11.1 Gas Exchange in Humans

Question 1

Describe the features of gas exchange surfaces in humans, limited to: large surface area, thin surface, good blood supply and good ventilation with air

Answer 1

• Large surface area: Allow faster diffusion of gasses across the surface
• Thin surface(/wall): Short distance for gases to diffuse over. Hence easier for gas exchange to happen
• Good blood supply: By a network of capillaries around an alveoli. Creating and maintaining the concentration gradients for oxygen and carbon dioxide
• Good ventilation with air (airflow around the gas exchange surface): Maintains the concentration gradients for oxygen and ca

Question 2

State the function of cartilage in the trachea

Answer 2

Support the airways and keep them open during breathing (if not, the sides could collapse inwards when the air pressure drops in the tubes)

Question 3

Explain the role of the ribs, the internal and external intercostal muscles and the diaphragm in producing volume and pressure changes in the thorax leading to the ventilation of the lungs

Answer 3

• Inhalation: External intercostal muscles contract, pulling the ribs up and out. The diaphragm flattens as it contracts. Increasing the volume of the thorax and causing a decrease in pressure inside the lungs (relative to outside the body); drawing air into the lungs.
• Exhalation: External intercostal muscles relax, pulling the ribs down and in. The diaphragm moves upwards back to its domed shape as it relaxes. Decreasing the volume of the thorax and causing an increase in pressure inside the lungs (relative to outside the body); forcing air out.

Question 4

investigate the differences in composition between inspired and expired air using limewater as a test for carbon dioxide

Answer 4

• Tube A: Inhalation and Tube B: Exhalation
• Lime Water becomes from clear to cloudy if CO₂ is bubbled through
• Results: tube A is clear whereas tube B is cloudy
• Proof that % of CO₂ is higher in inhaled air than exhaled air

Question 5

Explain the differences in composition between inspired and expired air

Answer 5

check online notes

Question 6

Describe the differences in composition between inspired and expired air, limited to: oxygen, carbon dioxide and water vapour

Answer 6

Inhaled air’s gas composition matches atmospheric levels. During gas exchange: oxygen enters the blood from the alveoli whilst carbon dioxide and water vapour leave the blood and enter the alveoli. Hence, the gas composition of exhaled air differs from that of inhaled air [then state the statistics]

Question 7

Investigate the effects of physical activity on the rate and depth of breathing

Answer 7

1. Calculate the breathing rate at rest
2. Measure the average chest expansion over 5 breaths at rest
3. Carry out a physical exercise
4. Recalculate the breathing rate
5. Calculate the change in breathing rate
   Variables
   a) Independent: Whether the participant is exercising, effects of different exercises or time exercised
   b) Dependent: Breaths per minute
   c) Control: Same participant and time exercised

Question 8

Describe the effects of physical activity on the rate and depth of breathing

Answer 8

• Breathing rate will increase after physical activity
• Muscles are working harder, respiring at a greater rate
• Respiring cells require more oxygen to keep up with the energy demand and carbon dioxide must be removed
• To achieve this, the respiratory muscles increase contraction and depth of breath

Question 9

Explain the link between physical activity and the rate and depth of breathing in terms of: an increased carbon dioxide concentration in the blood, which is detected by the brain, leading to an increased rate and greater depth of breathing

Answer 9

• CO₂ diffuses out the cells and into the blood plasma, increasing carbon dioxide concentration in the blood
• Blood flows around the circulatory system and passes to the brain where the increased carbon dioxide levels are detected by chemoreceptors in the brain
• Nerve impulses are sent to the diaphragm and the intercostal muscles to increase the rate and depth of muscle contraction

Question 10

Explain the role of goblet cells, mucus and ciliated cells in protecting the breathing system from pathogens and particles

Answer 10

1. Ciliated cells have tiny hairs at the end that beat
2. And push mucus away from the lungs towards the nose and throat where it can be removed
3. Mucus produce goblet cells, trapping particles, pathogens and dust
   - Preventing them from getting into the lungs and damaging the cells there