CBSE Class 9 > Class 9 Notes > Science New NCERT 2026-27 (New Syllabus) > Cheat Sheet: How Life Continues
Cheat Sheet: How Life Continues
1. Reproduction - Overview
1.1 Definition & Types
| Term | Definition |
|---|---|
| Reproduction | Biological process by which organisms produce new individuals of the same species. |
| Asexual reproduction | Single parent produces offspring that are genetically identical via mitosis. |
| Sexual reproduction | Two parents contribute genetic material producing genetically varied offspring via meiosis. |
1.2 Asexual Reproduction in Plants
| Term | Definition / Key points |
|---|---|
| Vegetative propagation | New plants arise from vegetative parts (shoots, roots, stems, leaves). |
| Cutting | Shoot cuttings inserted in soil develop into new plants with watering. |
| Grafting | Stem piece of one variety fitted into a slit of a rooted plant of another variety and joined until healed. |
| Layering | Flexible twig buried under soil forms roots, then is cut to grow independently (roots form in ~10-15 days). |
| Tissue culture | Mass-production of disease-free plantlets from apical meristem or shoot tip on nutrient media. |
| Mitosis | Cell division mechanism underlying all asexual reproduction producing genetically identical daughter cells (clones). |
1.3 Asexual Reproduction in Other Organisms
| Term | Definition / Key points |
|---|---|
| Budding (yeast) | Small outgrowths (buds) form on parent, grow and detach as new yeast cells. |
| Budding (Hydra) | Repeated cell division at a body location produces an outgrowth (bud) that separates to live independently. |
| Spore formation | Fungi produce light, single-celled spores in sacs or on vesicles that disperse and germinate on suitable substrates. |
2. Sexual Reproduction
2.1 Meiosis, Gametes & Variation
| Term | Definition / Key points |
|---|---|
| Meiosis | Specialised cell division that halves chromosome number to produce haploid gametes. |
| Gamete | Reproductive cell produced by meiosis (male and female gametes). |
| Diploid (2n) | Full chromosome set present in body cells. |
| Haploid (n) | Half chromosome set present in gametes. |
| Genetic variation | Created by random distribution of chromosomes during meiosis producing unique gametes. |
| Fertilisation | Fusion of male and female gametes producing a zygote. |
| Zygote | Fertilised egg that develops into an embryo. |
2.2 Sexual Reproduction in Flowering Plants
2.2.1 Flower Structure
| Part | Function / Description |
|---|---|
| Sepal | Outer green whorl protecting the flower bud. |
| Petal | Brightly coloured projections that attract pollinators. |
| Stamen | Male part composed of filament and anther; anther produces pollen grains carrying male gametes. |
| Pistil | Female part with stigma (receives pollen), style (tube), and ovary (contains ovules with egg cells). |
2.2.2 Pollination
| Term | Definition |
|---|---|
| Pollination | Transfer of pollen grains from anther to stigma. |
| Self-pollination | Pollen transfer to stigma of same flower or another flower on same plant. |
| Cross-pollination | Pollen transfer from anther of one plant to stigma of another plant of same species. |
2.2.3 Pollination Strategies
| Pollination strategy | Description / pollen & seed numbers |
|---|---|
| Wind pollination (maize, wheat) | Pollen light and small; produced in large quantities - 5,00,000-10,00,000 pollen grains per flower; estimated seeds formed 50-200. |
| Insect pollination (sunflower) | Flowers brightly coloured, fragrant, nectar-producing; pollen large and sticky - 20,000-40,000 pollen grains per flower; estimated seeds formed 800-1,000. |
| Water pollination (Vallisneria, Hydrilla) | Water currents carry pollen between aquatic flowers. |
| Bird pollination (coral tree, hibiscus) | Pollination carried out by birds such as sunbirds and Indian white-eye. |
2.2.4 Fertilisation & Seed Formation
| Term | Definition / Key points |
|---|---|
| Pollen tube | Tube produced by a germinated pollen grain that grows through the style into the ovary carrying the male gamete. |
| Fertilisation | Fusion of male and female gametes resulting in a zygote. |
| Seed | Developed ovule that can germinate into a new plant under suitable conditions. |
| Fruit | Enlarged ovary that surrounds seeds. |
| Seed dispersal | Seeds dispersed by wind, water, or animals. |
3. Reproduction in Animals
3.1 Fertilisation Types
| Type | Definition / Examples |
|---|---|
| External fertilisation | Fertilisation outside the body; seen in frogs and most fish; large numbers of eggs released into water. |
| Internal fertilisation | Fertilisation inside female body; seen in reptiles, birds, mammals; offspring better protected. |
3.2 Variations by Animal
- Fish - Habitat: Water; Fertilisation: External; Eggs produced: 100s-1000s; Survival of young: Low.
- Frog - Habitat: Water/land; Fertilisation: External; Eggs produced: 5,000-50,000; Survival of young: Low.
- Lizard - Habitat: Land; Fertilisation: Internal; Eggs produced: 2-20; Survival of young: Moderate.
