Class 12 Biology Chapter 1 – Long Questions

Long Answer Questions

 

1. Describe the different types of asexual reproduction with examples.

Answer:

Asexual reproduction occurs without gamete fusion and produces identical offspring. Types include:

1. • Binary fission (Amoeba, Paramecium) – Parent splits into two equal daughter cells.

   • Budding (Hydra, Yeast) – Small outgrowth (bud) develops and detaches as a new organism.

   • Fragmentation (Spirogyra) – Organism breaks into fragments, each growing into a new individual.

   • Spore Formation (Fungi, Mosses) – Spores are released from sporangia and develop into new individuals.

   • Vegetative Propagation (Potato, Bryophyllum) – New plants arise from roots, stems, or leaves.

 

2. Explain the various phases of sexual reproduction in organisms.

Answer:

Sexual reproduction involves three phases:

1. • Pre-fertilization phase – Gametogenesis (formation of gametes) and gamete transfer.

   • Fertilization (Syngamy) – Fusion of male and female gametes to form a zygote.

   • Post-fertilization phase – Zygote undergoes mitotic division (embryogenesis), leading to the development of a new organism.

 

3. Discuss the process of binary fission in Amoeba and multiple fission in Plasmodium.

Answer:

1. • Binary Fission in Amoeba: The nucleus divides mitotically, followed by cytoplasmic division, producing two daughter cells.

   • Multiple Fission in Plasmodium: The nucleus undergoes multiple divisions before the cytoplasm splits into several new cells, allowing rapid multiplication, especially during unfavorable conditions.

 

4. What are the differences between asexual and sexual reproduction?

 

Answer:

5. Explain the events of sexual reproduction, including pre-fertilization, fertilization, and post-fertilization events.

Answer:

Sexual reproduction occurs in three stages:

1. • Pre-fertilization events: Involves gametogenesis (formation of male and female gametes) and gamete transfer (pollination in plants, sperm transfer in animals).

   • Fertilization (Syngamy): The fusion of male and female gametes forms a diploid zygote.

   • Post-fertilization events: The zygote undergoes embryogenesis (mitotic division and differentiation) leading to the development of a new organism.

 

6. Write a short note on juvenile, reproductive, and senescent phases in organisms.

Answer:

• • Juvenile Phase: The period of growth from birth to reproductive maturity. Example: The growth phase in a human before puberty.

  • Reproductive Phase: The period during which an organism is capable of producing offspring. Example: Humans reproduce after puberty.

  • Senescent Phase: The aging phase marked by a decline in reproductive ability and metabolic activity. Example: Post-menopausal stage in women.

These phases together define the life span and reproductive potential of an organism.