The cell membrane separates living cells from their environment and regulates the movement of substances in and out of the cell through selective permeability. It is composed of lipids, primarily phospholipids, and proteins that define its specific functions, including passive and active transport mechanisms. Movement of large molecules occurs via processes like endocytosis and exocytosis.

1. CELL MEMBRANE

2. A CELL MEMBRANE IS:
• The boundary that separates the living cells from its surrounding and controls the movements
into and out of the cell it surrounds.
• it allows selective permeability. This means that it does not allow everything to enter nor leave
the cell.

3. What makes a membrane
-Membranes are made up of Lipids, Proteins and other
macromolecules.
-The most abundant lipids in most membranes are phospholipids.
-Phospholipid is an amphipathic molecule. Meaning it has both a
hydrophilic part and a hydrophobic region.

4. Phospholipids
-They are made up of fatty acid tails and these fatty acid tails are hydrophobic. This means that
they do not mix with water.
-Their heads are made up of phosphate group which are hydrophilic. This means that they mix
with water.
PHOSPHATE
FATTY ACID TAIL

5. Proteins
-Proteins determines a membranes specific function. Therefore the proteins that makes up a cell
membrane and a protein that makes up a membrane of an organelle are different.
Peripheral proteins.
-Loosely bound to the surface of the membrane.
Integral proteins.
-They penetrate the bilayer of the cell membrane
-They are transmembrane protein.

6. Below is a picture of how a channel protein looks like
https://tinyurl.com/yddz7efr

7. Passing through a membrane
1. PASSIVE TRANSPORT.
• Simple diffusion
-diffusion of nonpolar molecules, hydrophobic molecules such as fats.
• Facilitated transport.
-diffusion of polar molecules, hydrophilic molecules using a protein channel.
2. ACTIVE TRANSPORT
-Uses protein pump.
-Requires energy (ATP)

8. Summary of diffusion through a membrane

9. Moving large molecules
1. Endocytosis
Phagocytosis- Cellular intake of food.
Pinocytosis-Cellular intake of liquid
2. Exocytosis

10. References
Bester, M. et al. (2013). Platinum: Natural Sciences. Cape Town: CTP Printers.
Dschreiber44. (2009). Cell membrane. Available from slideshare at
https://www.slideshare.net/dschreiber44/cell-membrane
Foley, T. (2011). Cell membrane and transport. Available from slideshare at
https://www.slideshare.net/ToniFoley/24-cell-membrane-and-transport
Ravagnan, M. (2012). PowerPoint cell membrane transport copy. Available from slideshare at
https://tinyurl.com/ybxa5xvz
Saikia, A. (2018). Transport across the cell membrane. Available from slideshare at
https://www.slideshare.net/AnkurSaikia3/transport-across-the-cell-membrane