CBSE Class 10 Science How do Organisms Reproduce Notes
How These Notes Will Help You
Reproduction is the chapter that students either find surprisingly fascinating or uncomfortably vague — and the difference almost always comes down to how it was taught. When you understand that reproduction is fundamentally about passing on DNA to the next generation, and that every mechanism — from binary fission in bacteria to sexual reproduction in humans — is just a different strategy for achieving that goal, the entire chapter becomes logical rather than a list of disconnected facts. These notes are built around that central idea. Every section explains not just the what, but the why — why organisms evolved these different strategies, what advantages each method offers, and how the mechanism connects to the bigger picture of life.
This chapter carries significant marks in the CBSE board exam. Questions appear on asexual reproduction methods (often as match-the-column or identify-the-type), flower anatomy (frequently a diagram question worth 3–5 marks), the human reproductive system (consistently a 5-mark question), and reproductive health (appearing as short answers and assertion-reason questions). These notes cover all of these systematically, with the kind of depth that lets you answer not just straightforward recall questions but also application-based questions that CBSE has been asking more frequently in recent papers.
What You Get in These Notes ✅ Clear explanation of WHY organisms reproduce and what reproduction actually achieves biologically ✅ All 7 methods of asexual reproduction covered with real organism examples and key distinctions ✅ Complete flower anatomy — male and female parts, pollination types, fertilisation, seed and fruit formation ✅ Full human male and female reproductive system — structure, function, and hormonal control ✅ Sexual reproduction in plants — from pollination to double fertilisation — explained step by step ✅ Reproductive health — contraception methods, STDs, importance of sex education — as per CBSE syllabus ✅ Comparison tables: asexual vs sexual, self vs cross pollination, and more — board exam ready ✅ Common mistakes, key definitions, practice questions (1M / 3M / 5M), and printable PDF |
Who are these notes for? These notes are written for CBSE Class 10 students preparing for board exams, students who found this chapter too biology-heavy to follow in class, and students who want to ensure they can answer both the diagram and the explanation components of a 5-mark question confidently. The notes are designed to be read once for understanding and then used as a quick-reference tool during revision.
How to use these notes: Read each section to understand the concept, then focus on the comparison tables and definition boxes — these are the most directly testable items. After reading the flower anatomy section, try to draw and label the diagram from memory. For the human reproductive system, practise writing the function of each part in one sentence. This kind of active recall builds the memory you need for a board exam setting.
1. Introduction — Why Do Organisms Reproduce?
Reproduction is the biological process by which living organisms produce new individuals of the same species. Unlike the other life processes (nutrition, respiration, excretion), reproduction is not essential for the survival of an individual organism — a single organism can live its entire life without reproducing. However, it is absolutely essential for the survival of a species. Without reproduction, a species would go extinct as its members aged and died.
At the most fundamental level, reproduction is about DNA — passing on genetic information to the next generation. Every mechanism of reproduction, however different it may look, is ultimately a strategy for copying and transmitting DNA. The diversity of reproductive strategies we see in nature reflects the trade-offs organisms make between speed, efficiency, genetic diversity, and resource investment.
The Core Purpose of Reproduction Reproduction = mechanism to pass on DNA to the next generation.
Individual survival → Does NOT require reproduction Species survival → REQUIRES reproduction
Every reproductive strategy is a trade-off between: • Speed and simplicity (asexual — fast, requires one parent) • Genetic diversity and adaptability (sexual — slower, requires two parents)
DNA copying is never 100% perfect — minor variations arise → basis of evolution. |
Two Major Types of Reproduction 1. ASEXUAL REPRODUCTION • Only ONE parent involved • No formation of gametes (sex cells) • Offspring are genetically identical to parent (clones) • Fast, efficient, requires less energy • Common in simpler organisms: bacteria, fungi, simple plants
2. SEXUAL REPRODUCTION • TWO parents (male and female) involved — or both in one organism (hermaphrodites) • Involves formation and fusion of gametes (sperm and egg) • Offspring are genetically different from both parents • Slower, requires more energy, but creates genetic variation • Common in complex animals and most flowering plants |
2. Asexual Reproduction
Asexual reproduction involves a single parent producing genetically identical offspring without the formation of gametes. It is the dominant reproductive strategy in unicellular organisms and is also common in many multicellular plants and some animals. The key advantage is speed — an organism can rapidly produce a large population of offspring in favourable conditions. The key disadvantage is lack of genetic variation — all offspring are identical clones of the parent, so the entire population is equally vulnerable to the same diseases or environmental changes.
2.1 Binary Fission
Definition: Binary fission is the simplest form of asexual reproduction in which a single-celled organism divides into two equal daughter cells, each of which grows into a new organism. It occurs in prokaryotes (organisms without a defined nucleus).
• Mechanism: The DNA of the parent cell first replicates (makes a copy). The cell then elongates and divides in the middle (by cytokinesis), producing two genetically identical daughter cells.
