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How does gas exchange occur in single-celled organisms?
- small=large SA:Vol
- Absorb O2/Expels CO2: diffusion across body surface (cell surface membrane)
- cell wall=no additional barrier to diffusion of gases
How does gas exchange occur in insects?
- exchange respiratory gases directly with the air
- air channeled into trachae (internal tube network)=supported by strengthening rings to prevent collapse
- divide into small dead end tubes (tracheoles)=extend through all body tissues
What are spiracles?
Tiny pores on insect body surface=gases enter/leave trachae (opened/closed by valve)
What are the three reasons why respiratory gases move in and out of the tracheal system?
- Across the diffusion gradient
- Mass transport
- End of tracheoles have water
How does the diffusion gradient allow respiratory gases to move in/out the tracheal system?
- respiring cells use O2=lower conc. to tracheoles=diffusion gradient;atmosphere to tracheoles to cells
- respiring cells produce CO2=higher conc. to tracheoles=diffusion gradient: cells to tracheoles to atmosphere
How does mass transport allow respiratory gases to move in/out the tracheal system?
- contracting muscles=squeeze trachea=mass movement of air in/out=speeds respiratory gas exchange
How do the end of tracheoles containing water allow respiratory gases to move in/out the tracheal system?
- Major activity: muscle cells around tracheoles anaerobic respire=lactate (soluble/lower water potential of muscle cells)=water moves (osmosis) from tracheoles to cells = vol water in tracheole lower, draw air in =rapid diffusion=greater water evaporation
Why are spiracles not constantly open?
- spiracles open=water evaporates from insect
- majority of time spiracles closed=prevent water loss
- periodically open=gas exchange
How are insects adapted to minimise water loss from their bodies?
- Small SA:Vol
- Ability to close spiracles
- Waterproof outer cuticle
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