Question

The exchange of gases in the alveoli of the lungs taken place by
A. Osmosis
B. Simple diffusion
C. Passive transport
D. Active transport

Answer 1

Gases diffuse across the systemic capillary membrane and the cell membranes of the target tissue. Carbon dioxide diffuses from systemic tissues to the lungs, and oxygen diffuses from lungs to systemic tissues.

Complete answer:
1. The primary function of the respiratory system is to take in oxygen and eliminate carbon dioxide. Inhaled oxygen enters the lungs and reaches the alveoli.
2. The layers of cells lining the alveoli and the surrounding capillaries are each only one cell thick and are in very close contact with each other.
3. The primary function of the respiratory system is to take in oxygen and eliminate carbon dioxide. Inhaled oxygen enters the lungs and reaches the alveoli.
4. The layers of cells lining the alveoli and the surrounding capillaries are each only one cell thick and are in very close contact with each other.
5. Oxygen passes quickly through this air-blood barrier into the blood in the capillaries. Similarly, carbon dioxide passes from the blood into the alveoli and is then exhaled.
6. The body’s circulation is an essential link between the atmosphere, which contains oxygen, and the cells of the body, which consume oxygen. For example, the delivery of oxygen to the muscle cells throughout the body depends not only on the lungs but also on the ability of the blood to carry oxygen and on the ability of the circulation to transport blood to the muscle.
7. In addition, a small fraction of the blood pumped from the heart enters the bronchial arteries and nourishes the airways. Ventilation is the process by which air moves in and out of the lungs.
8. The structure of the lung maximizes its surface area to increase gas diffusion. Because of the enormous number of alveoli (approximately 300 million in each human lung), the surface area of the lung is very large (75 m2).
9. Having such a large surface area increases the amount of gas that can diffuse into and out of the lungs. Gas exchange during respiration occurs primarily through diffusion.
10. Diffusion is a process in which transport is driven by a concentration gradient. Gas molecules move from a region of high concentration to a region of low concentration.
11. Blood that is low in oxygen concentration and high in carbon dioxide concentration undergoes gas exchange with air in the lungs. The air in the lungs has a higher concentration of oxygen than that of oxygen-depleted blood and a lower concentration of carbon dioxide.
12. This concentration gradient allows for gas exchange during respiration. Partial pressure is a measure of the concentration of the individual components in a mixture of gases.
13. The total pressure exerted by the mixture is the sum of the partial pressures of the components in the mixture. The rate of diffusion of a gas is proportional to its partial pressure within the total gas mixture.

So, the correct answer is “Option B. Simple diffusion ”.

Note: The lungs can hold a large volume of air, but they are not usually filled to maximal capacity. Lung volume measurements include tidal volume, expiratory reserve volume, inspiratory reserve volume, and residual volume. The sum of these equals the total lung capacity. Gas movement into or out of the lungs is dependent on the pressure of the gas. Air is a mixture of gases; therefore, the partial pressure of each gas can be calculated to determine how the gas will flow in the lung.