• Plane of division: The plane in which the cell divides varies by organism. Amoeba divides in any plane (irregular). Leishmania (the organism causing kala-azar) divides in a fixed plane — always from the anterior end where the flagellum is attached.
• Examples: Amoeba, Bacteria (e.g., E. coli), Leishmania, Paramoecium.
• Speed: Under ideal conditions, E. coli can divide every 20 minutes — producing millions of cells within hours. This is why bacterial infections can spread so rapidly.
CBSE Question — Binary Fission in Leishmania Q: 'How does Leishmania reproduce? How does it differ from Amoeba?'
Answer: Both Amoeba and Leishmania reproduce by binary fission. • Amoeba: Divides in any plane — no fixed orientation. • Leishmania: Divides in a specific, fixed plane — always from the anterior end where the whip-like flagellum is attached. The difference lies in the PLANE of division, not the process itself. |
2.2 Multiple Fission
Definition: Multiple fission is a form of asexual reproduction in which the nucleus of a single cell divides multiple times, producing many daughter cells simultaneously. The single parent cell effectively produces many offspring at once.
• Mechanism: The nucleus divides repeatedly (multiple times) through mitosis. Each nucleus then gets surrounded by cytoplasm and a membrane, forming multiple daughter cells inside the parent. The parent's outer membrane eventually bursts, releasing all daughter cells.
• Protective cyst: When conditions are unfavourable (e.g., drought, cold), Plasmodium forms a protective cyst around itself. Inside the cyst, multiple fission occurs. When conditions improve, the cyst bursts and releases the daughter cells.
• Examples: Plasmodium (the malaria-causing parasite), Amoeba (under harsh conditions).
2.3 Fragmentation
Definition: Fragmentation is a form of asexual reproduction in which the parent organism breaks into two or more fragments, and each fragment grows into a complete, new organism. This occurs in relatively simple multicellular organisms where each fragment has the potential to develop into a whole individual.
• Condition: Works only in organisms where cells have not become so specialised that they cannot regenerate missing parts. The organism must retain totipotency — the ability of each cell to produce all types of cells.
• Examples: Spirogyra (a green alga) — breaks into fragments, each of which grows into a new Spirogyra filament. Planaria (flatworm) — each fragment regenerates into a complete worm. Starfish — a single arm can regenerate into a whole starfish.
2.4 Regeneration
Definition: Regeneration is the ability of an organism to regrow damaged or lost body parts. It is closely related to fragmentation but is distinct — in regeneration, the organism is cut or damaged and regrows the missing part, while fragmentation involves each piece becoming a complete new organism.
• Examples: Planaria — if cut into pieces, each piece regenerates a complete organism. Hydra — can regenerate from any piece. Lizards — regenerate lost tails (though the regenerated tail has cartilage instead of bone).
• Mechanism: Specialised undifferentiated cells called totipotent or pluripotent cells (called neoblasts in Planaria) divide and differentiate to form the missing tissues and organs.
• Important distinction: Not all organisms can regenerate. In humans, regeneration is limited — we can regenerate liver cells, skin cells, and red blood cells, but cannot regenerate a lost limb or complex organ.
Fragmentation vs Regeneration — A Common Confusion FRAGMENTATION: Organism breaks into pieces → each piece becomes a COMPLETE NEW organism. Example: Spirogyra — each fragment grows into a new Spirogyra.
REGENERATION: Organism is cut or damaged → missing parts REGROW on the original. Example: Planaria cut into 3 → 3 new Planaria (this is actually BOTH).
Key line for board: 'Regeneration is a broader capacity. Fragmentation is a specific reproductive strategy where fragmentation + regeneration together produce new organisms.' |
2.5 Budding
Definition: Budding is a form of asexual reproduction in which a small outgrowth called a bud develops from the parent organism. The bud grows, eventually detaches, and develops into a new independent organism genetically identical to the parent.
• In Hydra: A small bulge (bud) appears on the body wall of Hydra, gradually develops tentacles and a mouth, and eventually detaches to form a new Hydra. Multiple buds can grow simultaneously.
• In Yeast: Yeast (a unicellular fungus) forms a small bud from the parent cell. The bud grows, receives a copy of the nucleus (through mitosis), and separates when mature. Under favourable conditions, yeast can produce long chains of buds before separation.
• In plants: Bryophyllum (Sprout leaf / Kalanchoe) — buds develop along the notches of its leaves. Each bud can fall off and grow into a new plant.
2.6 Vegetative Propagation in Plants
Definition: Vegetative propagation is a form of asexual reproduction in plants in which a vegetative part of the plant (root, stem, or leaf — not seeds) gives rise to a new plant. It is the most common and economically important form of asexual reproduction in plants.
• Advantage 1 — Genetic uniformity: Since offspring are genetically identical to the parent, desirable traits (taste, disease resistance, yield) are preserved exactly. This is invaluable in agriculture — seedless varieties of banana and grapes are maintained this way.
