Class 12 Biology Chapter 1 Question Answer | Reproduction in Organisms | English Medium

Class 12 Biology Chapter 1 Question Answer | Reproduction in Organisms | English Medium | ASSEB

Reproduction in Organisms

Welcome to HSLC Guru! In this lesson on Chapter 1 — Reproduction in Organisms (ASSEB Class 12 Biology), we explore how living organisms produce offspring of their own kind to ensure the continuity of species. The chapter covers the meaning and significance of reproduction, the lifespan of organisms, the two broad modes of reproduction (asexual and sexual), and the events occurring before and after fertilisation. This complete guide includes a clear summary, board-style questions and answers, MCQs, fill in the blanks, true or false statements, and a glossary table — all aligned to the ASSEB syllabus and exam pattern.

Summary

Meaning and Importance of Reproduction: Reproduction is a biological process in which an organism produces young ones (offspring) similar to itself. It is one of the most important characteristics of life because it ensures the continuity of species generation after generation. Without reproduction, life on Earth would come to an end. Reproduction also helps in introducing variations in offspring, which provides the raw material for evolution and adaptation to changing environmental conditions. Every organism, whether unicellular or multicellular, plant or animal, possesses some mechanism of reproduction.

Lifespan: The period from birth till the natural death of an organism is called its lifespan. Lifespans of different organisms vary greatly — a mayfly lives only for a day, while a tortoise may live for 100–150 years and certain trees like the banyan or sequoia live for thousands of years. Lifespan is not directly related to body size; for example, a crow lives much longer than an elephant in proportion to size. Whatever the lifespan, every organism must reproduce before death so that the species continues.

Types of Reproduction — Asexual: When a single parent produces offspring without the formation and fusion of gametes, it is called asexual reproduction. The offspring are genetically identical to the parent and are called clones. Common methods include binary fission (Amoeba, Paramecium), budding (Hydra, yeast), fragmentation (Spirogyra, Planaria), gemmule formation (sponges), conidia (Penicillium), and zoospores (Chlamydomonas, algae). In flowering plants, vegetative propagation is widespread through specialised structures such as runners (grass, strawberry), rhizomes (ginger, turmeric), suckers (mint, banana), tubers (potato — eyes), offsets (Pistia, Eichhornia / water hyacinth), and bulbs (onion, garlic). Vegetative propagation is rapid, true to type and useful in horticulture.

Sexual Reproduction and Fertilisation Events: Sexual reproduction involves two parents and the fusion of male and female gametes. It is divided into three phases — pre-fertilisation, fertilisation and post-fertilisation. Pre-fertilisation events include gametogenesis (formation of haploid gametes by meiosis) and gamete transfer. When the two gametes are morphologically similar they are called homogametes (isogametes), and when they are dissimilar they are called heterogametes (e.g., sperm and egg). Fertilisation is the fusion of male and female gametes (syngamy) to form a diploid zygote. It may be external (in water — fishes, frogs) or internal (inside the female body — reptiles, birds, mammals, most flowering plants). Post-fertilisation events begin with the formation of the zygote, which divides repeatedly through mitosis (embryogenesis) to form an embryo. In oviparous animals the embryo develops inside an egg laid outside the body, while in viviparous animals it develops inside the mother. In flowering plants, the zygote develops into the embryo within the seed and the ovary matures into the fruit.

Very Short Answer Type Questions (1 Mark)

Q1. Define reproduction.

Answer: Reproduction is a biological process in which an organism produces young ones (offspring) similar to itself, ensuring the continuity of the species.

Q2. What is meant by lifespan?

Answer: The period from the birth of an organism until its natural death is called its lifespan.

Q3. Name the type of reproduction in Amoeba.

Answer: Amoeba reproduces by binary fission, a type of asexual reproduction.

Q4. What are clones?

Answer: Offspring that are morphologically and genetically identical to their parent, produced by asexual reproduction, are called clones.

Q5. Define syngamy.

Answer: The fusion of a male gamete with a female gamete to form a diploid zygote is called syngamy or fertilisation.

Q6. Give one example of an organism showing external fertilisation.

Answer: Frog (bony fishes, starfish) shows external fertilisation in water.

Q7. What are gemmules?

Answer: Gemmules are internal buds produced by sponges that help in asexual reproduction during unfavourable conditions.

Q8. Name the vegetative propagule of potato.

Answer: The eyes of the tuber serve as the vegetative propagule of potato.

Q9. Define gametogenesis.

Answer: Gametogenesis is the process of formation of two types of haploid gametes (male and female) in an organism.

