CELL MEMBRANE

The cell membrane -- lipid bilayer.
The lipids are arranged within the membrane with the polar head towards the outer sides and the hydrophobic tails towards the inner part, which ensures that the nonpolar tail of saturated hydrocarbons is protected from the aqueous environment.

The lipid component -- phosphoglycerides.
Cell membranes also possess protein and carbohydrate.
Membrane proteins can be classified as
1. Peripheral proteins lie on the surface of membrane 2. integral proteins are partially or totally buried in the membrane.
Fluid mosaic model of cell membrane was proposed by Singer and Nicolson.
Fluid mosaic model -- fluid nature of lipid -- lateral movement of proteins within the overall bilayer, and the ability to move within the membrane is measured as its fluidity.

FUNCTIONS

Transport across membrane
Movement of water by diffusion from higher to lower concentration - osmosis - passive transport

The energy dependent process, in which ATP is utilised and a few ions or molecules are transported across the membrane against their concentration gradient is called active transport. Example- Na+/K+ Pump.

CELL WALL

non-living rigid outer covering
gives shape to the cell, protects the cell from mechanical damage and infection, helps in cell-to-cell interaction and provides barrier to undesirable macromolecules.
Algae have cell wall, made of cellulose, galactans, mannans and minerals like calcium carbonate,
In other plants it consists of cellulose, hemicellulose, pectins and proteins.
Primary wall - cell wall of a young plant cell, which is capable of growth and gradually diminishes as the cell matures and the secondary wall is formed on the inner side of the cell.
The middle lamella is a layer mainly of calcium pectate which holds or glues the different neighbouring cells together.

The cell wall and middle lamellae may be traversed by plasmodesmata which connect the cytoplasm of neighbouring cells