Insect respiration

When an organism is large, there is a small surface area to volume ratio, when an organism is small there is a large surface area to volume ratio. Large organism increase surface area to volume ratio by having a more flattened shape, and having specialised exchanged surfaces.

Specialised exchange surfaces are adapted for exchange by that they:

• Have a large surface area to volume ratio,
  
• Thin => short diffusion distance
• Movement of external/internal medium to maintain diffusion gradient,
• Paritally permeable.

Four things that need to be exchanged are: Respiritory gases, nutrients, heat, excretory waste.

Single celled organisms exchange gas through diffsuin along their bodies.

Insects are terrestrial. They live on land, but water easily evaporates from their surface, leaving them dehydrated. They need to conserve water.

Conserving water opposes the needs of gas exchange: Thin (short diffusion distance), large SA/V ratio, and partially permeable.

Insects have a waterproof covering; a waxxy cuticle all over thier body. Also, they have a large surface area to volume ratio, these are both to prevent water loss, and yet as predicted, they do indeed, combat gas exchange.

So that gas exchage can take place, there is an external network of tubes called Trachae. The trachae divide into smaller tubes, that extend through the tissues, which means air is brought directly to the respiring tissues. At the ends of these smaller tube, Tracheoles, cells are respiring, so the concentration of oxygen is low, which means where the spiracles (pores on hte body) are open, air will diffuse in. Also, as carbon dioxide is in high concentration at the respiring tissues, but not outside of the spiracles, this will diffuse out.

The spiracle's ability to open and close can also control water loss, as when they are closed, water can;t evaportate out.

The diffusion distance needs to be short, so this limits the size of the insect.