gas exchange in insects

Question 1

describe 3 insect adaptations to reduce WATER LOSS

(not gas exchange)

Answer 1

• insects have a small surface area to volume ratio where water can evapourate from
• spiracles can open and close to reduce water loss
• insects have waterproof exoskeleton

Question 2

describe 4 insect adapations for efficient GAS EXCHANGE

Answer 2

• short distance between spiracles and muscle fibres- shortens diffusion distance of gases to cells
  - tracheoles are highly branched –> increases surface area for gas exchange
  - fluid in ends of trachea where it joins tissues -->gas exchange form air to liquid occurs in tracheole, allows gases to diffuse to tissues faster
  - muscles pump body to force air in/out–> maintains concentration gradient for gas exchange

Question 3

what are the structures found within insects (and why do they help gas exchange?)

Answer 3

1) spiracles
- valve openings
- o2 + co2 enter and leave via spiracles

2) trachea
- network of internal tubes
- contain rings to strengthen tubes and keep them open

3) tracheoles
- smaller tubes
- extend throughout all tissues in insect to deliver oxygen to all respiring cells

Question 4

what are the three methods of moving gases in the tracheal system?

Answer 4

1) diffusion
- cells respire, use up oxygen, and produce carbon dioxide
- creates a conc gradient from tracheoles to atmosphere
- causes oxygen to diffuse in
2) mass transport
- insect contracts + relaxes abdominal muscles
- moves gases on mass

3) anaerobic respiration
- produces lactate
- lowers water potential
- so water moves into tracheoles by osmosis
- this decreases volume, so air from atmosphere is drawn in

Question 5

Practice exam q:
Explain what causes the oxygen concentration in the trachea to fall when spiracles are closed

Answer 5

• oxygen used in areobic tissues in cells
• oxygen diffuses from trachea to tissue cells
• spiracles closed so oxygen cant be replaced + cant enter

Question 6

what stimulates spiracles to open?

Answer 6

• increased levels of carbon dioxide

Question 7

why is gas exchange by diffusion only possible in very small animals?

Answer 7

• smaller animals have large surface area:volume ratio
• cells on inside of organism will be close to gas exchange surface
• all cells will be a short distance from gas exchange surface

Question 8

why do cells of greater mass have higher metabolic rate?

Answer 8

they have more cells so require more energy

Question 9

practice exam question:
an insect lives in dry conditions. suggest an advantage of the pattern of spiracle movements

spiracle movements essentially means the opening and closing of the spiracles

Answer 9

• spiracles are not open all the time
• so less water loss through spiracles occurs

Question 10

practice exam question:
explain the need for greater abdominal pumping during exercise (3 marks)

Answer 10

• abdominal pumping leads to mass transport of oxygen in tracheoles(1 mark)
• oxygen required for areobic respiration ( 1 mark)
• areobic respiration releases energy for muscle contraction in exercise(1 mark)