6.4 – Gas Exchange

6.4 – Gas Exchange

6.4.1 – Distinguish between ventilation, gas exchange and cell respiration

Ventilation – The pumping mechanism that moves air in and out of the lungs efficiently, thereby maintaining the concentration gradient for diffusion.

Gas Exchange – The exchange of gases between an organism and its surroundings, including the uptake of oxygen and the release of carbon dioxide in animals and plants.

Cell Respiration – The controlled release of energy in the form of ATP from organic compounds in cells. It is a continuous process in all cells.


6.4.2 – Explain the need for a ventilation system
The ventilation system is needed to maintain a high concentration gradient in the alveoli. Given that humans have such high demand for oxygen, it needs to be able to be delivered to all their cells in order to support respiration.

The lungs are the respiratory surfaces used for gas exchange. The action of ventilation brings air down into the lungs for exchange. Without it, the lungs would be useless, as no air would be able to reach their surface.

The concentration gradient in the alveoli is maintained using air flow and blood flow. Oxygen (O2) enters the lungs, diffuses across, and enters the bloodstream. Carbon dioxide (CO2) leaves the blood. The concentration of oxygen on one side is kept high, while the concentration of carbon dioxide remains low.


6.4.3 – Describe the features of alveoli that adapt themselves to gas exchange

The alveoli have a large total surface area, which increases the amount of gas that can be diffused across at any given time. This is the result of their spherical shape.

They form a thin layer of flattened cells, which allows for close association with the capillaries and a shorter distance for diffusion into the bloodstream. The wall of alveoli is only one cell thick.

The alveoli are surrounded by a dense capillary network. These then carry the oxygen in the blood to the pulmonary vein to be taken to the heart.

They have a film of moisture for the solutions of gases. The oxygen is able to dissolve in the lipoprotein-based lubricating film.

6.4.4 – Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli

6.4.5 – Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles

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When the chest cavity enlarges, the pressure changes, causing air to enter the lungs to equalise it. The air is then pushed back out when the diaphragm relaxes. The diaphragm is attached to the base of the sternum, the lower parts of the rib cage and the spine.

The lungs are surrounded and protected by the rib cage. The intercostal muscles are attached to the rib cage. The area inside is called the thorax, where the lungs are. The inner surface of the thorax holds the pleural membrane, which secrete pleural fluid. This fluid protects the lungs from friction caused by breathing.