• Advantage 2 — Speed: Plants produced by vegetative propagation reach maturity much faster than seed-grown plants and often flower/fruit sooner.
• Advantage 3 — No seeds needed: Many plants either produce very few seeds, or their seeds have very low germination rates. Vegetative propagation bypasses this problem entirely.
Method | Plant Part Used | Examples | How it Works |
Natural — Runners/Stolons | Horizontal stem along ground | Strawberry, Grass (doob) | Stem grows along ground; nodes produce roots and new shoots |
Natural — Rhizomes | Underground horizontal stem | Ginger, Turmeric, Mint | Underground stem grows horizontally; nodes sprout new shoots |
Natural — Tubers | Swollen underground stem | Potato | Eyes (nodes) on potato sprout new plants |
Natural — Bulbs | Thick fleshy leaves on disc | Onion, Garlic, Tulip | Leaves store food; new bulb develops and separates |
Natural — Leaf buds | Leaf margins/notches | Bryophyllum (Sprout leaf) | Buds on leaf margins fall off and grow into new plants |
Artificial — Cutting | Cut stem/leaf placed in soil | Rose, Sugarcane, Croton | Cut stem develops roots and grows into new plant |
Artificial — Layering | Branch bent to touch soil | Jasmine, Strawberry | Branch forms roots while still attached; then cut and planted |
Artificial — Grafting | Join stem of two plants | Apple, Mango, Rose | Scion (desired) joined to rootstock (strong roots); tissues fuse |
2.7 Spore Formation (Sporulation)
Definition: Spore formation is a form of asexual reproduction in which an organism produces tiny, lightweight reproductive units called spores. Each spore has a thick protective wall and can remain dormant for long periods under unfavourable conditions. When conditions become favourable, the spore germinates into a new organism.
• Structure of spores: Spores are non-motile (cannot move on their own). They are extremely lightweight and are dispersed by wind, water, or animals over long distances. Each spore contains a nucleus and sufficient cytoplasm to begin growth.
• Sporangium: In Rhizopus (bread mould), spores are produced in specialised sac-like structures called sporangia (singular: sporangium), which appear as black dots on the mould. When mature, the sporangium bursts and releases thousands of spores.
• Examples: Rhizopus (bread mould), Mucor (pin mould), Penicillium, ferns, mosses.
2.8 Summary of Asexual Reproduction Methods
Method | Organisms | Key Feature | No. of Parents |
Binary Fission | Amoeba, Bacteria, Leishmania | One cell → two equal cells | 1 |
Multiple Fission | Plasmodium, Amoeba | One cell → many cells simultaneously | 1 |
Fragmentation | Spirogyra, Planaria, Starfish | Body breaks → each piece → new organism | 1 |
Regeneration | Planaria, Hydra, Lizard (tail) | Lost parts regrow from specialised cells | 1 |
Budding | Hydra, Yeast, Bryophyllum | Small bud grows, detaches, new organism | 1 |
Vegetative Propagation | Most plants — potato, onion, rose, etc. | Vegetative parts grow into new plants | 1 |
Spore Formation | Rhizopus, Mucor, ferns, mosses | Tiny spores dispersed, germinate when favourable | 1 |
3. Sexual Reproduction in Flowering Plants
Sexual reproduction in plants involves the production of male and female gametes, their fusion (fertilisation), and the development of seeds that grow into new plants. In flowering plants (angiosperms), the flower is the reproductive organ — it contains both male and female parts (or sometimes just one). Understanding flower anatomy is essential because CBSE board exams almost always include a labelled diagram question on the flower or the process of fertilisation.
3.1 Structure of a Flower — The Reproductive Organ
A flower is the sexual reproductive structure of angiosperms. A typical flower has four whorls (rings) of organs, arranged from the outside inward: Sepals → Petals → Stamens (male) → Carpels/Pistil (female).
3.1a Male Reproductive Parts — Stamen
• Stamen: The male reproductive organ of the flower. Each flower may have multiple stamens.
• Filament: The long stalk-like part of the stamen that holds the anther up so pollen can be easily dispersed.
• Anther: The knob-like structure at the top of the filament. Contains pollen sacs (microsporangia) in which pollen grains (male gametophytes) are produced through meiosis. Each pollen grain contains the male gamete.
3.1b Female Reproductive Parts — Pistil (Carpel)
• Pistil (Carpel): The female reproductive organ of the flower. It is flask-shaped and consists of three parts.
• Stigma: The sticky, expanded top of the pistil. It receives pollen grains during pollination. The surface is often sticky or hairy to trap pollen.
• Style: The long, slender tube connecting the stigma to the ovary. After pollination, the pollen tube grows down through the style to reach the ovary.
• Ovary: The swollen base of the pistil that contains one or more ovules. Each ovule contains the female gamete (egg cell). After fertilisation, the ovary develops into the fruit and the ovule develops into the seed.
• Ovule: Contains the embryo sac, within which the female gamete (egg) is located. After fertilisation, the ovule becomes the seed.
