2. Cell Membrane and Cell Wall

Cell Size

The cell size is variable. In the living organisms, the cell size may be as small as a millionth of a metre or may be as large as a few centimetres. Usually, all the cells are microscopic in size and aren’t visible to the naked eye. Thus, they need to be enlarged by a microscope for seeing.

Cell Shape

• Usually, the cells are round, elongated or spherical.
• There are also some cells which are long and pointed on both the ends. Such cells exhibit spindle shape.
• In some cases, the cells are very long.
• Some may be branched like the neuron or the nerve cell. The nerve cell transfers and receives messages.

It, therefore, helps in coordinating and controlling the working of the different parts of the body. The components of the cell are enclosed in a membrane. This membrane provides shape to the cells of animals and plants. There is a cell wall surrounding them. The cell wall is an additional covering over the cell membrane in the plant cells. It offers rigidity and shape to the cells.

Depending on the purpose, the cell takes on a number of forms. Cells come in a variety of forms, including:

Skin cells

1. These skin cells have a flat surface.
2. They are a protective body cover with a flat form that allows them to cover a large area.

Muscle cells

            i. Muscle cells are long, thin, and elongated.
            ii. Muscle cells expand and contract, and their long and thin structure aids in this process.

Nerve cells

            i. These nerve cells have a lengthy fibrous structure.
            ii. Long, thin extensions (axons and dendrites) connect these nerve cells to other nerve cells.
            iii. The extensions aid the neuron in swiftly transmitting chemical and electrical information throughout                    the body.
            iv. Nerve cells can contain fibres that are over a metre long.
             v. Messages are transmitted down these fibres from one nerve cell to the next.

 Blood cells

            i. White blood cells are disc-shaped but have the ability to alter form.
            ii. WBC in the blood alters their form to kill bacteria or any pathogens that are disease-causing                                organisms.                                                                                                                                                           iii. The structure of red blood cells (erythrocytes) allows them to pass through capillaries with ease.

Plant cells

            i. Depending on their purpose, plant cells might be rectangular, circular, oval, or elongated. Plant cells                   on the outside of the stem give the plant its strength.
            ii. For support, these cells have strong cell walls. Food is stored in specific cells in plants, and these                       cells are bigger than other cells.

Cell Wall

           The cell wall is the outer covering of a cell, present adjacent to the cell membrane, which is also called the plasma membrane. The cell wall is normally present in all plant cells, fungi, bacteria, algae, and some archaea. Animal cells are not regular in their shape and this is mainly due to the lack of cell walls in their cells. Cell wall composition usually varies along with organisms.

The Function of the Cell Wall

There are various functions of cell wall like:

•    The cell wall of the plants provides definite shape, strength, and rigidity.
•    The cell wall also protects against mechanical stress and physical shocks.
•    Cell wall helps to control cell expansion due to the intake of water.
•    The cell wall also helps in preventing water loss from the cell.
•    The cell wall is responsible for transporting substances between and across the cell.
•    The cell wall acts as a barrier between the interior cellular components and the external environment.
Cell Membrane

•    The cell membrane is also called the plasma membrane. 
•    Cell membrane is found in all cells and separates the interior of the cell from the outside environment.
•     The cell membrane also consists of a lipid bilayer that is semipermeable. 
•    The cell membrane is also responsible for the transportation of materials entering and exiting the cell.
•     The thin membrane surrounds every living cell, fixing the cell from the environment around it. 
•    The cell membranes are the cell’s constituents, often large, water-soluble, highly charged molecules such as proteins, nucleic acid, carbohydrates, and substances involved in cellular metabolism. 
•    The surrounding of the cell membrane is a water-based environment, containing ions, acids, and alkalis that are toxic to the cell, as well as nutrients that the cell must absorb to live and grow. 

Functions of the Cell Membrane

•    There are various functions of cell membrane-like:
•    The cell membrane protects the integrity of the interior cell.
•    The cell membrane provides support and maintains the shape of the cell.
•    The cell membrane helps in regulating cell growth through the balance of endocytosis and exocytosis.
•    It also plays an important role in cell signalling and communication.
•    The cell membrane acts as a selectively permeable membrane by allowing the entry of only selected substances into the cell.