3.3.2 - GAS EXCHANGE

Question 1

breathing out as hard as you can is called forced expiration.

describe and explain the mechanism that causes forced expiration. (4)

Answer 1

1. diaphragm (muscles) relaxes and moves up
2. internal intercostal muscles contract and ribcages moves in and down
3. causes volume decrease and pressure increase in lungs
4. air moves down a pressure gradient

Question 2

describe and explain the mechanism that causes lungs to fill with air (4)

Answer 2

1. diaphragm (muscles) contracts and flattens
2. external intercostal muscles contract and ribcage is pulled up and out
3. causes volume increase and pressure decrease in lungs
4. air moves down a pressure gradient

Question 3

describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.

details of breathing are not required. (4)

Answer 3

1. trachea, bronchi and bronchioles
2. oxygen moves down a pressure gradient
3. oxygen moves down a diffusion gradient
4. across alveolar epithelium
5. across capillary endothelium/epithelium

Question 4

describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange.

do not refer to surface area or moisture in your answer (2)

Answer 4

ANY PAIR:

1. single layer of cells
2. reduces diffusion distance

OR

1. permeable
2. allows diffusion of oxygen/carbon dioxide

Question 5

tidal volume is the volume of air inhaled and exhaled during a single breath when a person is resting. the tidal volume in a person with emphysema is reduced compared with the tidal volume in a healthy person.

suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and the alveoli (3)

Answer 5

1. less carbon dioxide exhaled/moves out of the lungs OR more carbon dioxide remains in lung
2. so reduced diffusion/concentration gradient between blood and alveoli
3. less/slower movement of carbon dioxide out of the blood OR more carbon dioxide stays in the blood

Question 6

explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system (2)

Answer 6

1. blood and water flow in opposite directions
2. diffusion/concentration gradient is maintained along the length of the lamella/filament

Question 7

two solutions often used to stain tissues are haematoxylin solution and iodine solution.

• haematoxylin solution stains DNA a blue colour
• iodine solution stains starch a blue-black colour

the scientist used haematoxylin solution and not iodine to stain the lung tissue.

suggest why (2)

Answer 7

1. this lung tissue does not contain starch
2. haematoxylin makes nucleus visible (nucleus contains DNA

Question 8

if alveolar epithelium cells die inside the human body they are replaced by non-specialised, thickened tissue.

explain why death of alveolar epithelium cells reduces gas exchange in human lungs (3)

Answer 8

1. reduced surface area
2. increased distance for diffusion
3. reduced rate of gas exchange

Question 9

describe and explain the advantage of the counter-current principle in gas exchange across a fish gill (3)

Answer 9

1. water and blood flow in opposite directions
2. maintains diffusion/concentration gradient of oxygen OR oxygen concentration always higher in water
3. diffusion along length of lamellae/filament/capillary/gill

Question 10

use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow only slowly (2)

Answer 10

1. stomata close
2. less carbon dioxide uptake for less photosynthesis/glucose production

Question 11

describe the pathway taken by an oxygen molecule from an alveolus to the blood (2)

Answer 11

1. across the alveolar epithelium
2. across endothelium/epithelium of capillary

Question 12

explain how one feature of an alveolus allows efficient gas exchange to occur (2)

Answer 12

1. the alveolar epithelium is one cell thick
2. creating a short diffusion pathway

Question 13

describe the gross structure of the human gas exchange system and how we breathe in and out (6)

Answer 13

1. trachea, bronchi, bronchioles, alveoli
2. structures names in correct order
3. breathing in: diaphragm contracts and external intercostal muscles contract
4. causes volume increase and pressure decrease in thorax (to below atmospheric, resulting in air moving in)
5. breathing out: diaphragm relaxes and internal intercostal muscles contract
6. causes volume decrease and pressure increase in thorax (to above atmospheric, resulting in air moving out)

Question 14

explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange (3)

Answer 14

any three:

1. tracheoles have thin walls so short diffusion distance to cells
2. large number of tracheoles so short diffusion distance to the cells
3. large number of tracheoles so large surface area for gas exchange
4. tracheae provide tubes full of air so fast diffusion into insect cells
5. fluid in the end of the tracheoles that moves out into tissues during exercise so: faster diffusion through the air to the gas exchange surface/larger surface area for gas exchnage

Question 15

explain two ways in which the structure of fish gills is adapted for efficient gas exchange (2)

Answer 15

1. many lamellae/filaments so large surface area
2. thin surface so short diffusion pathway

