7.6 gas exchange in insects

What anatomical and physiological features require insects to have a specialised gas exchange system?

1. They have a tough, chitinous exoskeleton through which little to no gas exchange can occur

2. They have active lifestyles and therefore high oxygen requirements

What are spiracles and where are they located in insects?

Spiracles are openings on the body surface that allow air to enter an insect's tracheal system.

Spiracles are located on the insect's exoskeleton along the abdomen and thorax.

How do insects regulate water loss through the spiracles?

Spiracles can open and close to regulate water loss.

When the insect is inactive, spiracles remain closed to prevent excess evaporation.

What are tracheae and what is their role in insect gas exchange?

Tracheae are air-filled tubes branching throughout the insect's body.

Tracheae deliver oxygen directly to cells and remove carbon dioxide from cells.

The tracheal system replaces the circulatory system's role.

What is the function of chitin in insect tracheae?

The spirals of chitin that line the tracheae prevent them from collapsing, keeping them open for air flow.

What are tracheoles and where are they located?

Tracheoles are the smallest tracheal branches, which penetrate into insect tissues where gas exchange occurs.

How does air generally flow through the insect tracheal system?

Air passively diffuses into the spiracles and flows through the tracheae and tracheoles down a concentration gradient, from high to low concentration.

Insect movement helps circulate air to maintain this concentration gradient.

What adaptations make tracheoles ideal sites for gas exchange?

1. Penetrate directly into tissues - reduces the gas diffusion distance

2. Thin walls - reduce the gas diffusion distance

3. Highly branched - maximises the surface area

4. Not reinforced with chitin - allows gas exchange to occur

5. Fluid at the ends of the tracheoles (tracheal fluid) - allows oxygen to dissolve to aid diffusion and reduces water loss

What are some ventilation mechanisms that some insects use when oxygen demand rises?

1. More spiracles open - allows more oxygen to enter the tracheal system

2. Breathing rate increases - allows more oxygen to enter the tracheal system

3. Mechanical active ventilation - muscles around tracheae contract and relax, squeezing tracheae to pump air in/out of spiracles

4. Movement of tracheal fluid out into tissues - increases the diffusion rate and surface area for gas exchange

5. Enlarged collapsible tracheae, accessory sacs, and air reservoirs - these inflate or deflate to ventilate the tracheal system

6. Movement of wing muscles connected to sacs - pump air to ventilate the tracheal system

7. Vibration of thoracic muscles - pumps air to ventilate the tracheal system