CBSE Class 10 · Science · board exam 2027
Chapter 7: How do Organisms Reproduce? — notes
The chapter’s 11 parts in the book’s order — the first idea of each and the points Medha Ma’am writes on the board — and the summary at the end. The full lesson and a check question for each part are in the app.
1. Why reproduce: DNA copying and variation
First, a question.
- • Reproduction: producing new individuals of the same kind
- • Reproduction → continuity of the species
- • DNA in the nucleus = information for the body design
- • Basic event in reproduction: creating a DNA copy
- • DNA copy + additional cellular apparatus → two daughter cells
- • DNA copying is not perfectly accurate → slight variation
- • Example: bacteria in temperate water, temperature rises
- • Most die; heat-resistant variants survive
- • Variation → survival of the species over time
2. Asexual reproduction: fission
The first way is asexual reproduction.
- • Asexual reproduction: a single parent, no gametes
- • Fission: the single cell divides
- • Binary fission: one cell → two daughter cells
- • Amoeba: division in any plane
- • Leishmania (kala-azar): flagellum at one end
- • Binary fission in a definite plane
- • Multiple fission: one cell → many daughter cells at once
- • Example: Plasmodium (malarial parasite)
3. Fragmentation and regeneration
Many-celled organisms with a simple body.
- • Fragmentation: the mature organism breaks into fragments
- • Each fragment → a new individual (e.g. Spirogyra)
- • Regeneration: a cut piece grows into a complete organism
- • e.g. Hydra, Planaria
- • Specialised cells → proliferate → many cells → tissues (development)
- • | Fragmentation | Regeneration |
- • | breaks up on its own on maturing | a piece cut by accident |
- • | simple body, no specialised cells | specialised cells rebuild the body |
- • | e.g. Spirogyra | e.g. Hydra, Planaria |
4. Budding and spore formation
Hydra has a second way.
- • Budding: repeated cell division at one site → outgrowth (bud)
- • Bud → tiny individual → detaches → independent organism
- • e.g. Hydra, yeast
- • Rhizopus: hyphae, sporangium, spores
- • Spore: thick protective wall
- • On a moist surface: spore → germinates → new individual
5. Vegetative propagation
Plants.
- • Vegetative propagation: root, stem or leaf → new plant (asexual)
- • Methods: layering, grafting (and cutting)
- • Sugarcane, roses, grapes; potato, money-plant → stem
- • Bryophyllum: buds in the notches of the leaf margin → new plants
- • Advantages:
- • ① flowers and fruits earlier than from seeds
- • ② plants that have lost seeds can be grown (banana, orange, rose, jasmine)
- • ③ all plants genetically similar to the parent
- • Disadvantage: no variation → all may be wiped out together
6. Sexual reproduction: why two parents, and half the chromosomes
The second way, sexual reproduction.
- • Sexual reproduction: two individuals (male and female)
- • DNA of two individuals → new combinations of variation
- • Sexual reproduction → more variation → evolution
- • Gametes (by meiosis): half the chromosomes and half the DNA of a body cell
- • Body cell: 23 pairs = 23 × 2 = 46 chromosomes
- • Gamete: 46/2 = 23
- • Sperm + egg → zygote: 23 + 23 = 46
7. Sexual reproduction in flowering plants: the flower and pollination
The flower.
- • Parts of a flower: sepals, petals, stamens, pistil
- • Stamen (male) = filament + anther → pollen grains
- • Pistil (female) = stigma + style + ovary
- • Ovary → ovules → egg cell
- • Sepals: protect the bud; petals: attract insects
- • Bisexual flower: stamens + pistil (Hibiscus, mustard)
- • Unisexual flower: only one (papaya, watermelon)
- • Pollination: transfer of pollen from the anther to the stigma
- • | Self-pollination | Cross-pollination |
- • | same flower or same plant | flower of another plant, same species |
- • | no new variation | by wind, water, insects, birds; brings variation |
8. Fertilisation, seed, fruit and germination
The pollen grain has reached the stigma.
