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Biology: Human Physiology, Health, and Response - Nutrition, Balanced Diet, Nutrients, and Food Tests

Grade 8IB

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

🔑Concepts

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A balanced diet consists of seven main groups: carbohydrates, proteins, lipids (fats and oils), vitamins, minerals, water, and dietary fiber in the correct proportions.

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Carbohydrates (such as glucose C6H12O6C_6H_{12}O_6 and starch) provide the primary source of energy for cellular respiration.

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Proteins are large molecules made of chains of amino acids; they are essential for growth and the repair of body tissues.

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Lipids are made of glycerol and fatty acids; they serve as long-term energy stores, provide insulation, and protect internal organs.

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Micronutrients like Vitamin C (prevents scurvy), Vitamin D (prevents rickets), Iron (prevents anemia), and Calcium (for strong bones and teeth) are required in smaller quantities.

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Food Tests: 1. Starch: Iodine solution (yellow-brown to blue-black). 2. Reducing Sugars: Benedict's solution + heat (blue to brick-red). 3. Proteins: Biuret reagent (blue to lilac/purple). 4. Lipids: Ethanol emulsion test (clear to cloudy/milky emulsion).

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Energy requirements vary between individuals based on factors such as age, biological sex, activity level, and pregnancy status.

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Malnutrition occurs when a person's diet does not contain the right amount of nutrients, leading to conditions like obesity or deficiency diseases such as Kwashiorkor (protein deficiency).

📐Formulae

Q=m×c×ΔTQ = m \times c \times \Delta T

Energy content per gram (J/g)=mass of water (g)×4.2 (J/g∘C)×temperature rise (∘C)mass of food sample (g)Energy\ content\ per\ gram\ (J/g) = \frac{mass\ of\ water\ (g) \times 4.2\ (J/g^{\circ}C) \times temperature\ rise\ (^{\circ}C)}{mass\ of\ food\ sample\ (g)}

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

💡Examples

Problem 1:

A student burns a 0.5 g0.5\ g sample of dried bread under a test tube containing 20 g20\ g of water. The temperature of the water rises from 20∘C20^{\circ}C to 35∘C35^{\circ}C. Calculate the energy released by the food per gram. (Assume c=4.2 J/g∘Cc = 4.2\ J/g^{\circ}C)

Solution:

ΔT=35∘C−20∘C=15∘C\Delta T = 35^{\circ}C - 20^{\circ}C = 15^{\circ}C Q=20 g×4.2 J/g∘C×15∘C=1260 JQ = 20\ g \times 4.2\ J/g^{\circ}C \times 15^{\circ}C = 1260\ J Energy per gram=1260 J0.5 g=2520 J/gEnergy\ per\ gram = \frac{1260\ J}{0.5\ g} = 2520\ J/g

Explanation:

First, calculate the temperature change (ΔT\Delta T). Then use the specific heat capacity formula to find total energy (QQ). Finally, divide by the mass of the food to find energy density.

Problem 2:

Identify the nutrient present in a food sample that turns Biuret reagent purple but remains orange-brown when tested with Iodine solution.

Solution:

The nutrient is Protein.

Explanation:

A positive Biuret test (color change to lilac/purple) indicates the presence of peptide bonds found in proteins. A negative Iodine test (remaining orange-brown) indicates that starch is absent.