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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 called trachae which are 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 with oxygen is brought directly to respiring tissues as there is a 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
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 causing gaseous o2 to diffuse 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.
respiratory gases move in and out of tracheal system- 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
respiratory gases move in and out of tracheal system: ENDS OF TRACHEOLES ARE FILLED WITH WATER
during major activity, muscle cells around tracheoles respire and carry out aerobic respiration. produces lactate which is soluble and lowers water potential of muscle cells. therefore 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 therefore 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
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
