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Biology - The Human Respiratory System

Grade 7Cambridge (IGCSE)

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

🔑Concepts

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The human respiratory system is responsible for gas exchange, allowing the body to take in oxygen (O2O_2) and remove carbon dioxide (CO2CO_2).

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The pathway of air involves the nasal cavity, trachea, bronchi, bronchioles, and finally the alveoli where gas exchange occurs.

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Alveoli are adapted for efficient gas exchange by having a large surface area, walls that are only one cell thick, a moist lining, and an extensive network of blood capillaries.

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Breathing (ventilation) is the mechanical process of moving air in and out of the lungs, driven by the diaphragm and intercostal muscles.

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During inhalation, the diaphragm contracts and moves downwards, and the external intercostal muscles contract to move the ribcage up and out, increasing the thoracic volume and decreasing pressure.

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During exhalation, the diaphragm relaxes and moves upwards, and the external intercostal muscles relax, decreasing thoracic volume and increasing pressure, forcing air out.

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Aerobic respiration is a chemical process that occurs in the mitochondria of cells to release energy: C6H12O6+6O2→6CO2+6H2O+EnergyC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}.

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Gas exchange occurs via diffusion; O2O_2 moves from a high concentration in the alveoli to a lower concentration in the red blood cells, while CO2CO_2 moves from the plasma to the alveoli.

📐Formulae

Glucose+Oxygen→Carbon Dioxide+Water+Energy\text{Glucose} + \text{Oxygen} \rightarrow \text{Carbon Dioxide} + \text{Water} + \text{Energy}

C6H12O6+6O2→6CO2+6H2OC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O

Glucose→Lactic Acid+Energy (low yield)\text{Glucose} \rightarrow \text{Lactic Acid} + \text{Energy (low yield)}

C6H12O6→2C3H6O3C_6H_{12}O_6 \rightarrow 2C_3H_6O_3

Total Lung Capacity=Vital Capacity+Residual Volume\text{Total Lung Capacity} = \text{Vital Capacity} + \text{Residual Volume}

💡Examples

Problem 1:

During a science experiment, a student measures the concentration of gases in exhaled air. If the inhaled air contains 0.04%0.04\% CO2CO_2, why does the exhaled air contain approximately 4%4\% CO2CO_2?

Solution:

The concentration increases from 0.04%0.04\% to 4%4\% because CO2CO_2 is a waste product of aerobic respiration occurring in the body's cells.

Explanation:

Cells use oxygen to break down glucose for energy, producing CO2CO_2 as a byproduct. This CO2CO_2 is transported by the blood to the lungs, where it diffuses into the alveoli to be exhaled.

Problem 2:

Calculate the ventilation rate of a Grade 7 student who takes 1616 breaths per minute, with each breath (tidal volume) being 0.50.5 liters (LL).

Solution:

16×0.5=8 L/min16 \times 0.5 = 8 \text{ L/min}

Explanation:

The ventilation rate is calculated by multiplying the breathing rate (breaths per minute) by the tidal volume (volume per breath).

Problem 3:

Explain the movement of the ribcage and diaphragm during exhalation.

Solution:

The diaphragm relaxes and moves upwards into a dome shape, while the external intercostal muscles relax, causing the ribcage to move downwards and inwards.

Explanation:

This combined action reduces the volume of the chest cavity, which increases the air pressure inside the lungs relative to the atmospheric pressure, causing air to be pushed out.