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Reproduction - Sexual reproduction in humans

Grade 11IGCSEBiology

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

🔑Concepts

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Sexual reproduction is the process involving the fusion of the nuclei of two gametes to form a zygote and the production of offspring that are genetically different. Gametes are haploid (nn), containing 23 chromosomes, while the zygote is diploid (2n2n), containing 46 chromosomes.

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The male reproductive system includes the testes (production of sperm and testosterone), scrotum, sperm ducts, prostate gland (fluid production), and urethra/penis.

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The female reproductive system includes the ovaries (production of eggs, estrogen, and progesterone), oviducts (site of fertilization), uterus (site of implantation), cervix, and vagina.

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The Menstrual Cycle is controlled by four main hormones: FSHFSH (stimulates follicle growth), LHLH (triggers ovulation), estrogen (repairs the uterine lining), and progesterone (maintains the uterine lining).

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Fertilization occurs in the oviduct. The resulting zygote divides by mitosis to form an embryo, which implants into the lining of the uterus (endometriumendometrium).

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The placenta allows for the exchange of soluble nutrients (such as glucose and amino acids) and O2O_2 from the mother to the fetus, and the removal of waste products like CO2CO_2 and urea from the fetus via diffusion across a semi-permeable membrane.

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The amniotic sac contains amniotic fluid, which protects the developing fetus against mechanical shock and provides a constant temperature environment.

📐Formulae

n+n→2nn + n \rightarrow 2n

Magnification=Measured Image SizeActual Size of Specimen\text{Magnification} = \frac{\text{Measured Image Size}}{\text{Actual Size of Specimen}}

Day of Ovulation≈Length of Cycle−14 days\text{Day of Ovulation} \approx \text{Length of Cycle} - 14 \text{ days}

💡Examples

Problem 1:

A sperm cell is measured in a textbook diagram. The tail length in the image is 3030 mm. If the actual length of the sperm tail is 5050 μm\mu m, calculate the magnification of the diagram.

Solution:

Magnification=30,000 μm50 μm=600×\text{Magnification} = \frac{30,000 \text{ } \mu m}{50 \text{ } \mu m} = 600 \times

Explanation:

First, convert 3030 mm to μm\mu m by multiplying by 10001000 (30×1000=30,000μm30 \times 1000 = 30,000 \mu m). Then, use the magnification formula IA\frac{I}{A}.

Problem 2:

During the menstrual cycle, if the level of progesterone drops significantly on day 28, what event is likely to occur next?

Solution:

Menstruation (the breakdown of the uterine lining).

Explanation:

Progesterone is responsible for maintaining the thickness of the uterine lining (endometriumendometrium). When its concentration decreases due to the degeneration of the corpus luteum, the lining can no longer be maintained and is shed.

Sexual reproduction in humans - Revision Notes & Key Diagrams | IGCSE Grade 11 Biology