Reproduction: How Life Continues

Vegetative propagation in plants

• Vegetative propagation: new plants arise from the vegetative parts (growing parts) of a plant: only one parent, so genetically identical offspring.
• Natural examples: potato and ginger (fleshy underground stems), money plant and sugarcane stem cuttings, Bryophyllum (plantlets on leaves).

• Why useful in agriculture: efficient, large-scale growing of desirable crops; Krishi Vigyan Kendras (KVKs) under ICAR train farmers in modern grafting.

Other organisms

• Budding in yeast: small round outgrowths (buds) emerge from parent cells and separate. Budding in Hydra: repeated cell division at a site forms a bud that enlarges and separates; many buds may grow at once.
• Spore formation (fungi, eg: Rhizopus, Aspergillus): spores form in a sac (sporangium) or on a swollen vesicle on hyphae (thread-like structures). Spores are lightweight, usually single-celled, produced in millions, spread by air and germinate when moisture and nutrients are available (mould on moist bread; warm 25–35°C favours growth, refrigeration slows it).
• Louis Pasteur: showed life arises from pre-existing life (not spontaneously); germ theory of disease; strengthened cell theory; led to sterilisation.
• Fungi benefits: degrade organic wastes and pollutants, remove heavy metals from industrial waste, give antibiotics (penicillin, amoxicillin).
• Mechanism: asexual reproduction is by mitosis: offspring have identical chromosomes and are clones. It is fast, quickly increasing the population in favourable conditions.

• Two parents contribute genetic material. If both gave a full set of chromosomes every generation, the number would double each generation; meiosis solves this by halving the number in gametes.
• Chromosomes: thread-like structures in the nucleus carrying genetic information; each species has a fixed number. Humans have 23 pairs = 46 chromosomes (one of each pair from each parent).
• Meiosis forms gametes: diploid parent cell $\to$ haploid gametes (chromosome number halved). Each human gamete has 23 chromosomes. Gametes: sperm (male) and egg (female) in animals; pollen grain (male gametes) and ovule (female gamete, egg) in plants.
• Variation: in meiosis, chromosomes of each pair separate randomly. Bead activity: 3 pairs of characters give $2^3 = 8$ combinations; 23 pairs give an enormous number, so children differ from parents and siblings.
• Importance: variation helps some individuals adapt to changing environments and drives evolution (eg: tolerance of low oxygen at high altitude; digesting milk in adulthood).

• Flowers are the reproductive organs of angiosperms (flowering plants). Non-flowering plants such as pines also reproduce sexually.
• A complete flower has four parts (whorls, outer to inner): sepals, petals, stamens, pistil.

• Inference: wind pollination is less efficient (very low seeds per pollen grain), but huge pollen numbers make up for the loss; insect pollination is more efficient.
• P. Maheshwari: 'Father of Indian Embryology'; developed in-vitro fertilisation in flowering plants and grew plant embryos on artificial media; book An Introduction to the Embryology of Angiosperms (1950).
• Plant breeding: selective breeding, artificial hybridisation (remove stamens, bag the flower to prevent self-pollination, manually transfer chosen pollen), genetic engineering: give high-yielding and disease-resistant varieties.
• Declining pollinators reduce yields (eg: apple orchards), so beekeeping alongside farming can improve fruit set.

• Pollen on a compatible stigma produces a pollen tube that grows through the style into the ovary. The male gamete moves through it to the ovule and fuses with the egg cell.
• Fertilisation: fusion of male and female gametes. The fertilised egg is the zygote, which develops into an embryo.
• Ovary $\to$ fruit; ovules $\to$ seeds. Seeds are dispersed by wind, water and animals (eg: light, hairy seeds of madar and dandelion are dispersed by wind). With favourable water, air and temperature, a seed germinates into a new plant.
• Sexual reproduction creates new plants and variation.

