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Biology - Reproduction

Grade 9IGCSE

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

🔑Concepts

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Asexual reproduction is a process resulting in the production of genetically identical offspring from one parent via mitosis.

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Sexual reproduction is a process involving the fusion of the nuclei of two gametes (haploid cells, nn) to form a zygote (diploid cell, 2n2n) and the production of offspring that are genetically different from each other.

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Gametes are produced through meiosis, resulting in cells with half the number of chromosomes (nn). In humans, n=23n = 23 and 2n=462n = 46.

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In flowers, the male gametes are found in pollen grains (produced in the anther) and the female gametes are found in the ovules (produced in the ovary).

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Pollination is the transfer of pollen grains from the anther to the stigma. This can occur via insects or wind.

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The menstrual cycle is controlled by four main hormones: FSHFSH (Follicle Stimulating Hormone), LHLH (Luteinizing Hormone), Estrogen, and Progesterone.

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The placenta is a specialized organ that allows the exchange of nutrients (O2O_2, glucose, amino acids) and waste products (CO2CO_2, urea) between the maternal and fetal blood through diffusion.

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Human Immunodeficiency Virus (HIVHIV) is a pathogen that can lead to AIDSAIDS. It is transmitted through the exchange of body fluids such as blood or semen.

📐Formulae

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

Magnification=Measured size of imageActual size of specimen\text{Magnification} = \frac{\text{Measured size of image}}{\text{Actual size of specimen}}

2n=46 (in humans)2n = 46 \text{ (in humans)}

n=23 (in humans)n = 23 \text{ (in humans)}

💡Examples

Problem 1:

During a laboratory observation, a student measures a diagram of a human sperm cell. The image length is 50 mm50\text{ mm}, and the magnification is ×1000\times 1000. Calculate the actual length of the sperm cell in μm\mu m.

Solution:

ActualSize=ImageSizeMagnification=50 mm1000=0.05 mmActual Size = \frac{Image Size}{Magnification} = \frac{50\text{ mm}}{1000} = 0.05\text{ mm} 0.05 mm×1000=50 μm0.05\text{ mm} \times 1000 = 50\text{ }\mu m

Explanation:

To find the actual size, divide the image size by the magnification. Since the question asks for μm\mu m, convert the result from mmmm to μm\mu m by multiplying by 10310^3.

Problem 2:

Explain the role of FSHFSH and LHLH in the menstrual cycle.

Solution:

FSHFSH (Follicle Stimulating Hormone) is secreted by the pituitary gland; it stimulates the maturation of an egg follicle in the ovary. LHLH (Luteinizing Hormone) peaks around day 1414 of the cycle, triggering ovulation (the release of the egg).

Explanation:

These hormones coordinate the timing of the cycle to ensure an egg is ready and released for potential fertilization.

Problem 3:

Contrast the structure of wind-pollinated and insect-pollinated flowers.

Solution:

Insect-pollinated flowers have large, brightly colored petals and sticky pollen to adhere to insects. Wind-pollinated flowers have small, dull petals, long filaments so anthers hang outside the flower to release pollen into the air, and feathery stigmas to catch drifting pollen.

Explanation:

Structure is directly related to the method of pollen transfer. Wind-pollination requires a high surface area for the stigma (A∝capture rateA \propto \text{capture rate}) and exposed anthers.