2.1.2 Features of exchange surfaces which aid passive and active transport

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  • Created by: Rachael
  • Created on: 22-05-13 19:02

Methods of Increasing Surface Area

  • Biconcave - the biconcave shape of erythrocytes 
  • Large Number - the millions of alveoli in the lungs
  • Long Extension - the long extension of the Root Hair Cell
  • Air Spaces in Spongy Mesophyll - increases surface area in contact with gases
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Thin Separating Surface

A thin separating surface speeds up the rate of passive or active transport by reducing the distance molecules have to move to pass through the membrane.

  • Squamous epithelia cells - root hair cells one cell thick
  • Vaculole extending into extension - root hair cells. Speeds up osmosis
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Concentration Gradients

The higher the difference in concentration gradiants, the faster the rate of transport.

  • CIrculation - rich blood supply to alveoli maintains diff in conc of O2 between alveolus and capillary
  • Ventilation - air flow continuously moving into lungs and alveoli maintains diff in conc
  • Air Spaces - in spongy mesophyll increases difference in concentration of cell and air space
  • Capillaries One Erythrocyte in Diameter - enhances diffusion gradients by reducing the distance molecules have to move. 
    Also the fact erythrocytes are constantly moving through capillaries maintains conc gradients
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Palisade Mesophyll

  • Tightly Packed
  • Top of leaf
  • Many Mobile Chloroplasts

Spongy Mesophyll

  • Loosly packed
  • Air Spaces (^ conc grad)
  • Xylem within layer (^ SA in contact with gases)

Root hairs

  • Long cell extension (^ SA)
  • One Cell Thick (V distance for diff)
  • Vacuole extends into extension to speed up osmosis
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  • Diameter of an erythrocyte - single file erythrocytes (V distance for erythrocytes to move)
  • Wall is 1 cell thick
  • Erythrocytes constantly moving through (maintains conc grad)


  • Biconcave (^ SA)
  • No nucleus (^ volume to store haemoglobin)
  • Diameter close to diameter of capillary (one at a time)


  • Large Number (^ SA)
  • Squamous Epithelial Cell lining (thin)
  • Rich blood supply (maintain conc grad)
  • Continuous Airflow - Ventilation (maintain conc grad)
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