- • Pollen grain → pollen tube → style → ovule
- • Fertilisation: male gamete + female gamete → zygote
- • Zygote → embryo
- • Ovule → seed
- • Ovary → fruit
- • Sepals, petals, stamens, style, stigma → shrivel and fall off
- • Seed coat: protection; cotyledon: stored food
- • Plumule → future shoot; radicle → future root
- • Germination: seed → seedling
9. Human reproduction: puberty and the male system
Human beings.
- • Puberty: the period in adolescence when the reproductive tissues begin to mature
- • Both: hair in armpits and genital area, oily skin, pimples
- • | Girls | Boys |
- • | breast size increases | thick hair on the face |
- • | menstruation begins | voice begins to crack |
- • Testes: form sperms + secrete testosterone
- • In the scrotum, outside the abdomen: lower temperature for sperms
- • Testes → vas deferens → urethra → out through the penis
- • Seminal vesicles, prostate: secretions → easy transport + nutrition
- • Sperm: long tail → swims towards the egg
10. The female system, fertilisation and the placenta
The female reproductive system.
- • Ovaries: make eggs + hormones
- • One egg released every month by one ovary
- • Ovary → oviduct (fallopian tube) → uterus → cervix → vagina
- • Fertilisation: in the oviduct
- • Zygote → embryo → implanted in the uterine lining
- • Embryo develops in the uterus
- • Placenta: disc in the uterine wall; villi → large surface area
- • Mother → embryo: glucose, oxygen; embryo → mother: wastes
- • No fertilisation → the thick uterine lining breaks down
- • Blood + mucus out = menstruation, roughly every month
11. Reproductive health: diseases and contraception
Something important, listen carefully.
- • Sexually transmitted diseases:
- • bacterial: gonorrhoea, syphilis
- • viral: warts, HIV-AIDS
- • Methods of contraception:
- • ① mechanical barrier: condom, coverings in the vagina → sperm cannot reach the egg
- • ② oral pills: change the hormonal balance → no egg released
- • ③ loop or copper-T in the uterus (may irritate the uterus)
- • ④ surgical: vas deferens blocked (male), fallopian tube blocked (female)
- • → no fertilisation
- • Female foeticide: illegal; keep a healthy sex ratio
Summary
Very good! You learnt a lot today, so let us revise it once together. The basic event of reproduction is DNA copying, which is never perfectly accurate, so variation comes, and variation helps the species survive. Asexual reproduction needs one parent: binary and multiple fission, fragmentation, regeneration, budding, spore formation and vegetative propagation. Sexual reproduction needs two parents. Gametes carry half the chromosomes, and the zygote gets the full number back. In the flower, pollination, then fertilisation, then the ovule becomes the seed and the ovary the fruit. In human beings, puberty, the male and female systems, fertilisation in the oviduct, nutrition through the placenta, and the methods of contraception. Here is your homework. Draw the section of a flower, the germination of pollen on the stigma, budding in Hydra and the human male and female systems, labelled, once without looking. The board asks them again and again. If anything was not clear, press the Ask button and ask me. Done, you worked very well today!
AskMedha · Medha Ma’am — CBSE Class 10 Science, Chapter 7. Written from the textbook, checked twice.
Questions parents and students ask
- How do I get the "How do Organisms Reproduce?" notes as a PDF?
- Press "Save as PDF" — the phone’s print sheet opens; choose "Save as PDF" there. The PDF holds the notes only.
- Where are these notes written from?
- From the chapter’s own textbook text, part by part, in the book’s own terms; a second, independent model then checked every part against the book. The full lesson, a check question for each part and the practice are in the AskMedha app.
The same preparation, with Medha Ma’am — on your phone
Every question of every chapter with its model answer, practice questions in the board’s own shapes, 60 minutes of class a day, written answers marked, a test every Sunday and a WhatsApp report to parents.
Medha Ma’am is an AI teacher, not a live tutor. Every answer is checked twice; a person takes responsibility.