Structure of Cell

A typical plant and animal cell consists of the following parts.

1. Cell Wall:

Definition:

Cell wall is the outermost boundary of plant cells, bacterial cells and fungal cells. It is not found in animal cells.

Chemical Composition:

It is secreted by the protoplasm of the plant cell.
In plant cells it is mainly composed of cellulose and pectin.
Bacterial cell wall is made up of protein and carbohydrate.
Fungal cell wall is made up of fungal cellulose and chitin.

Structure:

Ultra microscope structure of cell wall shows that cellulose make the fibers which are arranged in crises cross manner. These fibers are kept in their position by a commenting material called calcium pectate (Pectin)
Thickness of the cell wall is different in different plant cells.
Cell wall is composed of three main layers,

i. Middle lamella
ii. Primary wall
iii. Secondary wall

Middle Lamella:

Middle lamella is formed between the primary walls of two neighboring cells, It is a cementing layer between two cells.

Primary Cell Wall:

Primary wall is the first wall of the plant cell. Chemically it is composed of cellulose and pectin sometimes, lignin.

Secondary Wall:

Secondary wall is formed by deposition of cellulose at the inside of the primary wall.

Functions:

It provides protection and mechanical support to the cell.
It acts like a skeletal framework of plants.
It performs the function of transport of material (water and solute) from outside to inside, therefore it is permeable in nature.

2. Cell Membrane:

Definition:

The cell membrane is the outermost living boundary of all cells.

Brief Description:

The cell membrane, also called the plasma membrane, physically separates the intracellular space (inside the cell) from the extracellular environment (outside the cell). The cell membrane surrounds and protects the cytoplasm.

Function of Cell Membrane:

It is a semi-permeable membrane and regulates the flow of solution and materials in and out of the cell.
It maintains the fluid concentration within the cell.
Cell membrane takes in particular materials by the process of Endocytosis.
It also intakes fluid material through the process of pinocytosis.

Fluid-Mosaic Model of Structure of Cell Membrane:

According to the fluid-mosaic model, by S.J. Singer and G.I. Nicholson (1972) plasma membrane composed of a phospholipids bi-layer as the core layer.
The phospholipids layers lie parallel to each other.
The lipid molecules are capable of rotating and moving within the membrane.
Protein molecules within the bi-layer float like icebergs.
Cell-membrane which is selectively permeable to ions, small molecules and even larger molecules allows the movement of substances in and out of the cells.
Cell-membrane performs many important functions for cells such as osmosis, diffusion, transport of nutrients and processes of ingestion and secretion.