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Biology - Human Reproduction and Puberty

Grade 8Cambridge (IGCSE)

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

🔑Concepts

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Puberty is the period during which adolescents reach sexual maturity and become capable of reproduction, triggered by hormones: testosterone in males and estrogen in females.

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The male reproductive system includes the testes (produce sperm and testosterone), sperm duct, prostate gland (adds fluid to sperm to create semen), and the urethra.

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The female reproductive system includes the ovaries (produce eggs and estrogen), oviducts (site of fertilization), uterus (where the fetus develops), and the cervix.

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Gametes are haploid cells (nn), meaning they contain half the number of chromosomes. In humans, n=23n = 23.

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Fertilization is the fusion of the nuclei of a male gamete (sperm) and a female gamete (egg) to form a diploid zygote (2n2n), where 2n=462n = 46.

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The Menstrual Cycle is a roughly 2828-day cycle. Ovulation (release of an egg) occurs around day 1414. If no fertilization occurs, the uterus lining breaks down (menstruation).

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The placenta is a specialized organ that allows for the exchange of substances: O2O_2, glucose, and nutrients diffuse from maternal blood to fetal blood; CO2CO_2 and urea diffuse from fetal blood to maternal blood.

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The amniotic sac contains amniotic fluid, which cushions the fetus and protects it from physical trauma and temperature fluctuations.

📐Formulae

Sperm (n=23)+Egg (n=23)→Zygote (2n=46)\text{Sperm } (n=23) + \text{Egg } (n=23) \rightarrow \text{Zygote } (2n=46)

Average Menstrual Cycle Length≈28 days\text{Average Menstrual Cycle Length} \approx 28 \text{ days}

Human Gestation Period≈9 months≈40 weeks\text{Human Gestation Period} \approx 9 \text{ months} \approx 40 \text{ weeks}

💡Examples

Problem 1:

Calculate the number of chromosomes in a human zygote if the sperm and egg each contain nn chromosomes.

Solution:

n+n=2nn + n = 2n. Since n=23n = 23, the zygote contains 23+23=4623 + 23 = 46 chromosomes.

Explanation:

Human gametes are haploid (nn). During fertilization, their nuclei fuse to restore the diploid number (2n2n) in the zygote.

Problem 2:

A woman has a regular 2828-day menstrual cycle. If her period (Day 11) started on March 1st, when is she most likely to undergo ovulation?

Solution:

March 14th14^{th}.

Explanation:

Ovulation typically occurs at the midpoint of the cycle. For a 2828-day cycle, 28÷2=1428 \div 2 = 14. Therefore, ovulation occurs on Day 1414.

Problem 3:

List the substances that move across the placenta via diffusion from the fetus to the mother.

Solution:

CO2CO_2 and urea.

Explanation:

The fetus produces metabolic waste products such as carbon dioxide (CO2CO_2) and urea, which must be removed via the mother's circulatory system.