Gas exchange in single-celled oeganisms and insects

Adaptations to reduce water loss in insects

Small SA:V ratio to minimise the area over which water is lost

Waterproof coverings

Spiracles can close to reduce water loss

Describe the conflict in terrestrial insects between gas exchange and conserving water

Gas exchange requires a thin permeable surface with large area

Conserving water requires thick waterproof surfaces with small area

Describe why the tracheal system limits the size of insects

Because it relies on diffusion to bring oxygen to the respiring tissues

If insects were large it would take too long for oxygen to reach the tissues rapidly enough to supply their needs

Spiracles opening and closing data analysis

Increase in carbon dioxide concentration stimulates spiracles to open

Oxygen concentration in the tracheae falls when spiracles are closed because oxygen is used in aerobic respiration diffusion to tissues

If spiracles are closed, oxygen unable to enter organism

State an advantage of these spiracles movements to a terrestrial insect

Helps conserve water because the spiracles are not open continuously and therefore does not diffuse out