- In secondary active
transport or coupled transport
the energy required is obtained from the
transport of sodium into the cell. This transport
is down the sodium concentration gradient and as
such no direct energy expenditure occurs.
- On the other hand, to produce the
gradient, energy is utilised when sodium is
pumped into the extracellular space through the
sodium/potassium pump.
- If the other ion transported in
the same time as sodium moves in the same
direction of sodium then the transport is called
co-transport if in the oppposite direction it is
called coutertransport.
- examples include cotransport of
glucose and the countertransport of calcium.
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