6.2- GAS EXCHANGE IN SINGLE-CELLED ORGANISMS AND INSECTS

Question 1

What happens to single celled organisms SA:V as they are small?

Answer 1

have a large SA:V

Question 2

How is oxygen absorbed + across where in single celled organisms?

Answer 2

by diffusion across body surface

Question 3

What is the body surface of a single celled organism covered by?

Answer 3

cell-surface membrane

Question 4

How is carbon dioxide from respiration removed in single-celled organisms?

Answer 4

diffuses out across body surface

Question 5

Are there additional barriers when living cell surrounded by cell wall?

Answer 5

no additional barrier to diffusion of gases

Question 6

What does the increase in SA required for gas exchange conflict with in terrestrial organisms?

Answer 6

conflicts with conserving water as water will evaporate from it

Question 7

What have insects evolved for gas exchange?

Answer 7

internal network of tubes called tracheae

Question 8

What is the tracheae in insects supported by?

Answer 8

strengthened rings to prevent them from collapsing

Question 9

What does the trachea in insects divide into?

Answer 9

smaller dead-end tubes called tracheoles

Question 10

Where do the tracheoles in insects spread throughout?

Answer 10

all the body tissues of insect

Question 11

What happens as the tracheoles in insects spread throughout all the body tissues of insect?

Answer 11

atmospheric air, with oxygen it contains, bought directly to respiring tissues

Question 12

How is the oxygen bough directly to respiring tissues in insects? (Property)

Answer 12

short diffusion pathway from tracheole to any body cell

Question 13

What are the 3 ways respiratory gases move in and out of the tracheal system?

Answer 13

along diffusion gradient

mass transport

ends of tracheoles filled with water

Question 14

How are respiratory gases moved along by a diffusion gradient in the tracheal system?

Answer 14

when cell respiring, oxygen used up so its conc. towards ends of tracheoles falls

creates diffusion gradient that causes gaseous oxygen to diffuse from atmosphere along tracheae + tracheoles to cells

CO2 produced by cells during respiration

creates diffusion gradient in opposite direction

causes gaseous CO2 to diffuse along tracheoles + tracheae from cells to atmosphere

as diffusion in air much more rapid than in water, respiratory gases exchanged quickly by this method

Question 15

How are respiratory gases moved by mass transport in the tracheal system?

Answer 15

contraction of muscles in insects can squeeze trachea enabling mass movements of air in + out
further speeds up exchange of respiratory gases

Question 16

How are respiratory gases moved with the ends of the tracheoles being filled with water in the tracheal system?

Answer 16

during periods of major activity, muscle cells around tracheoles respire carry out some anaerobic respiration

produces lactate-soluble + lowers water potential of muscle cells

so water moves into cells from tracheoles by osmosis

water in ends of tracheoles decreases in volume + in doing so draws air further into them

means final diffusion pathway is in gas rather than liquid phase, and so diffusion more rapid

increases rate at which air moved in tracheoles but leads to greater water evaporation

Question 17

Through what do gases enter + leave tracheae?

Answer 17

through tiny pores, called spiracles, on body surface

Question 18

How can the spiracle be due to a valve?

Answer 18

opened or closed by a valve

Question 19

What happens when spiracles are open?

Answer 19

water vapour can evaporate from insect

Question 20

For much of the time how do insects keep the spiracles?

Answer 20

spiracles closed

Question 21

Why do insects keep the spiracles closed for most of the time?

Answer 21

prevent water loss

Question 22

When do insects open to spiracles?

Answer 22

periodically to allow gas exchange

Question 23

What limitation does the tracheal system have?

Answer 23

relies mostly on diffusion to exchange gases between environment + cells

Question 24

For diffusion to be effective, how does the diffusion pathway have to be like? (hint: insect)

Answer 24

short diffusion pathway which is why insects are of small size

Question 25

What is limited for insects due to short length of diffusion pathway?

Answer 25

limits size insects can attain