Gas Exchange

Question 1

Explain the variety of gas exchange surfaces using different examples.

Answer 1

• entire body can be gas exchange surface
• spiracles present in tracheae to help increase SA:V ratio
• can have external gills, however these are more vulnerable to damage
• suck water over gills and have internal gills which increase SA:V ratio
• can have internal lungs which are highly protected but it’s more difficult to get gas exchange medium IN

Question 2

Describe the key features of a gas exchange surface.

Answer 2

1. Large SA:V ratio
2. Very thin barrier (small diffusion distance between air and blood)
3. Concentration gradient (in order to avoid equilibrium by by allowing movement of internal and external media)
4. Selectively permeable (to ensure only the target molecules pass through)

Question 3

What is Fick’s Law?

Answer 3

Rate of gas exchange = (surface area x concentration gradient x diffusion coefficient) / diffusion distance

Question 4

How is gas exchange maximised?

Answer 4

• increase area
• increase pressure difference
• decrease diffusion distance

Question 5

Describe the advantages and disadvantages of breathing air versus water.

Answer 5

• oxygen diffuses 8000x more rapidly in air than in water
• water is harder to move as it is 800x denser and 50x more viscous than air
• more CO2 in water because is is 20x more soluble in water than in air

Question 6

How are CO2 and O2 transported across the alveolar membrane?

Answer 6

• capillary transports CO2 to alveolus

- alveolus transports O2 to capillary

Question 7

How is increased surface area in the lung achieved?

Answer 7

• branching of bronchioles

- many alveoli

Question 8

Why is water inside alveoli an issue? Explain using an animal example.

Answer 8

Water is sticky and can cause alveoli to stick together; therefore cannot breathe. E.g fish when out of water cannot breathe bc gills contain water and stick together bc of surface tension

Question 9

What is used to disrupt surface tension within alveoli and lungs?

Answer 9

Surfactant. It is phospholipoprotein.

Question 10

Why are premature babies unable to breathe?

Answer 10

They don’t have surfactant to disrupt surface tension in alveoli

Question 11

What type of exchange flow occurs in gills? How does it work?

Answer 11

Counter-current flow. H2O and blood travelling opposite to each other across gills

Question 12

What is co-current and counter-current flow? Which one maximises gas exchange more and how is this done?

Answer 12

Co-current flow: oxygen in water travels in same direction as oxygen in haemolymph. Pressure difference is not maintained

Counter current flow: oxygen in water travels in opposite direction to oxygen in haemolymph. Maintains pressure difference and therefore maximises gas exchange.

Question 13

What factors affect solubility of oxygen in water?

Answer 13

• salinity
• temperature
• pressure

Question 14

What is eutrophication?

Answer 14

• applies to still moving water where pressure gradient is not maintained
• in summer, algal growth occurs which lead to O2 depletion, bad for fish.
• in winter, decay occurs leading to O2 depletion again

Question 15

What is diaphragm movement in lung controlled by?

Answer 15

Controlled by phrenic nerves

Question 16

Describe the pleural pressure and what the lungs look like when inhaling. Describe the same when exhaling.

Answer 16

Negative plural pressure, keeps lung stuck to thoracic wall.
Movement of diaphragm, releases

When exhaling, pleural pressure is equal to atmospheric pressure. Lungs are no longer stuck to thoracic wall. Lung is collapsedi. Produces pneumothorax which is presence of air between lung and chest wall, causing collapse of lung

Question 17

What are the two reserves in a human lung? What are the two volumes?

Answer 17

Reserves: inspiration to and expiratory
Volumes: tidal and residual

Question 18

Why is there always air left in our lungs even after we breath all the air out?

Answer 18

Can’t breathe everything out otherwise lung system would collapse. This is residual volume

Question 19

What is eupnea?

Answer 19

Normal breathing

Question 20

Describe the properties of alveolar air.

Answer 20

It is fairly stagnant and has lower %O2 than air. Still higher level than in the blood though

Question 21

What is haemoglobin?

Answer 21

Main vertebrate respiratory pigment

Question 22

Why does O2 binding cause colour change?

Answer 22

Due to metal ion in pigment leg haemocyanin turns blood bluish

Question 23

What is haemoglobin composed of? What does each heme group contain?

Answer 23

4 globin protein subunits, each containing a heme group. Therefore 4 heme units.

Each heme group contains an iron ion which binds to O2.

Question 24

Compare the colours of oxygenate vs deoxygenate blood.

Answer 24

Oxygenated blood is lighter red than deoxygenated blood.

Question 25

Does CO have a stronger or lesser group binding affinity to heme group than O2?

Answer 25

Stronger, therefore can cause poisoning

Question 26

What defines affinity of haemoglobin binding to O2?

Answer 26

pH, which indirectly measures CO2 concentration.

Question 27

What is P50 in oxygen dissociation curve?

Answer 27

PO2 at which 50% of Hb sites have O2 bound.

Question 28

Compare the O2 dissociation curves for when exercise is occurring vs no exercise.

Answer 28

When no exercise is occurring, low CO2 and increased pH, more oxygen binding earlier.

When exercise is occurring, high CO2 and low pH, low percentage of oxygen binding

Question 29

Why is it dangerous to hyperventilate before diving?

Answer 29

• CO2 level too low prior to O2 blackout zone (diving)
• high CO2 is what triggers breathing, however because threshold has not been reached, blackout kicks in and urgent need to breathe is triggered past point where brain already cuts off