Q10. What is a zygote?

Answer: A zygote is the diploid cell formed by the fusion of male and female gametes during fertilisation; it develops into a new organism.

Q11. Define embryogenesis.

Answer: Embryogenesis is the process of development of an embryo from the zygote through repeated mitotic divisions and cell differentiation.

Q12. Name the propagule of Bryophyllum.

Answer: Adventitious leaf buds (epiphyllous buds) borne on the leaf margins of Bryophyllum serve as the vegetative propagule.

Short Answer Type Questions (2–3 Marks)

Q1. Differentiate between asexual and sexual reproduction.

Answer: Asexual reproduction involves only one parent, no gametes are formed, no fusion occurs, and offspring are genetically identical clones. Sexual reproduction involves two parents, formation and fusion of gametes (syngamy), and offspring show genetic variation. Asexual is faster while sexual reproduction promotes variation and evolution.

Q2. Distinguish between homogametes and heterogametes with examples.

Answer: Homogametes (isogametes) are gametes that look morphologically similar and cannot be classified as male or female (e.g., Cladophora, some algae). Heterogametes are morphologically distinct gametes — a small motile male gamete (sperm/antherozoid) and a large non-motile female gamete (egg/ovum). Examples: humans, Fucus, flowering plants.

Q3. Differentiate between external and internal fertilisation.

Answer: In external fertilisation, fusion of gametes occurs outside the body of the organism, usually in water (e.g., fish, frog); large numbers of gametes are released. In internal fertilisation, fusion occurs inside the female body (e.g., reptiles, birds, mammals, flowering plants); the number of eggs produced is small but chances of survival of zygote are higher.

Q4. What is vegetative propagation? Give four examples with their propagules.

Answer: Vegetative propagation is a type of asexual reproduction in plants in which new individuals develop from vegetative parts (root, stem, leaf) without the formation of seeds. Examples — (i) Potato — eye of the tuber, (ii) Ginger — rhizome, (iii) Onion — bulb, (iv) Bryophyllum — leaf buds (also strawberry — runner; banana — sucker).

Q5. Why is sexual reproduction considered better than asexual reproduction?

Answer: Sexual reproduction involves the fusion of gametes from two parents, leading to genetic recombination and variation among offspring. These variations help organisms to adapt to changing environments, resist diseases and provide raw material for evolution and natural selection. Asexual reproduction produces identical clones with little scope for adaptation.

Q6. Define oviparous and viviparous animals with examples.

Answer: Oviparous animals are those that lay fertilised or unfertilised eggs outside the body, and the embryo develops inside the egg (e.g., birds, reptiles, frogs). Viviparous animals are those in which the embryo develops inside the mother’s body and the young one is born alive (e.g., humans, cow, dog). Viviparity provides better protection and survival for the offspring.

Q7. What is parthenogenesis? Give two examples.

Answer: Parthenogenesis is the development of a new individual from an unfertilised egg without fusion of gametes. Examples — drones (male honeybees) develop from unfertilised eggs of the queen bee; rotifers and some lizards (Whiptail lizard) also reproduce by parthenogenesis.

Long Answer Type Questions (5–7 Marks)

Q1. Explain various methods of asexual reproduction with suitable examples.

Answer: Asexual reproduction is the formation of new individuals from a single parent without involving the fusion of gametes. The chief methods are:

Binary fission: The parent cell divides into two equal halves, each becoming a new individual. Example — Amoeba, Paramecium, bacteria.
Budding: A small outgrowth (bud) develops on the parent body, grows, and detaches as a new individual. Example — Hydra, yeast.
Fragmentation: The body of the parent breaks into several pieces, each of which grows into a new individual. Example — Spirogyra, Planaria.
Gemmule formation: Internal buds with food reserves produced by sponges develop into new individuals during favourable conditions.
Conidia: Non-motile asexual spores formed exogenously on conidiophores. Example — Penicillium, Aspergillus.
Zoospores: Motile, flagellated asexual spores formed in aquatic algae. Example — Chlamydomonas, Ulothrix.
Vegetative propagation: In higher plants, new plants arise from vegetative parts such as runners (grass), rhizomes (ginger), suckers (mint), tubers (potato), offsets (water hyacinth) and bulbs (onion).

Q2. Describe in detail the pre-fertilisation events in sexual reproduction.

Answer: Pre-fertilisation events include all the changes that take place before the fusion of gametes. The two main events are gametogenesis and gamete transfer.

