insect and fish gas exchange unit 3

Question 1

The adult damselfly uses a tracheal system for gas exchange.
Explain three ways in which an insect’s tracheal system is adapted for efficient gas
exchange. (3marks)

Answer 1

• Large number of tracheoles increase the surface area
• Thin walls of tracheoles decreases diffusion pathway
• Ventilation mechanisms such as abdominal pumping body movement maintains steep diffusion gradient

Question 2

Name the structure through which gases enter and leave the body of an insect.

Answer 2

Spiracles

Question 3

Name the small tubes that carry gases directly to and from the cells of an insect.

Answer 3

Tracheoles

Question 4

Explain the movement of oxygen into the gas exchange system of an insect when it is at
rest.

Answer 4

Oxygen used in (aerobic) respiration;
2. (so) oxygen (concentration) gradient (established); (so) oxygen diffuses in;

Question 5

Describe how the structure of the insect gas exchange system:
*   provides cells with sufficient oxygen
*   limits water loss. (5 marks)

Answer 5

• Spiracles lead to trachea which lead to the tracheoles.
• Open spiracles allow diffusion of oxygen through the tracheoles.
• Tracheoles are highly branched which leads increased surface area
• Thin walls of tracheoles provide a short diffusion pathway
• Spiracles close during inactivity preventing water loss

Question 6

Describe how humans breathe in and out. (5 marks)

Answer 6

Breath in:
- External intercoastal muscles and diaphragm: contracts
- Internal intercostal muscles: relax
- Volume in thoracic cavity increases - pressure decreases
- Air moves down a concentration gradient.

Breath out:
External intercostal muscles + diaphragm: relaxes
Internal intercostal muscles : contract
Volume in thoracic cavity decreases and pressure increases
Air moves up a concentration gradient