Gas exchange

Question 1

(i) Explain the fluctuations in the carbon dioxide concentration which take place at point A over a 24-hour period
(ii) At 1600 hours, the carbon dioxide concentrations at points Aand B differ from each other. Explain why.

Answer 1

(i) Carbon dioxide lower when plants photosynthesising (during day/light);
(ii) At point B no/little light reaches forest floor;

Little photosynthesis on forest floor/respiration occurring;(accept converse for point A)

Question 2

Use information in the diagram to help explain why replacing rain forest with agricultural crops will reduce the diversity of animals.

Answer 2

Forest has wider range of vegetation types/heights/diversity of plants;

Different/more niches/habitats/food types available foranimals/use of pesticides;

Question 3

(a) Smaller species of annelid do not have gills. Explain why these small worms do not need gills to obtain sufficient oxygen.
(b) In many of the lugworm gills, the blood flows in the opposite direction to the current of water passing over them. Explain the advantage of this arrangement.

Answer 3

(a) Large surface area: volume ratio;meet requirements by diffusion (over body surface);
(b) Maintains a concentration gradient;

(allowing diffusion of oxygen) across width of gill;

Question 4

(c) Explain two ways, other than that described in part (b), in which the structure of a lugworm gill is adapted for efficient gas exchange
(d) Explain why water is always lost from the gas exchange surfaces of terrestrial organisms.

Answer 4

(c)Large surface area for diffusion /O2uptake / gaseous exchange;

short diffusion path;

highly vascularised / many blood capillaries for O2 transport;

(d)Gas exchange surfaces are permeable (to small molecules);

higher concentration of water molecules inside animal than out /water potential gradient;

water will diffuse outwards / evaporation;

Question 5

Give two explanations as to why the rate of water loss during gas exchange is very low in most insects.

Answer 5

EITHER

Reference to spiracles;

limits exposure of respiratory surface / can close spiracles;

OR

sunken spiracles / hair round spiracles;

trapping moist air;

OR

trachea cuticle lined;only lose water through tracheoles;

OR

trachea /tracheoles inside;

limiting exposure of respiratory surface;

Question 6

During exercise, the rate of respiration of muscle cells increases. Explain what causes human haemoglobin to unload more oxygen to these cells.

Answer 6

Partial pressure on oxygen in muscle falls more;

high / more carbon dioxide produced;

lowers PH;

increase in temperature;

percentage saturation of Hb falls / lowers affinity /increase dissociation;

displaces curve to right / results in Bohr shift;

Question 7

The lugworm lives in a burrow in the sand on the seashore. When the tide is out, water bringing a fresh supply of oxygen no longer flows through the burrow. Suggest how the lugworm’s haemoglobin allows it to survive in these conditions.

Answer 7

In absence of oxygen / low partial pressure of oxygen in tissues /oxygen still used in respiration;

haemoglobin acts as an oxygen store;

releases (large amount of) oxygen when low level in tissues;

Question 8

Describe and explain two similarities in the way in which the structures shown in these diagrams limit water loss from these organisms.

Answer 8

Waxy cuticle;

Prevents passage/evaporation of water;

OR

Hairs on surface (allow description);

Moist air trapped/reduces water potential gradient;

OR

Sunken “openings”;

Moist air trapped/reduces water potential gradient;

OR

Stomata/spiracles can close;

Reduces evaporation;

Question 9

Answer 9

Carbon dioxide in tracheae;

Therefore spiracles open;

allowing water vapour to escape;

Question 10

(i) What is the name given to the volume of air labelled A?
(ii) Explain how you would calculate the volume of air taken into the lungs in one minute.

Answer 10

(i) Tidal volume;
(ii) Multiply A/ tidal volume / volume of breath by number of breaths per minute / breathing rate;

Question 11

One way in which hospitals test how well the lungs are working is to measure the gas transfer factor. This is done by measuring the uptake of carbon monoxide from a single breath of air containing 0.3% carbon monoxide.

(b) (i)By what process would carbon monoxide pass from the air in the alveoli to the blood in the lung capillaries?
(ii) Suggest why carbon monoxide is used for this test.

