Module 3: Exchange Surfaces

Question 1

Why do multicellular organisms need exchange surfaces?

Answer 1

Multicellular organisms have a small SA:V ratio
Cells in the centre of the organism would not receive any materials if organisms survived on diffusion alone e.g. O2
High metabolic rate - need to exchange a lot of materials quickly.

Question 2

What types of tissues does the trachea have?

Answer 2

Cartilage (C-shaped), goblet cells, ciliated cells, smooth muscle and elastic fibres.

Question 3

What type of tissue does the bronchus have?

Answer 3

Cartilage )irregular rings), goblet cells, ciliated cells, smooth muscle, squamous epithelium and elastic fibres.

Question 4

What type of tissues do the bronchioles have?

Answer 4

Goblet cells, ciliated ells, smooth muscle, squamous epithelium and elastic fibres.

Question 5

What tissue does the alveolus have?

Answer 5

Squamous epithelium, elastic fibres, and site of gas exchange.

Question 6

What is the function of cartilage in both the bronchi and bronchioles, as well as the trachea?

Answer 6

Bronchi + Bronchioles = prevent collapse during inhalation by having rings of irregular blocks.
Trachea = C-shaped to prevent collapse due to the pressure changes in ventilation Provides the flexibility to for this.

Question 7

What is the function of smooth muscle?

Answer 7

Contracts unconsciously. Allows lumen to constrict and useful to reduce harmful substances being breathed in.

Question 8

What is the function of elastic fibres?

Answer 8

Elongate smooth muscle after contraction. In the alveoli, it stretches the alveolus wall during inspiration, and recoil to help force air out during expiration.

Question 9

What is the function of goblet cells?

Answer 9

Release mucus to trap pathogens, which is then swallowed. The pathogens are then killed by the HCl in the stomach.

Question 10

What is the function of ciliated epithelium cells?

Answer 10

Move mucus up the throat to the top of the airways to be swallowed, to prevent infection of the lungs.

Question 11

What is the function of squamous epithelium ?

Answer 11

Single layer of cells to provide a short diffusion distance.

Question 12

Name some adaptations of the alveoli to reduce the diffusion distance

Answer 12

Large blood supply from the capillaries - close to alveoli.
One cell thick alveoli.
Capillaries are narrow so erythrocytes are squeezed against the capillary walls.
One cell thick capillary wall.
Both walls consist of squamous cells - flattened.

Question 13

How does a good blood supply help ensure CO2 is always moving into the lungs and O2 into the blood?

Answer 13

Helps maintain a steep concentration gradient for diffusion.
CO2 from tissues to lungs, so concentration of CO2 is higher in the blood than the air of the alveoli.
O2 from lungs to tissue, so concentration of O2 is higher in the air of the alveoli to than than the blood.

Question 14

What happens during inspiration?

Answer 14

Diaphragm shifts downwards and contracts. The external intercostal muscles also contract and raise the ribs. The volume of the chest cavity increases as the diaphragm moves downwards. This decreases the pressure in the lungs as air moves in.

Question 15

What happens during expiration?

Answer 15

The diaphragm shifts upwards and relaxes. The external intercostal muscles relax and lower the ribs. The volume of the chest cavity decreases as the diaphragm moves upwards. This increases the pressure in the lungs as air moves out.

Question 16

How does an increased surface area aid gas exchange?

Answer 16

This is advantageous as it increases the area over which gases and other materials can be transported into and out of the organism, via diffusion and active transport.

Question 17

What is the benefit of thin layers in a gas exchange system?

Answer 17

Reduces the diffusion distance, making it short. This means the process of gas exchange is faster and more efficient.

Question 18

What is the benefit of good ventilation for gas exchange?

Answer 18

Helps to maintain a steep concentration gradient, making the process more efficient. Causes a sufficient high partial pressure of O2 in the lungs, and means gases are constantly moved in and out of the lungs.

Question 19

What is the diameter of the bronchioles?

Answer 19

1mm or less

Question 20

What is the diameter of the alveoli?

Answer 20

200-300 um

Question 21

What is lung surfactant and how does it help with gas exchange?

Answer 21

Thin layer of lubricant, which increases surface tension as the lungs expand during inspiration, by slowing the rate of expansion. This helps to prevent collapse of the lungs, due to no friction and ensures all alveoli expand at the same rate.

Question 22

What does Fick’s Law state?

Answer 22

Rate of diffusion is (proportional) to surface area x difference in concentration / length of diffusion pathway (membrane thickness)

Question 23

Give the order of pathway for air to be inspired into the lungs

Answer 23

Nose/ mouth, nasal cavity/ oral cavity, larynx, trachea, bronchi, bronchioles, alveoli.

