V. Bulk Transport (Not in syllabus)

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The cell membrane is mainly made up of lipids (fats) and it allows small particles to pass through. Large particles like antibodies, enzymes or highly water-soluble particles cannot pass through the cell membrane directly.

These problems are overcame by having bulk transport which involve enclosing the large and/or water-soluble particles within a membrane enclosed vesicle or vacuole. This process however requires ATP.

When large or water-soluble particles are released from cells, the bulk transport process is known as exocytosis.

Figure 13 Materials to be released are enclosed within cell vacuole/vesicle. The vacuole/vesicle is made up of lipids (fats) similar to that of the cell surface membrane. When the vacuole/vesicle join with the cell surface membrane, the materials stored within the vacuole/vesicle is released into the external surrounding. Process is known as exocytosis.

Large particles enter the cells by endocytosis.

Figure 14 Large particles fuse with the cell surface membrane and a membrane-enclosed vesicle or vacuole forms around it. The vesicle or vacuole then enters the animal cell.