Mass Transport - Recall Qs

Question 1

Describe and explain how fish maintain a flow of water over their gills. (5 marks)

Answer 1

1. mouth opens, operculum shuts;
2. floor of mouth lowered
3. water enters due to decreased pressure
4. mouth closes, operculum opens;
5. floor raised results in increased pressure
6. increased pressure forces / pushes water over
   gills

Question 2

Describe and explain how the structure of the mammalian breathing system enables
efficient uptake of oxygen into the blood. (6 marks)

Answer 2

1. Alveoli provide a large surface area;
2. Walls of alveoli thin to provide a short
   diffusion pathway;
3. Walls of capillary are thin between the alveoli
   so provides a short diffusion pathway;
4. Walls of capillaries/alveoli have flattened cells;
5. Cell membrane permeable to gases;
6. Many blood capillaries provide a large surface
   area;
7. Intercostal muscles & diaphragm muscles
   used to ventilate lungs to maintain a
   diffusion gradient;
8. Wide trachea & branching of
   bronchi/bronchioles for efficient flow of air;
9. Cartilage rings used to keep airways open

Question 3

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 marks)

Answer 3

1.Many alveoli provide a large surface
area;
2.Many capillaries provide a large surface area;
3.(So) fastdiffusion;
4.Alveoli or capillary walls / epithelium / lining
are thin / short distance
between alveoli and blood;
5.Flattened / squamous epithelium;
6.(So) shortdiffusiondistance / pathway;
7.(So) fastdiffusion;
8.Ventilation / circulation;
9.Maintains a diffusion / concentration gradient;
10.(So) fastdiffusion;

Question 4

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

Answer 4

1. trachea, bronchi, bronchioles, alveoli
2. breathing in: diaphragm contracts and
   external intercostal muscles contract
3. (causes) volume increase and pressure
   decrease in thoracic cavity (to below ATM ,
   resulting in air moving in)
4. breathing out: diaphragm relaxes and internal
   intercostal muscles contract
5. (causes) volume decrease and pressure
   increase in thoracic cavity (to above ATM,
   resulting in air moving out)

Question 5

Explain how the ventilation mechanism of a fish and the structure of its gills result in the efficient uptake of oxygen from water (6 marks)

Answer 5

1. filaments/lamellae; large SA
2. gill plates or secondary lamellae
3. large number of capillaries; to remove
   oxygen/maintain gradient
4. thin epithelium; short diffusion pathway
5. pressure changes; to bring in more
   water/maintain gradient
6. countercurrent flow; Exchange occurs along
   the whole length as a concentration gradient is
   maintained & an equilibrium is not achieved

Question 6

Explain how the heart muscle and the heart valves maintain a one-way flow of blood
from the left atrium to the aorta. (5 marks)

Answer 6

1.Atrium has higher pressure than ventricle due
to filling / contraction. This causes the
atrioventricular valves to open
2.Ventricle now has higher pressure than atrium
(due to filling /contraction). This causes
atrioventricular valves to close;
3.Ventricle has higher pressure than aorta
causing semilunar valve to open;
4.This leads to a higher pressure in the aorta
than the ventricle (as heart
relaxes) causing semilunar valve to close;
5.(Muscle / atrial / ventricular) contraction
causes increase in pressure;

Question 7

Describe and explain four ways in which the structure of a capillary adapts it for the
exchange of substances between blood and the surrounding tissue. (4 marks)

Answer 7

1.Permeable capillary membrane;
2.Single cell thick walls - reduces diffusion
distance;
3.Flattened (endothelial) cells - reduces diffusion
distance;
4.Fenestrations - allows large molecules
through;
5.Small diameter/ narrow - gives a large surface
area to volume / short diffusion distance;
6.Narrow lumen - reduces flow rate giving more
time for diffusion;
7.Red blood cells in contact with wall / pass
singly - gives short diffusion distance