Gametogenesis: It is the process of formation of haploid gametes by meiosis. The male gametes are called sperms/antherozoids and the female gametes are called ova/eggs. Based on morphology, gametes may be homogametes (similar, e.g., Cladophora) or heterogametes (dissimilar, e.g., humans, angiosperms).
Sex of organisms: Plants may be bisexual (hermaphrodite/monoecious — Chara, mustard) or unisexual (dioecious — papaya, marchantia). Among animals, earthworms and sponges are bisexual while cockroach and humans are unisexual.
Gamete transfer: After formation, gametes must be brought together for fertilisation. In most organisms, the male gamete is motile and the female gamete is stationary. In algae, bryophytes and pteridophytes water is the medium of transfer. In flowering plants pollination transfers pollen from anther to stigma. In animals, mating brings the gametes together.

Q3. Explain fertilisation. Differentiate between external and internal fertilisation with examples.

Answer: Fertilisation, also known as syngamy, is the process of fusion of a haploid male gamete with a haploid female gamete to form a diploid zygote. It restores the diploid number of chromosomes and is the most vital event of sexual reproduction.

External fertilisation: Fusion of gametes occurs outside the body of the organism, usually in water. Both parents release a large number of gametes into water. Examples — bony fishes, frogs, starfish, most algae and bryophytes. Disadvantages: many gametes wasted, offspring exposed to predators.
Internal fertilisation: Fusion of gametes occurs inside the female body. Male gamete is motile and seeks the egg. Number of eggs produced is small but chances of survival are very high because the embryo is protected. Examples — reptiles, birds, mammals, higher plants (angiosperms, gymnosperms), bryophytes/pteridophytes (where archegonium retains the egg).

In some organisms, fertilisation does not take place yet the female gamete develops into a new individual; this is called parthenogenesis (e.g., honeybee drones, rotifers, some lizards).

Q4. Describe the post-fertilisation events in sexual reproduction.

Answer: Post-fertilisation events include all changes from the formation of zygote to the development of mature offspring.

Zygote formation: The diploid zygote formed after syngamy is the vital link that ensures continuity of species. Every sexually reproducing organism begins life as a single-celled zygote.
Embryogenesis: The zygote undergoes repeated mitotic divisions and cell differentiation to develop into an embryo. Cells divide to increase the number, and differentiate to form specialised tissues and organs.
Development in animals: Oviparous animals (reptiles, birds) lay fertilised eggs covered by hard shells in safe places; the embryo develops inside the egg using stored yolk and finally hatches as a young one. Viviparous animals (mammals including humans) retain the embryo inside the uterus where it gets nourishment through the placenta and is born as a young one — providing greater protection and higher survival.
Development in plants: After fertilisation in flowering plants, the zygote inside the ovule develops into the embryo. The ovule matures into a seed and the ovary develops into the fruit. The fruit protects the seeds and helps in their dispersal, ensuring the next generation.

Q5. Discuss the importance of reproduction. Why is variation important in offspring produced by sexual reproduction?

Answer: Importance of reproduction:

It ensures the continuity of species generation after generation.
It replaces individuals lost due to natural death, accidents, or predation.
It maintains a balance in the population of various species in nature.
It introduces variations in offspring (sexual reproduction), forming the basis of evolution.
It is exploited by humans for agriculture, horticulture, animal husbandry and biotechnology.

Importance of variation: Variations arising from sexual reproduction help individuals to adapt to changing environments, withstand diseases, and survive natural calamities. They provide the raw material on which natural selection acts, leading to the evolution of better-adapted species. Without variation, all individuals would be identical, and a single unfavourable change could wipe out the entire population.

Multiple Choice Questions (MCQs)

Q1. The mode of reproduction in Amoeba is —
(a) Budding (b) Binary fission (c) Fragmentation (d) Conidia
Answer: (b) Binary fission

Q2. Vegetative propagule of ginger is —
(a) Tuber (b) Bulb (c) Rhizome (d) Sucker
Answer: (c) Rhizome

Q3. Fusion of male and female gametes is called —
(a) Mitosis (b) Meiosis (c) Syngamy (d) Cleavage
Answer: (c) Syngamy

Q4. Hydra reproduces asexually by —
(a) Fragmentation (b) Budding (c) Binary fission (d) Spore formation
Answer: (b) Budding

Q5. Gemmules are formed in —
(a) Hydra (b) Sponges (c) Yeast (d) Planaria
Answer: (b) Sponges

Q6. Which of the following shows external fertilisation?
(a) Birds (b) Mammals (c) Frog (d) Reptiles
Answer: (c) Frog