Part | Type | Structure | Function |
Sepal | Vegetative | Green leaf-like structure (whorl 1 — outermost) | Protects the flower bud before it opens |
Petal | Vegetative | Colourful, often fragrant (whorl 2) | Attracts pollinators (insects, birds) |
Stamen | Male reproductive | Filament + Anther (whorl 3) | Produces pollen grains (male gametes) |
Anther | Male reproductive | Knob at top of filament | Site of pollen grain production (meiosis) |
Filament | Male reproductive | Slender stalk of stamen | Holds anther in position for pollen dispersal |
Pistil | Female reproductive | Stigma + Style + Ovary (whorl 4 — innermost) | Receives pollen; houses ovule; becomes fruit |
Stigma | Female reproductive | Sticky/hairy top of pistil | Receives and traps pollen grains |
Style | Female reproductive | Tube connecting stigma to ovary | Pollen tube grows through here to reach ovule |
Ovary | Female reproductive | Swollen base of pistil | Contains ovules; becomes fruit after fertilisation |
Ovule | Female reproductive | Inside ovary | Contains egg cell; becomes seed after fertilisation |
3.2 Pollination
Definition: Pollination is the transfer of pollen grains from the anther (male part) of a flower to the stigma (female part) of the same or different flower of the same species. Pollination is a necessary first step — it brings the male gamete close to the female gamete so that fertilisation can occur.
Feature | Self-Pollination | Cross-Pollination |
Definition | Pollen transferred from anther to stigma of the SAME flower or another flower on the SAME plant | Pollen transferred from anther of one plant to stigma of a DIFFERENT plant of the same species |
Agents needed | No external agent needed | Wind, water, insects, birds, animals |
Genetic result | Offspring are genetically identical to parent | Offspring have genetic variation — NEW combinations |
Reliability | Very reliable — always produces seeds | Less reliable — depends on pollinator availability |
Examples | Wheat, rice, pea, tomato | Maize, sunflower, apple, mango, most flowers |
Adaptation | No need for attractive petals/nectar | Colourful petals, nectar, scent to attract pollinators |
Disadvantage | Reduces genetic diversity over generations | Requires pollinators — can fail if none available |
Agents of Pollination — Quick Reference Wind-pollinated flowers: Small, dull, no fragrance, no nectar. Light, smooth pollen in huge quantities. Examples: Maize, rice, wheat, grasses.
Insect-pollinated flowers: Large, colourful, fragrant, produce nectar. Sticky/rough pollen. Examples: Rose, sunflower, orchid, jasmine.
Water-pollinated flowers: Submerged or floating; pollen released underwater or on surface. Examples: Vallisneria, Hydrilla. |
3.3 Fertilisation in Plants — Double Fertilisation
After pollination, the pollen grain germinates on the stigma and grows a pollen tube down through the style toward the ovule. The pollen grain contains two nuclei — the generative nucleus divides to produce two male gametes (sperm nuclei) which travel down the pollen tube. When the tube reaches the ovule, a remarkable process unique to angiosperms called double fertilisation occurs.
DOUBLE FERTILISATION (unique to angiosperms):
Male gamete 1 (sperm) + Egg cell (female gamete) → Fusion → ZYGOTE → develops into EMBRYO (future plant)
Male gamete 2 (sperm) + Secondary nucleus (2 polar nuclei fused) → Fusion → PRIMARY ENDOSPERM NUCLEUS (3n) → develops into ENDOSPERM (food store for developing seed)
Result after fertilisation: Ovule → Seed (contains embryo + endosperm) Ovary → Fruit (surrounds and protects seeds) Ovary wall → Pericarp (fruit wall) |
CBSE Board Question — Double Fertilisation Q: 'What is double fertilisation? Why is it significant?'
Answer: Double fertilisation is a unique process in angiosperms where two male gametes each fuse with different cells in the embryo sac: 1st fusion: Sperm + Egg → Zygote → Embryo (the actual plant) 2nd fusion: Sperm + Secondary nucleus → Primary Endosperm Nucleus → Endosperm (nutritive tissue that feeds the developing embryo)
Significance: The endosperm ensures the embryo has a ready food supply during germination and early growth — before the seedling can photosynthesise for itself. This gives angiosperms a major reproductive advantage. |
3.4 Seed and Fruit Formation
• Seed: After fertilisation, the ovule develops into the seed. The seed contains the embryo (future plant), the endosperm (food store), and a protective seed coat (testa) derived from the integuments of the ovule.
• Fruit: The ovary wall (and sometimes other floral parts) develops into the fruit, which surrounds and protects the seeds. Fruits aid in seed dispersal — through animals eating them, or by wind, water, or explosive mechanisms.
• Germination: When the seed finds suitable conditions (moisture, warmth, oxygen), it germinates — the embryo grows out of the seed coat, using the endosperm as food, until it can photosynthesise independently.
