4.2 - Gas Exchange in Insects

Question 1

What gas exchange system do insects have

Answer 1

they have an open circulatory system called the tracheal system

Question 2

what does it mean that insects have an open circulatory system?

Answer 2

• body fluid acts as both blood and tissue fluid
• circulation is slow and affected by body movements

Question 3

What does the tracheal system consist of?

Answer 3

TRACHEA
- air-filled tubes
- have spiralling strands of chitin in the walls making them rigid, protecting against compression and is impermeable to gas exchange

SPIRACLES
- small holes in the exoskeleton

TRACHEOLES
- the subdivisions of the trachea
- gas exchange occurs across the fluid-filled tips of the tracheoles

Question 4

what is the purpose of air sacs?

Answer 4

• they are reserves of air
• in aquatic insects they consume the stored air while underwater or used it to regulate bouyancy

Question 5

explain the gas exchange in a resting insect.

Answer 5

• tracheoles are filled with a water fluid that diffuses from the hypotonic cytoplasm of the resting cells
• the diffusion of oxygen through this water medium relatively slowly but still meets the metabolic demands of the resting insect
• oxygen diffuses into the cells along a diffusion gradient, where ppo2 in cells is lower than that in the tracheoles
• co2 diffuses from cells to tracheole

Question 6

explain gas exchange in active insects

Answer 6

• during periods of high activity, the increased rate of metabolism within the insect’s muscle cells leads to the accumulation of lactic acid within the cells
• lactic acid reduces the osmotic potential of the cells and fluid is withdrawn from the tracheoles by osmosis
• air moves in to replace the fluid, and gases diffuse more rapidly across the air-filled tracheoles

Question 7

How are insects ventilated?

Answer 7

1. sections of the tracheal system are expanded and have flexible walls, and they act as air sacs which can be squeezed by the action of flight muscles. This repetitive action can ventilate the tracheal system
2. in larger, more active insects air is forced in and out by body/wing movements as they alter the thorax volume. if the thorax volume decreases, the air in the tracheal system is under pressure and pushed out of the tracheal system and vice versa

Question 8

adaptations in insects

Answer 8

1. Large surface area provided by the extensive network of
   tracheoles, which is further increased when fluid is
   withdrawn from the tracheoles during periods of high
   metabolic activity.
2. Steep concentration gradients are maintained between the
   tracheoles and body cells due to tissue respiration.
3. In larger, more active insects, the pumping movements of
   the abdomen increases the steepness of this diffusion
   gradients to meet the metabolic
   demands of the organism.
4. A short diffusion path exists between the thin tracheole
   walls and the tissues.
5. The continual flow of
   air through the tracheal
   system maintains the
   ventilation of the tissues,