Gas exchange in humans

Question 1

Thorax

Answer 1

Human chest cavity
Consists of ribs, intercostal diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes

Question 2

Ribs

Answer 2

Bone structure that protects internal organs e.g. lungs

Question 3

Intercostal muscle

Answer 3

Muscles between the ribs which control their movement during inhalation/exhalation

Question 4

Diaphragm

Answer 4

Sheet of connective tissue and muscle at the bottom of the thorax
Changes volume of thorax (resulting in change in pressure) for inhalation/exhalation

Question 5

Trachea

Answer 5

Windpipe that connects mouth and nose to the lungs

Question 6

Bronchi

Answer 6

Large tubes branching off trachea (one bronchus per lung)

Question 7

Bronchioles

Answer 7

Bronchi split to form smaller tubes called bronchioles in lungs connected to alveoli

Question 8

Alveoli

Answer 8

Tiny air sacs where gas exchange takes place

Question 9

Pleural cavity

Answer 9

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

Question 10

Breathing in

Answer 10

External intercostal muscles contract
Internal intercostal muscles relax
Ribs move up
Diaphragm muscles contract so it flattens
Volume ^, Pressure 🔽
Pressure outside higher, air rushes in

Question 11

Breathing out

Answer 11

External intercostal muscles relax
Internal intercostal muscles contract
Ribs move down
Diaphragm muscles relax so it raises
Volume 🔽, Pressure ^
Pressure outside lower, air rushes out

Question 12

Adaptations of alveoli

Answer 12

Have many alveolar sacs (large SA:V ratio)
Alveolar wall is 1 cell thick (short diff. distance)
(Capillary wall is also 1 cell thick)
Ventilation maintains high O2 levels and low CO2 levels in the alveolar air space (steep concentration gradient)
Good blood supply high in CO2 and low in O2 (steep concentration gradient)
Layer of moisture on alveoli surface helps gases dissolve

Question 13

Nicotine from smoking

Answer 13

Narrows blood vessels and increases heart rate, leading to increased blood pressure
High BP leads to blood clots in arteries, potentially resulting in heart attack or stroke

Question 14

Carbon monoxide from smoking

Answer 14

Binds irreversibly to haemoglobin, reduces blood’s oxygen capacity
Breathing frequency and depth need to increase to supply same amount of oxygen
Faster pumping of blood results in BP and risk of coronary heart disease and stroke

Question 15

Tar from smoking

Answer 15

Carcinogen linked to increased chances of cancerous cells developing in lungs
Contributes to chronic bronchitis

Question 16

Chronic bronchitis

Answer 16

Tar stimulates goblet cells and mucus glands to enlarge and produce more mucus
Mucus builds up, blocking small bronchioles and leading to infection, which damages cilia and prevents them from removing the mucus
Smokers cough is the attempt to move the mucus

Question 17

Emphysema

Answer 17

Result of frequent infection (from mucus)
Phagocytes that enter the lungs release an enzyme that breaks down elastic fibres in the alveoli
Alveoli are less elastic and cannot stretch, so many burst
Breakdown of alveoli reduces SA for gas exchange
Patients become breathless and wheezy

Question 18

Effect of Exercise on Breathing Practical

Answer 18

Measure breathing rate at rest: Count number of breaths in 15s and multiply by 4 (repeat)
Exercise for set time (e.g. 1 min)
Immediately count breaths in 15s after exercise and multiply by 4
Repeat this step every minute after exercise for 5 minutes
Repeat with 10 other students

Question 19

Oxygen Debt

Answer 19

Muscles are working harder during exercise and respire aerobically, needing O2 to meet energy demand
If they cannot meet the energy demand they will respire anaerobically and produce lactic acid
After exercise lactic acid built up needs to be oxidised as it lowers the pH of cells and can denature enzymes
It can be removed by combining with oxygen