2.7 Absorption of Materials

National 5 Biology

Oxygen and nutrients from food must be absorbed into the bloodstream to be delivered to cells for respiration.
Waste materials, such as carbon dioxide, must be removed from cells into the bloodstream.
Tissues contain capillary networks to allow the exchange of materials at cellular level.
Surfaces involved in the absorption of materials have certain features in common:
- large surface area
- thin walls
- extensive blood supply
These increase the efficiency of absorption.
Lungs are gas exchange organs.
They consist of a large number of alveoli providing a large surface area.
Oxygen and carbon dioxide are absorbed through the thin alveolar walls to or from the many blood capillaries.
Nutrients from food are absorbed into the villi in the small intestine.
The large number of thin walled villi provides a large surface area.
Each villus contains a network of capillaries to absorb glucose and amino acids and a lacteal to absorb fatty acids and glycerol.