Why is Reproduction Important?
Reproduction is the biological process by which organisms produce new individuals of the same species. It ensures:
- Continuity of the species
- Transfer of genetic information to offspring
- Evolution through variation (in sexual reproduction)
Asexual Reproduction
In asexual reproduction, only one parent is involved. Offspring are genetically identical to the parent (clones).
1. Binary Fission
The parent organism divides into two equal halves, each becoming a new individual.
- Amoeba: The cell divides in any plane
- Paramecium: Division along a definite plane
- Bacteria: Very rapid; can divide every 20 minutes
2. Multiple Fission
The parent nucleus divides repeatedly and then the cell divides into many daughter cells simultaneously.
- Example: Plasmodium (malaria parasite) — divides into many new parasites inside RBCs
3. Budding
A small outgrowth (bud) develops on the parent, grows, and detaches to form a new organism.
- Hydra: A bud develops on the side, grows tentacles, and eventually breaks off
- Yeast: A small bud forms, grows, and separates (or a chain of buds may form)
4. Spore Formation
The organism produces spores — tiny, light, protected reproductive units that germinate when conditions are favourable.
- Example: Rhizopus (bread mould) — black dot-like sporangia burst open, releasing hundreds of spores
5. Regeneration
The ability to regrow a complete organism from a part of the body.
- Example: Planaria (flatworm) — even a small piece can grow into a complete organism
- Example: Hydra — can regenerate lost body parts
6. Vegetative Propagation (in Plants)
New plants grow from vegetative parts (root, stem, leaf) of the parent plant.
| Part used | Example |
|---|---|
| Stem (underground) | Potato (tuber), Ginger (rhizome), Onion (bulb) |
| Stem (runners) | Mint, Strawberry |
| Leaf | Bryophyllum (buds on leaf margins) |
| Root | Sweet potato, Dahlia |
Artificial vegetative propagation methods:
- Cutting: A stem cutting is planted — roses, sugarcane
- Grafting: A shoot (scion) from one plant joined to the rooted part (stock) of another — mango, apple
- Layering: A stem branch is bent to touch the soil and covered until roots develop, then cut — jasmine, strawberry
Sexual Reproduction in Flowering Plants
Parts of a Flower
| Part | Function |
|---|---|
| Sepal | Protects flower bud |
| Petal | Attracts pollinators |
| Stamen | Male reproductive organ (anther + filament) |
| Pistil/Carpel | Female reproductive organ (stigma + style + ovary) |
| Ovary | Contains ovules; develops into fruit after fertilisation |
| Ovule | Contains egg cell; develops into seed after fertilisation |
Pollination
Transfer of pollen grains from anther to stigma.
| Type | Description | Agents |
|---|---|---|
| Self-pollination | Within same flower or same plant | — |
| Cross-pollination | Between two different plants of same species | Wind, insects, water, birds |
Fertilisation in Plants
1. Pollen grain lands on stigma 2. Pollen tube grows down through style into ovary 3. Male gamete (sperm) travels through pollen tube 4. Male gamete fuses with egg cell in ovule → zygote (fertilisation) 5. Double fertilisation (unique to flowering plants): One sperm fuses with egg → zygote; another sperm fuses with polar nuclei → endosperm (food for developing seed)
After fertilisation:
- Ovule → Seed (contains embryo)
- Ovary → Fruit (protects seed)
Sexual Reproduction in Humans
Male Reproductive System
| Part | Function |
|---|---|
| Testes | Produce sperms; secrete testosterone |
| Epididymis | Storage and maturation of sperms |
| Vas deferens | Carries sperms to urethra |
| Seminal vesicles, Prostate, Cowper's gland | Secrete fluids that form semen |
| Urethra | Carries semen out of body |
| Penis | Organ for transfer of semen |
Testes are located in scrotum (outside body cavity) because sperm production requires slightly lower temperature than body temperature (~2–3°C lower).
