absorption of materials

• Oxygen and nutrients from food must be absorbed into the bloodstream to be delivered to cells for respiration. which creates energy for the organs.

  Waste materials such as carbon dioxide, must be removed from cells into the bloodstream.

  Tissues contain capillary networks that allow the exchange of materials to a 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 at which materials are absorbed.
• The lungs are the gas exchange organs. They consist of a large number of alveoli providing a large surface area for gas exchange.

  Oxygen into the blood is exchanged for carbon dioxide out of the blood.

  A) trachea

  B) bronchi

  C) bronchioles

  D) alveoli

  
• Alveolus gas exchange

  A) alveoli

  B) capillary

  C) carbon dioxide out

  D) oxygen in

  E) red blood cells

  F) carbon dioxide

  G) oxygen

  H) air

  
• • Thin lining: the lining of the alveoli is very thin so that gases can quickly diffuse through it.
• • Large surface area: human lungs contain about 500 million alveoli, which creates a surface area around half the size of a tennis court. This speeds up diffusion because gases have more area over which to diffuse.
• • Good blood supply: the alveoli have a dense capillary network so that large volumes of gases can be exchanged.
• The lining of the small intestine is folded into millions of finger-like projections called villi. This provides a very large surface area, which increases the speed of absorption of small soluble food molecules.
• Each villus has the following specialisations to aid absorption:

  • Its lining is only one cell thick, which increases speed of absorption.
  • Capillaries in each villus to provide a good blood supply to take up and transport glucose and amino acids.
• the lacteal absorbs fatty acids and glycerol.
• a villus in the small intestine:

  A) thin lining

  B) lacteal

  C) capillary