GASEXCHANGE

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6.4.1VentilationThe movement of air into and out of the lungs in two stages: inspiration and expiration. This is controlled by movement of the diaphragm and ribcage.

The exchange (diffusion) of oxygen and carbon dioxide to and from the blood at the alveoli and the respiring tissues down the concentration gradient.

Gas Exchange

Cell Respiration This is production of ATP at the cellular level (mitochondria). Aerobic respiration uses oxygen, where anaerobic does not.

Small organisms, such as flatworms, protists and bacteria, can exchange gases directly with their surroundings through diffusion. Larger organisms have adaptations that reflect their environments.

Insects use trachea-tubes from the exoskeleton for gas exchange, due to their small size and therefore short diffusion path.

Explain the need for the ventilation system.6.4.2

Land-based animals (and waterborne mammals), including humans, have internal ventilation systems which allow gas to exchange with the blood.

Gills extract O2 from and remove CO2 from water.

A ventilation system is needed to maintain high concentration gradients in the alveoli.

6.4.3Describe the features of the alveoli that adapt them to gas exchange.Alveoli increase the surface area for gas exchange. They are millions in number, each within their own network of capillaries. A rich blood supply maintains a high concentration gradient of O2 and CO2.

Membranes are very thin, both the alveoli and the capillaries, so the diffusion path is short.

Surfaces are wet, so gases are dissolved, making diffusion easier.

6.4.4The Ventilation System

6.4.5Mechanism of Ventilation of the LungsINSPIRATIONExternal intercostal muscles contract.Diaphragm contracts (drops).Abdominal muscles relax.

Chest volume increases,pressure in the lungs decreases,air enters.

EXPIRATIONInternal intercostal muscles contract.Diaphragm relaxes (rises).Abdominal muscles contract.

Chest volume decreases,Pressure in the lunges increases,air is pushed out.

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