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Summary Biology Unit 3 AQA ALEVEL New Spec Full Revision Notes
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Full Revision Notes on Unit 3 A-Level Biology; Organisms exchange substances with their environment.
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Section 3: Organisms exchangesubstances with their
environment
How do microorganisms obtain nutrients and remove waste?
- By exchange via their surface.
- Nutrients (e.g. glucose, oxygen) move in by difusion via their surface.
- Waste (e.g. carbon dioxide) move out by difusion via their surface.
Why are microorganisms able to perform exchange via their surface?
- Have a large surface area to volume rato.
- Have a short difusion pathway.
- Have low demand.
Why can’t animals/plants perform exchange via their surface
- Have a small surface area to volume rato.
- Multcellular (large difusion pathway and high demand).
- Impermeable surface (prevent pathogens entering and reduce water
loss).
- Therefore, require specialised exchange and transport systems.
- Exchange system = increase rate of difusion of nutrients in and waste
out.
- Transport system = deliver nutrients and remove waste from all cells.
Why do fsh have specialised gas exchange systems?
- Multcellular organism so has a small surface area to volume rato, large
difusion distance, high demand body surface impermeable.
- Therefore, cannot perform gas exchange (O2 in/CO2 out) via their
surface, they require a specialised gas exchange system called Gills.
Structure of gills in fsh?
- Many gill filaments and gill lamellae = large surface area.
- Gill lamellae have a thin wall (short difusion distance) and are
permeable.
- Ventlaton brings in pure water (high oxygen, low carbon dioxide) and
circulaton brings in deoxygenated blood (low oxygen, high carbon
dioxide), the water and blood pass over in opposite directons
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