1.2.1 - Exchange Surfaces (Specialised Exchange Surfaces) Part 1, 2, 3 & 4

Question 1

What is the role of the elastic fibres in the trachea and bronchi?

Answer 1

When the smooth muscle contracts, this reduces the diameter of the lumen. As it relaxes, the elastic fibres recoils to their original size and shape because the smooth musce cannot reverse the deformed effect.

Question 2

Why do multicellular organisms need specialised exchange surface and single-celled organisms do not?

Answer 2

• Multicellular organisms have a small surface area to volume ratio.
• This means they cannot use their body as an exchange surface because they cannot intake the large amount of oxygen they need in one go - diffusion will be too slow.
• Limited amount of oxygen will be able to reach the inner cells.
• Single-celled organisms have a large surface area to volume ratio.
• They do not need a large supply of oxygen.
• They can intake the amount they need in one go using diffusion.

Question 3

List four features of an efficient exchange surface, with reference to the diffusion of oxygen and carbon dioxide as an example.

Answer 3

• The exchange surface must have a large surfce area.
• It must be a barrier permeable to oxygen and carbon dioxide.
• The barrier must be thin.
• It must be able to maintain a steep diffusion gradient.

Question 4

How can you work out the breathing rate on a spirogram?

Answer 4

You must count the amount of breaths (one up and one down) over a minute to work out the breathing rate.

Question 4

Explain can a spirometer be used to determine a person’s oxygen uptake.

Answer 4

• As the person inhales, oxygen is taken from the chamber.
• As the person exhales, CO₂ is absorbed by the soda lime.
• As time passes, the level of oxygen will decrease in the chamber.
• Therefore, the oxygen uptake will be - the difference between the starting amount of oxygen and the final volume over a minute.

Question 5

Which of the following does the alveolus have:

• Smooth muscle?
• Elastic fibres?
• Goblet cells?
• Cartilage?
• Ciliated epithelium?

Answer 5

Alveoli only have elastic fibres.

Question 6

Describe what happens to the diaphragm during inspiration and expiration.

Answer 6

• Inspiration - The diaphragm contracts to become flatter and pushes the digestive organs down.
• Expiration - The diaphragm relaxes and is pushed up by the organs.

Question 7

How does the body maintain a steep diffusion gradient across an alveolus?

Answer 7

For a steep diffusion gradient, there must be a constant supply of fresh molecules e.g:

• Blood constantly brings CO₂ to the lungs to ensure the concentration of CO₂ is higher than the CO₂ in the air of the alveolus.
• Blood constantly carries oxygen away from the lungs to ensure that the concentration of oxgen in the blood is lower than the air in the aveoli.

Question 8

Briefly describe how a spirometer works and how it can be used to measure the vital capacity and tidal volume.

Answer 8

• A spirometer consists of an air chamber with oxygen floating on top of a water tank.
• As the person breathes in, the oxygen chamber sinks.
• As the person breathes out, the oxygen chamber rises.
• For tidal volume - The person must be breathing nomally whilst resting.
• For vital capacity - The person must breathe as deeply as possible.

Question 10

Ciliated epithelium is the inner lining of the trachea and bronchi with two types of cells. What cells are these and how does their function help the trachea and bronchi?

Answer 10

Ciliated epithelium consist of goblet cells and cilia.

Goblet cells secrete mucus under the epithelium in order to trap tiny particles like bacteria in the air. This reduces the risk of infection.

Ciliated cells have tiny, hair-like projections that waft the mucus to the throat to be swallowed.

Question 11

How does the structure of the trachea differ from the bronchi?

Answer 11

• The trachea has an incomplete ring of cartilage which is less common in the bronchi.
• The bronchi is narrower than the trachea.

Question 11

Explain the meaning of the terms:

• Tidal volume.
• Vital capacity.

Answer 11

• Tidal volume - The volume of air breathed in and out in each breath at rest.
• Vital capacity - The largest volume of air breathed in and out in one breath.

Question 13

Describe what happens to the ribcage and intercostal muscles during inhalation and expiration?

How does this affect the pressure in the lungs?

Answer 13

• Inhalation - The external intercostal muscles contract to raise the ribs. This ensures the pressure in the lungs drops below atmospheric pressure.
• Expiration - The external intercostal muscles relax to let the ribs fall. This ensures the pressure increases above atmospheric pressure.

Question 14

Alveoli are very small. Their walls are made of squamous cells.

Why is this vital as an exchange surface?

Answer 14

The fact that the aveoli are very small indicates it has a large surface area to volume ration. This means more of the surface is exposed for diffusion, thus a faster rate of diffusion can take place.

Squamous cells are flattened, thin cells. This means the pathway for diffusion is very short and therefore diffusion can happen at a faster rate.

Question 15

1. What is the role of the cartilage in the trachea and bronchi?
2. In the trachea, why is the cartilage not a complete ring?

Answer 15

1. The caritlage plays a structural role. It supports the trachea and bronchi by preventing it from collapsing when air pressure is low during inhalation.
2. The form of an incomplete ring allows for flexibility of neck without constriction of the airway.

Question 16

1. Describe where the smooth muscle is in the transverse section of a trachea.
2. What is its function in the trachea?

Answer 16

1. The smooth muscle is located on the inside surface of the cartilage.
2. Its role is to narrow the lumen by contracting so that it constricts the airway. This is useful as it is able to be controlled when there are harmful substances in the air.