3.1 Exchange Surfaces

Question 1

Why do bony fish need specialised gas exchange surfaces?

Answer 1

• Multicellular
• High demand for oxygen
• Small SA:V ratio
• Scaly surface prevents gaseous exchange

Question 2

Why do gills make good exchange surfaces?

Answer 2

• Site of gaseous exchange
• Large surface area
• Good blood supply

Question 3

What is the function of gill lamellae and why is it good for this?

Answer 3

• Gas exchange
• Rich blood supply
• Large surface area
• Have overlapping tips to slow water

Question 4

What are the features of gill filaments and how are they specialised?

Answer 4

• Occur in large stacks and are kept apart by water exposing large surface area
• Thin reducing diffusion distance

Question 5

What is counter-current flow?

Answer 5

Where blood and water flow in opposite direction to maintain concentration gradient across entire length of the gill

Question 6

What happens in bony fish when the buccal cavity lowers?

Answer 6

• The volume of buccal cavity decreases
• Pressure inside buccal cavity decreases and water is forced in

Question 7

What happens in bony fish when the opercular valve is shut?

Answer 7

• Opercular cavity expands
• Pressure in opercular cavity decreases
• Floor of buccal cavity increases,increasing pressure and forcing water over the gills

Question 8

Why can’t insects have a normal gas exchange surface?

Answer 8

• Exoskeleton is too tough
• Do not have blood pigments that carry oxygen

Question 9

What are spiracles?

Answer 9

• Small openings along thorax and abdomen where air enters and water and air leaves

Question 10

How do insects minimise water loss through respiration?

Answer 10

• Sphincters in spiracles which open and close
• Mostly closed unless oxygen demand increases or CO2 builds up

Question 11

What are trachae and how do their features help?

Answer 11

• 1mm in diameter taking air out the body
• Lined with chitin which keeps them open when bent

Question 12

What are the features of the tracheole?

Answer 12

• NO chitin
• Freely permeable to gases
• Site of most gaseous exchange

Question 13

What is tracheal fluid?

Answer 13

• Found at the ends of the trachioles and limits penetration of air via diffusion

Question 14

How does oxygen diffuse across in insects?

Answer 14

Diffuses in lining of trachae and tracheole

Question 15

What happens if an increase in oxygen need happens in insects?

Answer 15

• Lactic acid builds up in tissues
• Water moves out of tracheole via osmosis
• Exposes more surface area for gaseous exchange

Question 16

What happens in larger insects in terms of respiration?

Answer 16

• Mechanical ventilation where air is manually moved in through muscular pumping movements
• Collapsible enlarge trachae which act as air reservoirs to increase amount of air moved through gas system

Question 17

Why might higher temperatures increase volume of water passing over gills?

Answer 17

Metabolism is faster so more oxygen is required