Gas exchange in insects

Describe insects and their need for gas exchange surfaces

Insects have a high surface area:volume ratio so they are susceptible to water loss and desiccation (drying out). An adaptation for their terrestrial mode of life is their chitin exoskeleton with a layer of waterproof wax, which prevents them from exchanging gases over their surface area as wax is impermeable to gases

What is the specialised gas exchange surface of an insect?

Holes in their exoskeletons are called spiracles which lead to tracheae, a system of chitin lined tubes. The chitin supports the tracheae and prevents them from collapsing. The tracheae terminate in trachioles which are close to the cells of the insect and these are the gas exchange surface

What is the circulatory system in insects?

Open - blood is not contained within vessels and is in contact with cells directly. Circulation depends on diffusion alone (and the maintenance of these diffusion gradients)

What are spiracles?

Rows of holes down the sides of an insect, in both the thorax and abdomen. They have valves to reduce water loss when closed

How do spiracles work?

The spiracles must be open for gas exchange. The buildup of carbon dioxide at the spiracles stimulates these to open, which also lets oxygen rich air in. The drop in carbon dioxide levels in the tracheae stimulates the spiracles to close

What is spiracular fluttering?

The rapid partial opening and closing of spiracles to allow gases to enter and leave. This is punctuated by the full opening of the spiracles

How does ventilation in insects occur?

It is accomplished by muscular movements in the abdomen. To bring oxygenated air into the insect, the abdomen expands, lowering the pressure inside. The abdominal spiracles are closed and the spiracles on the thorax are open. The lower pressure on the abdomen pulls the air through the thoracic spiracles. To expel carbon dioxide rich air, the abdomen contracts, lowering the volume and increasing the pressure. The thoracic spiracles are closed and the abdominal spiracles open. The stale air is forced out of the open spiracles

What is insect flight muscle?

A highly active tissue, with the cells containing many mitochondria to utilise oxygen in aerobic respiration and release ATP to be used in muscle contraction. The tracheoles in flight muscle penetrate the cells.

What happens to insect ventilation during flight?

At rest, the tracheole ends are fluid filled. During flight, available oxygen is used rapidly and some anaerobic respiration takes place, producing lactic acid and lowering the water potential of the muscle cells. Water leaves the tracheoles by osmosis. The result of this is that there is no more air in contact with the muscle cells to raise the rate of diffusion of oxygen into the cells