Q7. Conidia are produced in —
(a) Penicillium (b) Chlamydomonas (c) Spirogyra (d) Yeast
Answer: (a) Penicillium

Q8. Offspring produced by asexual reproduction are called —
(a) Hybrids (b) Clones (c) Variants (d) Mutants
Answer: (b) Clones

Q9. Which of the following is a viviparous animal?
(a) Hen (b) Snake (c) Cow (d) Frog
Answer: (c) Cow

Q10. The eye of potato is a —
(a) Bulb (b) Rhizome (c) Sucker (d) Tuber bud
Answer: (d) Tuber bud

Q11. Drones in honeybees develop by —
(a) Syngamy (b) Parthenogenesis (c) Budding (d) Fragmentation
Answer: (b) Parthenogenesis

Q12. Vegetative propagule of onion is —
(a) Tuber (b) Rhizome (c) Bulb (d) Runner
Answer: (c) Bulb

Q13. Eichhornia (water hyacinth) propagates by —
(a) Tuber (b) Bulb (c) Offset (d) Conidia
Answer: (c) Offset

Fill in the Blanks

Q1. The period from birth to natural death of an organism is called its __________.
Answer: lifespan

Q2. __________ are the motile asexual spores produced by Chlamydomonas.
Answer: Zoospores

Q3. The fusion of male and female gametes is called __________.
Answer: syngamy / fertilisation

Q4. When gametes are morphologically similar they are called __________.
Answer: homogametes (isogametes)

Q5. The diploid cell formed after fertilisation is called the __________.
Answer: zygote

Q6. The development of an embryo from a zygote is called __________.
Answer: embryogenesis

Q7. Animals that give birth to young ones are called __________.
Answer: viviparous

True or False

Q1. Asexual reproduction always involves the fusion of gametes.
Answer: False

Q2. Yeast reproduces by budding.
Answer: True

Q3. Birds are oviparous animals.
Answer: True

Q4. Internal fertilisation occurs in fishes.
Answer: False

Q5. Sexual reproduction introduces variations in offspring.
Answer: True

Q6. Conidia are motile spores produced in algae.
Answer: False

Q7. Vegetative propagation produces clones.
Answer: True

Q8. Parthenogenesis involves the fusion of two gametes.
Answer: False

Glossary

Term	Meaning
Reproduction	Biological process of producing young ones similar to the parent.
Lifespan	Period from birth to natural death of an organism.
Asexual reproduction	Reproduction by a single parent without fusion of gametes; offspring are clones.
Sexual reproduction	Reproduction involving two parents and fusion of male and female gametes.
Binary fission	Division of parent cell into two equal halves; e.g., Amoeba.
Budding	A small outgrowth on the parent develops into a new individual; e.g., Hydra, yeast.
Fragmentation	Body of parent breaks into pieces, each forming a new organism; e.g., Spirogyra.
Gemmule	Internal bud produced by sponges for asexual reproduction.
Conidia	Non-motile asexual spores formed on conidiophores; e.g., Penicillium.
Zoospore	Motile, flagellated asexual spore in aquatic algae; e.g., Chlamydomonas.
Vegetative propagation	Asexual reproduction in plants from vegetative parts like root, stem and leaf.
Runner	Sub-aerial weak stem propagule; e.g., grass, strawberry.
Rhizome	Underground horizontal stem; e.g., ginger, turmeric.
Sucker	Lateral underground branch growing into a new shoot; e.g., mint, banana.
Tuber	Swollen underground stem bearing eyes/buds; e.g., potato.
Offset	Short, thick lateral branch in aquatic plants; e.g., Pistia, Eichhornia.
Bulb	Underground modified stem with fleshy scales; e.g., onion, garlic.
Gametogenesis	Process of formation of haploid male and female gametes.
Homogametes	Gametes that are morphologically similar (isogametes).
Heterogametes	Gametes that are morphologically different — sperm and egg.
Syngamy	Fusion of male and female gametes to form a diploid zygote.
External fertilisation	Fusion of gametes outside the body, usually in water; e.g., frog, fish.
Internal fertilisation	Fusion of gametes inside the female body; e.g., birds, mammals.
Zygote	Diploid cell formed by fertilisation; develops into an embryo.
Embryogenesis	Development of embryo from zygote by mitotic divisions and differentiation.
Oviparous	Animals that lay eggs; embryo develops outside the body; e.g., birds.
Viviparous	Animals that give birth to young ones; embryo develops inside body; e.g., mammals.
Parthenogenesis	Development of new individual from an unfertilised egg; e.g., honeybee drones.
Clone	Genetically identical offspring produced by asexual reproduction.