Exchange surfaces - Mammalian gas exchange. Flashcards Preview

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Describe how diffusion distance, SA, Volume and SA:Vol ratio vary with increasing organism size.

As the organism increases in size the SA and volume increases. However, a large organism has a smaller SA:Vol ratio.


State the formulae for the circumference and area of a circle.

Circumference - 2πr
Area - πr^2


SA and vol of sphere

SA - 4πr^3
Vol - 4/3(πr^3)


SA and vol of rectangular prism.

SA - 2(bh + bl + hl)
Vol - hbl


SA and vol of cylindrical prism.

SA - 2πr(r+l)
Vol - πr^2l


Describe how the level of activity of an organism is related to demand for oxygen and glucose.

If an organism is v active its cell has very high metabolic demands, meaning requirement loads of oxygen and glucose.


Explain how volume is related to demand and surface area is related to supply. Also explain why supply
meeting demand requires adaptations as organisms increase in size.

A high volume means the organism has a lot of cells which all have a metabolic requirement. The larger the SA of the organism, the faster these can be supplied with the necessary nutrients.
Some larger organism have a very small SA:Vol ratio, meaning that they cannot get sufficient nutrients by diffusion alone. They must adapt to form more specialised exchange surfaces.


Suggest some reasons why some organisms need specialised exchange surfaces.

- When they a small SA: vol ratio diffusion is too slow to obtain sufficient nutrients so they need to have a specialised exchange system in order to keep up with metabolic demands.


State 4 features of efficient exchange surfaces. For each feature explain how it increases efficiency of
the exchange surface.

1) Increased SA - provides SA needed for exchange, overcoming limitations of SA:vol ratio e.g. root hairs, villi.
2) Thin layers - shorter distances for substances to diffuse so it is faster and more efficient e.g. alveoli, villi
3) Good blood supply - steeper concentration gradient = faster diffusion e.g. alveoli, gills. villi
4) Ventilation - maintains concentration gradient so faster diffusion e.g. gills where flow of water carrying dissolved gases, alveoli.


State Fick’s law and show how the importance of each of the 4 features of efficient exchange surfaces
can be explained by Fick’s law.

Rate of diffusion is proportional to (SA x Concentration gradient)/ thickness of barrier.


Draw and label a diagram of the human gaseous exchange system.

Find online labelling quiz.


Describe the structure of the nasal cavity.

- Large SA with good blood supply which warms air to body temperature.
- Hairy lining which secretes mucus to trap dust and bacteria, protecting delicate lung tissue from infection.
- Moist surfaces increase humidity of incoming air, reducing evaporation from exchange surfaces.


Describe the structure of the trachea.

- Wide tube supported by incomplete rings of strong flexible cartilage. Stops it from collapsing.
- Lined with a ciliated epithelium with goblet cells between and below the epithelial cells.
- Goblet cells secrete mucus onto lining of trachea to trap dust and microorganisms that have escaped the nose lining.
- Cilia beat and move the mucus along with trapped dirt and microorganisms away from lungs.


Describe the structure of the bronchus.

- The trachea divides to form bronchi, each leading to a lung.
- Similar in structure to trachea with same supporting rings of cartilage.


Describe the structure of the bronchioles.

- Bronchi divide to make many small bronchioles
- Smaller bronchioles have no cartilage rings
- Walls of bronchioles contain smooth muscle, when it contracts the bronchioles constrict. When it relaxes they dilate.
- This changes the amount of air reaching the lungs.
- They are lined with a layer of flattened epithelium so some gaseous exchange can happen.


Describe the structure of the alveoli.

- Consist of layer of thin. flattened layer of epithelial cells along with some collagen and elastic fibres. This allows the alveoli to stretch as air is drawn in. When they return to resting size is squeezed out. This is called the elastic recoil of lungs.
- They have a large SA
- Thin layers, only one cell thick
- Good blood supply, surrounded by capillaries to maintain steep concentration gradient.
- Good ventilation.
- Inner surface is covered by thin layer of solution of water, salts and lung surfactant allows alveoli to remain inflated and oxygen is dissolved in the water before diffusing into the blood stream.


Define the term breathing.

A behaviour that you do by muscle contraction and relaxation.


Define ventilation.

The air flow generated by breathing. Inhalation/exhalation.


Define gas exchange.

The diffusion of gases from an area of higher concentration to an area of lower concentration, especially the exchange of oxygen and carbon dioxide between an organism and its environment.


Draw and label a diagram showing the arrangement of the structures involved in breathing.

Trachea divides into bronchi, which then branch off into bronchioles which end in alveoli.
Two lungs and a diaphragm under the lungs.
Ribs over the lungs with intercostal muscles between them.
- Do an online labelling exercise-


Define the term inspiration.

Taking air in or inhalation. Active (energy-using) process.


Define the term expiration.

Normal expiration (breathing out or exhalation) is a passive process.


Define the term active process.

A process that uses energy.


Define the term passive process.

A process that does not use energy.


Describe the process of inspiration linking the action of muscles, to the movement of structures, the
change in pressure within the lungs and the direction of airflow

1) The external intercostal muscles and diaphragm contract.
2) This causes the rib cage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thorax.
3) As the volume of the thorax increases the lung pressure decreases (to below atmospheric pressure).
4) This causes air flow into the lungs
5) Inspiration is an active process.


Describe the process of normal expiration linking the action of muscles, to the movement of structures,
the change in pressure within the lungs and the direction of airflow.

1) The external intercostal and diaphragm muscles relax.
2) The ribcage moves downwards and inwards and the diaphragm becomes curved again.
3) The thorax volume decreases, causing the air pressure to increase (to above atmospheric pressure).
4) Air is forced out of the lungs.
5) Normal expiration is a passive process.


Describe how the process of forced expiration is different from normal expiration and suggest when it
might be used.

During forced expiration, the internal intercostal muscles contract, pulling the rib cage down and in, making it an active process instead of a passive one.
It could be used during intense exercise, the increases the speed of gas exchange.


State 3 pieces of equipment used to measure the functioning of the lungs. For each outline how they

1) A peak flow meter - simple, measure the rate at which air can be expelled from the lungs.
2) A vitalograph - a more sophisticated version of a peak flow meter. Tests the amount of air they breathe out and how quickly this is done. Measure forced expiatory volume in 1 sec.
3) Spirometer - can be used to measure several different aspects of a lung volume.


Label a diagram of a spirometer and annotate with the function of each component

- Subject breathes in and out until O2 is used up. They breathe into a tube connected to the oxygen chamber, wearing a nose clip.
- The tube the subject breathes into has a soda lime in it to absorb carbon dioxide.
- As the person breathes in and out the lid of the chamber moves up and down. These movements are recorded by a pen attached to the lid of the chamber.
- This writes on a rotating drum, creating a spirometer trace.
- Do an online labelling exercise -


Describe how a spirometer measures change in lung volume and explain why it cannot measure
total lung volume.

The spirometer cannot measure residual volume (the volume of air left in your lungs after you have exhaled as much as possible), it only measure what you actually breathe out.
Total lung volume includes residual volume so it cannot be measured with a spirometer.