Notes For All Chapters Science Class 10 CBSE
1. Introduction
Reproduction is not essential for the survival of an individual (unlike nutrition, respiration, excretion).
It ensures the continuation of species.
Organisms reproduce to create new individuals of the same kind.
Key Point: Reproduction is linked with the transfer of DNA (genetic information).
2. Do Organisms Create Exact Copies of Themselves?
Organisms look similar because of similar body designs.
DNA:
- Present in chromosomes in the nucleus.
- Carries information for inheritance.
- Provides instructions for making proteins.
DNA copying:
- Essential event in reproduction.
- Cell builds copies of DNA → divides into two cells.
Accuracy of DNA copying:
- Not 100% perfect.
- Small variations occur → some may be harmful, others useful.
Variation:
- Basis of evolution.
- Helps species survive when environment changes.
3. Modes of Reproduction in Organisms
3.1 Asexual Reproduction (single parent involved)
(a) Fission
- Common in unicellular organisms.
- Binary fission: Parent cell divides into two equal halves.
- Example: Amoeba (any plane), Leishmania (definite orientation due to flagellum).
- Multiple fission: Parent divides into many daughter cells.
- Example: Plasmodium (malarial parasite).
(b) Fragmentation
- Seen in simple multicellular organisms.
- Example: Spirogyra → body breaks into fragments → each fragment grows into new organism.
- Not possible in complex multicellular organisms because of organ-system level organisation.
(c) Regeneration
- Organisms regrow from body parts.
- Example: Hydra, Planaria.
- Requires special cells → divide and differentiate into tissues/organs.
- Note: Regeneration ≠ normal reproduction (organisms do not normally depend on being cut).
(d) Budding
- New organism grows as outgrowth (bud) from parent’s body.
- Example: Hydra, Yeast.
- Bud detaches when mature.
(e) Vegetative Propagation (plants)
- New plants from roots, stems, leaves.
- Examples: Bryophyllum (leaf buds), potato (tubers), sugarcane, rose, grape.
- Methods: layering, grafting, tissue culture.
- Advantages:
- Early flowering and fruiting.
- Seedless plants (banana, orange) can reproduce.
- Offspring genetically identical to parent.
(f) Spore Formation
- Example: Rhizopus (bread mould).
- Tiny blob-on-stick structures = sporangia.
- Sporangia contain spores → develop into new organisms.
- Spores protected by thick walls → survive harsh conditions.
3.2 Sexual Reproduction (two parents involved)
Importance
- Produces more variation than asexual reproduction.
- Variations improve chances of survival.
- Involves fusion of male and female gametes.
- Uses meiosis → gametes have half DNA → ensures stability of chromosome number.
4. Sexual Reproduction in Flowering Plants
Reproductive parts: Stamen (male) and Pistil (female).
Stamen: produces pollen grains (male gametes).
Pistil: ovary (contains ovules with egg cell), style, stigma.
Pollination:
- Self-pollination (same flower).
- Cross-pollination (different flowers).
- Agents: wind, water, animals.
Fertilisation:
- Pollen lands on stigma → pollen tube grows through style → reaches ovary.
- Male gamete fuses with egg cell → zygote.
After fertilisation:
- Zygote → embryo.
- Ovule → seed.
- Ovary → fruit.
- Other flower parts wither away.
Seed germination: Seed develops into seedling under suitable conditions.
5. Sexual Reproduction in Human Beings
5.1 Puberty
- Age when reproductive organs mature.
- Changes common to both: hair in armpits/genital area, oily skin, pimples.
- Girls: breast development, menstruation.
- Boys: facial hair, voice change, enlargement of penis/testes.
5.2 Male Reproductive System
- Testes: produce sperms + hormone testosterone.
- Scrotum: keeps testes at lower temperature for sperm production.
- Vas deferens: carries sperms.
- Seminal vesicle + Prostate gland: add fluid → semen (nutrition + easy transport).
- Urethra: common passage for urine and sperms.
- Sperm: head (DNA), tail (movement).
5.3 Female Reproductive System
- Ovaries: produce eggs + hormones.
- Oviducts (fallopian tubes): carry egg; site of fertilisation.
- Uterus: elastic sac where embryo develops.
- Vagina: receives sperms.
- Fertilisation: sperm + egg in fallopian tube → zygote → embryo → foetus.
- Placenta: tissue that connects mother and embryo → exchange of food, oxygen, waste.
- Pregnancy duration: ~9 months.
- Childbirth: uterus muscles contract → baby delivered.
5.4 Menstruation
If egg not fertilised:
- Uterus lining (thick, spongy, blood-rich) breaks.
- Discharged as blood and mucus → menstruation.
- Cycle ~28 days.
6. Reproductive Health
Sexually Transmitted Diseases (STDs):
- Bacterial: gonorrhoea, syphilis.
- Viral: HIV-AIDS, warts.
- Prevention: condoms.
Contraceptive methods:
- Barrier methods: Condoms.
- Hormonal methods: Oral pills.
- Intrauterine devices: Copper-T, loop.
- Surgical methods: Vasectomy (male), Tubectomy (female).
Population control: family planning needed for better living standards.
Sex ratio concern: female foeticide illegal → must be avoided.
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