Chapter 11. Gas Exchange In Humans

Question 1

What are the 4 features of gas exchange surfaces in humans?

Answer 1

1. Large surface area
2. Thin surface
3. Good blood supply
4. Good ventilation with air

Question 2

Explain these 4 features of gas exchange surfaces in the body:
1. Large Surface Area
2. Thin Surface
3. Good blood supply
4. Good ventilation with air

Answer 2

Gas exchange surfaces:
1. Have a large surface area to allow a lot of gas to diffuse across at the same time.
2. Have thin surfaces to allow gases to diffuse across them quickly.
3. Are close to an efficient transport system to take gases to and from the exchange site.
4. Good ventilation with air for a good supply of Oxygen.

1. Large surface area for maximum gas diffusion.
2. Thin surface for quick gas diffusion.
3. Good blood supply for easy gas exchange on site.
4. Good air ventilation for good oxygen supply

Question 3

Outline the steps for investigation for the differences in composition between inspired and expired air using limewater to test for Carbon Dioxide.

Answer 3

1. Set up glass tubes, rubber tubing, and two test tubes as shown p223
2. Breathe gently into and out of the rubber tubing making sure not to suck too hard, until one of the test tubes becomes cloudy.
3. Continue breathing in and out for a while, you may find that the limewater in the other test-tube also becomes cloudy.

Question 4

What are the 4 precautions to be taken when carrying out the test to identify the differences in composition between inspired and expired air using lime water as a test for carbon dioxide?

Answer 4

1. Do not get the lime water in your mouth. Do not suck too hard.
2. Wear safety goggles when breathing in and out through the tubing.
3. Make sure rubber tubing is really clean before putting mouth over it.
4. Use new piece of tubing for each new person who uses the apparatus.

Risk of the experiment:
1. Lime water is an irritant.
2. Lime water can be accidentally sucked in.

Question 5

What is the result of the test to identify the differences in composition between inspired and expired air using lime water as a test for carbon dioxide?

Answer 5

The lime water in the test tube with the longer tube being blown into will turn cloudy or will turn cloudy before the other test tube.

Refer to page 223 for diagram

Question 6

What is the composition, as a percentage, of Oxygen in
a) Inspired air
b) Expired air

Answer 6

The composition of Oxygen in
a) Inspired air is 21%
b) Expired air is 16%

Question 7

What is the composition, as a percentage, of Carbon Dioxide in
a) Inspired air
b) Expired air

Answer 7

The compostion of Carbon Dioxide in
a) Inspired air is 0.04%
b) Expired air is 4%

Question 8

What is the composition, as a comparison of low to high, of Water Vapour in
a) Inspired air
b) Expired air

Answer 8

The compostion of water vapour in
a) Inspired air is variable
b) Expired air is usually very high

Low to High.

Question 9

In 5 steps, how do you investigate the effects of physical activity on the rate and depth of breathing?

Answer 9

1. Measure and record breathing rate at rest by counting number of breathes per minute.
2. Measure and record depth of breathing at rest by using a tape measure to find out average chest expansion over 5 breathes.
3. Exercise for a fixed amount of time e.g. 3 minutes
4. Immediately after, measure number of breathes per minute as in 1.
5. Measure average chest expansion over 5 breathes as in 2.

Apparatus for:
Breathing rate - Stopwatch
Average chest expansion - Tape measure

Question 10

1. What are the effects of physical activity on
   a) the rate of breathing
   b) the depth of breathing

and

2. Why does this happen?

Answer 10

1. After physical activity:
   a) the rate of breathing increases
   b) the depth of breathing increases
2. This happens to get more oxygen into the blood during activity.

Question 11

Why does physical activity increase rate and depth of breathing?

In 2 points.

Answer 11

Physical activity increases rate and depth of breathing in order:
i. for more oxygen required for aerobic respiration to produce energy
ii. for more carbon dioxide to be excreted because carbon dioxide is toxic

Question 12

State the function of the cartilage in the trachea.

Answer 12

The cartilage helps to prevent the trachea collapsing at times when the pressure inside it is lower than the pressure of the air outside it (atmospheric pressure).

Question 13

What is the 1. role [1] and the 2. effect [2] of the external intercostal muscles in inspiration (breathing in)?

