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Summary Insect and fish gas exchange A level biology
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- AQA
Year 1 Biology AQA A level notes. Achieved an A* in my final exam using these notes. They are based on the mark scheme requirements.
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Insect and fish gas exchange summary notes05 December 2022 11:11
Insect tracheal system
- Increased SA required for gas exchange conflicts with conserving water as water
evaporates
- Overcome water loss by trachea - internal network of tubes
Tracheal system
- Have strengthened rings to prevent them from collapsing
- Have tracheoles- smaller dead-end tubes- extend throughout all body tissues of an ins
provide short diffusion pathway from tracheole to any body cell
- Have tiny pores called spiracles on body surface- open and closed by valve
- When spiracles are open water vapour can evaporate - so spiracles often closed to
prevent water loss
Movement in the system:
1. Along diffusion gradient- oxygen is used in respiration so concentration of oxygen in t
end of the tracheoles falls- creates a diffusion gradient
- Carbon dioxide is produced by cells during respiration- diffusion gradient in opposite
direction
2. Mass transport- contraction of muscles squeezes the trachea which enables mass
movements of air
3. Ends of tracheoles are filled with water- muscle cells around tracheoles may carry out
anaerobic respiration during high activity- produces lactate which is soluble and lower
the water potential of the muscle cells (more negative)- therefore water moves into th
cells from the tracheoles (less negative) by osmosis. Water in tracheoles decreases in
volume so draws air further into them
- Final diffusion pathway is in a gas rather than liquid phase- more rapid diffusion- great
water evaporation but increased rate of air movement
Limitations:
- Relies on diffusion- means diffusion distance must be short- insects are small- length o
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