- Bird - Habitat: Water/land; Fertilisation: Internal; Eggs produced: 1-15; Survival of young: Moderate to High.
3.3 Developmental Modes
- Larva
- Metamorphosis
- Yolk-rich eggs (reptiles, birds)
- Mammalian internal development
4. Human Reproduction
4.1 Reproductive Maturity
| Term | Definition / Key points |
|---|---|
| Reproductive maturity | Stage when reproductive organs produce gametes (sperm in males, eggs in females). |
4.2 Male Reproductive System
| Part | Function / Description |
|---|---|
| Testes | Two oval organs in scrotum; produce sperm and hormones; scrotum keeps testes cooler than body temperature. |
| Vas deferens | Tube through which sperm travel from testes to urethra. |
| Seminal vesicles & Prostate gland | Secrete fluids that nourish and activate sperm. |
| Sperm structure | Head contains genetic material; long tail provides motility. |
4.3 Female Reproductive System
| Part | Function / Description |
|---|---|
| Ovaries | Produce eggs and hormones. |
| Oviducts (Fallopian tubes) | Connect ovaries to uterus; site where sperm may fuse with egg. |
| Uterus | Bag-like organ where foetus develops; opens into vagina via cervix. |
| Cervix | Narrow passage connecting uterus to vagina. |
4.4 Gametogenesis & Gamete Comparison
| Term | Definition / Key points |
|---|---|
| Gametogenesis | Process of gamete formation by meiosis in testes and ovaries. |
| Male vs Female gametes | Male: millions of tiny, motile sperm. Female: single large, non-motile egg produced at a time. |
| Feature | Comparison |
|---|---|
| Size | Sperm - Very small; Egg - Large. |
| Number produced | Sperm - Millions; Egg - Few. |
| Stored nutrients | Sperm - Absent; Egg - Present. |
| Motility | Sperm - Actively motile; Egg - Non-motile. |
4.5 Ovulation, Menstruation & Cycle
| Term | Definition / Key points |
|---|---|
| Ovulation | Release of one mature egg monthly from an ovary. |
| Menstruation | Shedding of uterine lining with blood lasting usually 3-7 days. |
- Cycle length: approximately 21-35 days (often ~28 days).
- Puberty onset: ages 10-14.
- Menopause: around age 50.
- Menstrual cycle stages (typical 28-day period): Day 1-5 menstruation; Day 6-14 lining rebuilds and egg matures; Day 14 ovulation; Day 15-28 lining thickens then breaks down if no fertilisation.
4.6 Fertilisation, Pregnancy & Childbirth
| Term | Definition / Key points |
|---|---|
| Fertilisation site | Usually in oviduct where sperm fuses with egg forming a zygote. |
| Pregnancy duration | About nine months divided into three trimesters. |
| First trimester | Fertilised egg develops into embryo; from ~ninth week called foetus. |
| Second trimester | Foetus grows bigger and movements felt by mother. |
| Third trimester | Rapid growth as baby prepares for birth. |
| Childbirth | Uterine contractions push foetus through birth canal; medical/surgical procedures used when required. |
| Breastfeeding | Mother's milk provides complete nutrition and infection protection for the infant. |
4.7 Sex Determination
| Term | Definition / Key points |
|---|---|
| Chromosomal basis | Females carry XX; males carry XY; father contributes X or Y determining baby's biological sex. |
4.8 Menstrual Hygiene & Post-partum
- Menstrual hygiene: use biodegradable sanitary products; wash genital area with water only; change pads every 4-6 hours; wrap and bin used products (do not flush).
- Post-partum depression: recognised treatable condition; seek healthcare support if feeling low.
- ASHA workers: more than 10 lakh workers under National Health Mission provide maternal and family-planning support.
4.9 Prevention: STIs & Contraception
| Term | Definition / Examples |
|---|---|
| Sexually Transmitted Infections (STIs) | Infections transmitted via sexual contact; examples: gonorrhoea, herpes, syphilis, genital warts, HIV. |
| Barrier methods | Condoms and vaginal covers physically prevent sperm reaching egg; reduce STI risk. |
| Oral contraceptive pills | Hormonal pills that suppress ovulation; may have side effects. |
| IUD (Copper-T) | Placed in uterus to prevent pregnancy; may occasionally cause uterine irritation. |
| Surgical methods | Vasectomy (male) or tubectomy (female) permanently prevent gamete meeting. |
| Abortion | Surgical removal of unwanted pregnancy, generally within first trimester. |
4.10 Legal & Scientific Notes
- Prenatal sex determination is strictly prohibited by law in India.
- Central Drug Research Institute, Lucknow developed a non-steroidal, non-hormonal oral contraceptive pill taken once weekly.
- Subhash Mukhopadhyay (Kolkata) pioneered India's first test-tube baby, Kanupriya Agarwal (Durga), in 1978 (experimental IVF work).
- P. Maheshwari authored An Introduction to the Embryology of Angiosperms (1950) and developed in-vitro fertilisation techniques in flowering plants.
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