3.3.2 - gas exchange

Question 1

what are the key structures within the human gas exchange system?

Answer 1

alveoli, bronchi, bronchioles, trachea, lungs

Question 2

what is the role of cartilage in the human gas exchange system?

Answer 2

it holds the trachea and bronchi open so they don’t collapse during exhalation

Question 3

what does antagonistic mean?

Answer 3

muscles work in opposite ways - when one contracts, the other relaxes

Question 4

what is an example of an antagonistic muscle pair in the human gas exchange system?

Answer 4

the external and internal intercostal muscles (muscles between ribs)

Question 5

what happens when the external intercostal muscles contract?

Answer 5

inspiration/inhalation

Question 6

what happens when the internal intercostal muscles contract?

Answer 6

expiration/exhalation

Question 7

what happens during inspiration?

Answer 7

external intercostal muscles contract and internal intercostal muscles relax

diaphragm contracts (pulls downwards from dome position so flattens)

air pressure in lungs decreases (below atmospheric pressure) because lung volume increases

air moves into lungs down pressure gradient (higher pressure in atmosphere than lungs)

Question 8

what happens during exhalation?

Answer 8

external intercostal muscles relax and internal intercostal muscles contract

diaphragm relaxes (returns to domed position)

air pressure in lungs increases (above atmospheric pressure) because lung volume decreases

air moves out of the lungs down pressure gradient (higher pressure in lungs than atmosphere)

Question 9

what happens in the thoracic cavity during inspiration and exhalation?

Answer 9

inspiration - thoracic cavity expands so pressure decreases as large volume
exhalation - thoracic cavity reduces so pressure increases as less volume

Question 10

what are alveoli?

Answer 10

tiny air sacs at the end of the bronchioles

Question 11

how is the alveolar epithelium adapted for gas exchange?

Answer 11

1. there are 300 million alveoli in each lung creating a large surface area for gas exchange
2. the alveoli epithelium cells are thin (one cell thick as made of squamous/flattened cells) to minimise diffusion distance
3. each alveolus is surrounded by a network of capillaries in close contact with the alveolus walls to remove exchanged gases, maintaining a concentration gradient
4. capillaries are narrow so red blood cells are squeezed against the walls - this reduces the rate they flow in the blood so there is more time for gas exchange

Question 12

how are the lungs protected from drying out to aid gas exchange?

Answer 12

the alveoli are tucked deep in the body, away from exposure to air
a thin layer of moisture lines the alveoli (some is lost via evaporation when we exhale)
the lungs secrete a surfactant which reduces the cohesive forces between the molecules lining them so the alveoli don’t collapse

Question 13

what is tidal volume?

Answer 13

the volume of air breathed in and out of the lungs per breath

Question 14

what is vital capacity?

Answer 14

the volume of air that can be forcibly expired after a maximal intake of air

Question 15

what is residual volume?

Answer 15

the volume of air remaining in the lungs at the end of a maximal expiration

Question 16

what is total lung capacity?

Answer 16

vital capacity + residual volume

Question 17

what is pulmonary ventilation?

Answer 17

the total volume of air that is moved into the lungs during one minute

Question 18

how do you calculate pulmonary ventilation rate (PVR)?

Answer 18

tidal volume x breathing rate (no. of breaths per minute)

tidal volume in dm3
breathing rate in min-1
PVR in dm3 min-1

Question 19

what device is used to measure lung capacity?

Answer 19

a spirometer

Question 20

what is Fick’s law?

Answer 20

rate of diffusion is proportional to:
surface area x difference in concentration/ thickness of surface

Question 21

what are the key structures in the tracheal system of an insect?

Answer 21

spiracles - small pores on surface of exoskeleton allowing gases to diffuse in and out
trachea - tube of approx 1mm which branches directly from spiracles
tracheoles - narrow tubes of less than 1um which branch from trachea in large numbers

Question 22

what is unique about insects?

Answer 22

they don’t contain blood as they have no red blood cells (contain hemolymph instead)

Question 23

how are gases drawn into an insect through the spiracles?

