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Chapter 2.3 ­ Transport across membranes

All membranes act as barriers controlling what passes through them and allowing the fluids either
side of them to have different compositions. Many chemical processes take place on membrane

The cell surface membrane must be flexible to allow the cell to change shape…

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Other molecules move by diffusion through protein-lined pores. This is a form of passive transport.

Substances with a strong positive or negative charge and large molecules can't pass through cell
membranes by single diffusion. They are passed through facilitated diffusion. This is when proteins
allow specific substances to move through…

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Fick's Law:-
Surface area × concentration gradient
Rate of diffusion Thickness of exchange membrane of barriers.

"proportional to"

Gaseous exchange happens in the alveoli.

An alveolus is made up of a single layer of flattened epithelial cells. The capillaries close to the
alveoli have a wall which is one cell…


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