Quick Revision Notes: Reproduction in Animals

Class: 8 Science (MP Board)

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### 1. Introduction to Reproduction

• Reproduction (जनन): The biological process by which living organisms produce new individuals of their own kind. It is essential for the continuation of a species on Earth.

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### 2. Modes of Reproduction

Animals reproduce mainly by two methods:

1. Sexual Reproduction (लैंगिक जनन)
2. Asexual Reproduction (अलैंगिक जनन)

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### 3. Sexual Reproduction

• Definition: The type of reproduction that begins with the fusion of male and female gametes.
• Male Gamete: Sperm (शुक्राणु) produced in the testes (वृषण).
• Female Gamete: Ovum or Egg (अंडाणु) produced in the ovaries (अंडाशय).
• Fertilization (निषेचन): The fusion of sperm and egg to form a single cell called a Zygote (युग्मज).

Types of Fertilization:

1. Internal Fertilization (आंतरिक निषेचन):
   • Fertilization takes place inside the female body.
   • Examples: Humans, cows, dogs, hens.
2. External Fertilization (बाह्य निषेचन):
   • Fertilization takes place outside the female body (usually in water).
   • Examples: Frogs, fish, starfish.

Development of Embryo:

• The zygote divides repeatedly to form a ball of cells called an Embryo (भ्रूण).
• The embryo gets embedded in the wall of the uterus for further development.
• Foetus (गर्भ): The stage of the embryo in which all the body parts can be identified (at about 8 weeks of pregnancy).

Classification of Animals based on Birth:

• Viviparous Animals (जरायुज जंतु): Animals that give birth to young ones. (e.g., Humans, cats, dogs).
• Oviparous Animals (अंडप्रजक जंतु): Animals that lay eggs. (e.g., Birds, frogs, reptiles, fish).

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### 4. Metamorphosis (कायांतरण)

• Definition: The dramatic transformation of a larva into an adult through drastic changes.
• Examples:
  • Frog: Egg $\rightarrow$ Tadpole (Larva) $\rightarrow$ Adult Frog.
  • Silkworm: Egg $\rightarrow$ Caterpillar $\rightarrow$ Pupa $\rightarrow$ Adult Silk Moth.

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### 5. Asexual Reproduction

• Definition: The type of reproduction in which only a single parent is involved, and no gametes are formed.

Common Types in Animals:

1. Budding (मुकुलन):
   • A small outgrowth called a bud develops on the body of the parent, which detaches later to grow into a new individual.
   • Examples: Hydra, Yeast.
2. Binary Fission (द्विखंडन):
   • A single parent organism divides into two independent individuals.
   • Example: Amoeba.

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### 6. Key Terms to Remember (Important Vocabulary)

• Gamete (युग्मक): Sex cells (Sperm or Egg).
• Zygote (युग्मज): The fertilized egg formed by the fusion of sperm and egg.
• Clone (क्लोन): An exact copy of an organism, produced from a single parent (e.g., Dolly the sheep).
• Tadpole (टेडपोल): The larval stage of a frog.