TalentJR

How do Organisms Reproduce? – Class 10 Science Chapter 7 Notes & NCERT PDF

Class 10ScienceChapter 7NCERT book: Science - Class 10

Notes and a simple summary of Chapter 7 of the NCERT Class 10 Science book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

🎧 Listen to the content

Chapter 7: How do Organisms Reproduce?

Introduction

Organisms do not need reproduction to stay alive as individuals, yet species would disappear without it. The chapter asks why organisms reproduce and how. At the heart of reproduction is the copying of DNA — the information source for making proteins, which gives a body its design. Copies of DNA are never absolutely identical, so reproduction produces variations. Variations help populations survive changes in their surroundings (niches), which makes them the basis of evolution.

Key Concepts

1. Why variation matters

The chapter's example: if a population of bacteria lives in temperate water and the water temperature rises because of global warming, most bacteria may die — but a few variants that can resist heat will survive and grow. So variation is useful for the survival of species over time.

2. Modes of asexual reproduction (single parent)

  • Fission — unicellular organisms split into two (binary fission, e.g., Amoeba, Leishmania, where splitting happens along a definite plane related to the flagellum) or into many daughter cells at once (multiple fission, e.g., the malaria parasite Plasmodium).
  • Fragmentation — a simple multicellular organism breaks into pieces that each grow into new individuals, e.g., Spirogyra.
  • Regeneration — the ability of a fully differentiated organism to give rise to new individuals from its body parts, e.g., Hydra and Planaria; it is carried out by specialised cells that divide and form different cell types.
  • Budding — an outgrowth (bud) develops from the parent due to repeated cell division and detaches when mature, e.g., Hydra.
  • Vegetative propagation — new plants grow from roots, stems or leaves, e.g., layering and grafting in sugarcane, roses and grapes; buds on the leaf margin of *Bryophyllum* fall and grow into new plants. Advantages: plants that cannot produce seeds (banana, orange, rose, jasmine) can be grown, flowers and fruits come earlier, and all plants are genetically similar to the parent.
  • Spore formation — e.g., bread mould *Rhizopus*: thread-like hyphae carry sporangia containing spores; spores have thick walls that protect them until they reach a moist surface.

    • 3. Sexual reproduction — why?

    Combining DNA from two individuals creates new combinations of variations. If germ cells had the full amount of DNA, the amount would double each generation. So germ cells (gametes) have half the number of chromosomes, and fusion restores the number. Often one germ cell is large with food stores (female) and the other small and motile (male).

    4. Sexual reproduction in flowering plants

  • The flower's reproductive parts are the stamens (male; anthers produce pollen) and the pistil (female: ovary at the base, middle style, sticky stigma at the top). Flowers with only one of these are unisexual (papaya, watermelon); with both they are bisexual (hibiscus, mustard).
  • Pollination — transfer of pollen to the stigma: self-pollination (same flower) or cross-pollination (another flower), via wind, water or animals.
  • A pollen tube grows from the pollen grain through the style to the ovule; fertilisation forms a zygote. The ovule becomes a seed, the ovary becomes the fruit, and petals, sepals, stamens, style and stigma may shrivel and fall off.
  • The seed contains the future plant or embryo, which develops into a seedling under suitable conditions — germination (plumule = future shoot, radicle = future root).

    • 5. Reproduction in human beings

    Growth and sexual maturation happen together at puberty — changes include new hair growth, voice changes in boys, development of breasts in girls and start of menstruation. The chapter presents the systems factually:

  • Male reproductive system — sperm are formed in the testes, which lie outside the abdominal cavity in the scrotum because sperm formation needs a lower temperature. The testes also secrete testosterone. Sperm travel through the vas deferens, which unites with a tube from the urinary bladder; glands like the prostate and seminal vesicles add secretions.
  • Female reproductive system — eggs are made in the ovaries, which also produce hormones. One egg is released each month and travels through the oviduct (fallopian tube) to the uterus, which opens into the vagina through the cervix. Fertilisation takes place in the oviduct; the zygote divides to form an embryo, which is implanted in the uterine lining. The embryo gets nutrition from the mother's blood through the placenta, a disc with villi that provide a large surface for exchange of glucose, oxygen and wastes. Development takes about nine months.
  • When the egg is not fertilised — it lives for about one day. The thickened uterine lining is not needed, so it breaks down and comes out as blood and mucus — menstruation, roughly every month, lasting about two to eight days.

    • 6. Reproductive health

    The chapter stresses that sexual maturation does not mean the body or mind is ready for having children, and that young people face pressures from friends, families and society. Diseases can be sexually transmitted — bacterial (gonorrhoea, syphilis) and viral (warts, HIV-AIDS). Methods to avoid pregnancy include:

  • Mechanical barriers — condoms, which also reduce transmission of infections to some extent.
  • Hormonal pills — stop the release of eggs; may have side effects.
  • Devices in the uterus — loop or copper-T; may cause irritation.
  • Surgical methods — blocking the vas deferens or fallopian tube.

    • The book warns that illegal sex-selective abortion of female foetuses is harming the sex ratio; prenatal sex determination is prohibited by law, and a healthy society needs a balanced female-male ratio.

    Diagrams to Draw (described in words)

  • Binary fission in Amoeba and multiple fission in Plasmodium.
  • Budding in Hydra and regeneration in Planaria.
  • Spore formation in Rhizopus — hyphae with round sporangia at the tips.
  • Longitudinal section of a flower — sepals, petals, stamen (anther, filament), pistil (stigma, style, ovary with ovules).
  • Germination of pollen on stigma — pollen tube growing down to the ovule.
  • Germination of a seed (Bengal gram) — plumule, radicle, cotyledons.
  • Human male and female reproductive systems with the parts named above.

