gas exchange

Question 1

ficks law

Answer 1

(SA x CG) / DD

Question 2

what makes a good exchange surface?

Answer 2

• large SA
• large CG
• thin exchange surface

Question 3

what features may insects have to balance water loss

Answer 3

• waterproof covering: rigid outer skeleton covered with wax cuticle
• relatively small SA:V ratio to minimise the area over which water is lost

Question 4

how does oxygen move through an insect?

Answer 4

• oxygen diffuses in through the spiracles
• spiracles close
• oxygen diffuses through the trachea into the trachioles
• oxygen delivered directly to the respiring tissues

Question 5

explain 3 ways in which an insect’s tracheal system is adapted for efficient gas exchange

Answer 5

• tracheoles have thin walls so short diffusion distance
• highly branched so short diffusion distance
• highly branched so large SA
• trachea provides tubes full of air so fast diffusion
• fluid at end of tracheoles moves out during exercise so large SA
• body can be moved by muscles to move air so maintains concentration gradient

Question 6

explain two ways in which the structure of the gills are adapted for efficient gas exchange?

Answer 6

• many lamellae so large sa
• lamellae are thin for a short diffusion pathway

Question 7

countercurrent flow

Answer 7

blood and water flow in opposite directions
- maintains a cg across the whole length of the lamellae

Question 8

describe and explain the advantage of the counter current principles in gas exchange across a fish gill

Answer 8

• water and blood flow in opposite directions
• maintains concentration gradient of oxygen
• diffusion along the whole lengtjh of the lamellae

Question 9

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

Answer 9

• large SA provided by many lamellae over many gill filaments so increases diffusion
• thin epithelium between water and blood so short dd
• water and blood flow in opposite directions so maintains a cg
• as water always next to blood with a lower conc of oxygen
• circulation replaces blood saturated with oxygen
• ventilation replaces water when oxygen removed

Question 10

explain how the counter current mechanism in fish gills ensures the maximum amount of oxygen passes into the blood flowing through the gills

Answer 10

• water and blood flow in oppsoite directions
• blood always passing water with a higher oxygen concentration
• cg maintained across whole length of lamellae

Question 11

desribe how carbon dioxide in the air outside a leaf reaches the mesophyll cells inside the lead

Answer 11

• CO2 enters via stomata
• stomata opened by guard cells
• diffuses through air space
• down a concentration gradient

Question 12

adaptations for a leaf

Answer 12

flat - large sa:v
many stomata - more airflow
air spaces - short distance ebtween mesophyll cells and leaf

Question 13

xerophytic plant adaptations

Answer 13

small no of stomata = less sa for water loss
- stomata in pits = reduced cg
- hairs to trap water vapour - reduced cg
- rolled leaves = reduced cg
- leaves reduced to spines = less sa for water loss
- thick waxy cuticle - icreased dd

Question 14

explain why plants grown in soil with very little water grow slowly

Answer 14

• stomata close
• less CO2
• less PS