Chapter 11 — Reproduction
Key Concepts Quick Recap
| Term | Definition |
|---|
| Asexual reproduction | Single parent; offspring genetically identical (clones) |
| Sexual reproduction | Two parents; gamete fusion; genetic variation |
| Parthenogenesis | Development of unfertilised egg |
| Oviparous | Egg-laying; development outside mother (birds, reptiles) |
| Viviparous | Live birth; development inside uterus (most mammals) |
| Ovoviviparous | Eggs retained inside; hatched internally (some sharks, snakes) |
| Spermatogenesis | Production of sperms in testis |
| Oogenesis | Production of eggs (ova) in ovary |
| External fertilisation | Gametes meet outside body (fish, frogs) |
| Internal fertilisation | Fertilisation inside female body (reptiles, birds, mammals) |
I. Choose the Best Answer (MCQs)
1. Budding as a mode of reproduction is seen in: (a) Amoeba (b) Hydra (c) Plasmodium (d) Planaria
Answer(b) Hydra Budding: a small outgrowth (bud) develops on parent → grows → detaches as new individual. Seen in Hydra, sponges, yeast. In Hydra, the bud forms on the body wall and eventually pinches off.
2. Binary fission occurs in: (a) Hydra (b) Starfish (c) Amoeba (d) Earthworm
Answer(c) Amoeba Binary fission: the organism splits into two equal halves, each forming a new individual. Seen in Amoeba, Paramoecium, many bacteria. Longitudinal binary fission: Euglena; transverse: Paramoecium.
3. Parthenogenesis in honeybees produces: (a) Workers (b) Queens (c) Drones (males) (d) Both queens and workers
Answer(c) Drones (males) In honeybees: drones (males) develop from unfertilised eggs (parthenogenesis — they are haploid, n). Workers and queens develop from fertilised eggs (diploid, 2n). This is called haplodiploidy. Parthenogenesis also seen in some lizards, wasps, aphids.
4. Sea urchins and frogs exhibit: (a) Internal fertilisation (b) External fertilisation (c) Parthenogenesis (d) Budding
Answer(b) External fertilisation External fertilisation: gametes released into water where fertilisation takes place. Seen in most fish, amphibians (frogs, toads), sea urchins. Disadvantage: low success rate → large numbers of gametes produced. Advantage: no need for copulation; possible in aquatic environment.
5. Which of the following is a viviparous animal? (a) Shark (b) Hen (c) Frog (d) Whale
Answer(d) Whale Whales are mammals → viviparous (young develop inside uterus, fed via placenta, born live). Hen and frog are oviparous. Most sharks are ovoviviparous; some are viviparous.
6. Regeneration — the ability to regrow lost body parts — is well-developed in: (a) Earthworm only (b) Starfish and Planaria (c) Cockroach (d) Snake
Answer(b) Starfish and Planaria Starfish (Asterias): a single arm can regenerate an entire starfish (if it contains part of the central disc). Planaria (flatworm): cut into pieces — each piece regenerates a whole organism. Hydra also shows good regeneration.
7. Gametogenesis refers to: (a) Fertilisation of gametes (b) Migration of gametes (c) Formation of gametes (d) Fusion of gametes
Answer(c) Formation of gametes Gametogenesis = formation of gametes.
Both involve meiosis to produce haploid gametes.
- Spermatogenesis: formation of sperms in testis (seminiferous tubules).
- Oogenesis: formation of ova (eggs) in ovary.
II. Short Answer Questions
Q1. Describe the types of asexual reproduction in animals with examples.
Answer
Asexual reproduction: single parent, no gamete formation, offspring genetically identical to parent (clones).
Types:
| Type | Process | Example |
|---|
| Binary fission | Parent divides into two equal individuals | Amoeba, Paramoecium |
| Budding | Small outgrowth forms, detaches | Hydra, Yeast |
| Fragmentation | Body breaks into pieces; each regenerates | Planaria, Spirogyra |
| Sporulation | Spores formed in sporangia | Plasmodium |
| Regeneration | Lost parts regrow to form new individual | Starfish, Hydra |
| Parthenogenesis | Unfertilised egg develops | Honeybee (drones), aphids |
Advantages of asexual reproduction:
- Fast; large numbers produced quickly.
- No need for mate.
- Identical offspring (good if parent is well-adapted).
Disadvantage: No genetic variation → susceptible to environmental change/disease.
Q2. Compare external and internal fertilisation.
Answer
| Feature | External Fertilisation | Internal Fertilisation |
|---|
| Site | Outside body (in water) | Inside female body |
| Animals | Fish, frogs, sea urchins | Reptiles, birds, mammals |
| Number of gametes | Very large (millions) | Fewer |
| Success rate | Low (many wasted) | Higher |
| Parental care | Usually less | Usually more |
| Environment | Aquatic | Terrestrial or aquatic |
Internal fertilisation is an adaptation to land — prevents gametes from drying out.
Common Mistakes
- Confusing regeneration (Planaria — full organism from fragment) with healing (just repair of wound).
- Saying drones develop from fertilised eggs — drones from UNFERTILISED eggs (parthenogenesis, haploid).
- Saying external fertilisation happens in terrestrial animals — it requires water medium.
- Confusing oviparous (egg-laying), viviparous (live birth), ovoviviparous (eggs retained internally).
Exam Checklist
- Binary fission: Amoeba; budding: Hydra; fragmentation: Planaria; parthenogenesis: honeybee drones.
- Oviparous: birds/reptiles; viviparous: mammals; ovoviviparous: some sharks/snakes.
- External fertilisation: fish, frogs (aquatic, many gametes); internal: reptiles, birds, mammals.
- Spermatogenesis (testis) + oogenesis (ovary) = gametogenesis → haploid gametes.
- Regeneration: starfish (arm → whole organism), Planaria (each piece → whole).