4. Human Reproduction — Sexual Reproduction in Humans
Humans reproduce sexually. This means the process involves the production of specialised sex cells (gametes) — sperm in males and eggs (ova) in females — and their fusion (fertilisation) to produce a zygote that develops into a new individual inside the mother's body. Human sexual reproduction is associated with puberty — the period of physical and hormonal changes that marks the transition from childhood to sexual maturity.
4.1 Puberty — The Beginning of Reproductive Maturity
Puberty is triggered by the release of sex hormones — testosterone in males and oestrogen and progesterone in females — which cause the development of secondary sexual characteristics and the maturation of the reproductive organs.
Change | In Males (Testosterone) | In Females (Oestrogen/Progesterone) |
Primary change | Testes become functional — produce sperm | Ovaries become functional — begin releasing eggs (menstrual cycle starts) |
Body hair | Pubic hair, underarm hair, facial hair | Pubic hair, underarm hair |
Voice | Voice deepens (voice box enlarges) | Slight change, not significant |
Body shape | Shoulders broaden, muscles develop | Hips widen, breasts develop |
Skin | Skin becomes oilier, acne may appear | Skin becomes oilier, acne may appear |
Spurt in height | Rapid increase in height | Rapid increase in height |
Age of onset | Approximately 12–14 years | Approximately 10–12 years |
4.2 Male Reproductive System
The male reproductive system is responsible for producing, storing, and delivering sperm (the male gamete) to fertilise the female egg. It consists of the testes, a series of ducts, accessory glands, and the penis.
Part | Location | Function |
Testes (singular: testis) | Scrotum (outside body cavity) | Produce sperm (spermatogenesis) and testosterone; located outside body because sperm production requires temperature 2–3°C below body temperature |
Scrotum | External sac outside body | Houses testes; maintains optimal temperature for sperm production (~35°C vs body's 37°C) |
Epididymis | Coiled tube behind testis | Stores sperm after production; sperm mature here and gain motility (ability to swim) |
Vas Deferens (Sperm duct) | Tube from epididymis to urethra | Transports mature sperm from epididymis toward the urethra during ejaculation |
Seminal Vesicles | Behind bladder | Secrete a fructose-rich fluid that provides energy (ATP) for sperm movement |
Prostate Gland | Below bladder | Secretes alkaline fluid that protects sperm from the acidic vaginal environment |
Cowper's Glands (Bulbourethral) | Below prostate | Secrete mucus that lubricates and neutralises any acidic urine remaining in urethra |
Urethra | Passes through penis | Common passage for both urine and semen (never simultaneously — valves prevent mixing) |
Penis | External organ | Organ for introducing semen (sperm + seminal fluid) into the female reproductive tract |
Semen = Sperm + Seminal fluid Seminal fluid = secretions from Seminal Vesicles + Prostate Gland + Cowper's Glands
Path of sperm: Testes → Epididymis → Vas Deferens → Urethra → Penis |
4.3 Female Reproductive System
The female reproductive system produces eggs, receives sperm, provides the site for fertilisation, nurtures the developing embryo for nine months, and delivers the baby at birth. It is far more anatomically complex than the male system because of the additional functions of pregnancy, nourishment of the foetus, and childbirth.
Part | Location | Function |
Ovaries (2) | Pelvic cavity (one on each side of uterus) | Produce eggs (ova) — oogenesis; secrete oestrogen and progesterone |
Fallopian Tubes (Oviducts) (2) | Connect ovaries to uterus | Site of FERTILISATION; transport egg from ovary to uterus; ciliated lining helps move egg |
Uterus (Womb) | Central pelvic cavity | Site of IMPLANTATION and DEVELOPMENT of the embryo/foetus; lined with endometrium |
Endometrium | Inner lining of uterus | Thickens each month to prepare for implantation; sheds if no fertilisation occurs (menstruation) |
Cervix | Lower narrow part of uterus | Opening between uterus and vagina; dilates during childbirth |
Vagina | Between cervix and exterior | Birth canal; receives penis during sexual intercourse; semen deposited here |
4.4 Fertilisation and Development
Fertilisation in humans occurs when a single sperm fuses with the egg cell (ovum) to form a zygote. This usually takes place in the fallopian tube. Of the 200–400 million sperm that are deposited in the vagina during intercourse, only about 100–200 reach the fallopian tube, and only one successfully fertilises the egg.
FERTILISATION (in Fallopian Tube): Sperm (n) + Egg/Ovum (n) → Zygote (2n)
Zygote → undergoes repeated mitotic divisions → Embryo (ball of cells) → Travels down fallopian tube to uterus → IMPLANTATION — embryo embeds in endometrium (thickened uterine lining) → PLACENTA forms — connects foetus to mother's blood supply → Foetus develops over 9 months (gestation period) → PARTURITION (childbirth) — baby delivered through vagina |
• Placenta: The placenta is a disc-shaped organ that develops in the uterus during pregnancy. It connects the foetus to the mother's blood supply and serves as the interface for exchange of nutrients, oxygen, and waste. The foetus receives glucose and oxygen from mother's blood and returns CO₂ and urea. The placenta also produces hormones (HCG, progesterone, oestrogen) that maintain the pregnancy.