Female Reproductive System
| Part | Function |
|---|---|
| Ovaries | Produce eggs (ova); secrete oestrogen, progesterone |
| Fallopian tubes (oviducts) | Carry egg from ovary to uterus; fertilisation occurs here |
| Uterus (womb) | Where embryo implants and develops during pregnancy |
| Cervix | Lower part of uterus; opens into vagina |
| Vagina | Birth canal; receives semen during intercourse |
Fertilisation in Humans
1. Ovum released from ovary (ovulation) travels into Fallopian tube 2. Sperm travels from vagina → uterus → Fallopian tube 3. One sperm fuses with egg in Fallopian tube → zygote 4. Zygote divides and moves toward uterus 5. Implantation: Embryo embeds in uterus lining 6. Placenta forms → connects embryo to mother's blood supply 7. Development continues for ~9 months (gestation period)
Placenta
- Disc-shaped tissue embedded in uterus wall
- Connected to embryo via umbilical cord
- Functions:
- Supplies O₂ and nutrients from mother to embryo
- Removes CO₂ and waste from embryo to mother
- Secretes hormones (HCG, progesterone) to maintain pregnancy
- Acts as a barrier (though some viruses like HIV can cross)
Menstrual Cycle
- Duration: ~28 days
- Day 1–5: Menstruation (shedding of uterus lining if no fertilisation)
- Day 6–13: Follicular phase (egg matures; oestrogen rises; uterus lining thickens)
- Day 14: Ovulation (egg released)
- Day 15–28: Luteal phase (progesterone rises; uterus stays thick, ready for implantation)
- If no fertilisation: progesterone falls → menstruation begins again
Reproductive Health
Contraception Methods
| Method | Type | Examples |
|---|---|---|
| Barrier | Prevents sperm from reaching egg | Condoms (also prevents STIs), diaphragm |
| Hormonal | Prevents ovulation | Oral contraceptive pills, injection |
| Intrauterine | Prevents implantation | IUD (copper-T) |
| Surgical | Permanent | Vasectomy (male), Tubectomy (female) |
Sexually Transmitted Infections (STIs)
- HIV/AIDS, Gonorrhoea, Syphilis, Herpes, Hepatitis B, Warts
- Spread by unprotected sexual contact, contaminated blood, shared needles
- Prevention: Condoms, testing, sterile needles, faithful partnerships
Board Exam Tips
- 8–10 marks from this chapter
- Flower diagram — fully labelled flower is frequently asked (3–5 marks)
- Know the difference between self-pollination and cross-pollination
- Double fertilisation in flowering plants — often 2 marks
- Human male/female reproductive system diagrams with functions
- Placenta functions — common 3-mark question
- All asexual reproduction modes with one example each (table format)
- STI prevention — always mention condoms as the method that prevents BOTH pregnancy AND STIs
📚 Lakhmir Singh Science Class 10 — Reproduction Chapter Solutions
📝 Oswaal CBSE Question Bank — Chapter 7 Board Questions
NCERT Exercise Solutions
Intext Questions
Page 128, Q1: What is the importance of variation in a species?
Without variation, all members of a species would be identical, and a single disease or environmental change could wipe out the entire population.
Page 133, Q2: Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
- Their cells are less specialised (less differentiated)
- Simple body organisation means each part can regenerate the whole
In complex organisms (like humans), cells are highly differentiated (specialized for specific functions — nerve cells, muscle cells). These specialized cells cannot de-differentiate and grow into a completely new organism. Also, the body plan of complex organisms is far more intricate — recreating the entire organization from a body part is not possible with existing cellular machinery.
Chapter-End Exercise
Q1. How does binary fission differ from multiple fission?
| Feature | Binary fission | Multiple fission |
|---|---|---|
| Number of offspring | 2 | Many (multiple) |
| Nuclear divisions | 1 | Many simultaneous |
| Cytoplasm division | After 1 nuclear division | After multiple nuclear divisions |
| Example | Amoeba, bacteria | Plasmodium (malarial parasite) |
| Conditions | Normal conditions | Often during adverse conditions |
In binary fission, the nucleus divides once → cytoplasm splits into 2. In multiple fission, the nucleus divides repeatedly, many daughter nuclei form → each gets surrounded by cytoplasm → many offspring released simultaneously (e.g., from a cyst).
Q2. How does the process of sexual reproduction lead to more variation than asexual reproduction?
In sexual reproduction: 1. Meiosis (formation of gametes) creates variation through crossing over and independent assortment of chromosomes 2. Fertilisation combines genetic material from two different parents 3. Each offspring receives a unique combination of genes from both parents 4. This results in much greater genetic diversity among offspring
Greater variation → better chance of surviving environmental changes → evolutionary advantage.
Q3. What are the advantages of sexual reproduction over asexual reproduction?
Disadvantages: Requires finding a mate; slower process; less efficient for population growth.
Q4. What does the term 'double fertilisation' refer to in flowering plants?
This is called double fertilisation — it is unique to angiosperms (flowering plants). It ensures that the endosperm (food reserve) develops only when fertilisation occurs, preventing wastage of resources.
Q5. Mention the steps involved in sexual reproduction in flowering plants.
Q6. What are the different methods of contraception? Name one example for each.
| Category | Method | Example |
|---|---|---|
| Barrier | Prevents sperm meeting egg | Condom, diaphragm |
| Chemical | Hormones to prevent ovulation | Oral contraceptive pills |
| Intrauterine | Device in uterus prevents implantation | Copper-T, IUD |
| Surgical | Permanent — tubes cut/tied | Vasectomy (male), Tubectomy (female) |
| Natural | Avoiding intercourse during fertile days | Rhythm method |
Condoms also provide protection against STDs (sexually transmitted diseases) — important additional benefit.