3.3.2 Gas exchange

Question 1

what type of gas exchange system do terrestrial insects have?

Answer 1

a tracheal system

Question 2

what are the three features of an insect’s tracheal system?

Answer 2

• spiracles
• tracheae
• tracheoles

Question 3

what are spiracles?

Answer 3

• round, valve-like openings which run along the length of the abdomen
• oxygen and carbon dioxide enter and leave via the spiracles
• the tracheae attach to these openings

Question 4

what are tracheae?

Answer 4

• a network of internal tubes
• tubes have rings within them to strengthen them and keep them open

Question 5

tracheae branch into…

Answer 5

smaller tubes, deeper into the abdomen of the insect called tracheoles

Question 6

what are tracheoles?

Answer 6

small tubes which extend throughout all the tissues in the insect to deliver oxygen to all respiring cells

Question 7

what are the three methods of moving gases in the tracheal system?

Answer 7

• diffusion
• mass transport
• creating a pressure gradient

Question 8

how do gases move in the tracheal systems by diffusion?

Answer 8

• when cells respire, they use up oxygen and produce carbon dioxide
• this creates a concentration gradient (of carbon dioxide) from the tracheoles to the atmosphere

Question 9

how do gases move in the tracheal systems by mass transport?

Answer 9

insects contract and relax their abdominal muscles to move gases

Question 10

do gases move in the tracheal systems by creating a pressure gradient?

Answer 10

• when the insect is in flight, muscle cells start to respire anaerobically to produce lactate
• this lowers the water potential of cells, so water moves from the tracheoles into the cells by osmosis
• less water increases the volume of gas in the tracheoles which decreases the pressure
• as a result, more air from the atmosphere is drawn in down a pressure gradient

Question 11

what are the 3 key adaptations of the tracheal system for efficient diffusion?

Answer 11

• large number of fine tracheoles –> large surface area
• walls of tracheoles are thin and there is a short distance between spiracles and tracheoles –> short diffusion pathway
• use of oxygen and production of carbon dioxide –> steep diffusion gradients

Question 12

what are the 2 key adaptations of insects to limit water loss?

Answer 12

• have a waterproof exoskeleton
• spiracles can open and close

Question 13

describe the structure of the gills

Answer 13

• there are four layers of gills on both sides of the head, each supported by a bony arch
• the gills are made up of stacks of gill filaments
• each gill filament is covered in gill lamellae, positioned at right angles to the filament
• this creates a large surface area

Question 14

what are the 3 adaptations of gills for efficient gas exchange?

Answer 14

• many gill filaments covered in many gill lamellae –> large surface area
• a capillary network in every lamellae and very thin gill lamellae –> short diffusion distance
• countercurrent flow mechanism –> maintains the concentration gradient

Question 15

how does the countercurrent exchange principle work?

Answer 15

• water flows over the gills in the opposite direction to the flow of blood in the capillaries
• countercurrent flow ensures that equilibrium is not reached
• this ensures that a diffusion gradient is maintained across the entire length of the gill lamellae

Question 16

describe the structures required for ventilation

Answer 16

• internal gills protected by an operculum
• fish takes water in through the buccal cavity
• water then flows through the pharynx and over the gill plates
• water leaves via the opercular opening on each side of the fish’s head

Question 17

how does ventilation occur in a fish?

Answer 17

• mouth opens and operculum shuts
• water enters the buccal cavity due to decreased pressure
• mouth closes and operculum opens
• this results in increased pressure which forces water out over the gills

Question 18

what is the structure of a dicotyledonous leaf from top to bottom?

Answer 18

• waxy cuticle
• upper epidermis
• palisade mesophyll
• spongy mesophyll
• lower epidermis
• stomata (each one surrounded by two guard cells)

Question 19

how does gas exchange occur at the stomata?

Answer 19

• oxygen diffuses out and carbon dioxide diffuses in
• to reduce water loss by evaporation, the stomata close at night when photosynthesis would not be occurring

Question 20

what is a xerophyte?

Answer 20

a plant adapted to survive in environments with limited water

Question 21

what are the 5 structural adaptations of xerophytes to limit water loss?

Answer 21

• curled leaves to trap moisture to increase local humidity
• hairs to trap moisture to increase local humidity
• sunken stomata to trap moisture to increase local humidity
• thicker cuticle to reduce evaporation
• longer root network to reach more water

Question 22

what is the structure of the human gas exchange system?

Answer 22

trachea –> bronchi –> bronchioles in the lungs –> alveoli in the lungs

Question 23

how does gas exchange take place in humans?

Answer 23

• oxygen diffuses out of alveoli and into blood
• carbon dioxide diffuses out of blood and into alveoli

Question 24

what are the 3 key adaptations of the alveoli?

Answer 24

• lots of alveoli (around 300 million in each lung) so large surface area for diffusion
• alveoli epithelium are very thin so a short diffusion pathway
• each alevolus is surrounded by a network of capillaries so concentration gradient maintained

Question 25

the external and internal intercostal muscles have which type of interaction?

Answer 25

antagonistic

Question 26

what happens during inspiration (inhalation)?

Answer 26

• external intercostal muscles contract
• internal intercostal muscles relax
• diaphragm contracts
• volume of thoracic cavity increases so volume of lungs increases
• therefore, air pressure in lungs drop
• air moves into the lungs, from atmospheric pressure to a lower pressure
• this causes air pressure in lungs to rise above atmospheric pressure as air moves in

Question 27

what happens during expiration (exhalation)?

Answer 27

• external intercostal muscles relax
• internal intercostal muscles contract
• diaphragm relaxes
• volume of thoracic cavity decreases so volume of lungs decreases
• therefore, air pressure in lungs increases
• air moves out of the lungs, from a higher pressure to atmospheric pressure
• this causes air pressure in lungs to drop as air moves out

Question 28

what are the two key points of ventilation in humans?

Answer 28

• contraction of external intercostal muscles leads to inspiration
• contraction of internal intercostal muscles leads to expiration

Question 29

what is tidal volume?

Answer 29

the volume of air that enters and leaves the lungs at normal resting breath

Question 30

what is vital capacity?

Answer 30

the maximum volume of air we can inhale and exhale

Question 31

what is residual volume?

Answer 31

the volume of air left in the lungs after the strongest exhalation

Question 32

how can you calculate the total lung capacity?

Answer 32

vital capacity + residual capacity/volume

Question 33

what is pulmonary ventilation?

Answer 33

the total volume of air that is moved into the lungs during one minute (dm^3 min^-1)

Question 34

what is the equation to calculate pulmonary ventilation?

Answer 34

• pulmonary ventilation = tidal volume x ventilation rate
• dm^3 min^-1 = dm^3 x min^-1