Life exists from the tiniest of molecules known as cells. These molecules are important to the birth of life that we live today. Without these cells, life won’t be worth living as its forms the basic fundamental part of life.

Cell which gotten from the latin word “cella” means very small is the basic, fundamental, structural, functional biological unit of life. A cell known to be the smallest unit of life replicates independently of itself and they are usually called “the building blocks of life” as life started from them. Cell biology is a term that is used when studying cells.

The cell is made up of cytoplasm which is enclosed in the cell membrane which constitutes biomolecules such as nucleic acids and proteins. Organisms can be grouped into two namely; Unicellular organisms which are composed of only a single cell which includes bacteria and multi cellular cells which is composed of more than one cell which includes animals and plants. The number of cells in plants vary among different species while humans contains more than 10 trillion cells. Plant and animals cells are most visible under an electron microscope with a dimension of between 1 and 100 micrometres.

Cell was first discovered by Robert Hooke in the year 1665 who named it after the resemblance of cells which the Christian monks inhabited. The cell theory was first developed by Matthias Jakob Schleiden and Theodor Schwann in 1839. The cell theory states that “all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms, that all cells come from pre-existing cells, and that all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells”.

The cell is basically made up of two types; the Prokaryotic cells and the eukaryotic cells.

Prokaryotes are organisms which have single cells, while eukaryotes are organisms which have single cells or multi cells.

Prokaryotic cells were the first form of cells on Earth, having important biological processes which includes cell signalling and they are self-sustaining. They are simpler and smaller than eukaryotic cells, and lack membrane-bound organelles such as the nucleus. Prokaryotes include two of the important phases of life; arachaea and bacteria.

A prokaryotic cells has three regions

The cell envelope which is consisted of the plasma membrane which is covered by the cell wall. Bacteria are also further covered by a third layer called the capsule. Though most prokaryotes have both a cell membrane and a cell wall, there are exceptions such as bacteria and archaea which only possess the cells membrane layer. The envelope gives strength to the cell and also separates the interior of the cell from its environment, serving as a protective filter.

Inside the cell is the cytoplasmic region that contains the DNA, ribosomes and other components. The genetic material which is the DNA is freely found in the cytoplasm. Prokaryotes can carry extra chromosomal DNA elements called plasmids, which are usually circular. Though not forming a nucleus, the DNA is condensed in a nucleoid. Plasmids encode additional genes, such as antibiotic resistance genes.

The pili and flagella protect the cell’s surface on the outside. These are not all present in prokaryotes which are usually made of protein that helps in the movement and communication between cells.


Plants, animals, fungi, slime moulds, protozoa, and algae are all composed of the eukaryotic cells. These cells are fifteen times wider than the prokaryotic cells and are a thousand times greater than them in volume.

The main difference between the eukaryotic cells and the prokaryotic cells is that they are compartmentalized in the presence of membrane-bound organelles compartments in which specific metabolic activities takes place. The most important of them all is the cell nucleus which is an organelle that houses the DNA. It is the nucleus that gives the eukaryote its real name meaning true nucleus. Other differences are
• The plasma membrane works in resemblance to that of prokaryotes in function, but with minor differences in the setup. Cell walls may or may not be present.
• The eukaryotic DNA is organized in one or more linear molecules, called chromosomes. These chromosomes are associated with histone proteins. All chromosomal DNA is stored in the cell nucleus which is separated from the cytoplasm by a membrane. Some eukaryotic organelles such as mitochondria also contain some DNA.
• Motile cells of eukaryotes moves using motile cilia or flagella. Motile cells are not present in conifers and flowering plants. Eukaryotic flagella are less complex than those of prokaryotes.


Many cells have structures that exist wholly or partially outside the cell membrane. These structures are important because they are not protected from the external environment by the semipermeable cell membrane. In order to assemble these structures, their components must be carried across the cell membrane by export processes.


Many types of prokaryotic and eukaryotic cell are composed of a cell wall. The cell wall protects the cell mechanically and chemically from its environment, and is an additional layer of protection to the cell membrane. Different types of cell have cell walls made up of different materials; plant cell walls are primarily made up of cellulose, fungi cell walls are made up of chitin and bacteria cell walls are made up of peptidoglycan.

The gelatinous capsule is present in some bacteria outside the cell membrane and cell wall. This capsule present maybe polysaccharide. They are not marked by normal staining procedures but can only be detected by india ink or methyl blue. These markings allows for observations between the cells of higher contrast.

These are organelles that allows the cells to be mobile. The bacterial flagellum stretches from cytoplasm through the cell membrane(s) and extrudes through the cell wall. They are long and thick thread-like appendages, protein in nature. A different type of flagellum is found in archaea and a different type is found in eukaryotes.



Cells grow through cellular metabolism functions in between successive cell divisions. Cell metabolism can be defined as the process by which cells individually process nutrient molecules. Metabolism occurs in two phases namely; Anabolism and Catabolism.

Anabolism is the process by which the cell uses energy to build complex molecules and perform other biological functions. While Catabolism is the process by which cells breaks down complex molecules to produce energy. These complex molecules which are often consumed by organisms are broken down into simpler sugars called monosaccharides such as glucose. When inside the cell, this glucose is broken down to produce adenosine triphosphate(ATP) which is a molecule that produces available energy through different ways.


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