What is cell?
We know that, Life originated as a single cell. Cell is the structural and functional unit of life, except viruses. The "Cell" has been derived from the Latin word "Cellula" meaning a small compartment. All living organisms are made up of cells. It is the basic structural and functional unit of an organism. So, in this article we will discuss about - What is Cell? Types of cell, Cell structure and functions etc.
Cells contain genetic information which is passed on form cell to cell during cell division. Cells are similar in their chemical composition and in their metabolic activity. All cells arise from pre-existing cells. This clearly indicates that a single - celled, organism gave rise to a multicellular organism. Whether it is a plant or an animal, both the organisms grow from a single cell called zygote.
All cells have certain common characteristics such as:
1) Each cell is enclosed by a plasma membrane made up of lipo-proteins.
2) All cells have protoplasm consisting of water and various organic and inorganic substances.
3) Each living cell posseses genetic material which directs and controls the cellular functions.
4) Protein synthesis is an important metabolic function.
5) The protein produced within a cell determines the form and structure of a cell.
6) A cell is an independent unit by itself and has a capacity to duplicate.
7) All cells arise only by division of pre-existing cells.
8) Genetic information is passed on from one generation to the next by the cells through genes.
9) The basic composition of protopalsm of different cells remains same in all organisms.
The microscopic examination of a wide variety of living organisms shows that a cell has a self - contained integrated machinery. It helps the cell to survive, either singly (unicellular) or in groups (multicellular). In unicellular organisms, a single cell has to perform large number of functions to sustain.
In multicellular organisms, however, there is a distinct division of labour which increases the efficiency of the organisms. There are specialised cells to carry out important functions. Living organisms are grouped into two main categories, the
Prokaryotes and Eukaryotes. The Prokaryotes have a simple cellular organization while the Eukaryotes exhibit high degree of organization.
The average diameter of a bacterial cell is about 1um. If a protein molecule has a 10nm diameter, 100 such Molecules will fit end to end in such a cell. The size of most of the cells ranges between 0.5um and 20um. The shape of the cell is also variable depending upon its function, mechanical pressure, environmental conditions, etc.
Prokaryotic cells are usually independent and found in unicellular organisms while Eukaryotic cells are found in multicellular organisms.
Most of the prokaryotic cells have a chemically complex cell envelope. It consists of three basic layers, namely glycocalyx, cell wall and plasma membrane.
Cytoplasm is a semi-fluid ground substance or matrix present inner to the cell membrane. It consists of a variety of inorganic and organic compounds which provide a suitable chemical environment for cellular activities.
The cytoplasmic matrix of a prokaryotic cell posseses dense particles called ribosomes. They are made up of RNA and protein.
The Prokaryotes do not have membrane - bound nucleus. The genetic material consists of a long, double -stranded, circular DNA molecule known as prokaryotic chromosome. It is highly looped and coiled with associated proteins.
The Prokaryotic cell may possess one or more additional molecules of circular DNA or mini chromosomes. This extra chromosomal DNA is called plasmid. Plasmid is autonomous and self-replicating with few genes which provide extra-survial advantage.
Eukaryotic cells generally have dimensions ten times greater than Prokaryotes. The cell wall of eukaryotic cell is thick, strong, rigid and measures 0.1nm to several nm in thickness. The chemical composition of the cell wall differs according to the cell type and function.
Cells contain genetic information which is passed on form cell to cell during cell division. Cells are similar in their chemical composition and in their metabolic activity. All cells arise from pre-existing cells. This clearly indicates that a single - celled, organism gave rise to a multicellular organism. Whether it is a plant or an animal, both the organisms grow from a single cell called zygote.
Characteristics of cells:
All cells have certain common characteristics such as:
1) Each cell is enclosed by a plasma membrane made up of lipo-proteins.
2) All cells have protoplasm consisting of water and various organic and inorganic substances.
3) Each living cell posseses genetic material which directs and controls the cellular functions.
4) Protein synthesis is an important metabolic function.
5) The protein produced within a cell determines the form and structure of a cell.
6) A cell is an independent unit by itself and has a capacity to duplicate.
7) All cells arise only by division of pre-existing cells.
8) Genetic information is passed on from one generation to the next by the cells through genes.
9) The basic composition of protopalsm of different cells remains same in all organisms.
Concept of Unicellular and Multicellular organisms:
The microscopic examination of a wide variety of living organisms shows that a cell has a self - contained integrated machinery. It helps the cell to survive, either singly (unicellular) or in groups (multicellular). In unicellular organisms, a single cell has to perform large number of functions to sustain.
In multicellular organisms, however, there is a distinct division of labour which increases the efficiency of the organisms. There are specialised cells to carry out important functions. Living organisms are grouped into two main categories, the
Prokaryotes and Eukaryotes. The Prokaryotes have a simple cellular organization while the Eukaryotes exhibit high degree of organization.
Types of Cell:
Prokaryotic cell :
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| Prokaryotic cell |
The average diameter of a bacterial cell is about 1um. If a protein molecule has a 10nm diameter, 100 such Molecules will fit end to end in such a cell. The size of most of the cells ranges between 0.5um and 20um. The shape of the cell is also variable depending upon its function, mechanical pressure, environmental conditions, etc.
Prokaryotic cells are usually independent and found in unicellular organisms while Eukaryotic cells are found in multicellular organisms.
1) Cell Envelope:
Most of the prokaryotic cells have a chemically complex cell envelope. It consists of three basic layers, namely glycocalyx, cell wall and plasma membrane.
2) Cytoplasm:
Cytoplasm is a semi-fluid ground substance or matrix present inner to the cell membrane. It consists of a variety of inorganic and organic compounds which provide a suitable chemical environment for cellular activities.
3) Ribosomes:
The cytoplasmic matrix of a prokaryotic cell posseses dense particles called ribosomes. They are made up of RNA and protein.
4) Genetic material :
The Prokaryotes do not have membrane - bound nucleus. The genetic material consists of a long, double -stranded, circular DNA molecule known as prokaryotic chromosome. It is highly looped and coiled with associated proteins.
5) Plasmids:
The Prokaryotic cell may possess one or more additional molecules of circular DNA or mini chromosomes. This extra chromosomal DNA is called plasmid. Plasmid is autonomous and self-replicating with few genes which provide extra-survial advantage.
Eukaryotic cell:
Eukaryotic cells generally have dimensions ten times greater than Prokaryotes. The cell wall of eukaryotic cell is thick, strong, rigid and measures 0.1nm to several nm in thickness. The chemical composition of the cell wall differs according to the cell type and function.
