Gas exchange ppq

Describe and explain one feature of the alveolar epithelium that makes the epithelium well

adapted as a surface for gas exchange. Do not refer to surface area or moisture in your

answer.

1. Flattened cells

OR

Single layer of cells;

Reject thin cell wall/membrane

Accept thin cells

Accept ‘one cell thick’

2. Reduces diffusion distance/pathway;

3. Permeable;

4. Allows diffusion of oxygen/carbon dioxide;

Ignore gas exchange

Tidal volume is the volume of air inhaled and exhaled during a single breath when a person

is resting. The tidal volume in a person with emphysema is reduced compared with the tidal

volume in a healthy person.

Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide

between the blood and the alveoli.

1. Less carbon dioxide exhaled/moves out (of lung)

OR

More carbon dioxide remains (in lung);

2. (So) reduced diffusion/concentration gradient (between blood and alveoli);

3. Less/slower movement of carbon dioxide out of blood

OR

More carbon dioxide stays in blood;

1. Water has low(er) oxygen partial pressure/concentration (than air);

2. So (system on outside) gives large surface area (in contact with water)

OR

So (system on outside) reduces diffusion distance (between water and

blood);

3. Water is dense(r) (than air);

4. (So) water supports the systems/gills;

Explain how the counter cirrent principle allows efficient oxygen uptake in fish gas exchange system

1. Blood and water flow in opposite directions;

2. Diffusion/concentration gradient (maintained) along (length of)

lamella/filament;

) K = Bronchiole and

L = artery/arteriole/vein/venule;

Two solutions often used to stain tissues are haematoxylin solution and iodine solution.

• Haematoxylin solution stains DNA a blue colour.

• Iodine solution stains starch a blue-black colour.

The scientist used haematoxylin solution and not iodine solution to stain the lung tissue.

Suggest why.

1. This/animal/lung tissue does not contain starch;

Accept cell(s) for ‘tissue’

2. (Makes) nucleus visible;

OR

Nucleus contains DNA;

A student who looked at these results concluded that all three risk factors are linked with

asthma. Evaluate this conclusion.

(d) In support

1. (Link/risk with asthma and) living with cat or dog is (statistically) significant;

2. (Link with) obesity is most/highly significant;

Reject ‘results are significant’

Not supported

3. (Link/risk with asthma and) burned wood (indoors) is not (statistically) significant;

Accept ‘due to chance’ for ‘not significant’ and converse

F = Filament and

G = (Secondary) lamella(e) / (gill) plate;

Reject gill arch

Accept primary lamella(e) for F

(b)  Describe and explain the advantage of the counter-current principle in gas exchange

across a fish gill.

(b)  1.   Water and blood flow in opposite directions;

2.   Maintains diffusion/concentration gradient of oxygen

Accept: converse for carbon dioxide

Accept: equilibrium not reached

OR

Oxygen concentration always higher (in water);

3.   (Diffusion) along length of lamellae/filament/gill/capillary;

Accept: all/whole of lamellae/filament//gill/capillary

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

(Across) alveolar epithelium;

2. Endothelium / epithelium of capillary;

Incorrect sequence = maximum of 1 mark

Breathing out as hard as you can is called forced expiration.

(a) Describe and explain the mechanism that causes forced expiration.

(a) 1. Contraction of internal intercostal muscles;

2. Relaxation of diaphragm muscles / of external intercostal muscles;

3. Causes decrease in volume of chest / thoracic cavity;

4. Air pushed down pressure gradient.

(c) The people in group B were recovering from an asthma attack.

Explain how an asthma attack caused the drop in the mean FEV shown in the figure above.

(c) 1. Muscle walls of bronchi / bronchioles contract;

2. Walls of bronchi / bronchioles secrete more mucus;

3. Diameter of airways reduced;

4. (Therefore) flow of air reduced.