2. Cell Membrane and Cell Wall

Cell Membrane and Cell Wall

Cell membrane and cell wall

This gives a covering to all cells and the characteristics that it possess are listed below :

• It is present in both plant & animal cell
• It is an outer covering of cell
• It is living, thin and delicate membrane.
• It is semi-permeable – “allows selective particle to pass through.”
• It is made up of lipids & proteins.

It allows only selected substances to move through it .The movement of substances takes place by activities like: –

• Diffusion – “movement of molecules from higher concentration to lower concentration”.  It is mostly seen in case of Gases.   For example: Cell respire i.e. intake of O2 & giving out CO2 take place through diffusion.
• Osmosis: “movement of solvent molecules from higher cone. to lower conc. across the semi-permeable membrane.

Functions of plasma membrane are as follows

a) It provides support to cell

b) It allow exchange of materials.

c) It provides shape to the cell.

In plant cells outer to cell membrane another layer or covering is present called as cell wall. It is present in all plant cells .It is somehow different from cell membrane in many aspects as it is listed below .

Cell wall

• It is outer to cell membrane
• It is dead
• It is present only in plant cell
• It is made up of cellulose (in fungus it is made of chitin)
• It is freely permeable

Functions of cell wall are as follows –

• It   provides mechanical support to cell.
• It allows materials to exchange.
• It maintains the shape of cells.

Now, if we go into detail, we can say that cell consist of cell membrane and it encloses called a living material protoplasm. Protoplasm is defined as living material of cell. The term protoplasm was coined by: J.E Purkinjee. It is further divided into two parts:

• Nucleus (discovered by Robert Brown)
• Cytoplasm

Nucleus

Like we have brain, the cell has a nucleus. All the activities are controlled by nucleus. It is located in the centre of the cell. It consists of different components:

1. Nuclear membrane

2. Nucleoplasm

3. Nuclear material

4. Nucleolus

1. Nuclear membrane: -It is the membrane that separates the nucleus from the cytoplasm. The membrane has pores in it which allow only selected exchange of materials. It is therefore called semi permeable in nature.

2. Nucleoplasm: It is the liquid in the nucleus that is cytoplasm of nucleus. It is similar to cytoplasm outer to nucleus except that it lacks organelles.

3. Nucleolus: It is a small oval body rich in proteins and RNA, RNA is ribonucleic acid and it is the genetic material. It is site for ribosome formation. That is why it is often termed as factory for ribosome.

4. Nuclear material: It contains thread like structures which further condense at the time of cell division to ribbon like structures called chromosomes. These chromosomes are made up of DNA and proteins. There are segments of DNA that are responsible for characters in a body or transfer of characters from parents to offspring and are called genes. They act as hereditary vehicles.

Functions of nucleus are as follows

• It regulates the cell cycle.
• It controls metabolic activities of cell.
• It contains genes that help in transmission of characters from parents to offspring .

Cytoplasm

It is the liquid material of cell. Its soluble part is called cytosol. It contains organelles. These organelles perform necessary functions for the cell like some organelles help in cleaning the cell, some help in synthesizing certain substances for the cell, some perform catabolic function like breakdown of food, etc. Let us study them in detail: