Reproduction Class 9 CBSE Important Questions with Answers

Answer: (b) Amoeba.

Amoeba divides into two equal daughter cells by binary fission. Hydra reproduces by budding, Spirogyra by fragmentation and yeast by budding.

Answer: (b) fertilisation.

Fertilisation is the fusion of male and female gametes to form a zygote. Pollination is only the transfer of pollen and precedes fertilisation in plants.

Answer: (b) placenta.

The embryo implants in the wall of the uterus and develops a disc-like tissue, the placenta, which joins it to the mother's blood. Nutrients and oxygen pass from the mother to the embryo through it, and wastes pass the other way.

Answer: (b) Vegetative propagation (grafting), because it produces genetically identical clones.

Seeds form by sexual reproduction and carry variation, so seed-grown mangoes differ from the parent. Vegetative methods such as grafting produce clones with identical fruit quality.

Answer: (a) Both A and R are true and R is the correct explanation of A.

Because gametes come from two parents and carry different combinations of genes, their fusion produces offspring with new combinations, i.e. variation.

Asexual reproduction: involves a single parent; offspring are genetically identical to the parent (clones).

Sexual reproduction: involves two parents (male and female); offspring show variation and are not identical to either parent.

Testes (male): produce male gametes (sperms) and the male hormone testosterone.

Ovaries (female): produce female gametes (ova/eggs) and female hormones such as oestrogen.

If all the seeds fell under the parent plant, the seedlings would be crowded and would compete with each other and the parent for light, water and minerals. Dispersal spreads seeds to new places where they have a better chance to grow.

Agents (any two): wind, e.g. the winged seeds of drumstick or the hairy seeds of madar (aak); water, e.g. the floating fibrous fruit of coconut; animals, e.g. the hooked fruits of Xanthium that stick to fur; explosion of the fruit, e.g. balsam and castor.

After fertilisation, the zygote inside the ovule divides and grows into an embryo. The ovule develops into a seed, and the ovary grows into a fruit. The petals, sepals, stamens, style and stigma usually wither and fall off.

Pollination is the transfer of pollen grains from the anther (male part, stamen) to the stigma (female part, carpel) of a flower. When pollen lands on its own flower's stigma it is self-pollination; when it is carried to another flower of the same kind (by wind, water or insects) it is cross-pollination.

Difference: Pollination is only the transfer of pollen and involves no fusion. Fertilisation is the fusion of the male gamete (from the pollen) with the egg inside the ovule, forming a zygote. Pollination always occurs before fertilisation.

Variations arise during sexual reproduction and are inherited by different individuals. For the species, a large pool of variations is beneficial because if the environment changes (temperature, disease, food), at least some individuals with a suitable variation survive and reproduce, so the species is not wiped out.

For an individual, a particular variation may be useless or even harmful under the current conditions. For example, a bacterium with a variation giving heat resistance gains nothing while the climate is cool, but if temperature suddenly rises, that variation lets it survive while others die. Thus the variation helps the species persist even though it did not help each individual earlier.

(a) From puberty, an ovary releases one egg roughly every $28$28 days, and each time the lining of the uterus becomes thick and rich in blood vessels, ready to receive a fertilised egg. If the egg is not fertilised, the thick lining is not needed: it breaks down and flows out through the vagina as blood and mucus for a few days. This is menstruation, and the cycle repeats every month. If the egg is fertilised, the embryo implants in the lining and menstruation stops during pregnancy. Using clean sanitary pads and changing them regularly is part of menstrual hygiene.

(b) Barrier method: the condom. Surgical methods: vasectomy in males or tubectomy in females. The condom also protects against sexually transmitted infections such as HIV-AIDS. Birth control lets couples space children, which protects the mother's health and helps control population growth.

1. Binary fission: the parent cell splits into two equal daughter cells. Example: Amoeba, bacteria.

2. Budding: a small bud grows on the parent, matures and detaches. Example: Hydra, yeast.

3. Fragmentation: the body breaks into pieces, each growing into a new organism. Example: Spirogyra.

4. Spore formation: the organism produces many spores that germinate into new individuals under favourable conditions. Example: Rhizopus (bread mould), ferns.

(Vegetative propagation in plants, e.g. potato tubers, is also acceptable as a method.)

Advantage: it is fast, needs only one parent, and preserves useful traits since offspring are identical.

Disadvantage: there is no variation, so the whole population can be destroyed by a single unfavourable change such as a new disease.

The pathway of gametes can be shown as:

Testes: produce the male gametes (sperms) and the hormone testosterone.

Ovary: produces the female gametes (ova) and hormones such as oestrogen and progesterone; one egg is usually released each month.

Oviduct (fallopian tube): carries the egg from the ovary towards the uterus; fertilisation normally takes place here when a sperm fuses with the egg.

Uterus (womb): the muscular organ in which the embryo implants in the thick lining and the baby develops until birth (about nine months). The embryo gets nutrients and oxygen from the mother's blood through the placenta.

(i) The mode of reproduction is spore formation (the mould is Rhizopus).

(ii) The black rounded structures are sporangia; each contains hundreds of tiny reproductive units called spores.

(iii) It is asexual, because a single parent produces offspring without the fusion of gametes, and the new moulds are identical to the parent.

(iv) Warm and moist (damp) conditions favour spore germination and growth (presence of food/humidity).