3.2 - Gas exchange

Question 1

Describe how gas exchange works across the body surface of a single-celled organism

Answer 1

No specialised gas exchange surfaces or transport systems, reliance on diffusion
Typically flat cells or folds in their cell surface membrane to increase surface area (and therefore SA:vol ratio) and ensure short diffusion distance
Small multi-cellular organisms without specialised gas exchange surfaces also typically have flat body shapes for the same reasons

Question 2

Describe how the tracheal system of an insect is specialised for gas exchange

Answer 2

Tracheoles have thin walls so short diffusion distance to cells
Highlight branched so short diffusion distance to cells/large surface area
Trachea provide tubes full of air so fast diffusion
Fluid in the end of tracheoles moves out during exercise so faster diffusion through air to gas exchange surface
Body can be moved by muscles to move air so maintains diffusion gradient for oxygen/carbon dioxide

Question 3

Describe how the gill system is specialised for gas exchange

Answer 3

Many lamellae/filaments so large surface area
Thin so short diffusion pathway

Question 4

Describe how the leaves of dicotyledonous plants are specialised for gas exchange

Answer 4

Stomata - small pores open and close to allow gases in and out of leaf. Controlled by guard cells
Turgid (full of water) = stomata open
Flacid = stomata close
Gas exchange surface = mesophyll cells, which have a high surface area

Question 5

Describe the structural and functional compromises between efficient gas exchange and water loss in terrestrial insects and xerophytic plants

Answer 5

Gas exchange causes water loss
Adaptations: insects close spiracles using muscles if water loss is too high
Insects have waterproof waxy cuticle on body surface and tiny hairs around spiracles to reduce evaporation
Dehydrated plants cause stomata to close

Question 6

Draw a diagram of the gross structure of the human gas exchange system

Answer 6

Alveoli
Bronchioles
Bronchi
Trachea
Lungs

Question 7

Name and describe the adaptations of xerophytic plants

Answer 7

Curled leaves - increases humidity and decreases water potential gradient
Sunken stomata - increases humidity and decreases water potential
Thicker waxy cuticle - increased diffusion distance
Hairs on leaves - increases humidity and decreases water potential
Less stomata - less pores for water loss

Question 8

Describe and explain how the countercurrent system leads to efficient gas exchange across the gills of a fish

Answer 8

Water and blood flow in opposite directions
Maintains diffusion gradient - blood always passing water with higher oxygen concentration
Along whole length of gill

Question 9

Describe adaptations of the alveolar epithelium for efficient gas exchange

Answer 9

Thin walls
Total surface area is large
One cell thick so short diffusion pathway

Question 10

Describe the mechanism of inhalation

Answer 10

Diagram contracts
External intercostal muscles contract
Internal intercostal muscles relax
Volume increases and pressure decreases in thoracic cavity
Air flows into lungs down pressure gradient

Question 11

Describe the mechanism of exhalation

Answer 11

Diaphragm relaxes
External intercostal muscles relax
Internal intercostal muscles contract
Volume decreases and pressure increases in thoracic cavity
Air flows out of lungs down pressure gradient

Question 12

Describe the pathway taken by an oxygen molecule from an alveolus to the blood

Answer 12

Across alveolar epithelium
Endothelium of capillary