The Cell – Its Structure, Functions, Parts and Characteristics

What is the cell

The Cell are the smallest functional unit of the body. A cell consist of a plasma membrane inside which are a number of organelles suspended in a watery fluid, called cytoplasm literally small organs have individual and highly specialized functions and are often enclosed in their own membrane within the cytoplasm.

The cell - structure and functions

A human is a multi-cellular animal, the human body consisting of trillions of cell of many different types. masses of similar cells are organized together to from tissues and organs, each of which have special function within the body. thus liver cells are different from kidney cells.

They all have some basic characteristics in common which indicate signs of life whether we consider a single celled organism or a highly developed multi-cellular animal such as a human.


Structure of The Cell / Parts of The Cell

All cells are made of protoplasm, the protoplasm forms the cytoplasm and nucleus. surrounding the cytoplasm is the cell membrane, a thin elastic and highly complex structure composed of proteins and lipids it is a semi permeable membrane containing ‘pores’ that allow the passage of water oxygen carbon-dioxide and some solutes in and out of the cell, and plays a vital part in maintaining the homeostatic balance of cell. basic structure of a cell

The world of the cell (parts of a human cell) is rich and in detail and cytoplasm contains a number of structures, called organelles, which are concerned witch are concerned with a variety of cellular functions. These include parts of a cell and their functions.


The nucleus contains the body’s genetic material, which directs all the metabolic activities of the cell. This consist of 46 chromosomes, which are made from deoxyribonucleic acid (DNA). Except during cell division the chromosomes resemble a fine network of threads called chromatin.


Mitochondria are membranous, sausage-shaped structures in the cytoplasm, some time described as the power house of the cell. They are involved  in the aerobic respiration, the processes by which chemical energy is made available in the cell. small granular structures containing enzymes which extract energy from nutrients and oxygen, in the form of ATP. this energy is made available for cellular activity.

Endoplasmic reticulum

Endoplasmic reticulum is an extensive series of interconnecting membranous canals in the cytoplasm. There are two types smooth and rough.
smooth Endoplasmic reticulum synthesises lipids and steroid hormones.
rough Endoplasmic reticulum is studded with ribosomes.


The granules compound of RNA and protine. They are responsible for protein synthesis in the cell, using RNA as the template.


Lysosomes in white blood cell contain enzymes that digest foreign materiel such as microbes which are useless, or may be harmful to the cell.

Golgi body / apparatus

The golgi body consists of stacks of closely folded flattened membranous sac. it is present in all cells but is larger in fine vesicles, and is especially prominent in secretory cells.


This lies close to the nucleus, and is made up of two centrioles, small structures that play a major role in initiating cell division.

Characteristics of cells

Irritability The cell has the ability to detect, and respond to changes in its environment.

Nutrition Cell is capable of absorbing fluids and dissolved substances directly through the cell membrane, and these can be used by the cell for growth and repair, or to provide energy and heat.

Respiration Cell has the ability to use oxygen combined with food substances to form carbon dioxide and water, whilst releasing energy  for intracellular activity.

Excretion Cell is able to discharge unused and waste materials through the cell membrane.

 Growth and reproduction The cell has the ability to increase in size, and when it reaches the limit of its growth it reproduces by dividing into two smaller cells.

Movement Some cells have the power of movement.

Functions of cell / Transport of substances across cell membranes

By diffusion :-

Molecules of gas and liquids are in constant motion, and tend to spread from a region of high concentration to a region of lower concentration until a uniform mixture is produced. Water, gases and some solutes diffuse easily through a permeable membrane, when the concentration of molecules is higher on one side than the other the molecules will move through the permeable membrane until both the concentrations are equal. Large molecules diffuse more slowly than small ones.

By osmosis :-

Osmosis is the movement of water through a semipermeable membrane, from a solution of low concentration to one of higher concentration. Molecules in solution tend to hold or attract water, this drawing power is known as osmotic pressure. Osmotic pressure is determined by the number of molecules dissolved in a solution, thus the greater the number of molecules in solution the greater its drawing power for water.

By active transport :- 

Some molecules are unable to pass through the cell membrane alone, and these molecules are linked to a special carrier substance in the cell membrane, often under the control of enzymes, and transported through the cell membrane to be released on the other side. The carriers are highly specific and usually only respond to. one type of molecule.

By pinocytosis :-

This is a mechanism by which the cell membrane indents and actually engulfs the substance to be absorbed into the cell.

By phagocytosis :-

This process is similar to pinocytosis, the major diference being that the cell extends pseudopodia to surrdmd and engulf larger particles such as bacteria and foreign material

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