3-2 Gas exchange

Question 1

Describe a fish’s exchange system?

Answer 1

• Fish have a small SA: V and an impermeable membrane so gases cannot diffuse through.
• This means that fish need a specialised exchange system.
• Bony fish have four pairs of gills, each gill supported by an arch.
• Along each arch, there are multiple projections called gill filaments, with lamellae on them which participate in gas exchange.
• Blood and water flow across the lamellae in a counter current direction meaning they flow in the opposite direction to one another.
• This ensures that a steep diffusion gradient is maintained so that the maximum amount of oxygen is diffusing into the deoxygenated blood from the water.
• The projections are held apart by water flow, therefore, in the absence of water they stick together, thus meaning fish cannot survive very long out of water.

Question 2

Describe a fish’s ventilation system?

Answer 2

• Ventilation is required to maintain a continuous unidirectional flow.
• Ventilation begins with the fish opening its mouth follow by lowering the floor of the buccal cavity.
• This enables water to flow in.
• Afterwards, fish closes its mouth, causing the buccal cavity floor to raise, thus increasing the pressure.
• The water is forced over the gill filaments by the difference in pressure between the mouth cavity and opercular cavity.
• The operculum acts as a valve and pump, letting water out and pumping it in.

Question 3

Describe a terrestrial insect’s exchange system?

Answer 3

• Insects do not possess a transport system therefore oxygen needs to be transported directly to tissues undergoing respiration.
• This is achieved with the help of spiracles, small openings of tubes, either bigger trachea or smaller tracheoles, which run into the body of an insect and supply it with the required gases.
• Gases move in and out through diffusion, mass transport because of muscle contraction and because of volume changes in the tracheoles.

Question 4

Describe a plant’s exchange system?

Answer 4

• Plants are adapted to efficient gas exchange through many adaptations in their leaves.
• Leaves have many small holes called stomata which allow gases to enter and exit the leaves.
• The large number of these means no cell is far from the stomata, reducing the diffusion distance.
• Leaves also possess air spaces to allow gases to move around the leaf and easily meet photosynthesising mesophyll cells.

Question 5

What are the lungs?

Answer 5

• The lungs are a pair of lobed structures with a large surface area located in the chest cavity that can inflate.

Question 6

What are the lungs surrounded by?

Answer 6

• The lungs are surrounded by the rib cage which serves to protect them.
• A lubricating substance is secreted to prevent friction between the rib cage and lungs during inflation and deflation.

Question 7

What are the external and internal intercostal muscles used for?

Answer 7

• External and internal intercostal muscles between the ribs contract to raise and lower the ribcage respectively.

Question 8

What does the diaphragm do?

Answer 8

• A structure called the diaphragm separates the lungs from abdomen area.

Question 9

Describe the flow of air through the respiratory system?

Answer 9

• The air enters through the nose, along the trachea, bronchi and bronchioles which are structures well adapted to their role in enabling passage of air into the lungs.

Question 10

Where does gaseous exchange take place?

Answer 10

• The gaseous exchange takes place in the walls of the alveoli, which are tiny sacs filled with air.

Question 11

What holds open the airways?

Answer 11

• Rings of cartilage, incomplete in the trachea to allow the passage of food down the oesophagus behind the trachea.

Question 12

Describe the structure of the trachea and bronchi?

Answer 12

• Several layers which together make up a thick wall.
• The wall is mostly composed of cartilage, in the form of incomplete C rings.
• The inside surface of the cartilage is a layer of glandular and connective tissue, elastic fibres, smooth muscle, and blood vessels.
• This is referred to as the ‘loose tissue’.
• The inner lining is an epithelial layer composed of ciliated epithelium and goblet cells.

Question 13

Describe the difference between trachea and bronchi?

Answer 13

• Bronchi are narrower.

Question 14

Describe the difference between bronchioles and bronchi?

Answer 14

• Bronchioles are narrower than bronchi.

Question 15

Describe the structure of bronchioles?

Answer 15

• Only the larger bronchioles contain cartilage.
• Their wall is made from smooth muscle and elastic fibres.
• The smallest bronchioles have alveoli clusters at the ends.

Question 16

How are the alveoli adapted for their function?

Answer 16

• The alveoli are very thin being only one cell thick, these are surrounded by capillaries which are also only cell thick, this reduces the diffusion pathway for gases.
• The constant blood supply by capillaries means that a steep concentration gradient is constantly maintained.
• There are many alveoli, collectively giving a large surface area.

Question 17

Describe the structure and function of the cartilage?

Answer 17

• Involved in supporting the trachea and bronchi, plays an important role in preventing the lungs from collapsing in the event of pressure drop during exhalation.

Question 18

Describe the structure and function of the ciliated epithelium?

Answer 18

• Present in bronchi, bronchioles, and trachea, involved in moving mucus along to prevent lung infection by moving it towards the throat where it can be swallowed.

Question 19

Describe the structure and function of goblet cells?

Answer 19

• Cells present in the trachea, bronchi and bronchioles involved in mucus secretion to trap bacteria and dust to reduce the risk of infection with the help of lysozymes which digest bacteria.

Question 20

Describe the structure and function of smooth muscle?

Answer 20

• Their ability to contract enables them to play a role in constricting the airway, thus controlling its diameter as a result, and thus controlling the flow of air to and from the alveoli.

Question 21

Describe the structure and function of elastic fibres?

Answer 21

• Stretch when we exhale and recoil when we inhale thus controlling the flow of air.

Question 22

What is ventilation?

Answer 22

• The flow of air in and out of the alveoli
• Composed of two stages, inspiration, and expiration.
• This process occurs with the help of two sets of muscles, the intercostal muscles and diaphragm.

Question 23

Describe the stages of inspiration?

Answer 23

• During inspiration, the external intercostal muscles contract whereas the internal muscles relax, as a result this causes to ribs to raise upwards.
• The diaphragm contracts and flattens.
• In combination, the intercostal muscles and diaphragm cause the volume inside the thorax to increase, thus lowering the pressure.
• The difference between the pressure inside the lungs and atmospheric pressure creates a gradient, thus causing the air to be forced into the lungs.

Question 24

Describe the stages of expiration?

Answer 24

• During expiration, the internal intercostal muscles contract whereas the external muscles relax therefore lowering the rib cage.
• The diaphragm relaxes and raises upwards.
• This action in combination decreases the volume inside the thorax, therefore increasing the pressure, forcing the air out of the lungs.

Question 25

What is a spirometer?

Answer 25

• A spirometer is a device used to measure lung volume.

Question 26

How does a spirometer work?

Answer 26

• A person using a spirometer breathes in and out of the airtight chamber, thus causing it to move up and down, leaving a trace on a graph which can then be interpreted.

Question 27

What is vital capacity?

Answer 27

• The maximum volume of air that can be inhaled or exhaled in a single breath.
• Varies depending on gender, age, size, and height.

Question 28

What is tidal volume?

Answer 28

• The volume of air we breathe in and out at each breath at rest.

Question 29

What is breathing rate?

Answer 29

• The number of breaths per minute.
• Can be calculated from the spirometer trace by counting the number of peaks or troughs in a minute.

Question 30

What is residual volume?

Answer 30

• The volume of air which is always present in the lungs.

Question 31

What is the expiratory reserve volume?

Answer 31

• Additional volume of air that can be exhaled on top of the tidal volume.

Question 32

When can the tidal volume be exceeded?

Answer 32

• During exercise where the inspiratory reserve volume is reached, to increase the amount of air breathed in.