All cells vary in their shape, size and activities and have three major functional regions, viz, plasma membrane, nucleus and cytoplasm.
Plasma Membrane or Cell Membrane: This is the outermost covering of the cell, that separates the contents of the cell from its external environment. The plasma membrane is a living, thin, delicate, elastic, a selectively permeable membrane made up of proteins and lipids and is present in both plant and animal cells.
Functions of Plasma Membrane:
(i) It gives definite shape to the cell.
(ii) It separates the contents of a cell from its surrounding medium.
(iii) It provides a mechanical barrier, for the protection of the internal contents of the cell.
(iv) It is a selectively permeable membrane.
(v) It regulates the movement of ions, in and out of the cell.
Nucleus: Robert Brown in 1831 discovered the nucleus in the cell. The nucleus is the largest cell structure. It is a spherical or oval, prominent structure, usually located in the centre of the cell. Nucleus has the following important parts:
Nuclear membrane: It is a double-layered membrane, which separates the nucleus from the cytoplasm. It has pores called nuclear pores, which allow the transfer of material from the nucleus to the cytoplasm. Nucleoplasm: It is a homogeneous and granular dense fluid, present inside the nucleus, in which chromatin and nucleolus are suspended.
Chromatin material: It consists of a long, coiled network of thread-like structures. The chromatin material is made up of deoxyribonucleic acid (DNA), which is responsible for storing and transmitting the hereditary information, from one generation to the other. It condenses into compact rod-like bodies, called chromosomes, at the time of cell division.
Nucleolus: It is more or less round in structure, found inside the nucleus. The nucleolus contains RNA (ribonucleic acid) and proteins. RNA is helpful in protein synthesis in the cytoplasm.
Functions of Nucleus:
The nucleus controls all the metabolic activities of the cell.
(i) It regulates the cell cycle.
(ii) It is concerned with the transmission of hereditary traits from the parent to offsprings.
(iii) Cytoplasm: It is the fluid content of the cell, which occurs between the plasma membrane and the nuclear envelope. It contains various cell organelles, which perform different functions of the cell.
Functions of Cytoplasm:
(i) Cytoplasm helps in exchange of materials between cell organelles.
(ii) It acts as a store of vital chemicals such as amino acids, glucose, vitamins, ions, etc.
(iii) It is the site of certain metabolic pathways, such as glycolysis, synthesis of fatty acids, nucleotides. Some amino acids are also synthesised in the cytoplasm.