Effect on ribs, and as a result, on thorax volume.

Answer 13

1. When breathing in, the external intercostal muscles contract.
2. The effect: i. this pulls the ribcage upwards and outwards and ii. causes an increase in the volume in the thorax.

During inspiration everything happens to increase volume in the thorax i.e. inspiration = increase in thorax volume.

Question 14

What is the 1. role [1] and the 2. effect [2] of the muscles of the diaphragm in inspiration (breathing in)?

Effect on diaphragm, and as a result, on thorax volume.

Answer 14

1. When breathing in, the diaphragm muscles contract.
2. The effect: i. this pulls the diaphragm downwards and ii. causes an increase in thorax volume

During inspiration everything happens to increase volume in the thorax i.e. inspiration = increase in thorax volume.

Question 15

Explain how the increase in volume in the thorax during inspiration helps in breathing in?

[2]

Answer 15

When volume increases in the thorax:
i. pressure inside it falls below atmospheric pressure
ii. air is sucked in, flowing in along the trachea and bronchi into the lungs

Question 16

What is the 1. role [1] and the 2. effect [2] of the external intercostal muscles in expiration (breathing out)?

Effect on ribs, and as a result, on thorax volume.

Answer 16

1. When breathing out, the external intercostal muscles relax.
2. The effect: i. this causes the ribcage to drop back down into its normal position and ii. causes decrease in the volume of the thorax

During expiration, everything happens to decrease volume in the thorax to push air out.

Question 17

What is the 1. role [1] and the 2. effect [2] of the muscles of the diaphragm in expiration (breathing out)?

Effect on diaphragm, and as a result, on thorax volume.

Answer 17

1. When breathing out, the muscles of the diaphragm relax.
2. The effect: i. due to the elastic tissue the diaphragm is made of it springs back into shape ii. this decreases the volume in the thorax.

During expiration, everything happens to decrease volume in the thorax to push air out.

Question 18

When one breathes out more forcefully, explain the role [1] and effects [2] of the internal intercostal muscles on expiration.

Such an example of forceful expiration is coughing.

Answer 18

1. When breathing out forcefully the internal intercostal muscles contract strongly.
2. The effect: i. the ribcage drops down further, and ii. the volume of the thorax is decreased more than normal

This is not a usual occurance. Usually the intercostal muscles do not affect the process of breathing in and out.

Question 19

When one breathes out more forcefully, explain the role [1] and effects [1] of the muscles of the abdomen wallon expiration.

Such an example of forceful expiration is coughing.

Answer 19

1. When breathing out forcefully, the muscles in the abdomen wall contract.
2. The effect: this squeezes extra air out of the thorax.

This is not a usual occurance. Usually the intercostal muscles do not affect the process of breathing in and out.

Question 20

Explain how the decrease in volume in the thorax during expiration helps in breathing out?

[2]

Answer 20

When volume decreases in the thorax:
i. pressure inside it rises above atmospheric pressure
ii. air is pushed out, flowing out along the trachea and bronchi out of the lungs

Question 21

Why is there less oxygen in expired air, than in inspired air?

[1]

Answer 21

There is less oxygen in the air we breathe out than in the air we breathe in because cells in the body use oxygen for aerobic respiration.

• However, the amount of oxygen is still significant in expired air, at 16%, and this is because normal air in the bronchi and trachea mixes with expired air so that what is breathed out is a mixture of air from the alveoli and atmospheric air.

Question 22

Why is there more carbon dioxide present in expired air than in inspired air?

[1]

Answer 22

Extra carbon dioxide is present in the air we breathe out, at 4% from 0.04%, because **the body cells produce carbon dioxide in aerobic respiration, and this carbon dioxide diffuses out of the blood into the alveoli. **

Question 23

Why is water vapour in expired air more saturated than in inspired air?

Answer 23

There is more wter vapour present in expired air than in inspired air, because the gases involved in gaseous exchange dissolve in water before they can diffuse.

Question 24

At what point is anaerobic respiration activated in the body?

Answer 24

In the body, anaerobic respiration is activated when the heart and lungs cannot supply oxygen to the muscles any faster, having reached a limit.

This occurs during times of activity when the muscles need more oxygen to produce energy through aerobic respiration.