Gas exchange betweeen single celled organisms and insects

Question 1

what are the features of a single celled organism?

Answer 1

• large SA:V ratio
• short diffusion distance
• no specialised gas exchange or circulatory system
• O2 absorbed by DIFFUSION across body surface covered by cell surface membrane

Question 2

why do insects have to balance opposing needs?

Answer 2

they need to exchange respiratory gases with reducing water loss

Question 3

how is water loss reduced in terrestrial organisms and why can’t they use their body surface to diffuse respiratory gases like a single celled organism?

Answer 3

• WATERPROOF COVERINGS over surface of body
• SMALL SURFACE AREA TO VOLUME RATIO to minimise the area over which water is lost

means insects cannot use their body surface to diffuse respiratory gases in the way a single celled organism does

Question 4

what have insects developed for gas exchange?

Answer 4

tracheae, an internal network of tubes

Question 5

what are tracheae supported by?

Answer 5

strengthened rings to prevent them from collapsing

Question 6

what do the tracheae divide into?

Answer 6

smaller tubes called tracheoles that extend throughout all the body tissues of the insect

Question 7

what two ways does respiratory gases move in and out of the tracheal system?

Answer 7

• Along a DIFFUSION GRADIENT

* VENTILATION

Question 8

how do gases enter and leave the tracheae?

Answer 8

through tiny pores called spiracles

Question 9

how are spiracles opened and closed?

Answer 9

through valves

Question 10

what happens to water when spiracles are open?

Answer 10

water can evaporate from the insect

Question 11

what are the limitations of spiracles?

Answer 11

they rely mostly on diffusion to exchange gases, for diffusion to work the pathway needs to be short so the SIZE OF THE INSECT IS LIMITED

Question 12

how does respiratory gases move in and out by diffusion gradient?

Answer 12

• cells respiring use up O2, concentration towards the end of tracheoles falls
• creates a diffusion gradient- causes O2 diffuse from atmosphere through tracheae to cells
• CO2 is produced during respiration, diffusion gradient OPPOSITE DIRECTION

Question 13

how does respiratory gases move in and out by ventilation?

Answer 13

movement of muscles in insects creates a mass movement of air IN + OUT of tracheae