krit.club logo

Biology - Human digestive system and healthy diets

Grade 4IGCSE

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

🔑Concepts

•

The human digestive system is a group of organs working together to break down food into small, soluble molecules like glucose (C6H12O6C_6H_{12}O_6) that the body can absorb.

•

Digestion begins in the mouth with mechanical breakdown by teeth and chemical breakdown by salivary amylase.

•

The stomach uses Hydrochloric acid (HClHCl) to provide the optimum pHpH for enzymes and to kill harmful bacteria.

•

A healthy diet must be 'balanced,' containing the correct proportions of carbohydrates, proteins, lipids (fats), vitamins, minerals, water, and fiber.

•

Nutrients are absorbed into the bloodstream in the small intestine, which has a large surface area due to structures called villi.

•

Energy is released from digested food through the process of cellular respiration: C6H12O6+6O2→6CO2+6H2O+EnergyC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}.

📐Formulae

Energy released (J)=mass of water (g)×4.2×ΔT (∘C)\text{Energy released (J)} = \text{mass of water (g)} \times 4.2 \times \Delta T \text{ (}^{\circ}C)

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

💡Examples

Problem 1:

A student burns a small piece of dried fruit under a test tube containing 20g20g of water. The temperature of the water rises from 20∘C20^{\circ}C to 35∘C35^{\circ}C. Calculate the energy released in Joules (JJ).

Solution:

Energy=20×4.2×(35−20)=20×4.2×15=1260J\text{Energy} = 20 \times 4.2 \times (35 - 20) = 20 \times 4.2 \times 15 = 1260J

Explanation:

To find the energy, we multiply the mass of the water by the specific heat capacity (4.2 J/g∘C4.2 \, J/g^{\circ}C) and the change in temperature (ΔT\Delta T).

Problem 2:

Identify the chemical formula for glucose and explain its role in a healthy diet.

Solution:

C6H12O6C_6H_{12}O_6

Explanation:

Glucose is a simple carbohydrate (sugar) that provides the primary source of energy for cells through the process of respiration.

Human digestive system and healthy diets Revision - Grade 4 Science IGCSE