Respiration and moving - Free MCQ Practice Test with solutions, Class 8

It is a common misunderstanding to think that all of the oxygen that goes into the lungs is taken into the body. If it was, mouth to mouth resuscitation would not be possible.

The percentage of carbon dioxide in inhaled air is approximately 0.03–0.04%. This small amount is sufficient for atmospheric processes but is significantly less than the CO₂ in exhaled air.

That is significantly higher than the amount breathed in. It is a common misunderstanding that we breathe out only carbon dioxide.

Oxygen enters the respiratory system through the trachea, passes through the bronchi, then the bronchioles, and finally reaches the alveoli, where gas exchange occurs. The alveoli’s thin, permeable walls and rich blood capillary network allow red blood cells to absorb oxygen efficiently.

They have a very large surface area which makes the absorption of oxygen and removal of carbon dioxide as efficient as possible. Smoking damages the alveoli and so getting oxygen into the blood is a lot harder.

Haemoglobin in red blood cells joins with oxygen.

The circulatory system, comprising the heart, blood vessels, and blood, is responsible for transporting oxygen, nutrients, hormones, and other substances throughout the body.

The excretory system, including the kidneys and urinary system, is responsible for eliminating metabolic wastes, maintaining water and electrolyte balance, and regulating pH levels in the body.

The animal uses its chest muscles to increase the volume of its lungs. The air inside the lungs is therefore more spread out than before, so it has a lower pressure. The higher pressure of the air outside of the lungs forces air into the lungs. The opposite is true of breathing out.

The immune system defends the body against pathogens, viruses, bacteria, and other harmful substances through a complex network of cells, tissues, and organs.