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Reproduction - Describe human reproductive systems, gamete formation, fertilisation, and embryo development

Grade 9CBSE

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

🔑Concepts

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Human reproduction is sexual, involving the fusion of male and female gametes through internal fertilisation.

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Male Reproductive System: Consists of a pair of testes, sperm ducts (vas deferens), and a penis. Testes produce sperm and the hormone testosterone. They are located in the scrotum, which maintains a temperature approximately 2∘C2^{\circ}C to 3∘C3^{\circ}C lower than the internal body temperature of 37∘C37^{\circ}C for efficient sperm production.

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Female Reproductive System: Consists of a pair of ovaries, oviducts (fallopian tubes), and the uterus. Ovaries produce ova (eggs) and hormones like estrogen and progesterone.

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Gamete Formation: Gametes are haploid cells (nn). Male gametes (sperm) are small and motile with a tail, while the female gamete (ovum) is larger and non-motile. In humans, each gamete contains 2323 chromosomes.

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Fertilisation: The process where the nucleus of a sperm fuses with the nucleus of an ovum in the fallopian tube to form a single-celled diploid zygote (2n2n) with 4646 chromosomes.

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Embryo Development: The zygote undergoes rapid cell division (cleavage) to form a ball of cells called an embryo. The embryo travels to the uterus and embeds itself in the uterine wall, a process called implantation.

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Foetus: The stage of the embryo in which all the body parts can be identified is called a foetus. In humans, the gestation period is approximately 99 months or 280280 days.

📐Formulae

n (Haploid Gamete)+n (Haploid Gamete)→2n (Diploid Zygote)n \text{ (Haploid Gamete)} + n \text{ (Haploid Gamete)} \rightarrow 2n \text{ (Diploid Zygote)}

Scrotal Temperature≈Body Temperature−2∘C\text{Scrotal Temperature} \approx \text{Body Temperature} - 2^{\circ}C

Total Chromosomes in Zygote=23 (maternal)+23 (paternal)=46\text{Total Chromosomes in Zygote} = 23 \text{ (maternal)} + 23 \text{ (paternal)} = 46

💡Examples

Problem 1:

If a human sperm cell contains 2323 chromosomes, how many chromosomes will be present in the zygote formed after fertilisation?

Solution:

23 (from sperm)+23 (from ovum)=46 chromosomes23 \text{ (from sperm)} + 23 \text{ (from ovum)} = 46 \text{ chromosomes}

Explanation:

During fertilisation, the haploid nucleus of the sperm (n=23n=23) fuses with the haploid nucleus of the ovum (n=23n=23). This restores the diploid number (2n2n) in the resulting zygote, ensuring the species-specific chromosome count is maintained.

Problem 2:

Calculate the approximate temperature of the scrotum if the normal human body temperature is 37∘C37^{\circ}C.

Solution:

37∘C−2∘C35∘C\begin{array}{r} 37^{\circ}C \\ - 2^{\circ}C \\ \hline 35^{\circ}C \end{array}

Explanation:

The scrotum is located outside the abdominal cavity because sperm production (spermatogenesis) requires a temperature that is lower than the normal internal body temperature by about 2∘C2^{\circ}C to 3∘C3^{\circ}C.

Problem 3:

Arrange the following stages of human development in the correct chronological order: Embryo, Zygote, Foetus, Gametes.

Solution:

Gametes →\rightarrow Zygote →\rightarrow Embryo →\rightarrow Foetus

Explanation:

First, gametes are formed. Their fusion results in a single-celled zygote. The zygote divides to become a multi-cellular embryo. Once the body parts are identifiable, it is termed a foetus.