• Umbilical cord: The cord connecting the foetus to the placenta, containing blood vessels that carry nutrients and waste.
4.5 The Menstrual Cycle
The menstrual cycle is the approximately 28-day cycle of hormonal and physical changes in the female body that prepares it for pregnancy. If no fertilisation occurs, the cycle resets and the thickened endometrium is shed (menstruation). The cycle is controlled by four hormones: FSH, LH (from pituitary) and Oestrogen, Progesterone (from ovaries).
Phase | Days (approx.) | What Happens |
Menstruation | Day 1–5 | Endometrium sheds — bleeding occurs. Occurs only if previous egg was NOT fertilised. |
Follicular Phase | Day 1–13 | FSH stimulates a follicle in ovary to mature. Oestrogen causes endometrium to thicken. |
Ovulation | Day 14 | LH surge triggers release of mature egg (ovum) from ovary — most fertile period. |
Luteal Phase | Day 15–28 | Empty follicle becomes corpus luteum, secretes progesterone — maintains thickened endometrium. If no fertilisation → corpus luteum degenerates → progesterone falls → menstruation begins. |
5. Reproductive Health
Reproductive health refers to a state of complete physical, mental, and social well-being in all matters relating to the reproductive system. It includes not only the absence of disease but also access to safe, effective, affordable family planning, the right to make informed reproductive choices, and freedom from sexual violence and exploitation. CBSE Class 10 covers reproductive health through the lens of contraception and sexually transmitted diseases.
5.1 Contraception — Methods of Birth Control
Contraception refers to methods used to prevent unwanted pregnancy. Different methods work at different stages — some prevent sperm from reaching the egg, some prevent ovulation, some prevent implantation, and some create a physical barrier. Choosing the right method depends on the individual's health, relationship status, and whether or not they want future pregnancies.
Method | Type | Mechanism | Examples / Notes |
Barrier Methods | Physical | Physically prevent sperm from reaching the egg | Condom (male/female), Diaphragm; Condom also protects against STDs |
Hormonal Methods | Chemical | Prevent ovulation or alter uterine lining | Oral contraceptive pills (oestrogen/progesterone); Patches, injections |
Intrauterine Device | Mechanical | Prevents implantation inside uterus | Copper-T, IUD — inserted by doctor; long-term, highly effective |
Emergency Contraception | Chemical | Prevents fertilisation or implantation after unprotected sex | Morning-after pill — within 72 hours; not for regular use |
Surgical Methods | Permanent | Permanently prevent gamete transport | Vasectomy (male), Tubectomy (female) — irreversible |
Natural Methods | Behavioural | Avoid intercourse during fertile days | Calendar/rhythm method, Abstinence — less reliable |
Why is Contraception Important? • Prevents unwanted pregnancies — allows families to plan responsibly. • Improves maternal health — reduces risk of closely spaced pregnancies. • Reduces infant mortality — children born into planned families receive better care. • Population control — important for managing resource availability nationally. • Condoms are the ONLY method that protects against both pregnancy AND STDs. (All other contraceptive methods protect against pregnancy only, not STDs.) |
5.2 Sexually Transmitted Diseases (STDs / STIs)
Sexually transmitted diseases (STDs), also called sexually transmitted infections (STIs), are infections spread primarily through sexual contact. They can also be transmitted through infected blood (transfusion, sharing needles) or from mother to child during pregnancy or childbirth. Early detection and treatment is crucial — many STDs are curable if caught early, but can cause serious long-term complications if left untreated.
Disease | Causative Agent | Type | Key Features / Complications |
Gonorrhoea | Neisseria gonorrhoeae (bacterium) | Bacterial | Burning urination, discharge; curable with antibiotics; can cause infertility if untreated |
Syphilis | Treponema pallidum (bacterium) | Bacterial | Painless sores then rash; curable early; advanced stages cause serious organ damage |
Chlamydia | Chlamydia trachomatis (bacterium) | Bacterial | Often symptomless; major cause of infertility; curable with antibiotics |
HIV/AIDS | HIV (Human Immunodeficiency Virus) | Viral | Attacks immune system (CD4 T cells); no cure; antiretroviral therapy manages it; transmitted through blood/semen/breast milk |
Genital Herpes | Herpes Simplex Virus (HSV-2) | Viral | Painful blisters; no cure — managed with antiviral drugs; lifelong infection |
Hepatitis B | Hepatitis B Virus (HBV) | Viral | Liver inflammation; can become chronic; vaccine available; transmitted through blood and sex |
Trichomoniasis | Trichomonas vaginalis (protozoan) | Protozoan | Itching, burning, discharge; curable with antibiotics |
HIV/AIDS — Important Points for CBSE HIV = Human Immunodeficiency Virus. AIDS = Acquired Immunodeficiency Syndrome. HIV attacks CD4 T-helper cells → weakens the immune system over time. AIDS is NOT transmitted by: handshakes, hugging, coughing, sneezing, sharing food. AIDS IS transmitted by: unprotected sex, infected blood transfusion, sharing needles, mother to child (during birth or breastfeeding). No cure exists — antiretroviral therapy (ART) manages the virus but does not eliminate it. Prevention: condoms, safe blood transfusion, sterile needles, mother-to-child prevention. |
5.3 Importance of Sex Education and Reproductive Health
• Reduces teenage pregnancies: Accurate information about puberty, contraception, and consequences of unprotected sex helps adolescents make informed decisions.
