Gas exchange

Question 1

How does oxygen move through the insect? (4)

Answer 1

1) oxygen diffuses in through the spiracles;
2) spiracles close
3) oxygen moves through the trachea into the tracheoles
4) oxygen delivered directly to the respiring tissues

Question 2

Explain three ways in which an insects tracheal system is adapted for efficient gas exchange

Answer 2

• tracheoles have thin walls so short diffusion distance to cells
• Highly branched tracheoles so short diffusion
• Highly branched so large surface area
• Tracheae provide tubes full of air so fast diffusion

Question 3

what makes a good exchange surface? (3)

Answer 3

• Large surface area
• large concentration gradients
• thin exchange surface

Question 4

Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill.

Answer 4

1. Water and blood flow in opposite directions;
2. Maintains diffusion/concentration gradient of oxygen OR Oxygen concentration always higher (in water);
3. (Diffusion) along length of lamellae/filament/gill/capillary;

Question 5

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange.

Answer 5

1 Large surface area provided by many lamellae over many gill filaments;
2 Increases diffusion/makes diffusion efficient;
3 Thin epithelium/distance between water and blood;
4 Water and blood flow in opposite directions/countercurrent;
5 (Point 4) maintains concentration gradient (along gill)/equilibrium not reached;
6 As water always next to blood with lower concentration of oxygen;
7 Circulation replaces blood saturated with oxygen;
8 Ventilation replaces water (as oxygen removed);

Question 6

Explain two ways in which the structure of fish gills is adapted for efficient gas exchange (2)

Answer 6

1. Many filament/lamellae so there’s a large surface area

2. Lamellae are thin for a short diffusion pathway

Question 7

Why does water and blood flow in opposite directions?

Answer 7

To maintain a concentration gradient across the whole length of the gill lamellae

Question 8

How do insects limit water loss

Answer 8

1. Waterproof covering over their body surfaces.

2. Small surface area to volume ratio

Question 9

Explain three ways in which an insect’s tracheal system is adapted for efficient gas

Answer 9

1. Tracheoles have thin walls so short diffusion distance to cells;
2. Highly branched / large number of tracheoles so short diffusion distance to cell
3. Highly branched / large number of tracheoles so large surface area (for gas
   exchange);
4. Tracheae provide tubes full of air so fast diffusion (into insect tissues);
5. Fluid in the end of the tracheoles that moves out (into tissues) during exercise:
   faster diffusion through the air to the gas exchange surface;
   OR
6. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);
7. Body can be moved (by muscles) to move air so maintains diffusion / concentrati
   gradient for oxygen / carbon dioxide;

Question 10

Describe inhalation

Answer 10

• External intercostal muscles contract pulling rib cage up & down
• Diaphragm contracts & pulls down
• Thoracic cavity volume increases
• Pressure in lungs lower than atmospheric pressure
• Air moves into lungs down a pressure gradient

Question 11

Describe exhalation

Answer 11

• External intercostal muscles relax
• Diaphragm relaxes and moves up
• Thoracic cavity volume decreases
• Pressure in lungs greater than atmospheric pressure
• Air moves out of lungs down a pressure gradient

Question 12

Give 5 adaptations xerophytic plants (plants in a dry environment) have to reduce water loss

Answer 12

1-Reduce number of stomata so less SA for water loss
2-Stomata in pits so a reduced water potential gradient
3-Hairs to trap water vapour so a reduced water potential gradient
4-Rolled leaves so a reduced water potential gradient
5-thick waxy cuticle so an increased diffusion distance