6 Exchange

Question 1

Describe gas exchange in single-celled organisms

Answer 1

• Large SA to VR
  -Oxygen is absorbed by diffusion across their body surface, which is covered only by the cell surface membrane
• CO2 from respiration diffuses out across their body surface.

Question 2

Describe gas exchange in insects

Answer 2

Mass transport-the contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out.
Ends of tracheoles are filled with water- lactic acid lowers the water potential so water moves into the cells from the tracheoles, final diffusion pathway is gas rather than a liquid phase, making diffusion more rapid.
Spiracles- open to allow gas exchange.

Question 3

Describe gas exchange in fish

Answer 3

Fish are specialised to carry out counter-current flow. This means that blood that is already loaded with oxygen meets water so that diffusion takes place from water to gills.
Blood with little oxygen meets water which has had most of its oxygen removed. diffusion from water to blood takes place.

Question 4

Describe human mechanisms of breathing

Answer 4

the diaphragm and external intercostal muscles contract. This causes the chest wall (rib cage) to move upwards and outwards as the diaphragm flattens, and so the thoracic cavity expands. As the volume of the thoracic cavity rises, the lung pressure decreases below atmospheric pressure.