).

Ques 4: Explain what happens when a sperm meets an egg in the human female body. Describe the events from fertilisation to the birth of a baby, including the three trimesters of pregnancy.

Ans: From puberty onwards, one mature egg is released every month from an ovary – a process called ovulation (usually around day 14 of the menstrual cycle). The egg travels from the ovary to the oviduct. During sexual intercourse, millions of sperm enter through the vagina and swim through the reproductive tract. If a sperm encounters and successfully fuses with the egg in the oviduct, a zygote is formed. This fusion of gametes is called fertilisation and marks the beginning of pregnancy.

The zygote undergoes a series of mitotic divisions while travelling to the uterus, and implants into the thickened inner lining of the uterus to receive nourishment. Pregnancy in humans lasts approximately nine months and is divided into three stages called trimesters:

First trimester (months 1-3): The fertilised egg develops into an embryo during the first two months, and major organs begin to form. From about the ninth week, the developing embryo is called a foetus.
Second trimester (months 4-6): The foetus grows bigger and stronger, and the mother can usually feel its movements.
Third trimester (months 7-9): The baby grows rapidly and prepares for life outside the womb. The uterus protects and nourishes the baby throughout.

During childbirth, strong contractions of the uterus muscles push the foetus out through the birth canal (vagina). After birth, breastfeeding is essential as mother’s milk provides complete nutrition and protects the infant from many diseases.

Ques 5: Compare asexual and sexual reproduction in terms of the number of parents involved, genetic similarity of offspring, type of cell division involved, and their advantages and disadvantages.

Ans:

Number of parents: Asexual reproduction involves only one parent, while sexual reproduction requires two parents – a male and a female – each contributing genetic material to the offspring.
Genetic similarity: Asexual reproduction produces offspring that are genetically identical to the parent (called clones), since no mixing of genetic material occurs. Sexual reproduction produces offspring that inherit a mix of characteristics from both parents and are therefore genetically different from each parent and from each other.
Cell division: The central process in asexual reproduction is mitosis, which produces two daughter cells each identical to the parent cell. Sexual reproduction requires meiosis to form gametes (reducing the chromosome number to half), followed by fertilisation (fusion of gametes) and then mitosis for growth of the new organism.
Advantages of asexual reproduction: It is fast and efficient, allows rapid population increase under favourable conditions, does not require a mate, and is widely used in agriculture to preserve desirable traits of plants.
Disadvantages of asexual reproduction: Since all offspring are genetically identical, if one individual is susceptible to a disease or environmental change, all are equally susceptible, making the population vulnerable.
Advantages of sexual reproduction: It produces genetic variation, which helps species adapt to changing environments and contributes to evolution over many generations. This is why most complex animals and flowering plants use sexual reproduction.
Disadvantages of sexual reproduction: It requires finding a mate, is slower than asexual reproduction, and involves more energy and resources