Question 24

How does the surface area to volume ratio change as the size of something increases?

Answer 24

The volume increases faster than the surface area. Surface area to volume ratio decreases as size increases.

Question 25

How do you find SA and volume in a cube?

Answer 25

SA = 6x (lengthxwidth)
Vol = length x width x height

Question 26

How do you find the SA and volume in a cuboid?

Answer 26

SA = (4 x length x height) + (2 x height x width)
Vol = length x width x height

Question 27

How do you find the SA and volume in a cylinder?

Answer 27

SA = ((pi x d) x height) + 2 pi r2
Vol = pi r2 x height

Question 28

How do you find the SA and volume of a sphere?

Answer 28

SA = 4 pi r2
Vol = 4/3 pi r3

Question 29

What is the role and adaptations of the nasal cavity in gas exchange?

Answer 29

Adaptations = large SA and good blood supply, goblet cells to secrete mucus, moist surfaces
Roles = blood warms the air, mucus traps particulates, humidifies air to protect more delicate structures of the lungs, by preventing evaporation of water in the lungs.

Question 30

What is the role and adaptations of the trachea in gas exchange?

Answer 30

Adaptations = incomplete C-shaped rings of cartilage and smooth muscle, lined with goblet cells + ciliated epithelium.
Roles = cartilage is strong and flexible to prevent collapse from pressure changes, smooth muscle can vasoconstrict to force air and mucus out of the lungs, smooth muscle + cilia expel foreign particles.

Question 31

What is the role and adaptations of the bronchi in gas exchange?

Answer 31

Adaptations = made of cartilage and smooth muscle tissue, lined with cilia /goblet cells.
Roles = divide into smaller subdivisions called bronchioles. Act as a passageway.

Question 32

What is the role and adaptations of the bronchioles in gas exchange?

Answer 32

Adaptations = cartilage replaced with elastic fibres, lined with goblet and cilium cells.
Roles = control muscle contraction or relaxation, due to being innervated by nerves and sympathetic and parasympathetic nervous system.

Question 33

What is the role and adaptations of the alveolus in gas exchange?

Answer 33

Adaptations = spherical in shape, one cell thick, surrounded by capillaries, collagen and elastic fibres for recoil, flattened epithelial layers, many. 
Roles = gas exchange, large SA, maintain blood concentration maintained, reduce diffusion distance, recoil for expiration to withstand vasoconstriction/dilation.

Question 34

What is ventilation, and what is the purpose?

Answer 34

Describes the action of breathing, whereby air is constantly moving in and out of the lungs.
Maintains a concentration gradient in the alveoli.

Question 35

What is the pleura?

Answer 35

Lungs are enclosed in a double membrane known as the pleural membrane. The space between the 2 membranes is the pleural cavity, and pleural fluid fills this.

Question 36

What is the function of the pleura?

Answer 36

The fluid lubricates the lungs, and adheres to the outer walls of the lungs in the thoracic cavity. As the chest expands, the lungs expand too.

Question 37

How does the diaphragm and intercostal muscles cause inspiration?

Answer 37

The diaphragm contracts, flattening and lowering, which increases the volume of the thoracic cavity. The intercostal muscles contract, moving the ribs upwards and outwards. This increases the size of the chest so more air can enter the lungs, and the diaphragm acts as a vacuum to pull air into the lungs, due to the decreases air pressure. Hence inspiration.

Question 38

What is tidal volume?

Answer 38

The volume of air normally taken in with each breath when the body is at rest. This is usually around 0.5dm3.

Question 39

How can pulmonary ventilation be calculated?

Answer 39

Tidal volume x ventilation rate

Question 40

What is ventilation rate?

Answer 40

The number of breaths taken in one minute. Normally 12-20

Question 41

How does increasing exercise intensity how does ventilation levels increase?

Answer 41

Increase ventilation rate - greater frequency of breaths to allow continuous exchange of gases.
Increase tidal volume - increasing volume of air taken in and out per breath allows for more air to be exchanged.

Question 42

What does spirometer involve?

Answer 42

Involves measuring the amount (volume) and speed (flow) at which air can be inhaled or exhaled. It detects the change in ventilation, and prevents the data on a digital display.

Question 43

Define total lung capacity

Answer 43

Volume of air in the lungs after a maximal inhalation.

Question 44

Define vital capacity

Answer 44

Volume of air that can be exchanged by the lungs via a maximal inhalation and exhalation.

Question 45

Define residual volume

Answer 45

Volume of air that is always present in the lungs.

Question 46

What happen to a spirometer trace with inspiration?

Answer 46

Air chamber decrease in volume.

Graph line goes down.

Question 47

What happens to a spirometer trace with expiration?

