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AQA Biology for AS ­ Bill Indge ­ Adaptation for mass transport ­ Page 166-169

3.2.7 Factors such as size and metabolic rate affect the requirements of organisms and this gives
rise to adaptations such as specialised exchange surfaces and mass transport systems.


The passage of water through a plant…

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AQA Biology for AS ­ Bill Indge ­ Adaptation for mass transport ­ Page 166-169




Before water can get into the xylem it has to pass through a single layer of cells called the endodermis.

Cannot go via fast route through the cell walls due to a waterproof barrier ­…

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AQA Biology for AS ­ Bill Indge ­ Adaptation for mass transport ­ Page 166-169

This pulling force is so great that the column of water is actually being stretched. The lignin in the walls is
strong enough to stop the vessels collapsing, just as the cartilages in the trachea…

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AQA Biology for AS ­ Bill Indge ­ Adaptation for mass transport ­ Page 166-169

o Often and in many plants the stomata close well before darkness falls and so bright sunlight
does not necessarily mean a high rate of transpiration.




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