3.3.2 Gas exchange (3.3 Organisms exchange substances with their environment)

Question 1

Explain how the body surface of a single celled organism is adapted for gas exchange

Answer 1

• Thin , flat shape and large surface area to volume ratio
• Short diffusion distance to all parts of cell => rapid diffusion

Question 2

Describe the tracheal system of an insect

Answer 2

1) spiracles = pores on surface that can open or close to allow diffusion
2) tracheae = large tubes full of air that allow diffusion
3) tracheoles = smaller branches from tracheae , permeable to allow gas exchange with cells

Question 3

Explain how an insects tracheal system is adapted for gas exchange

Answer 3

• Tracheoles have thin walls
  • So short diffusion distance to cells
• High numbers of highly branched tracheoles
  • So short diffusion distance to cells
  • So large surface area
• Tracheae provide tubes full of air
  • So fast diffusion
• Contraction of abdominal muscles changes pressure in body , causing air to move in and out
  • Maintains concentration gradient for diffusion
• Fluid in end of tracheoles drawn into tissues by osmosis during exercise.
  • as fluid is removed , air fills tracheoles
  • so rate of diffusion to gas exchange surface increases as diffusion is faster through air

Question 4

Explain structural and functional compromises in terrestrial insects that allow efficient gas exchange while limiting water loss

Answer 4

• Thick waxy cuticle -> increases diffusion distance so less water loss
• Spiracles can open to allow gas exchange and close to reduce water loss
• Hairs around spiracles => trap moist air , reduction water potential gradient so less water loss

Question 5

Explain how the gills of fish are adapted for gas exchange

Answer 5

• Gills made of many filaments covered with many lamellae
- Increases surface area for diffusion
• Thin lamellae wall
- So short diffusion distance between water / blood
• Lamellae have a large number of capillaries
- Remove O2 and bring CO2 quickly so maintains conc gradient
• Counter current flow

Question 6

what is counter current flow

Answer 6

1) blood and water flow in opposite directions through lamellae
2) so oxygen conc always higher in water
3) so maintains a conc gradient of O2 between water and blood
4) for diffusion along whole length of lamellae

Question 7

Explain how the leaves of dicotyledonous plants are adapted for gas exchange

Answer 7

• Many stomata (high density) => large surface area for gas exchange
• Spongy mesophyll contains air spaces => large surface area for gases to diffuse through
• Thin => short diffusion distance

Question 8

Explain structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss

Answer 8

-Thicker waxy cuticle
• Increases diffusion distance so less evaporation
- Sunken stomata in pits / hairs
• Trap water vapour / protect stomata from wind
• So reduced water potential gradient between leaf / air
• so less evaporation
- Spines / needles
• reduces surface area to volume ratio

Question 9

Describe the gross structure of the human gas exchange system

Answer 9

Trachea
Bronchi
bronchioles
capillary network
alveoli

Question 10

explain the essential features of the alveolar epithelium that make it adapted as a surface for gas exchange

Answer 10

• 1 cell thick => short diffusion distance
• Folded => large surface area
• Permeable => allows diffusion of O2/CO2
• Moist => gases can dissolve for diffusion
• Good blood supply from large network of capillaries => maintains a conc gradient

Question 11

Describe how gas exchange occurs in the lungs

Answer 11

• Oxygen diffuses from alveolar air space into blood down its conc gradient
• Across alveolar epithelium then across capillary endothelium
(Carbon dioxide opposite )

Question 12

Explain the importance of ventilation

Answer 12

• Brings in air containing higher conc of oxygen and removes air with lower conc of oxygen
• Maintaining conc gradient

Question 13

Explain how humans breathe in and out (ventilation)

Answer 13

Inspiration :
1) Diaphragm muscles contract => flattens
2) External intercostal muscles contract , internal intercostal muscles relax
3) ribcage pulled up / out
4) Increasing volume and decreasing pressure in thoracic cavity
5) Air moves into lungs down pressure gradient

Expiration :
1) Diaphragm relaxes => moves upwards
2) External intercostal muscles relax , internal intercostal muscles may contract
3) ribcage moved down / in
4) Decreasing volume and increasing pressure in thoracic cavity
5) air moves out of lungs down pressure gradient

Question 14

Suggest why expiration is normally passive at rest

Answer 14

• Internal intercostal muscles do not normally need to contract
• expiration aided by elastic recoil in alveoli

Question 15

Suggest how different lung diseases reduce rate of gas exchange

Answer 15

• Thickened alveolar tissue => increases diffusion distance
• Alveolar wall breakdown => reduces surface area
• Reduce lung elasticity => lungs expand / recoil less so reduces conc gradient of O2 / CO2

Question 16

Suggest how different lung diseases affect ventilation

Answer 16

• Reduce lung elasticity => lungs recoil less
- Reducing volume of air in each breath
- Reducing maximum volume of air breathed out in one breath
• Narrow airways / reduces airflow in and out of lungs
- Reducing maximum volume of air breathed out in 1 second
• Reduced rate of gas exchange => increased ventilation rate to compensate for reduced oxygen in blood

Question 17

Suggest why people with lung disease experience fatigue

Answer 17

cells receive less oxygen => rate of aerobic respiration reduced => less ATP made

Question 18

Suggest how you can analyse and interpret data to the effects of pollution , smoking and other risk factors in the incidence of lung disease

Answer 18

• Describe overall trend
• Manipulate data
• Interpret standard deviations
• Use statistical tests

Question 19

Explain the difference between correlations and casual relationships

Answer 19

• Correlation = change in one variable reflected by a change in another
• Causation = change in one variable causes a change in another variable