6.2- GAS EXCHANGE IN SINGLE-CELLED ORGANISMS AND INSECTS Flashcards
What happens to single celled organisms SA:V as they are small?
have a large SA:V
How is oxygen absorbed + across where in single celled organisms?
by diffusion across body surface
What is the body surface of a single celled organism covered by?
cell-surface membrane
How is carbon dioxide from respiration removed in single-celled organisms?
diffuses out across body surface
Are there additional barriers when living cell surrounded by cell wall?
no additional barrier to diffusion of gases
What does the increase in SA required for gas exchange conflict with in terrestrial organisms?
conflicts with conserving water as water will evaporate from it
What have insects evolved for gas exchange?
internal network of tubes called tracheae
What is the tracheae in insects supported by?
strengthened rings to prevent them from collapsing
What does the trachea in insects divide into?
smaller dead-end tubes called tracheoles
Where do the tracheoles in insects spread throughout?
all the body tissues of insect
What happens as the tracheoles in insects spread throughout all the body tissues of insect?
atmospheric air, with oxygen it contains, bought directly to respiring tissues
How is the oxygen bough directly to respiring tissues in insects? (Property)
short diffusion pathway from tracheole to any body cell
What are the 3 ways respiratory gases move in and out of the tracheal system?
along diffusion gradient
mass transport
ends of tracheoles filled with water
How are respiratory gases moved along by a diffusion gradient in the tracheal system?
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
How are respiratory gases moved by mass transport in the tracheal system?
contraction of muscles in insects can squeeze trachea enabling mass movements of air in + out
further speeds up exchange of respiratory gases
How are respiratory gases moved with the ends of the tracheoles being filled with water in the tracheal system?
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
Through what do gases enter + leave tracheae?
through tiny pores, called spiracles, on body surface
How can the spiracle be due to a valve?
opened or closed by a valve
What happens when spiracles are open?
water vapour can evaporate from insect
For much of the time how do insects keep the spiracles?
spiracles closed
Why do insects keep the spiracles closed for most of the time?
prevent water loss
When do insects open to spiracles?
periodically to allow gas exchange
What limitation does the tracheal system have?
relies mostly on diffusion to exchange gases between environment + cells
For diffusion to be effective, how does the diffusion pathway have to be like? (hint: insect)
short diffusion pathway which is why insects are of small size
What is limited for insects due to short length of diffusion pathway?
limits size insects can attain
