Ans: Variation refers to differences in characteristics among individuals of the same species. Significance: (1) Provides raw material for natural selection and evolution. (2) Organisms with advantageous variations are better adapted to their environment and more likely to survive and reproduce. (3) Genetic diversity helps species survive environmental changes — if all individuals were identical, a single disease or environmental change could wipe out the entire population. (4) Sexual reproduction generates maximum variation through combination of parental genes and crossing over. (5) Variation over millions of years has led to the enormous diversity of life on Earth.

Ans: Vegetative propagation is a type of asexual reproduction in plants where new plants grow from vegetative parts (roots, stems, leaves) without seeds. Examples: Potato — tubers (underground stem modifications) sprout into new plants. Bryophyllum — tiny plantlets (adventitious buds) grow from notches on leaf edges and fall to grow into new plants. Also: rose (stem cuttings), ginger (rhizomes), sweet potato (roots), banana (suckers). Advantages: (1) Faster than seed germination — new plants established quickly. (2) Produces genetically identical plants (useful in agriculture to maintain desirable traits). (3) Possible even when seeds are not viable or absent. Used in horticulture and agriculture for cultivating seedless fruits, roses, bananas.

Ans: The placenta is a special disc-shaped organ that forms inside the uterus during pregnancy, connecting the foetus to the mother's uterine wall via the umbilical cord. Functions: (1) Nutrition — delivers glucose, amino acids, vitamins, and minerals from mother's blood to foetus. (2) Gas exchange — provides oxygen to foetus; removes CO₂. (3) Waste removal — carries urea and other metabolic wastes from foetus to mother's blood for excretion. (4) Hormonal — secretes hormones (hCG, progesterone) to maintain pregnancy. (5) Immune protection — passes antibodies to foetus. The foetal and maternal blood do not actually mix; exchange occurs across thin membranes.

Ans: Pollination.

Ans: Gonorrhoea and syphilis (also warts and HIV-AIDS).

Ans: Multiple fission.

Ans: Tissue culture is the technique of growing new plants from a small piece of plant tissue in a sterile nutrient medium under controlled conditions. It is used to grow many identical plants quickly, e.g. ornamental plants, and to produce disease-free plants.

Ans: Spores of Rhizopus (bread mould) present in the air germinate on the moist bread in warm conditions and form thread-like hyphae that look like a cotton-like growth. Later black sporangia develop.

Ans: If a Planaria is cut into pieces, each piece can grow into a complete new individual. Specialised cells proliferate to make a large number of cells, which then change into various types of cells and tissues to form the missing parts.

Ans: They prevent pregnancy by stopping sperms from reaching the egg, and they protect against sexually transmitted infections including HIV-AIDS.

Ans: The zygote divides to form an embryo inside the ovule. The ovule develops a tough coat and becomes the seed. The ovary grows rapidly and ripens to become the fruit. Petals, sepals, stamens, style and stigma wither and fall off.

Ans: After a pollen grain lands on a suitable stigma, it grows a pollen tube through the style towards the ovary. The tube carries the male gametes to the ovule, where one male gamete fuses with the egg cell to form the zygote. Without the pollen tube, the male gamete could not reach the egg.

Ans: DNA carries the information for making proteins that determine body design, so each new cell and offspring needs a copy to inherit the features. The copying is not perfectly accurate, so small variations arise. These variations may help some individuals to survive changes in the environment and provide the raw material for evolution, though some may be harmful.

Ans: Fission: Amoeba (binary), Plasmodium (multiple). Fragmentation: Spirogyra breaks into pieces that grow into new filaments. Regeneration: Planaria and Hydra regrow lost parts or whole body. Budding: Hydra and yeast form buds that detach. Spore formation: Rhizopus forms spores in sporangia. Vegetative propagation: Bryophyllum leaf buds, potato eyes, rose cuttings, grafting in mango. Asexual reproduction needs only one parent and gives genetically similar offspring.

Ans: Reproductive health means a total well-being in all aspects of reproduction: physical, mental, social and behavioural. Contraceptive methods: barrier (condom, diaphragm), chemical (oral pills, copper-T), and surgical (vasectomy, tubectomy). Sexually transmitted diseases such as gonorrhoea, syphilis, warts and HIV-AIDS are caused by bacteria or viruses and spread by sexual contact. Prevention: use of condoms, avoiding multiple partners and safe, screened blood. Female foeticide is illegal and affects the sex ratio, so awareness and education are needed.