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Title: AQA AS BIOLOGY EXCHANGE
Description: Detailed first year (AS) biology notes to aid key revision of topics and enhance knowledge.
Description: Detailed first year (AS) biology notes to aid key revision of topics and enhance knowledge.
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The external environment is different from the internal environment found within an organism and
within its cells
...
This takes place at exchange surfaces and always
involves crossing cell plasma membranes
...
Because most cells
are too far from exchange surfaces for diffusion
alone to supply or remove various materials, once
absorbed these are rapidly distributed to the tissue fluid and waste products returned to the exchange surface from removal
...
Substances that need to be exchanged
include: respiratory gases (oxygen/CO2) nutrients
(glucose/fatty acids/amino acids/vitamins/
minerals) excretory products (urea/CO2)
...
•
Large surface area to volume ratio—increases
rate of exchange
•
Very thin so that the diffusion distance is
short—rapid exchange
•
Selectively permeable—allow secreted materials to cross
•
Transport system to ensure the movement of
the internal medium (such as blood) - maintain diffusion gradient
Surface Area:
Volume:
Title: AQA AS BIOLOGY EXCHANGE
Description: Detailed first year (AS) biology notes to aid key revision of topics and enhance knowledge.
Description: Detailed first year (AS) biology notes to aid key revision of topics and enhance knowledge.