In this topic of IBDP Biology, we will learn about 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.

• 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

• 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.

• 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.

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