The Fundamental Unit of Life (Part-1)

The spontaneous movement of a substance, from a region of higher concentration to lower concentration, is called diffusion.

Water also obeys the law of diffusion—the movement of water molecules through the selectively permeable membrane along the concentration gradient through Osmosis.

Hypotonic Solution

1.) The outermost covering of the cell.

2.) Separates contents of the cell from its external environment.

3.) It is made up of proteins and lipids.

Reasons why it is called the selectively permeable membrane:-

i.) Plasma Membrane allows and permits the entry or exit of some materials.

ii.) It also prevents the movement of some other materials.

It is flexible (made up of organic molecules called proteins and lipids).

It's flexibility enables cell to engulf in food and other from the external environment.

Cell Wall is another rigid outer covering found only in plant cell. The cell wall lies outside the plasma membrane.

It is mainly composes cellulose. Cellulose is a complex substance which provides structural strength to plants.

Cell Walls permit the cells of plants, fungi and bacteria to withstand very dilute (hypotonic) external media without bursting.

In such media the cells tend to take up water by osmosis. The cell swells, building up pressure against the cell wall. This wall exerts an equal pressure against the swollen cell.

Because of cell wall, cells can withstand much greater changes in the surrounding medium than animal cells.

When a living plant cell loses water through osmosis there is shrinkage or contraction of the content of the cell away from the cell wall. This phenomenon is known as Plasmolysis.