• Larval stage: fish, amphibians and insects lay many eggs with just enough yolk to make a larva, a feeding stage that eats organic waste. After enough nutrition it transforms into the adult (butterfly: egg → larva → pupa → adult; also frogs).
• Reptiles and birds: each egg has enough yolk to nourish the embryo until hatching. Mammals: the zygote develops inside the female; young are fed on milk.
• The length of care after birth depends on how long the embryo develops inside the egg or the mother's body.

• Gametogenesis: formation of gametes in testes and ovaries by meiosis (46 → 23 chromosomes). Males make numerous tiny motile sperm; females make a single large egg.
• Hormones bring about puberty changes (eg: rapid growth, voice change in boys).

• Ovulation: from puberty, usually one mature egg a month is released from an ovary and moves to the oviduct. Before ovulation the uterine lining thickens with blood vessels.
• Fertilisation: millions of sperm enter through the vagina; if one fuses with the egg (in the oviduct), a zygote forms. The zygote divides by mitosis while travelling to the uterus and implants in the lining: this marks the beginning of pregnancy.
• If the egg is not fertilised: it survives about a day and degenerates; the lining sheds with some blood through the vagina: menstruation (period), lasting 3–7 days.
• Cycle: repeats every 21–35 days (often about 28), starts at puberty (about 10–14 years), continues until menopause (about 50). Ovulation is around the 14th day of a 28-day cycle but not always exactly so (cycle length varies).

• Sex determination: females are XX, males XY. The mother always gives an X; the father gives X (girl) or Y (boy), so the father's chromosome determines the baby's sex.
• Menstrual hygiene: use clean products (pads, tampons, cups); wash the genital area with water (avoid soap); wash hands before and after changing; change pads every 4–6 hours; wrap and bin used pads (do not flush); dry reusable pads fully. Menstruation is a sign of a healthy reproductive system.
• The cycle stops during pregnancy because the thickened lining is needed to nourish the embryo.

• Duration: about nine months, in three trimesters. 1st: embryo forms, major organs start developing; from about the ninth week it is called a foetus. 2nd: foetus grows bigger and stronger; movements are felt. 3rd: rapid growth, ready for life outside.
• Childbirth: strong contractions of the uterine muscles push the foetus out through the birth canal; doctors may use medical or surgical procedures if a normal birth is unsafe.
• After birth: breastfeeding gives complete nutrition and protection from disease; keep newborns warm, vaccinate on time, handle gently. Mother needs nutritious food and rest; avoid smoking, alcohol and medicines without medical advice.
• During pregnancy: balanced diet (proteins, vitamins, minerals), regular check-ups, light exercise and rest, and emotional support.
• Post-partum depression: anxiety and fatigue after delivery; a treatable, recognised condition. Talk to a doctor, nurse or ASHA worker.
• ASHA workers: more than 10 lakh women health workers under the National Health Mission; promote hygiene, immunisation, maternal care, safe deliveries and family planning.
• IVF (in-vitro fertilisation): egg and sperm combined outside the body in a laboratory dish, then the fertilised egg is implanted in the uterus. India's first test-tube baby (1978): Kanupriya Agarwal (Durga), pioneered by Subhash Mukhopadhyay of Kolkata.

• Sexual maturity (sperm production, menstrual cycles) is gradual; emotional maturity takes longer (handling feelings, communicating clearly, making thoughtful decisions). Responsible choices prevent unplanned pregnancy and infections.
• Sexually transmitted infections (STIs): gonorrhoea, herpes, syphilis, genital warts, HIV (can lead to AIDS); some are not yet curable. Condoms help prevent STIs and pregnancy.

• Abortion: removal of an unwanted pregnancy by surgery, generally within the first trimester. Sex-selective abortion distorts the sex ratio, so prenatal sex determination is strictly prohibited by law in India.
• CDRI Lucknow: developed the world's first non-steroidal, non-hormonal oral contraceptive pill (taken once weekly); provided free under the National Family Planning Programme.
• Human babies depend on adults for a long time (a feature that allows care and learning but demands long parental investment).