Transport across cell membrane is of two major types; active transport and passive transport.
PASSIVE TRANSPORT:
In this transport, energy is not used and substances move along the concentration gradient from a higher concentration gradient towards a lower concentration gradient. It is further of two types; simple diffusion and facilitated diffusion.
Simple Diffusion:
In this transport, substances move along the concentration gradient directly through the cell membrane. Examples include oxygen, carbon dioxide, etc.
Facilitated/Carrier-Mediated Diffusion:
In this transport, substances move along the concentration gradient by using some carrier protein. This transport is also called carrier-mediated diffusion. Examples include movement of glucose into the muscles, etc.
ACTIVE TRANSPORT:
In this transport, energy is used and substances move against the concentration gradient from a lower concentration gradient towards a higher concentration gradient. It is further of two types; primary active transport and secondary active transport.
Primary Active Transport:
In this transport, energy is used directly from ATP to move substances against the concentration gradient. Example is Sodium-Potassium ATPase Pump in the cell membranes. These pumps use ATP energy to actively pump sodium outside the cell and potassium inside the cell.
Secondary Active Transport:
In this transport, one substance (which is usually sodium) moves along the concentration gradient. Energy of this movement is used to move another substance against the concentration gradient.
If both the substances move in the same direction, it is called "Co-Transport or Symport". For example, sodium-glucose co-transport.
If the substances move in the opposite directions, it is called "Counter-Transport or Antiport". For example, sodium-calcium counter-transport.
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#Cell #CellMembrane #diffusion
