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Human Nutrition - Diet and balanced nutrition

Grade 11IGCSEBiology

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

🔑Concepts

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A Balanced Diet is a diet that provides all seven groups of nutrients (carbohydrates, fats, proteins, vitamins, minerals, water, and fiber) in the correct proportions to maintain health.

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Carbohydrates (Cx(H2O)yC_x(H_2O)_y): Primarily used as an energy source. Found in foods like bread, rice, and potatoes. Glucose (C6H12O6C_6H_{12}O_6) is the primary substrate for respiration.

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Proteins: Essential for growth and tissue repair. Composed of amino acids containing CC, HH, OO, and NN (and sometimes SS). Deficiency can lead to Kwashiorkor.

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Lipids (Fats and Oils): Used for long-term energy storage, insulation, and protecting organs. They are made of one glycerol molecule and three fatty acid chains.

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Vitamin C: Found in citrus fruits; essential for maintaining healthy skin and gums. Deficiency causes Scurvy, characterized by bleeding gums and poor wound healing.

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Vitamin D and Calcium (Ca2+Ca^{2+}): Required for strong bones and teeth. Deficiency leads to Rickets in children, where bones become soft and deformed.

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Iron (Fe2+Fe^{2+}): A key component of hemoglobin in red blood cells, used for oxygen transport. Deficiency leads to Anemia, resulting in fatigue due to lack of O2O_2 for respiration.

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Dietary Fiber (Roughage): Provides bulk for the intestine to push against, aiding peristalsis and preventing constipation.

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Malnutrition: A condition caused by an unbalanced diet. This includes starvation, obesity (BMI>30BMI > 30), coronary heart disease (linked to saturated fats), and deficiency diseases.

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Energy Requirements: Vary depending on age, sex, activity level, and pregnancy. Energy is measured in kilojoules (kJkJ).

📐Formulae

Energy transferred (J)=mass of water (g)×4.2 J/g∘C×temperature rise (∘C)\text{Energy transferred (J)} = \text{mass of water (g)} \times 4.2 \text{ J/g}^\circ\text{C} \times \text{temperature rise } (^\circ\text{C})

Energy per gram of food (J/g)=Energy transferred (J)extMassoffood(g)\text{Energy per gram of food (J/g)} = \frac{\text{Energy transferred (J)}}{ ext{Mass of food (g)}}

BMI=Mass (kg)(Height (m))2\text{BMI} = \frac{\text{Mass (kg)}}{(\text{Height (m)})^2}

💡Examples

Problem 1:

A student burns a 0.5 g0.5\text{ g} sample of dried pasta under a test tube containing 20 g20\text{ g} of water. The temperature of the water rises from 20∘C20^\circ\text{C} to 45∘C45^\circ\text{C}. Calculate the energy content of the pasta per gram. (Specific heat capacity of water is 4.2 J/g∘C4.2\text{ J/g}^\circ\text{C})

Solution:

ΔT=45∘C−20∘C=25∘C\Delta T = 45^\circ\text{C} - 20^\circ\text{C} = 25^\circ\text{C} Energy=20 g×4.2 J/g∘C×25∘C=2100 J\text{Energy} = 20\text{ g} \times 4.2\text{ J/g}^\circ\text{C} \times 25^\circ\text{C} = 2100\text{ J} Energy per gram=2100 J0.5 g=4200 J/g=4.2 kJ/g\text{Energy per gram} = \frac{2100\text{ J}}{0.5\text{ g}} = 4200\text{ J/g} = 4.2\text{ kJ/g}

Explanation:

First, calculate the temperature change (ΔT\Delta T). Use the energy transfer formula to find total Joules absorbed by the water, then divide by the mass of the food sample to find the energy density.

Problem 2:

Explain why a pregnant woman requires more Fe2+Fe^{2+} and Ca2+Ca^{2+} in her diet compared to a non-pregnant woman.

Solution:

A pregnant woman needs extra Iron (Fe2+Fe^{2+}) to produce the extra hemoglobin required for the fetus's blood supply and to prevent maternal anemia. She needs extra Calcium (Ca2+Ca^{2+}) for the development of the fetus's bones and teeth.

Explanation:

Nutritional requirements shift during pregnancy to support the growth of the fetus and the physiological changes in the mother's body.

Diet and balanced nutrition - Revision Notes & Key Diagrams | IGCSE Grade 11 Biology