Gas Exchange In Insects

Question 1

How have insects adapted to minimise water loss?

Answer 1

• small SA:V ratio which minimises the area of which water is lost.
• waterproof coverings over body surfaces.

Question 2

Rate of diffusion =

Answer 2

              Distance

Question 3

So what do insects require to limit water loss?

Answer 3

Insects require a specialised system of internal tubing called the tracheae, they are supported by rings to stop them collapsing and then further into the insects divide into smaller tubes called tracheoles. Air enters the system via a small opening and closing holes on the surface called spiracles.

Question 4

Movement of gas through the tracheae in insects?

Answer 4

• diffusion, when oxygen is used its concentration falls towards the ends of the tracheoles creating a concentration gradient.
• mass transport, the contraction of muscles squeeze the trachea enabling mass movements of air in and out.
• ends of tracheoles filled with water, the muscle cells respire and carry out anaerobic respiration producing lactic acid which lowers the WP so water moves via osmosis so the water in the tracheoles decreases which draws in more air.

Question 5

What does movement of gas in the tracheae rely on?

Answer 5

A short diffusion pathway so insects must be small.

Question 6

Spiracles?

Answer 6

Air enters the spiracle allowing oxygen to travel along the trachea to reach the insect cells.

Question 7

What problems arise in insects?

Answer 7

The conflicting needs of an efficient gas exchange system and the need to conserve water. The air at the exchange surface is more or less 100% saturated with water vapour which means there is less evaporation of water from the exchange surface.

Question 8

How have insects evolved to conserve water?

Answer 8

• small SA:V ratio to minimise the area over which water can be lost.
• waterproof coverings over their body surfaces this is a rigid outer skeleton of chitin covered with a waterproof covering.
• spiracles which can be closed to reduce water loss, this conflicts with the need for oxygen so occurs when the insect rests

Therefore insects can’t use their body surfaces to diffuse respiratory gases instead tracheae carry oxygen directly to the tissues.