Question 16

explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills (3)

Answer 16

1. water and blood flow in opposite directions
2. blood always passing water which has a higher oxygen concentration
3. diffusion gradient maintained throughout length of the gill OR diffusion occurs throughout the length of the gill OR if water and blood flowed in the same directions equilibrium would be reached

Question 17

suggest a difficulty of counting movements of gill covers as a method of measuring ventilation in fish (1)

Answer 17

fish keep moving

Question 18

describe the relationship between temperature of water, oxygen in water and rate of ventilation (1)

Answer 18

as water temperature increases, oxygen concentration falls and ventilation rate increases

Question 19

amoebic gill disease (AGD) is caused by a parasite that lives on the gills of some species of fish. the disease causes the lamellae to become thicker and to fuse together.

AGD reduces the efficiency of gas exchange in fish. give two reasons why (2)

Answer 19

1. thicker lamellae so longer diffusion distance
2. lamellae fused together so reduced surface area

Question 20

the volume of water passing over the gills increases if the temperature of the water increases. suggest why (1)

Answer 20

1. increased metabolic rate/respiration/enzyme activity
2. less oxygen

Question 21

name the process by which oxygen passes from an alveolus in the lungs into the blood (1)

Answer 21

(simple) diffusion

Question 22

describe two adaptations of the structure of the alveoli for efficient gas exchange (2)

Answer 22

1. thin walls (one cell thick)
2. total surface area is large

Question 23

to breath fire, fire-breathers blow a fine mist of paraffin oil into a flame. some of this mist can be inhaled and eventually lead to fibrosis.

people who have been fire-breathers for many years often find they cannot breathe out properly. explain why (2)

Answer 23

1. loss of elastic tissue/increase in scar tissue
2. less recoil

Question 24

other than the distribution of stomata, suggest and explain two xerophytic features the leaves of this plant might have (2)

Answer 24

1. hairs so trap water vapour and WP gradient decreased
2. stomata in pits so ‘trap’ water vapour and WP gradient decreased
3. thick cuticle layer so increases diffusion distance
4. waxy layer so reduces evaporation/transpiration
5. curled leaves so ‘trap’ water vapour and WP decreased
6. spines/needles so reduces SA:V ratio

Question 25

describe how the structure of the insect gas exchange system:

• provides cells with sufficient oxygen
• limits water loss

explain your answers (5)

Answer 25

1. spiracles, tracheae, tracheoles
2. spiracles allow diffusion of oxygen
3. tracheoles are highly branched so large SA for exchange
4. highly branched tracheoles so short diffusion distance to cells
5. tracheole permeable to oxygen/air
6. exoskeleton impermeable so reduces water loss
7. spiracles can close so less water loss
8. hairs around spiracles reduce water loss

Question 26

describe how humans breathe in and out (5) [2022]

Answer 26

breathing in:
1. diaphragm (muscles) contracts and flattens
2. external intercostal muscles contract and ribcage is pulled up and out
3. causes volume increase and pressure decrease in lungs

breathing out:
1. diaphragm (muscles) relaxes and moves up
2. internal intercostal muscles contract and ribcages moves in and down
3. causes volume decrease and pressure increase in lungs

Question 27

describe how gas exchange occurs in single-celled organisms and explain why this method cannot be used by large, multicellular organisms (3)

Answer 27

1. diffusion across the cell surface membrane
2. large organisms have a smaller SA:V ratio
3. diffusion pathway would be too long

Question 28

chitin keeps the tracheae open in the tracheal system of gas exchange in an insect. gas exchange does not occur in the tracheae

explain the importance of one adaptation of the gas exchange surface in the tracheal system of an insect (2)

Answer 28

ANY PAIR:

1. tracheole wall is one cell thick
2. so rapid diffusion into cells/so short diffusion pathway

OR

3. tracheoles enter/supply tissues/muscle fibres
4. so rapid diffusion into cells/so short diffusion pathway

OR

5. tracheoles are highly branched
6. so rapid diffusion into cells/so short diffusion pathway

Question 29

scientists found that the insects moved for 94% of the time in the more humid side, but in the drier side they moved only 20% of the time. the scientists concluded that reduced movement in the drier side was an adaptation that reduced water loss.

use your own knowledge of gas exchange in insects to explain how this behaviour would reduce water loss in the insects (2)

Answer 29

1. less respiration so less gas exchange
2. so spiracles open less so less water loss