Gas exchange in an insect
- When it comes to IBDP Biology, insects were the first terrestrial animals.
- Insects exchange oxygen and carbon dioxide between their tissues and the air.
- Use a system of air-filled tubes called tracheae.
- Tracheae open to the outside through small holes called spiracles.
- The walls of the tracheal tubes are stiffened with bands of chitin.
- These, in turn, lead to ever-finer branches.
- The branches penetrate to every part of the body.
- Tracheoles at the ends may be less than 1 µm in diameter
- Every cell in the insect's body is adjacent, or very close to, the end of a tracheole.
- Even so, there is a limit to the pressure they can withstand without collapsing.
- This may be one reason why insects are relatively small.
Reducing water loss
- When it comes to IBDP Biology, water vapour as well as carbon dioxide diffuses out of the spiracles.
- This could lead to dehydration in dry environments.
- The spiracles are guarded by valves.
- These are controlled by muscles that enable the grasshopper to open and close them.
- When oxygen demand is less, they partially close the spiracles.
- There are hairs that filter out dust as the air enters the spiracles.
- These also trap moisture, reducing water loss.
- They also have a waterproof cuticle
Ventilation of the Tracheal System
- In smaller or less active insects, gas exchange though the tracheal system is by simple diffusion.
- Large, active insects like grasshoppers, forcibly ventilate their tracheae.
- Contraction of muscles in the abdomen compresses the internal organs and forces air out of the tracheae.
- As the muscles relax, the abdomen springs back to its normal volume and air is drawn in.
- Large air sacs attached to portions of the main tracheal tubes increase the effectiveness of this bellows-like action.
Maximising gas exchange when active
- When it comes to IBDP Biology, at rest, water tends to accumulate in the tracheoles.
- When active, lactic acid accumulates in the muscle cells.
- This reduces the water potential of the cells.
- Water passes from the tracheoles into the muscle cells by osmosis.
- This increases the surface area and reduces the diffusion distance for gas exchange,
This is the end of this topic.