Answer 11

(i) Diffusion;
(ii) Not normally present / needed;

Any detected must have come from this test;

Question 12

Interstitial lung disease is a disease in which the alveolar walls become thicker.Explain why the gas transfer factor would be low in a person who had interstitial lung disease.

Answer 12

Longer diffusion pathway / takes longer to diffuse /slower rate of diffusion;

Question 13

Describe one adaptation of the alveolar epithelium which allows efficient diffusion.

Answer 13

Thin / single layer of cells / large surface area;

Question 14

Emphysema is a condition in which the walls between the alveoli break down and enlarge the air spaces. The blood of a person with emphysema contains a higher concentration of carbon dioxide than the blood of a healthy person. Use Fick’s law to explain why.

Answer 14

Smaller surface area;

For diffusion of carbon dioxide from blood / into lungs /diffusion slower;

Question 15

(i) The concentration of oxygen in the blood in the arteries of people living at 3700m is higher than in the arteries of people living at 150 m. Use the information in the table to explain why
(ii) People who move from low to high altitude are often breathless at first.Suggest why this breathlessness disappears after living at high altitude for several weeks.

Answer 15

(i)Greater concentration / number of red blood cells;

More haemoglobin (to carry oxygen);

(ii)(For the body to produce) more red blood cells;

Link established between red blood cells and transport of oxygen;

Question 16

Answer 16

Picks up oxygen morereadily (in lungs) / greater affinity / idea of more readily saturated;

Where O2 is low;

Question 17

A diffusion gradient is essential for gas exchange. Describe two ways in which a diffusion gradient for oxygen is maintained at the gas exchange surface of a fish.

Answer 17

Accurate description of ventilation by water flow;

(Oxygen) removal by bloodstream;

Description of / countercurrent flow of blood and water (at gills);

Question 18

For how long were the insect’s spiracles open during the period shown in the graph? Explain how you arrived at your answer.

Answer 18

4.0 seconds/ s;

accept 2 x 2s(Total) time when oxygen (concentration) was increasing /oxygen diffusing in;

OR

(Total) time when carbon dioxide (concentration) was decreasing /carbon dioxide diffusing out;

Question 19

Explain why full lungs would make it ‘energetically expensive to swim down through the water’

Answer 19

More work done / more energy / ATP required;

To overcome greater buoyancy;

Question 20

Weddell seals can remain under water for longer than this. Describe two adaptations of the blood system which allow them to remain under water longer.

Answer 20

Heart rate slows;

Less blood flowing to / from muscles / liver / gut / blood flow to body other than brain reduced by 90%;

Large volume of blood compared with body mass;

Greater concentrationof haemoglobin;

Less blood required to supply heart / to heart muscle;

Question 21

Describe one way in which the change in blood flow to the organs of the body of a diving seal differs from that in a human undergoing moderate exercise.

Answer 21

Less blood to muscles / heart muscle / skin;

Question 22

There are about 150 000 000 alveoli in a human lung. Explain how this makes gas exchange very efficient.

Answer 22

Large surface area for diffusion;

Question 23

The capillaries in the lungs are very small in diameter. As a result, blood travels through them slowly. Explain two ways in which the small diameter of the capillaries results in the efficient transfer of oxygen from the alveoli to the red blood cells.

Answer 23

Red blood cells close to capillary wall/ thin capillary wall;

Short diffusion path/ distance for oxygen to diffuse;

Longer time for diffusion to take place/ diffusion is slow;

Question 24

During a breath, little of the air contained in alveoli at the top of the lungs is replaced. Explain how this makes gas exchange inefficient in these alveoli.

Answer 24

Less oxygen/ concentration gradient lower;

Therefore less diffusion;

Question 25

Explain how the structure of the gas exchange system of an insect ensures that there is a large surface area for gas exchange.

Answer 25

Many, small/ branching tracheoles;

Question 26

Describe one way in which the transport of oxygen to a muscle in an insect is different from that in a fish.

Answer 26

Blood not involved in transport of respiratory gases in insects;

Question 27

Describe how muscles in the thorax (chest) cause air to enter the lungs during breathing.

