Gas Exchange PPQs

Question 1

Describe how the SA:V ratio changes as the size of an organism increases.

Answer 1

As size increases, SA:V decreases because volume increases more rapidly than SA

Question 2

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

Answer 2

larger SA:V ration (like a mouse) have higher metabolic rate

Question 3

Describe two specialisations which organisms commonly have to increase the rate of diffusion.

Answer 3

• flattened body

- specialised gas exchange system

Question 4

Name the 5 features of a specialised exchange surface:

Answer 4

Large surface area relative to volume
Thin surface
Selectively permeable
Movement of the environmental medium
Mass transport system

Question 5

Explain why most specialised exchange surfaces are internal to the body

Answer 5

• they are thin and air is not a dense enough medium to support so would be easily damaged and unsupported
• they would dry out and lead to dehydration in the body because the surfaces are sites of extensive water and heat loss

Question 6

Explain, as fully as you can, how alveoli are specialised as a gas exchange surface.

Answer 6

• thin one cell epithelium shortens diffusion distance
• many means large surface area
• constant ventilation and blood flow through capillaries means steep and constant diffusion concentration gradient can be maintained
• thin one cell epithelial capillary means short diffusion distance
• slowed red blood cell flow through capillaries means maximum time for diffusion
• red blood cells flattened against capillary wall decreases diffusion distance to alveoli air
• pulmonary surfactant secreted by epithelial cells lowers surface tension stopping alveoli collapsing and sticking together after exhalation

Question 7

Where are the squamous epithelial cells?

Answer 7

alveoli and capillary wall

Question 8

Structure of human gas exchange system

Answer 8

• Pulmonary surfactant secreted by epithelial cells and spread across tissues surrounding alveoli - lowers surface tension to stop alveoli collapsing after exhalation
  
  • Trachea, bronchi, bronchiole, alveoli
  • Cartilage - prevents trachea from collapsing inwards as air pressure decreases when breathing in
  • Trachea: epithelial cells, goblet cells, muscle
  • Bronchioles - muscles allow them to constrict so they can control air flow in and out of the alveoli
  • Between alveoli = collagen and elastic fibres allowing them to stretch and fill with air
    Lungs inside body because air not dense enough to support structures and they would dry out outside + body would lose lots of water

Question 9

deoxygenated blood in

oxygenated blood out

Answer 9

through pulmonary artery

through pulmonary vein

Question 10

How do C shaped rings of cartilage in the trachea and bronchi help to maintain mass flow?

Answer 10

prevent airway collapsing as pressure decreasing during inhalation

allow expansion of oesophagus during swallowinh

Question 11

Smooth muscle in bronchi and bronchiole walls help to maintain mass flow?

Answer 11

allows diameter of airways to be altered to control movement of air into the alveoli

Question 12

Using the information provided, explain how two features of the body of the tubifex worm allow efficient gas exchange. (2)

Answer 12

• thin so fewer cells to the centre of the organism and so shorter diffusion distance
• small so have a large SA;V ratio

Question 13

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them. (5)

Answer 13

• many alveoli means large surface area
• alveoli and capillary walls are one cell thick so shorter diffusion distance
• slowed red blood cell flow through capillaries to maximise diffusion
• constant ventilation and blood flow through capillaries maintains steep constant high diffusion concentration gradient
• alveoli surrounded by large network of capillaries supply large blood flow and maintains high concentration gradient
• narrow capillaries mean red blood cells are flattened against wall so decreases diffusion distance (brings haemoglobin closer to alveoli air)

Question 14

Describe the gross structure of the human gas exchange system and how we breathe in and out. [6 marks]

Answer 14

trachea, bronchi, bronchioles, alveoli;

breathing in - diaphragm contracts and external intercostal muscles contract;

(causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);

breathing out- diaphragm relaxes and internal intercostal muscles contract;

(causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out)

Question 15

Fish gas exchange - things I always forget

Answer 15

1) water flows in opposite direction to capillary blood flow over the gill lamellae
2) Means that blood always meets water with a higher oxygen concentration across the whole length of the gill (and width of lamellae)
3) So maintains a steady constant diffusion gradient across the whole length of the gill (and width of lamellae)

• opercular suction pump and buccal pressure pump maintain unidirectional flow of water
• Continuous flow results in strong diffusion gradient
• Active fish have more gill lamellae/filaments/larger SA lamellae
• Lamellae positioned at right angles to the gill filament
• parallel flow: blood and water flow in same direction