A revision summary of OCR A level Biology Exchange Surfaces 3.1
Made by a student who achieved A* in A level Biology.
Covers all the points within the OCR Biology Specification.
Condenses 3 OCR specification books and class notes.
Exchange surface – specialised area Mammals – gaseous exchange surfaces are moist (so O2 dissolves). Ideal conditions for evaporation
adapted to make it easier for molecules of water.
to cross from one side of surface to other Gaseous exchange system – ↓water lost from body.
Gas exchange – process by which 1. Nasal Cavity – ↑SA, good blood supply to warm air to body temp. Hairy lining secretes mucus to
respiratory gases leave & enter the body trap bacteria. Moist surfaces ↑ humidity of incoming air reducing evaporation.
- Singled celled organisms survive 2. Trachea 3. Bronchi 4. Bronchioles
by diffusion – ↓metabolic activity, Function carrying air from larynx – Smaller. 2 bronchi. Branches (1mm)
↓O2 requirement & CO2 production. bronchi.
↑SA: V Cartilage C shape strong flexible Smaller supporting C No
- Multicellular organisms – ↑ rings. Support shape rings
metabolic activity, ↑O2 demands & Ciliated Lining. For gaseous Lining. For gaseous Thin layer of flattened
CO2 production, ↑distance between epithelium exchange to take place. exchange to take place. epithelium for some
O2 supply & where it is needed. ↓SA: Cilia waft mucus away from Cilia waft mucus gaseous exchange.
V lungs
SA: V = SA ➗ V. Goblet Secrete mucus to trap dust Secrete mucus to trap No
- ↑organism = ↓SA: V. ↑distance for cells & prevent infection dust & prevent infection
substances to travel. Harder to Smooth Contracts lumen to help Contracts lumen to help Contracts to constrict/
absorb enough O2 through available muscle expel air expel air relaxes to dilate
SA. Elastic Allow lumen to dilate. Allow lumen to dilate.
Efficient exchange surface fibres
- ↑SA - area needed for exchange.
Overcomes SA: V limitations. E.g. root
hair cell.
- Thin Layers - distance for diffusion is
short. Faster
- Good Blood Supply from dense
capillary network – maintain steep 5. Alveoli – tiny sacs (d 200-300um) for gaseous exchange.
conc gradient, ensures substances Squamous epithelial cells (pneumocytes)
constantly delivered & removed from - type 1 structural large, flattened cells, short distance for diffusion
exchange surface. - Type 2 secrete surfactant. Thin layer.
Connective tissue of collagen & elastin fibres – stretch & recoil to help expel air during
ventilation
Dense network of capillaries – maintains conc gradient, supply O2 & remove CO2cp. Alveolar
macrophages digest foreign particles.
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