Answer 27

Diaphragm/intercostal muscles contract;

Increases volume of thorax/chest/lungs;

Negative/lower pressure in lungs;

Question 28

The athlete cycled at the particular exercise rate for 5 minutes before the relevant readings were taken. Explain why the readings were taken only after the athlete had been cycling for 5 minutes

(ii)Calculate the total volume of air taken into the lungs in one minute at an exercise rate of 120 arbitrary units.

Answer 28

(i) Allows stabilisation/becomes steady/adapts;
(ii) 41.7 (dm3/litres);

Question 29

Give two conclusions that can be drawn from the figures in the table.

Answer 29

Tidal volume increases steadily then levels out;

Breathing rate changes little until highest exercise rate/180 reached then increases;

Question 30

Describe the features of fish gills that give them a large surface area.

Answer 30

(gills have) lamellae on filaments;

lots of both;

Question 31

(i) Describe the relationships between gill surface area, mass and swimming speed shown in the diagram
(ii) Explain the relationship between gill surface area and swimming speed.

Answer 31

(i) all 3 go up;
(ii) more oxygen can be supplied;

for more respiration;

Question 32

What is meant by the term partial pressure?

Answer 32

It is a measure of the concentration of a gas (in a mixture of gases or a liquid);

Question 33

(b)Use Table 1 and the graph to calculate the difference in the percentage saturation of haemoglobin in the tissues between rest and exercise.

Answer …%

(c)Explain the differences between the figures shown in Table 1 for rest and exercise.

Answer 33

(b) 37-38% [Accept 36 –39]
(c) muscle contraction causes increased respiration;

increased CO2 production lowering blood pH;

lactate released lowering blood pH;

increased heat released therefore increased temperature;

increased O2 consumption lowering tissue PO2;

Question 34

Explain the advantage of the difference in position of the dissociation curve during exercise.

Answer 34

haemoglobin has a lower affinity for oxygen;

more O2;

for respiration;

Question 35

Answer 35

3.4 times = 2 marks(incorrect answer in which candidate shows amount of oxygen removedat rest is 4.6 and amount removed during exercise is 15.8 = 1 mark)

Question 36

The change to the dissociation curve is one of a number of ways in which the total oxygen supplied to muscles is increased during exercise. Give two other ways in which the total oxygen supplied to muscles during exercise is increased.

Answer 36

increased depth / rate / pulmonary ventilation;

increase stroke volume/heart rate/Q increases blood flow rate;

arterioles [Acceptartery] supplying the muscles dilate / vasodilation / greater proportion of blood flow to the muscles;

Question 37

Land-dwelling insects lose water from their gas exchange surface. Use Fick’s law to explain why they lose less water when the air is humid.

Answer 37

Humidity reduces difference in concentration of water (vapour)between body and air;

reduces rate of diffusion (of water vapour)(as are proportional);

Question 38

Describe how an increase in lung volume leads to air entering the lungs.

Answer 38

Produces lower pressure (and air moves in down pressure gradient);

Question 39

Use Fick’s law to explain how breathing helps to ensure efficient gas exchange.

Answer 39

Rate of diffusion is proportional to concentration gradient / difference in concentration;

Breathing changes air / maintains gradient;

Question 40

(a) Using information from the diagram, suggest what stimulates the spiracles to open.
(b) Explain what causes the oxygen concentration in the tracheae to fall when the spiracles are closed.

Answer 40

(a)increasing carbon dioxide concentration / partial pressure;

(decrease in oxygen negates)

(b)(oxygen is used in) respiration;

therefore diffuses (from tracheae) to tissues;

oxygen unable to enter organism;

Question 41

The insect lives in dry conditions. Suggest an advantage of the pattern of spiracle movements shown in the diagram.

Answer 41

spiracles not open all the time;

therefore there is less water loss(by diffusion through spiracles);

Question 42

(i) Suggest why the rate of oxygen uptake through the skin remains nearly constant during the year.
(ii) Compare the relative importance of the skin and lungs in the uptake of oxygen in winter and summer.

Answer 42

(i) oxygen concentration in air / water constant / surface area /thickness of skin constant;
(ii) skin more important in winter and lungs in summer;