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Biology - Human nutrition (Balanced diet and digestive system)

Grade 9IGCSE

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

🔑Concepts

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A balanced diet contains all the necessary nutrients in the correct proportions: carbohydrates, fats, proteins, vitamins, minerals, fiber, and water.

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Carbohydrates (Cn(H2O)nC_n(H_2O)_n) are the primary energy source; fats provide long-term energy storage and insulation; proteins are essential for growth and tissue repair.

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Vitamin CC is needed for skin and gums (deficiency causes scurvy), while Vitamin DD and Calcium (Ca2+Ca^{2+}) are required for strong bones (deficiency causes rickets).

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Iron (Fe2+Fe^{2+}) is a critical component of hemoglobin for oxygen transport; deficiency leads to anemia.

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Ingestion is the taking of substances into the body through the mouth.

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Mechanical digestion is the breakdown of food into smaller pieces without chemical change (e.g., teeth, stomach churning), increasing the surface area for enzymes.

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Chemical digestion is the breakdown of large, insoluble molecules into small, soluble molecules by enzymes.

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Amylase breaks down starch into maltose; Protease breaks down proteins into amino acids; Lipase breaks down fats into fatty acids and glycerol.

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The stomach secretes Hydrochloric acid (HClHCl) to kill bacteria and provide the optimum acidic pHpH for pepsin (a protease).

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Bile is produced in the liver, stored in the gallbladder, and used to emulsify fats and neutralize the acidic mixture (chyme) entering the duodenum.

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Absorption occurs primarily in the small intestine (ileum), where villi increase the surface area for the movement of nutrients into the blood or lymph.

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Assimilation is the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells.

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Egestion is the passing out of food that has not been digested or absorbed, as feces, through the anus.

📐Formulae

Starch+H2O→AmylaseMaltose→MaltaseGlucoseStarch + H_2O \xrightarrow{Amylase} Maltose \xrightarrow{Maltase} Glucose

Proteins+H2O→ProteaseAmino AcidsProteins + H_2O \xrightarrow{Protease} Amino\ Acids

Lipids+3H2O→LipaseGlycerol+3 Fatty AcidsLipids + 3H_2O \xrightarrow{Lipase} Glycerol + 3\ Fatty\ Acids

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

💡Examples

Problem 1:

Explain the role of bile in the digestion of lipids and how it affects the rate of reaction.

Solution:

Bile performs two main functions: 1. It neutralizes the HClHCl from the stomach to provide an alkaline environment for enzymes in the small intestine. 2. It emulsifies fats, breaking large globules into smaller droplets.

Explanation:

Emulsification increases the surface area of the lipids, allowing the enzyme Lipase to collide with substrate molecules more frequently, thus increasing the rate of chemical digestion into fatty acids and glycerol.

Problem 2:

A student consumes a meal containing 50g50g of carbohydrates. If the energy content of carbohydrates is 17 kJ/g17\ kJ/g, calculate the total energy provided by the carbohydrates in kJkJ.

Solution:

Energy=50 g×17 kJ/g=850 kJEnergy = 50\ g \times 17\ kJ/g = 850\ kJ

Explanation:

The total energy is calculated by multiplying the mass of the nutrient by its specific energy value per gram.

Problem 3:

Describe how the structure of a villus is related to its function of absorption.

Solution:

Villi have a large surface area, a thin wall (one cell thick) for a short diffusion pathway, and a rich blood supply (capillaries) to maintain a concentration gradient.

Explanation:

The central lacteal absorbs fatty acids and glycerol into the lymphatic system, while the surrounding blood capillaries absorb glucose and amino acids directly into the bloodblood stream.