Biology Module 3 Exchange Surfaces

Question 1

Explain the basic exchange requirements of all cells

Answer 1

1. Cellular organisms require nutrients and oxygen for their metabolic activities (growth, respiration)
2. They also produce metabolic waste such as urea and carbon dioxide
3. Diffusion (the movement of substances from areas of high to low concentration) is the process by which cells get a supply of nutrients and oxygen, and removal of wastes such as carbon dioxide

Question 2

Explain why some organisms do not need specialised exchange surfaces

Answer 2

1. The higher the surface area to volume ratio, the higher the rate of diffusion
2. For organisms with a high SA:vol ratio (single cells, less complex), the rate of diffusion is sufficient for adequate supply and removal
3. Smaller (single celled), less complex organisms also have a lower energy requirement

Question 3

Explain why some organisms require specialised exchange surfaces

Answer 3

1. But for organisms with a low SA:vol ratio (larger, multicellular, more complex), the rate of diffusion is insufficient for supply and/or removal of substances to/from all the cells
2. Larger, more complex organisms have higher energy requirements
3. Organisms with a low SA:vol ratio therefore require specialised exchange surfaces

Question 4

Explain why mammals need a specialised gas exchange system

Answer 4

1. Mammals are large multicellular organisms
2. They have a low SA:vol ratio so rates of diffusion across the surface are low
3. They are endothermic, and can move around
4. so their metabolic requirements are high (lots of oxygen required, lots of carbon dioxide to remove)
5. Rates of gas exchange across the surface would be insufficient to meet these demands

Question 5

Describe the mammalian gas exchange system

Answer 5

1. The lungs are ventilated by changes in pressure caused by the action of the rib cage, the intercostal muscles and diaphragm
2. The nasal cavity humidifies incoming air
3. The trachea is the main airway, allowing air to flow to and from the lungs
4. The trachea branches into the left and right bronchi
5. Each bronchus branches into many bronchioles which are narrower airways that lead to the alveoli
6. At the alveoli, gas exchange occurs between the blood in capillaries and the air in the alveoli

Question 6

Explain the role of cartilage in lung function

Answer 6

1. The trachea and bronchi are supported with incomplete rings of cartilage
2. Cartilage is both flexible and strong
3. The cartilage rings prevent it from collapsing when the lung pressure is lower than the atmospheric pressure (inhaling)
4. They ensure that the airway is always open, allowing continuous ventilation of the lungs

Question 7

Explain the role of goblet cells and ciliated epithelium in lung function

Answer 7

1. The trachea, bronchi and (larger) bronchioles are lined with ciliated epithelium which prevents obstructions and infections
2. Mucus is secreted by goblet cells
3. The mucus traps pathogens and particulates
4. Cilia on the epithelial cells beat to waft the mucus back up the airway to be swallowed or expelled
5. This ensures unobstructed ventilation of the lungs

Question 8

Explain the role of smooth muscle in lung function

Answer 8

1. Smooth muscle surrounds the bronchioles
2. When smooth muscle contracts the bronchioles are narrowed and airflow is reduced
3. When smooth muscle relaxes, the bronchioles are widened and airflow is increased
4. Smooth muscle is controlled by the autonomic nervous system and allows airflow to increase during the fight-or-fight stress response

Question 9

Explain the role of elastic tissue in lung function

Answer 9

1. Elastic tissue contains the proteins collagen (strength, flexibility) and elastin (elasticity)
2. This can mainly be found around the alveoli
3. After inhaling, the elasticity of the alveoli helps them return to their normal size and shape
4. The collective elastic recoil of the many alveoli helps force air out of the lungs

Question 10

Explain how the lungs have the features of an effective gas exchange surface (short diffusion distances)

Answer 10

1. The alveoli are only one cell thick
2. The alveoli are made up of squamous epithelium (flat cells)
3. The distance between the alveoli and capillaries is very small
4. So the overall diffusion distance between the blood in the capillaries and the air in alveoli is minimised

Question 11

Explain how the lungs have the features of an effective gas exchange surface (concentration gradients)

Answer 11

1. Constant ventilation of the air in the alveolus maintains high oxygen concentration and low carbon dioxide concentration
2. Constant flow of blood in the capillaries (deoxygenated) maintains a low blood concentration of oxygen and a high blood concentration of carbon dioxide
3. This maintains a steep concentration gradient
4. For oxygen to diffuse from alveoli to blood
5. For carbon dioxide to diffuse from blood to alveoli

Question 12

Explain how the lungs have the features of an effective gas exchange surface (high surface area)

Answer 12

1. There are numerous alveoli
2. And there is an extensive network of capillaries
3. There is a high surface area of contact between alveoli and capillaries

Question 13

Describe the process of inspiration

Answer 13

1. The diaphragm contracts
2. The external intercostal muscles contract
3. (internal intercostal muscles relaxed)
4. This raises the rib cage and increases the volume of the thorax
5. As the thorax pressure is now lower than the atmospheric pressure
6. Air is drawn into the lungs (via nasal passages, trachea, bronchi etc.)