Answer 23

1. during high activity, insects cary out anaerobic respiration and produce lactate
2. lactate is soluble in water, so it decreases the water potential of respiring cells
3. this creates a concentration gradient - water in the tracheal fluid found at the ends of the tracheoles moves into the cells via osmosis
4. this movement of water decreases the pressure in the tracheoles, creating suction pressure which draws gases through the spiracles and down the tracheae and tracheoles

Question 24

how are insects adapted to reduce water loss?

Answer 24

they have a waxy cuticles made of chitin
a muscular sphincter surrounding the spiracles can contract to close them so water doesn’t escape

Question 25

what are the key structures within a leaf?

Answer 25

waxy cuticle on each side upper epidermis (clear so allows light through) palisade mesophyll spongy mesophyll lower epidermis stomata guard cells

Question 26

how are the structures within the leaves of dicotyledonous plants adapted for gas exchange?

Answer 26

spongy mesophyll contains many air spaces so gases can easily diffuse through and be exchanged (as diffusion fastest in gaseous phase) stomata are pores which allows gases to diffuse in and out guard cells open and close stomata (close when water moves in through osmosis and they swell)

Question 27

how are leaves adapted for gas exchange in terms of Fick's Law?

Answer 27

they are thin and flat giving them a large surface area and reducing the diffusion distance all cells are close to interconnecting air spaces creating a short diffusion distance guard cells allow stomata to open which creates concentration gradient on each side

Question 28

how are leaves adapted to reduce water loss?

Answer 28

each surface is covered with waxy cuticle which is impermeable to water guard cells can cause stomata to close so water can't move through

Question 29

what are xerophytic plants?

Answer 29

plants adapted to surviving in dry and arid conditions

Question 30

how do the stomata of xerophytes act as an adaptation to reduce water loss?

Answer 30

guard cells control their opening and closing they are sunken in pits which reduces the concentration gradient they open in the dark and close in the light - water needed for photosynthesis in light so you don't want to lose it, temperature generally higher when it is light so transpiration occurs at increased rate

Question 31

how do hinge cells act as an adaptation to reduce water loss?

Answer 31

they shrink when flaccid, causing the leaf to curve upwards which reduces the surface area so less water evaporates

Question 32

how do the leaves of xerophytes act as an adaptation to reduce water loss?

Answer 32

they are thin and pine-like, reducing their surface area so there is less evaporation

Question 33

what are the features of hydrophytic plants?

Answer 33

* live in freshwater * face the challenge of receiving enough CO2 during day and O2 during night (as water contains less CO2 and O2 than air)

Question 34

how are hydrophytic plants adapted?

Answer 34

* large air spaces in leaves * stomata concentrated on upper epidermis * flat leaves * small roots

Question 35

what problem do bony fish face relating to gas exchange?

Answer 35

they are active and have a high oxygen requirement, but their large size gives them a small surface area to volume ratio, and gases can't pass through their scaly surface

Question 36

where do fish get oxygen from?

Answer 36

water (but the concentration of oxygen is much lower than in air)

Question 37

how does oxygen enter fish?

Answer 37

1. oxygen-rich water enters the mouth of the fish 2. the water passes over the gills 3. in the gills, O2 diffuses from the water to the blood and CO2 diffuses from the blood to the water 4. water leaves through the opercular opening

Question 38

what is the structure of the gills?

Answer 38

there are several bony gill arches, with lots of gill filaments extending from each gill arch the gill filaments are covered with many gill lamellae (where gas exchange occurs as water flows between them)

Question 39

how are gill lamellae adapted for efficient diffusion of gases?

Answer 39

they have a large surface area for gases to diffuse over there is a short diffusion distance through the walls of the lamellae into the blood they have an extensive network of blood capillaries so as soon as oxygen diffuses into the blood it is carried away, maintaining a concentration gradient

Question 40

what happens in the counter-current system in the gill lamellae of fish?

Answer 40

1. blood with a low O2 concentration passes into the capillaries of the gill lamellae 2. as this blood passes through the lamellae, oxygen diffuses from the water into the blood 3. the now oxygen-rich blood passes out of the gill lamellae and leaves the gills

Question 41

why does the counter-current system have this name?

Answer 41

the flow of blood goes in the opposite direction to the flow of water

Question 42

what is the advantage of a counter-current system?

Answer 42

it maintains a steep concentration gradient for oxygen (equilibrium never reached so around 80% of oxygen in water enters fish)