Gas Exchange in Insects

Why do insects need gas exchange

Insects need efficient systems for exchanging gases for two main reasons:

To deliver oxygen to cells

This allows aerobic respiration to occur to release energy for cellular processes

To remove carbon dioxide from cells

The build up of carbon dioxide produced as a waste product of respiration reduces pH, which can denature enzymes.

What two confliciting needs does an insects gas exchange adapted to balance?

Maximising gas exchange efficiency

Minimising water loss

What is the structure of insect gas exchange system

Air moves into the tracheae through pores on the surface called spiracles

Oxygen travels down the concentration gradient (high to low concentration) towards the cells

The tracheae branches off into smaller tracheoles which have thin, permeable wall and go to individual cells

This means that oxygen diffuses directly into respiring cells - the insect's circulatory system doesn't transport oxygen

Carbon dioxide from the cells moves down its own concentration towards the spiracles to be released into the atmosphere

Why do insects do abdominal beating?

Muscular contractions in the abdomen help with ventilation maintaining a concentration gradient

Adapatations of the tracheae

Reinforced with spirals/rings of chitin: Prevents collapsing

Multiple tracheae: Increases surface area

Adaptations of tracheoles

Penetrate directly into tissues: Reduces gas diffusion distance

Thin walls: Reduce the gas diffusion distance

Highly branched: Maximises surface area

Fluid at the ends of the tracheoles (tracheal fluid)

Allows oxygen to dissolve to aid diffusion and reduce water loss

Adaptations of spiracles

Spiracles need to open for gas exchange. When the spiracles are open water can evaporate out. The spiracles are not always open; this conserves water

Spiracles are controlled by valves. Valves open when carbon dioxide concentration gets too high

What do larger insects also have?

Larger insects have air sacs

Inflates or deflates to ventilate the tracheal system and can increase the volume of air moved through the system

How is water loss reduced in insects

The exoskeleton is covered with a waterproof cuticle to help prevent water loss

Spiracles are not open all the time

Spiracles can be sunken, and/or surrounded by hair which traps a layer of moisture, reducing air movements, and reducing the concentration gradient (so less water will be moving out)

How does gas exchange occur in insects?

Air enters the tracheal system through open spiracles.

Air moves into larger tracheae and diffuses into smaller tracheoles.

Tracheoles branch throughout the body, transporting air directly to cells.

Oxygen dissolves in water in tracheal fluid and diffuses down its concentration gradient from tracheoles into body cells.

Carbon dioxide diffuses down its concentration gradient out of body cells into the tracheoles.

Air is then carried back to the spiracles via the tracheae and released from the body.