Answer 47

Air chamber increases in volume.

Graph line goes up.

Question 48

Name 3 things that should be done when using a spirometer

Answer 48

Use O2 as source of air, which is fresh.
Take a medical history to take into account for trace produced.
Clean the mouthpiece.

Question 49

How can the CO2 be absorbed in a spirometer?

Answer 49

Use soda lime.

Question 50

What can be done to ensure all the air remains in the spirometer?

Answer 50

Nose clips should be worn to ensure all air breathed comes from the chamber. This prevents entry of air through the nose which would make the results invalid.

Question 51

What factors contribute to a persons lung capacity and ventilation rate?

Answer 51

Height - taller people have larger chests so larger total lung capacities.
Location - high altitudes have larger capacities to compensate for lower atmospheric pressure.
Lifestyle - obese people and smokers have lower capacities and higher rates of ventilation.

Question 52

Describe the flow of water and gas exchange in fish during inspiration

Answer 52

Muscle contraction lowers the floor of the pharynx and the mouth opens.
The buccal cavity lowers and increases in volume, decreasing pressure in the cavity.
Water is sucked into the cavity, raising the buccal cavity.
The operculum bulges outwards.

Question 53

Describe the flow of water and gas exchange in fish during expiration

Answer 53

Buccal cavity contracts, closing the mouth.
The floor of the pharynx is raised.
The pressure increases, forcing water through the gills across the gill filaments, decreasing the volume in the cavity.
The opercular cavities contact, increasing pressure, the opercular valves open and water is expelled.

Question 54

What do very active fish rely upon for gas exchange?

Answer 54

Ram ventilation - use thrust and speed to force water out of the gills.

Question 55

Describe the countercurrent flow

Answer 55

Blood flows in one direction, and water flows in the opposite direction. This maintains a downwards concentration gradient across the entire length of the gill lamellae, whereby oxygen diffuses down the concentration gradient from the water to the blood. Without this equilibrium would be reached and only part of the lamellae would exchange oxygen.

Question 56

What does the graph for countercurrent flow look like?

Answer 56

Y-axis = % O2 saturation
X=axis = distance along the gill plate
Arrow of water down, and arrow of blood up

Question 57

Why do insects need a gas exchange system?

Answer 57

Tough exoskeleton preventing gas exchange by passive diffusion.
Do not have blood pigments that can carry oxygen.

Question 58

How does gas exchange take place in insects?

Answer 58

Spiracles along the thorax and abdomen (small openings) is where air enters and leaves the system, and water is lost. The tracheae joins from the spiracles (largest tubes up to 1mm) and carry air into the body. Lined with chitin to keep them open and prevent collapse under pressure. Branch into sub-divisions called tracheoles (0.6-0.8 um). No chitin and permeable. Run between individual cells, and where most gas exchange takes place.

Question 59

How do the spiracles change depending upon the level of activity? Why?

Answer 59

When inactive, oxygen demand is low, so the spiracles will be closed most of the time. When active, oxygen demand is high, so the spiracles open, to increase oxygen and remove CO2.
Happens to reduce water loss in the insect ], and maximise gas exchange efficiency.

Question 60

How are the spiracles controlled?

Answer 60

Sphincter muscles

Question 61

What is the role of the tracheal fluid?

Answer 61

Most of the time, air moves along the system and diffuses alone, reaching gall the tissues. The tracheoles provide a large surface area for this. O2 dissolves in the moisture of the walls. Tracheal fluid is at the end of the tracheoles, which limits the penetration of air for diffusion. During activity, O2 demands increase and lactic acid builds up in the tissues, causing the tracheal fluid to move out by osmosis into tissue fluid, thus exposing more surface area for gas exchange.

Question 62

How do larger insects fulfil very high oxygen demands?

Answer 62

Mechanical ventilation of tracheal system = rhythmic abdominal movements of the thorax/abdomen, changing the volume of the body and pressure in the tracheae and tracheoles. Air is drawn in and forced out.
Collapsible enlarged tracheae or air sacs (air reservoirs) = increase amount of air moved through gas exchange system. Inflated and deflated by ventilating movements of thorax/abdomen.

Question 63

How are the gills adapted for efficient gas exchange?

Answer 63

Lamellae provide a large surface area for gases to exchange on. Aided by secondary lamellae which provide an even larger surface area. This reduces the diffusion distance, and makes diffusion faster, as there is more surface for diffusion.
Gills run alongside the capillaries / blood flow, providing a short diffusion distance between blood and water. This helps to maintain a steep diffusion gradient with the blood.
Tips of adjacent gill filaments overlap, increasing resistance to the flow of water over the gill surfaces, and slows down the movement of water, allowing more time for gas exchange.