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Biology - Health and Disease

Grade 8IGCSE

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

🔑Concepts

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Health is defined as a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity.

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Pathogens are disease-causing organisms. These include bacteria (e.g., Vibrio choleraeVibrio \ cholerae), viruses (e.g., HIVHIV or InfluenzaInfluenza), fungi, and protists (e.g., PlasmodiumPlasmodium which causes Malaria).

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Transmission of pathogens can occur through direct contact (blood, body fluids), or indirect contact (contaminated food/water, airborne droplets, or vectors like mosquitoes).

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The body's first line of defense includes mechanical barriers (skin, hairs in the nose) and chemical barriers (stomach acid containing HClHCl, and mucus).

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The immune system involves white blood cells: Phagocytes perform phagocytosis (engulfing and digesting pathogens), and Lymphocytes produce antibodies which are specific to the antigens on the pathogen's surface.

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Vaccination involves the administration of weakened or dead pathogens to stimulate the production of memory cells, providing long-term active immunity.

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Antibiotics are chemicals (e.g., Penicillin) that kill or inhibit the growth of bacteria. They are ineffective against viruses because viruses reside inside host cells and do not have their own metabolic pathways to target.

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Non-communicable diseases are caused by lifestyle, environment, or genetics. Examples include Scurvy (deficiency of Vitamin CC) and Rickets (deficiency of Vitamin DD or Ca2+Ca^{2+} ions).

📐Formulae

BMI=mass (kg)height (m)2BMI = \frac{\text{mass (kg)}}{\text{height (m)}^2}

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

💡Examples

Problem 1:

An adult has a mass of 75 kg75\text{ kg} and a height of 1.75 m1.75\text{ m}. Calculate their Body Mass Index (BMIBMI) and state if they are in the healthy range (18.518.5 to 2525).

Solution:

BMI=751.752=753.0625≈24.49 kg/m2BMI = \frac{75}{1.75^2} = \frac{75}{3.0625} \approx 24.49\text{ kg/m}^2

Explanation:

By applying the BMIBMI formula, we find the value is approximately 24.4924.49. Since this is between 18.518.5 and 2525, the individual is within the healthy weight range.

Problem 2:

A micrograph of a bacterium shows the cell to be 20 mm20\text{ mm} long. If the magnification is ×4000\times 4000, calculate the actual size of the bacterium in micrometers (μm\mu m).

Solution:

Actual Size=Image SizeMagnificationActual \ Size = \frac{\text{Image Size}}{\text{Magnification}} Actual Size=20 mm4000=0.005 mmActual \ Size = \frac{20\text{ mm}}{4000} = 0.005\text{ mm} 0.005 mm×1000=5 μm0.005\text{ mm} \times 1000 = 5\text{ }\mu m

Explanation:

Rearranging the magnification formula M=I/AM = I/A gives A=I/MA = I/M. After calculating the size in mmmm, we convert to μm\mu m because biological cells are typically measured in that unit (1 mm=103 μm1\text{ mm} = 10^3\text{ }\mu m).

Health and Disease - Revision Notes & Key Formulas | IGCSE Grade 8 Science