• Prevents STDs: Knowledge of how STDs are transmitted and how to prevent them (especially condom use) is critical public health information.
• Reduces stigma: Open, scientifically accurate discussion of sexuality and reproduction reduces stigma and the shame that prevents people from seeking medical help.
• Empowers women: Women who understand their reproductive cycle and rights are better equipped to make decisions about their own bodies and health.
• Population management: Family planning education helps communities manage population growth in relation to available resources.
6. Asexual vs Sexual Reproduction — Complete Comparison
This table is one of the most frequently asked questions in CBSE board exams — it appears as a 3-mark tabular comparison. Memorise at least five points of difference.
Feature | Asexual Reproduction | Sexual Reproduction |
Parents required | One parent only | Two parents (male and female) — or one hermaphrodite |
Gametes | No gametes formed | Gametes (sperm and egg) are formed and fused |
Genetic variation | Offspring genetically IDENTICAL to parent (clones) | Offspring genetically DIFFERENT from parents |
Speed | Fast — population can grow rapidly | Slower — requires mating, fertilisation, gestation |
Energy required | Less energy — simpler process | More energy — complex processes involved |
Organs involved | No specialised reproductive organs needed | Specialised male and female organs required |
Evolution | Contributes very little to evolution | Major driver of evolution — creates genetic variation |
Advantages | Fast colonisation of favourable environments | Adaptability to changing environments; disease resistance |
Examples | Bacteria (binary fission), Hydra (budding), Potato (vegetative) | Humans, most animals, flowering plants |
7. Common Mistakes to Avoid
Mistake | Why It Is Wrong | Correct Understanding |
Saying the ovary becomes the seed | The ovule becomes the seed, not the ovary | Ovule → Seed; Ovary → Fruit; Ovary wall → Pericarp (fruit wall) |
Confusing pollination with fertilisation | Pollination transfers pollen; fertilisation fuses gametes | Pollination: pollen to stigma. Fertilisation: sperm fuses with egg inside ovule. |
Saying Amoeba and Leishmania differ in process | Both do binary fission — same process | Difference is only in the PLANE of division, not the process |
Calling spore formation sexual reproduction | Spores require only one parent and no gametes | Spore formation is ASEXUAL — spores are not gametes |
Saying fertilisation occurs in the uterus | Fertilisation occurs in the FALLOPIAN TUBE | Fertilisation: fallopian tube. Implantation: uterus. Delivery: vagina. |
Confusing endosperm and embryo | Students reverse which one is 'food' and which is 'baby' | Embryo = future plant (from 1st fusion). Endosperm = food store (from 2nd fusion) |
Saying condoms prevent all STDs | They significantly reduce risk but don't offer 100% protection | Condoms are highly effective at reducing STD transmission — most reliable barrier method |
Calling testes an endocrine gland only | Testes have BOTH functions | Testes = exocrine (sperm production) AND endocrine (testosterone secretion) |
8. Key Definitions and Summary Table
Term | Definition |
Reproduction | Biological process by which organisms produce new individuals of the same species |
Asexual Reproduction | One parent; no gametes; genetically identical offspring |
Sexual Reproduction | Two parents; gametes formed and fused; genetically varied offspring |
Binary Fission | One cell divides into two equal daughter cells — bacteria, Amoeba |
Multiple Fission | Nucleus divides many times → many cells released at once — Plasmodium |
Fragmentation | Body breaks into pieces; each grows into new organism — Spirogyra, Planaria |
Regeneration | Lost or damaged parts regrow from specialised cells — Planaria, Hydra |
Budding | Bud grows on parent, detaches and becomes new organism — Hydra, Yeast |
Vegetative Propagation | Vegetative parts (root/stem/leaf) produce new plant — Potato, Rose |
Spore Formation | Tiny spores produced in sporangium, dispersed, germinate — Rhizopus |
Pollination | Transfer of pollen from anther to stigma — self or cross |
Double Fertilisation | In angiosperms: sperm + egg → zygote; sperm + secondary nucleus → endosperm |
Stamen | Male reproductive part of flower = Anther + Filament |
Pistil (Carpel) | Female reproductive part = Stigma + Style + Ovary |
Ovulation | Release of a mature egg from the ovary — occurs around Day 14 of menstrual cycle |
Fertilisation | Fusion of sperm and egg to form zygote — occurs in fallopian tube |
Implantation | Embedding of embryo into endometrium of uterus |
Placenta | Organ connecting foetus to mother; site of nutrient, O₂, and waste exchange |
Menstrual Cycle | ~28-day hormonal cycle preparing female body for pregnancy |
Contraception | Methods to prevent pregnancy — barrier, hormonal, surgical, IUD, natural |
STD/STI | Infections transmitted through sexual contact — gonorrhoea, syphilis, HIV/AIDS |
Endosperm | Nutritive tissue in seed, formed by 2nd fusion in double fertilisation |
9. Key Points to Remember
• Reproduction ≠ survival of individual: Individuals can survive without reproducing; species cannot.
