Gas Exchange in Single-Celled Organisms and Insects

Gas Exchange in Single-Celled Organisms

Respiratory Gases Move in + out of Tracheal Sys.:

Small t/f large SA:V

Respiration:

O2 absorbed by diff. across body surf., covered by cell - surface membrane

CO2 diff. out of body surface

Cell wall of living cell, no barrier to diff.

Gas Exchange in Insects

Insects conserve water

Gas ex. SA required conflicts with conserving water b/c H2O will evap.

For gas ex. insects use TRACHEAE

Supported by strengthened rings that prevent collapse

Divide into smaller dead-end tubes, TRACHEOLES

Extend throughout boddy tissue

Atmospheric air with O2 is brought directly to respiring tissues b/c, short diff. path. from tracheal to any body cell

Along diff. grad.

When cells respire O2 is used up t/f conc. toward end of tracheoles fall = diff. grad. + causes O2 to diff. from tubes to cells. CO2 produced by cell res. = diff. grad. in opposite direction, from cells to tubes.

Diff. in air, much more rapid than in H2O, t/f respiratory gases r exchanged more rapidly

Mass Transport

Contraction of mucles = insects can squeeze trachea enabling mass movements of air in + out

Further speeds up ex. of respiratory gases

Ends of Tracheoles, Filled with H2O

Muscle cells, around tracheoles anaerobically respire, produces lactate, soluble + lowers water potential

H2O moves to cells from tracheoles by OSMOSIS, water @ ends decreases vol. + t/f draws further air in2 them t/f final diff. path. is in gas rather then liquid phase + t/f diff is more rapid

Inc. rate @ which air is moved in the tracheoles but leads to greater H2O evap.

Gas Exchange in Insects 2

Gases enter + leave trough SPIRACLES, on body surface

May be open/closed by a valve

When open, H2O vapour can evap.

Most of time spiracles are closed, prevent water loss

Periodically open to allow gas ex.

Tracheole System

Efficient method of transport

Limitations

Relies on diff. 2 ex. gases b/w environment and cells

For diff to be effective...

Diff. path. needs to be shot = insects are small

Length of diff. path. limits size of insects