Question 14

Describe the process of expiration

Answer 14

1. The diaphragm relaxes
2. The external intercostal muscles relax
3. The rib cage lowers
4. The thorax pressure is higher than the atmospheric pressure
5. Air is forced out of the lungs (through bronchioles, bronchi, trachea and nasal passages)
6. Forced expiration occurs when the internal intercostal muscles contract
7. Further increasing thorax pressure
8. And expelling more air into the atmosphere from the lungs

Question 15

Describe how a spirometer trace is produced

Answer 15

1. Person with an attached nose clip breathes into spirometer tube
2. When the person inhales, pure oxygen is drawn out of the airtight chamber, moving the lid down
3. When the person exhales, the expired air moves through a canister of soda lime which absorbs the carbon dioxide
4. The remaining oxygen re-enters the airtight chamber, raising the lid up
5. As the lid is moved, it creates a trace on the rotating drum

Question 16

Describe how the breathing rate can be determined from a spirometer trace

Answer 16

1. The y-axis shows lung volume
2. The x-axis shows time (in minutes or seconds)
3. Determine the distance (horizontal) between the same point in two consecutive breaths, and convert to time using the scale of the x axis
4. This is the time taken for one breath
5. Divide 60 seconds, or 1 minute (depending on the units used in step 3) by the time taken for one breath
6. This should result in a number of breaths per minute

Question 17

Describe how the rate of oxygen uptake can be determined from a spirometer trace

Answer 17

1. A certain volume of oxygen from the inhaled air enters the blood.
2. A corresponding volume of carbon dioxide enters the exhaled air
3. As this is absorbed by the soda lime, there is a smaller volume of oxygen returning to the airtight chamber than was inhaled
4. Over a number of breaths, the spirometer trace will slope downwards
5. The gradient of the slope is the rate of oxygen uptake into the blood

Question 18

Describe the structure of the gas exchange system in insects

Answer 18

1. On their surface they have openings called spiracles
2. These can be opened or closed
3. The spiracles lead on to tubes called tracheae
4. Tracheae are supported by spirals of chitin
5. Tracheae branch into narrower tubes called tracheoles
6. Tracheoles are moist and thin walled (single cells)
7. They are permeable to gases and spread throughout and close to tissue cells

Question 19

Describe the functioning of the gas exchange system in insects

Answer 19

1. Air enters the spiracles
2. It moves through the tracheae and tracheoles, which are near respiring cells
3. The air has a higher oxygen concentration than the respiring cells
4. The air has a lower carbon dioxide concentration than the respiring cells
5. Oxygen diffuses into the tracheal fluid and then respiring cells
6. Carbon dioxide diffuses into the tracheal fluid and then tracheoles

Question 20

Describe how structures in bony fish are involved enabling effective ventilation

Answer 20

1. The mouth is opened while the opercular valve is closed, increasing the volume of the buccal cavity
2. This lowers the pressure in the buccal cavity, drawing water in
3. The opercular cavity expands, lowering the pressure there and drawing in water through the gills
4. The mouth is closed and the opercular valve is opened
5. The pressure in the buccal cavity rises, forcing water to flow over and out through the gills
6. Water is needed to maximise the exchange surface area

Question 21

Explain how gas exchange occurs in bony fish

Answer 21

1. Water flows into the buccal cavity, through gills and out of the fish
2. Deoxygenated blood flows through afferent blood vessels into the gill lamellae
3. Oxygen from water diffuses into the blood
4. Carbon dioxide diffuses out of the blood into the water
5. Oxygenated blood flows away from the gills in efferent blood vessels

Question 22

Describe how dissection can be used to observe the features of the gas exchange system in bony fish

Answer 22

1. The operculum (gill flap) can be observed, which protects the gills
2. The operculum can be removed to observe gill lamellae underneath
3. The high number and fine, delicate structure of the gill lamellae can be observed
4. This can be more easily observed by placing the gill lamellae in water, which causes them to separate

Question 23

Describe how dissection can be used to observe the features of the gas exchange system in insects

Answer 23

1. The abdomen of an insect can be carefully cut open
2. This allows the observation of tracheae that lead inwards from spiracles at the insects surface
3. These branch out to form very fine tubes, showing their short diffusion distance and high surface area

Question 24

Describe the histological features of the mammalian gas exchange system made by observation of microscope slides

Answer 24

1. Lung tissue shows numerous, small air spaces which shows the high number and collective surface area of the alveoli
2. Blood vessels can be seen in close proximity to the alveolus wall (short diffusion distance).
3. The very thin alveolar walls can be seen (short diffusion distance)

Question 25

Describe the histological features of the gas exchange system of bony fish made by observation of microscope slides

Answer 25

1. Individual gill lamellae can be observed
2. The connective tissue that forms the gill structure can be seen (lighter staining)
3. The major afferent/efferent blood vessels can be observed
4. The darker outer layer shows the high density of capillaries (high surface area)
5. The gill lamellae are observed to be very small structures (short diffusion distance)

Question 26

Describe the histological features of the insect gas exchange system made by observation of microscope slides

Answer 26

1. The tracheae can be cut open and their structure observed

2. Shows rings of chitin