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Biology - Reproduction in Animals (Sexual and Asexual, Metamorphosis)

Grade 8ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Reproduction is the biological process by which organisms produce offspring of their own kind, ensuring the continuity of the species.

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Asexual Reproduction: Involves a single parent without the fusion of gametes. Methods include Binary Fission (e.g., Amoeba) and Budding (e.g., Hydra).

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Sexual Reproduction: Involves the fusion of male gametes (Sperm) and female gametes (Ova/Egg).

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Male Reproductive System: Consists of a pair of testes (produce sperm), sperm ducts, and a penis. Sperm is a single cell with a head, middle piece, and a tail.

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Female Reproductive System: Consists of a pair of ovaries (produce eggs), oviducts (Fallopian tubes), and the uterus (where the baby develops).

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Fertilization: The process where the nucleus of the sperm (nn) fuses with the nucleus of the egg (nn) to form a zygote (2n2n).

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Internal Fertilization occurs inside the female body (e.g., humans, cows, birds), while External Fertilization occurs outside (e.g., frogs, fish).

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Viviparous animals give birth to young ones (e.g., humans, dogs), whereas Oviparous animals lay eggs (e.g., hens, lizards).

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Metamorphosis: The transformation of a larva into an adult through drastic changes. Example in frogs: Egg→Tadpole (larva)→Adult frog\text{Egg} \rightarrow \text{Tadpole (larva)} \rightarrow \text{Adult frog}.

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In-vitro Fertilization (IVF): A technique where fertilization is brought about externally in a glass dish or test tube, often used to help couples with fertility issues.

📐Formulae

Sperm (n)+Ovum (n)→FertilizationZygote (2n)\text{Sperm } (n) + \text{Ovum } (n) \xrightarrow{\text{Fertilization}} \text{Zygote } (2n)

Binary Fission: 1 Parent Cell→2 Daughter Cells\text{Binary Fission: } 1 \text{ Parent Cell} \rightarrow 2 \text{ Daughter Cells}

Butterfly Life Cycle: Egg→Larva (Caterpillar)→Pupa→Adult\text{Butterfly Life Cycle: Egg} \rightarrow \text{Larva (Caterpillar)} \rightarrow \text{Pupa} \rightarrow \text{Adult}

💡Examples

Problem 1:

If a sperm cell contains 2323 chromosomes, how many chromosomes will be present in the zygote after fertilization with an ovum?

Solution:

The zygote will contain 4646 chromosomes.

Explanation:

Since the sperm is haploid (n=23n = 23) and the ovum is haploid (n=23n = 23), the fusion during fertilization results in a diploid zygote: n+n=2nn + n = 2n, which is 23+23=4623 + 23 = 46.

Problem 2:

Identify the type of reproduction in HydraHydra and describe the process.

Solution:

Asexual reproduction by Budding.

Explanation:

In HydraHydra, a small bulge called a 'bud' develops due to repeated cell division at one specific site. This bud grows into a tiny individual and eventually detaches from the parent body to live independently.

Problem 3:

Compare the respiratory organs of a frog at different stages of metamorphosis.

Solution:

Tadpole stage uses Gills; Adult stage uses Lungs and Skin.

Explanation:

During metamorphosis, the aquatic tadpole (larvalarva) breathes through gills to extract oxygen from water. As it transforms into a terrestrial/amphibious adult, it develops lungs for air breathing and uses its moist skin for cutaneous respiration.