Eukaryotic plasma membrane/ Cell membrane/ Biomembrane:
1. It is thin, quasi-fluid structure present both extracellularly and intracellularly.
2. Extracellularly, it is present around protoplast and intracellularly, it is present around most of the cell organelles in eukaryotic cell. It separates cell organelles from cytosol.
3. Thickness of bio-membrane is about 75A.
4. Cell membrane appears trilaminar (made up of three layers) when observed under electron microscope. It shows presence of lipids (mostly phospholipids) arranged in bilayer.
5. Lipids possess one hydrophilic polar head and two hydrophobic non-polar tails. Therefore, phospholipids are amphipathic.
6. Lipid molecules are arranged in two layers (bilayer) in such a way that their tails are sandwiched in between heads. Due to this, tails never come in direct contact with aqueous surrounding.
7. Cell membrane also shows presence of proteins and carbohydrates.
8. Ratio of proteins and lipids varies in different cells. For example, in human beings, RBCs show approximately 52% protein and 40% lipids.
