Insects

Question 1

Why not body surface?

Answer 1

Small SA:V and impermeable chitin exoskeleton so cannot use surface for sufficient diffusion

Question 2

Tracheal system

Answer 2

• Air enters through pores i.e. spiracles (2-4 thoracic + 6-8 abdominal = 10)
• Spiracles into chitin-lined air tubes tracheae
  which branch into smaller tracheoles
• End of tracheole has fluid (gas dissolves in) close to mucle fibres
• No transport system as exchange surface in contact with muscle

Question 3

Ventilation (In)

Answer 3

• Abdomen can expand and compress
• Abdomen expands and thoracic spiracles open after that
• Pressure decreases and air drawn in via thoracic spiracles

Question 4

Ventilation (out)

Answer 4

• Abdomen compressed before abdominal spiracles open
• Abdominal spiracles open second just as thoracic spiracles close
• Higher pressure so air forced out

Question 5

Adaptations

Answer 5

• Spiracles closed for long periods- prevent water loss
• Internal = reduces heat and water loss
• Hair covering spiracles trap dirt, dust and foreign particles
• Tracheoles thin = short distance lined with surfactant- reduce surface tension and prevents collapse
• Exoskeleton reduces water loss

Question 6

Advantages of tracheal system

Answer 6

• No respiratory pigment
• Reduced water loss
• Oxygen supplied directly to tissues
• No transport system needed
• Fast

Question 7

Why do muscle fibres have max diameter 20µm?

Answer 7

• Short diffusion pathway
• If muscle too large = greater diffusion distance to respiring cells
• Speed of diffusion would be too slow to supply enough oxygen

Question 8

Fluid level in tracheoles

Answer 8

• O2 dissolves in fluid and then diffuses into muscle cells
• Fluid level decreases during flight/ exercise
• More area for gaseous exchange and shorter diffusion pathway