• Asexual = 1 parent, no gametes, identical offspring. Sexual = 2 parents, gametes, varied offspring.
• Amoeba vs Leishmania: Both do binary fission; difference is only the PLANE of division.
• Ovule → Seed. Ovary → Fruit. This distinction appears in almost every board paper.
• Double fertilisation is unique to angiosperms. 1st fusion → zygote (embryo). 2nd fusion → endosperm (food).
• Fertilisation in humans: Occurs in the FALLOPIAN TUBE, not the uterus. Implantation is in the uterus.
• Testes outside body because sperm production requires temperature 2–3°C below body temperature.
• Placenta: Connects foetus to mother; exchanges nutrients, O₂, CO₂, and urea.
• Condoms: Only contraceptive method that protects against BOTH pregnancy AND STDs.
• HIV attacks CD4 T cells → weakens immune system → AIDS. Not curable; managed with ART.
• Menstrual cycle: ~28 days. Ovulation on Day ~14. Menstruation (Day 1–5) only if no fertilisation.
• Bryophyllum: Reproduces vegetatively through buds on leaf margins — often tested as an example.
10. Practice Questions
These questions are modelled on actual CBSE board exam patterns. For diagram questions, always include neat labels. For explain/describe questions, use the structure: Definition → Mechanism → Example → Significance.
10.1 — 1 Mark Questions (VSA)
1. Name the method of asexual reproduction used by Hydra.
2. What is the difference between binary fission in Amoeba and Leishmania?
3. Which part of the flower becomes the fruit after fertilisation?
4. Name the site of fertilisation in the human female.
5. What is the function of the placenta?
6. Name two sexually transmitted diseases caused by bacteria.
7. Which contraceptive method also protects against STDs?
8. What is double fertilisation? Name the organisms in which it occurs.
10.2 — 3 Mark Questions (SA)
9. Explain the process of vegetative propagation in plants. Give three examples with the plant part involved.
10. What is pollination? Distinguish between self-pollination and cross-pollination with two points each.
11. Draw a labelled diagram of the longitudinal section of a flower showing its reproductive parts.
12. Describe the path of sperm from the testes to the outside of the male body. Name the glands encountered and their secretions.
13. Explain the menstrual cycle. What happens to the endometrium if fertilisation does not occur?
14. Differentiate between asexual and sexual reproduction (any three points in tabular form).
10.3 — 5 Mark Questions (LA)
15. (a) Define asexual reproduction. Describe any four methods of asexual reproduction with examples and labelled diagrams where applicable. (b) State two advantages of asexual reproduction.
16. Describe the human female reproductive system with a labelled diagram. What happens when an egg released from the ovary is (i) fertilised, and (ii) not fertilised?
17. (a) Explain double fertilisation in flowering plants. Why is it significant? (b) What is the fate of the ovule and ovary after fertilisation? (c) Draw and label the structure of a typical angiosperm seed.
18. (a) What is reproductive health? Why is sex education important? (b) Describe any four methods of contraception with their mechanisms. (c) Name any three STDs and state one preventive measure for each.
19. Describe the process of sexual reproduction in flowering plants from pollination to seed formation. Include: types of pollination, the role of agents, the process of fertilisation, double fertilisation, and the development of seed and fruit.
Board Exam Strategy for How do Organisms Reproduce? 1. Learn the flower diagram cold — stigma, style, ovary, ovule, anther, filament, sepal, petal. 2. Ovule → Seed and Ovary → Fruit: this distinction appears in almost every paper. 3. Double fertilisation — know BOTH fusions and what each produces. Easy 2-mark question. 4. For asexual reproduction: memorise one organism example for each of the 7 methods. 5. Fertilisation = Fallopian tube. Implantation = Uterus. Don't swap these. 6. Testes outside body: always explain WHY (temperature requirement for sperm production). 7. For contraception: know the method, mechanism, and what it protects against. 8. HIV/AIDS: know what it is, how it's transmitted, and what it's NOT transmitted by. 9. 5-mark answers: Definition → Mechanism → Diagram → Example → Significance. 10. Comparison tables (asexual vs sexual, self vs cross pollination) are guaranteed marks. |
CBSE Class 10 Syllabus |
CBSE Class 10 Notes |
CBSE Class 10 Sample Papers |