6.2 gas exchange in single celled organisms and insects

exchange in single celled organisms (4)

small- large SA to volume ratio

oxygen absorbed by diffusion across body surface/co2 diffuses out

body surface only covered by a cell-surface membrane

if living cell is surrounded by a cell wall this is no barrier for gas diffusion

what problems do insects face with gas exchange?

increased SA needed for gas exchange, but conflicts with them conserving water

what is the missing term

muscle fibres

what is the missing term and what does it do

tracheoles- smaller dead end tubes. extend through all body tissues of insect.

what is the missing term and what does it do

trachea- internal network of tubes. supported by strengthened rings to prevent from collapsing.

what is the missing term and what does it do

fluid filled ends of tracheoles

TRACHEAL SYSTEM- LONG ANSWER.

internal network of tubes- trachae, supported by strengthened rings to keep from collapsing

divide into smaller dead end tubes called tracheoles

tracheoles extend through all body tissues of insect

atmospheric air w oxygen brought directly to respiring tissues- bc short diffusion pathway from tracheole to any body cell

respiratory gases move in and out of tracheal system in 3 ways (simplified)

along a diffusion gradient

mass transport

ends of tracheoles are filled with water

how do respiratory gases move in and out of tracheal system along a diffusion gradient

when cells respire, o2 used up, decreasing conc at end of tracheoles

creates diffusion gradient, gaseous o2 diffuses from atmosphere through trachae and tracheoles to cells

CO2 produced by cells during respiration creating diffusion gradient in opposite direction

causes gaseous co2 to diffuse across tracheoles and trachae from cells into atmosphere

gases exchanged quickly as diffusion in air is more rapid than water.

explain how respiratory gases move in and out of tracheal system by mass transport

contraction of muscles in insects can squeeze the trachea

enabling mass movements of air in and out

this further speeds up exchange of respiratory gases

explain how respiratory gases move in and out of tracheal system using fluid-filled ends of tracheoles

during major activity, muscle cells around tracheoles respire and carry out aerobic respiration

produces lactate- soluble, lowers water potential of muscle cells

water moves into cells from tracheoles by osmosis

water in ends of tracheoles decreases and draws air further into them

final diffusion pathway is in a gas phase, diffusion is more rapid

increased rate at which air is moved in the tracheoles but leads to greater water evaporation

what are spiracles

tiny pores on the surface of insects

limitations of the tracheal system

relies mostly on diffusion to exchange gases between environment and cells

for diffusion to be effective, diffusion pathway must be short, which is why insects are small

as a result, length of diffusion pathway limits the size that insects can attain

what is the importance of a surface area to volume ratio?

larger the sa, the smaller the volume means efficient exchange across their body surface.

as organisms become larger, volume increases at larger rate than surface area, so simple diffusion of substances on outer surface is only for relatively inactive organisms

when is a specialised gas exchange surface needed

to increase sa to volume ratio in animals that are larger, e.g. gills in fish

the amount of oxygen needed by an organism is determined by what 4 things

number of living cells

rate they need to respire

volume of organism

activity levels

how do small organisms get all the oxygen they need?

diffusion through cell surface as they have a high surface area to volume ratio

why do large organisms need specialised exchange surfaces?

they have a small surface area to volume ratio. so the external surface area isn’t large enough for oxygen to diffuse through it rapidly enough to supply cells with the oxygen it needs.

5 adaptations of gas exchange surfaces

large sa to volume ratio, increases rate of exchange

very thin- short diffusion distance, materials cross exchange surface rapidly.

selectively permeable- allow selected materials to cross.

movement of environmental medium e.g. air to maintain diffusion gradient.

transport system- ensure movement of internal medium e.g blood to maintain diffusion gradient