Section 3: Gas Exchange

Question 1

What is the relationship between SA:V and metabolic rate?

Answer 1

• Rate of heat loss per unit mass increases as SA: V increases - smaller animals
• So they need a higher metabolic rate/ faster respiration
• To generate enough heat to maintain a constant body temp

Question 2

What is the relationship between the size of the organism and its SA: V?

Answer 2

• Smaller organisms have a high SA:V

Question 3

What are the adaptations of gas exchange across the body surface of a single-celled organism?

Answer 3

• Thin, flat shape
  
  • Large SA: V
  • Short diffusion pathway
  • For rapid diffusion e.g oxygen/ carbon dioxide

Question 4

How does gas exchange occur in an insect?

Answer 4

• Air moves through spiracles on the surface of the insect
• Air moves through tracheae
• Gas exchange at tracheoles directly to/from cells
  
  • Oxygen diffuses down conc. gradient to respiring cells
  • CO2 diffuses down conc gradient from respiring cells

Question 5

What are the adaptations of the insect’s gas exchange system?

Answer 5

• Lots of thin, branched tracheoles - short diffusion pathway
• Large surface area - rapid diffusion
• Abdominal movements - increase the amount of O2 entering - maintains greater conc gradient for diffusion

Question 6

How does gas exchange occur in a fish?

Answer 6

• Counter current flow
• Blood flows through lamellae and water flows over lamellae in opposite directions
• Always a higher conc of O2 near blood - hence a conc gradient is maintained along the whole length of lamellae
• Maximising diffusion of oxygen

Question 7

What are the adaptations of the gas exchange of a fish?

Answer 7

• Each gill is made of lots of gill filaments which are covered in many lamellae - provide a large surface area
• Vast network of capillaries on lamellae - remove oxygen to maintain a conc gradient
• Thin/flattened epithelium - shorter diffusion pathway between water and blood

Question 8

What is the process of gas exchange in plants?

Answer 8

• Co2/ oxygen diffuses through the stomata
• Stomata opened by guard cells
• CO2 / oxygen diffuse into mesophyll layer into air spaces
• CO2/ oxygen diffuses down conc gradient

Question 9

What are the adaptations of the gas exchange system in plants?

Answer 9

• Lots of stomata that are close together
  
  • Large SA for gas exchange
• Interconnecting air space in mesophyll layers
• Mesophyll cells have a large surface area
• Thin - short diffusion pathway

Question 10

What are the adaptations in xerophytic plants?

Answer 10

• Thick waxy cuticle - increases diffusion distance
• Stomata in pits/grooves/ rolled leaves/ hairs - trap water vapour - WP gradient decreased - less evaporation
• Spindles/ needles - reduces SA:Vol