    • Activities in the Chapter

  • Activity 7.1 / 7.2 — Yeast in sugar solution observed under a microscope (budding) and mould growing on moist bread observed for a week.
  • Activity 7.3 — Permanent slides of Amoeba and of Amoeba showing binary fission.
  • Activity 7.4 — Filaments of Spirogyra from a green pond observed under a microscope.
  • Activity 7.6 — Money-plant cuttings with a leaf, and Bryophyllum leaf buds, grown to show vegetative propagation.
  • Activity 7.7 — Soaked Bengal gram (chana) seeds are cut open to identify the embryo parts.

    • Board Exam Focus

  • Importance of DNA copying and variation.
  • Differences between fission, fragmentation, regeneration, budding and spore formation — with examples.
  • Advantages of vegetative propagation.
  • Pollination vs fertilisation; post-fertilisation changes in a flower.
  • Role of placenta; why testes are in the scrotum; what happens if the egg is not fertilised.
  • Contraceptive methods and their categories; why prenatal sex determination is banned.

    • Key Terms

  • Variation (विभिन्नता) — small differences between offspring
  • Binary fission (द्विखंडन) — splitting into two
  • Multiple fission (बहुखंडन) — splitting into many
  • Regeneration (पुनरुद्भवन) — forming new organisms from body parts
  • Budding (मुकुलन) — growth of a new individual from a bud
  • Vegetative propagation (कायिक प्रवर्धन) — plants from roots, stems or leaves
  • Spore (बीजाणु) — reproductive body in Rhizopus
  • Pollination (परागण) — transfer of pollen to stigma
  • Fertilisation (निषेचन) — fusion of male and female gametes
  • Zygote (युग्मनज) — fertilised egg
  • Placenta (प्लेसेंटा/अपरा) — tissue that nourishes the embryo
  • Puberty (किशोरावस्था/यौवनारंभ) — period of sexual maturation
  • Menstruation (रजोधर्म/ऋतुस्राव) — monthly shedding of uterine lining
  • Contraception (गर्भनिरोधन) — methods to avoid pregnancy

    • Common Mistakes

  • Confusing regeneration (Planaria, from body pieces) with fragmentation (Spirogyra breaking up).
  • Saying fertilisation happens in the uterus — it happens in the oviduct.
  • Mixing up pollination (transfer of pollen) with fertilisation (fusion of gametes).
  • Writing that the ovule becomes the fruit — the ovule becomes the seed and the ovary becomes the fruit.
  • Forgetting that germ cells have half the chromosome number.

    • 💡 Key Learning Points

    • ✓Reproduction is based on DNA copying; small copying variations help species survive changes in their surroundings.
    • ✓Asexual modes — fission, fragmentation, regeneration, budding, vegetative propagation and spore formation — need a single parent.
    • ✓Sexual reproduction mixes DNA from two parents; germ cells carry half the chromosomes so the number stays constant.
    • ✓In flowers, pollination is followed by fertilisation; the ovule becomes the seed and the ovary becomes the fruit.
    • ✓Human reproduction involves puberty, fertilisation in the oviduct, nourishment through the placenta, and responsible reproductive health choices.

    👨‍🏫 Teaching Tips

    • →Start Activity 7.2 (mould on moist bread) a week early so students can compare observations day by day.
    • →Show permanent slides of Amoeba and Hydra, and let students sketch fission and budding.
    • →Bring a Bryophyllum leaf and a money-plant cutting to demonstrate vegetative propagation in class.
    • →Dissect a hibiscus flower in groups and label stamens and pistil on chart paper.
    • →Use Activity 7.7 (soaked chana seeds) to identify plumule, radicle and cotyledons.
    • →Teach the human reproduction section in a calm, factual, scientific tone and allow anonymous written questions.
    • →Connect the reproductive-health section to the law against prenatal sex determination and the sex ratio.

    📋 Assessment Questions

    1. Why is DNA copying essential in reproduction, and how do variations help a species?
    2. Distinguish between fission, fragmentation, regeneration and budding with one example each.
    3. What are the advantages of vegetative propagation?
    4. Describe the changes that take place in a flower after fertilisation.
    5. What is the role of the placenta? What happens when the egg is not fertilised?

    Ask the AI tutor about Class 10 Science Chapter 7

    Get question answers, important questions, a quick MCQ quiz or a simple explanation of “How do Organisms Reproduce?”. Free — sign in with Google.

    How the AI tutor works →

    👩‍🏫 Class 10 Science classes near you — online or at home

    Prefer a real teacher? TalentJR teachers take live online classes anywhere in India and visit homes in selected cities. Tell us what you need and our team will call you with timings and fees.

    • Live online classesSmall groups or 1:1 with a teacher, from home, any city.
    • Teacher at homeA TalentJR teacher visits your home (selected cities).
    • At a centreClasses at a TalentJR partner centre near you, where available.

    Keep learning

    All chapters in Science - Class 10

    1. 1. Chemical Reactions and Equations
    2. 2. Acids, Bases and Salts
    3. 3. Metals and Non-metals
    4. 4. Carbon and its Compounds
    5. 5. Life Processes
    6. 6. Control and Coordination
    7. 7. How do Organisms Reproduce?
    8. 8. Heredity
    9. 9. Light – Reflection and Refraction
    10. 10. The Human Eye and the Colourful World
    11. 11. Electricity
    12. 12. Magnetic Effects of Electric Current
    13. 13. Our Environment