krit.club logo

Biology - The Human Respiratory System

Grade 7IGCSE

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

🔑Concepts

•

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

•

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

•

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.

•

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

•

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.

•

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

•

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}.

•

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.

The Human Respiratory System - Revision Notes & Key Formulas | IGCSE Grade 7 Science