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The following nine points will highlight the nine important mechanisms involved in the movement of materials through cell membranes.
1. Physical Process:
Molecules are transported without the membrane and there is no expense of metabolic energy.
2. Diffusion:
Net movement of molecules (or ions) from a region of greater concentration to a region of lower concentration of concerned molecules.
3. Facilitated Diffusion:
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Carrier protein in cell membrane accelerates movement of relatively large molecules from region of their higher to region of their lower concentration
4. Osmosis:
Water molecules diffuse from region of their higher to region to their lower concentration through semipermeable membrane.
5. Physiological Process:
Molecules are transported across the membrane against concentration gradient at the expense of metabolic energy (ATP).
6. Active transport (pump):
Protein molecules in cell membranes transport ions or molecules through membrane; movement may be against concentration gradient (i.e., from region of lower to region of higher concentration of concerned molecules, and is supported by ATPase activity).
7. Endocytosis:
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Cell membrane encircles particle and brings it into cell by forming a vacuole around it.
8. Pinocytosis:
Cell membrane takes in fluid droplets by forming vesicles around them.
9. Exocytosis/Emeiocytosis:
Cell membrane ejects materials; vesicle filled with material fuses with cell membrane. It is cell vomiting process.
