Gas exchange in humans

Question 1

What are the features of gas exchange?

Answer 1

Large surface area to allow faster diffusion of gases across the surface
Thin walls to ensure diffusion distances remain short
Good ventilation with air so that diffusion gradients can be maintained
Good blood supply to maintain a high concentration gradient so diffusion occurs faster

Question 2

Ribs:

Answer 2

Bone structure that protects internal organs

Question 3

Intercostal muscle:

Answer 3

Muscles between the ribs which controls their movements causing inhalation and exhalation

Question 4

Diaphragm:

Answer 4

Sheet of connective tissues and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation

Question 5

Trachea:

Answer 5

Windpipe that connects the mouth and nose to the lungs

Question 6

Larynx:

Answer 6

The voice box, when air passes across here we are able to make sounds

Question 7

Bronchi (pl):

Answer 7

Large tubes branching the trachea with one bronchus for each lung

Question 8

Bronchioles:

Answer 8

Bronchi split to form smaller tubes in the lungs connected to the alveoli

Question 9

Alveoli:

Answer 9

Tiny air sacs where gas exchange takes place

Question 10

Pleural cavity:

Answer 10

The fluid filled space between the pleural membranes which reduces friction and allows the lung to move freely

Question 11

What do cilia cells do?

Answer 11

Cilia cells have tiny hairs on the end of them that beat and push mucus up the passages towards the nose and throat where it can be removed

Question 12

What does the mucus do?

Answer 12

The mucus traps particles, pathogens like bacteria or viruses, and dust and prevents them from getting into the lungs and damaging the cells there

Question 13

How is the alveoli specialized for gas exchange?

Answer 13

• They are many air sacs, which present a large surface area for diffusion
• The lining of the air sacs is only one cell thick for easy diffusion, as the gas only has to travel a short distance.
• The air sacs are supplied by a close and dense network of capillaries- this means it always has a fresh supply of blood.
• The lining of the air sacs is moist so that gases can dissolve before then diffuse across the thin membrane.

Question 14

External intercostal muscle:

Answer 14

Pulls the rib cage up

Question 15

Internal intercostal muscle:

Answer 15

Pulls the rib cage down

Question 16

What happens during inhalation?

Answer 16

External intercostal muscles contract
Internal intercostal muscles relax
Rib cage moves up and out
Diaphragm contracts and flattens
Volume of thorax increases
Pressure inside the thorax decreases
Air is drawn in

Question 17

What happens during exhalation?

Answer 17

External intercostol muscles relax 
Internal intercostal muscles contract
Rib cage moves down and in
Diaphragm relaxes and becomes dome-shaped
volume of thorax decreases
pressure inside thorax increases
Air is drawn out

Question 18

Describe the structure of the thorax

Answer 18

Once air is breathed in through the mouth or nose it travels down the trachea. The trachea splits into two- one going into the left lung and one going into the right lung- these pipes are called bronchi. Each bronchus will then divide further into many bronchioles: each ending in a sac called an alveoli. The trachea and bronchi have walls of muscle that are supported by cartilage. The cartilage is in partial rings so that the tubes can be moved in any direction. Cilia on the walls move mucus out of the breathing system and into the stomach.

Question 19

What are the chemicals in cigarettes?

Answer 19

Tar – a carcinogen (a substance that causes cancer)
Nicotine – an addictive substance which also narrows blood vessels
Carbon monoxide – reduces the oxygen-carrying capacity of the blood

Question 20

What does nicotine do?

Answer 20

Nicotine narrows blood vessels leading to an increased blood pressure
It also increases heart rate
Both of these effects can cause blood clots to form in the arteries leading to heart attack or stroke

Question 21

What does carbon monoxide do?

Answer 21

Carbon monoxide binds irreversibly to haemoglobin, reducing the capacity of blood to caryy oxygen.
This puts more strain on the breathing system as breathing frequency and depth needs to increase in order to get the same amount of oxygen into the blood.
It also puts more strain on the circulatory system to pump the blood faster around the body and increase the risk of coronary heart disease and strokes.

Question 22

What does tar do?

Answer 22

Tar is a carcinogen and it increases the chances of cancerous cells developing in the lungs.
Chronic bronchitis is caused by tar which stimulates goblet cells and mucus glands to enlarge, producing more mucus.
- It destroys cilia and mucus builds up blocking the smallest bronchioles and leading to infection.

Question 23

How Emphysema affects the alveoli?

Answer 23

Emphysema develops due to the frequent infections, phagocytes that enter the lungs release elastase, an enzyme that breaks down the elastic fibres in the alveoli.

• The alveoli becomes less elastic and cannot stretch
• The breakdown pf alveoli reduces the surface area for gas exchange
• Patients become breathless and wheezy

Question 24

Experiment to investigate the effect of exercise on breathing:

Answer 24

Record resting breathing rate

• Next, get them to do 10 sets of an exercise of your choice.
• Then record their breathing rate after the 10 sets.
• Once they reach their resting breathing rate again, have them increase the number of sets of the exercise you chose (for example, now do 20 sets).
• Record the person’s breathing rate after they’ve carried out the amount of sets you chose.
• Lastly, repeat step 4, increasing the amount of sets each round until a given amount of times.

Question 25

Results:

Answer 25

Breathing increases when exercising. This is because muscles are working hard and respiring aerobically and they need more oxygen to meet the energy demand. If they cannot meet the energy demand, they will respire anaerobically, producing lactic acid.

Question 26

Results pt2:

Answer 26

After the exercise has finished, the breathing rate remained elevated for some time. This is because the lactic acid that has build up needs to be removed as it lower the pH of cells, causing them to denature. It can only be removed by combining it with oxygen - this is called 'repaying the oxygen debt' The longer it takes, the more lactic acid produced and the more oxygen debt that needs to be repaid.

Question 27

Variables:

Answer 27

Ensure all students are similar size, general fitness, age, gender and provide them with the same meal before. Give students an exercise that is an easier type where intensity is easier to control. Begin counting the breathing rate as soon as the time interval begins and only measure for 15s (or less) then multiply up to calculate breaths per minute.

Question 28

Role of diffusion in gas exchange

Answer 28

Diffusion (in the alveoli) allows oxygen into the blood and carbon dioxide into the alveoli. Blood arriving at the alveoli has a higher concentration of CO2 than the air inside the alveoli. This difference in concentration creates a concentration gradient allowing carbon dioxide to diffuse into the alveoli air from the blood. The blood arriving in the alveoli has a lower concentration of oxygen than the air in the alveoli (as the oxygen has already been used for respiration inside cells). This allows the oxygen to move into the blood by diffusion.