What Is Cell and Cell Theory:
Here in this article, we will explain the question What is cell and Cell Theory in very detail and easy way. Students from all over the world search to find the good definition of a cell, Cell Theory and here their searches end. So take a sit, be concentrate and let's start.
What is cell:
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| What is cell |
cell is the basic unit of life. A cell is the basic structural and functional unit of all living organism. Cells are the building blocks of the body providing structure for the body tissue and organs, Ingesting nutrients and convert them into energy for the body.
Main parts of a cell:
1. Cell wall:
A plant cell is surrounded by a wall called cell wall. A cell wall is not living and is secreted by protoplasm. It is freely permeable it allows all soluble substance to pass freely.
A cell wall is composed of three main layers.
a.Middle Lamella:
The Middle lamella is composed of pectin in the form of calcium pectate. It does not contain cellulose. Middle lamella is the first formed layer and is present between the Primary wall of the adjacent Cells
b.Primary Wall:
On either side of the middle lamella, cellulose is deposited forming the primary wall. Cellulose is the principal structural component of the primary cell wall. It also contains pectic substances and lignin. Primary wall is the true wall. The cellulose is arranged in a cross manner.
c. Secondary wall:
It is formed inside the primary wall. It is much thicker than the primary wall. It consists of cellulose, Silica, Waxes, Lignin etc. It gives strength to the wall.
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| Cell wall |
Functions Of Cell Wall:
The different functions of cell wall are given below.
- Cell wall gives definite shape to the cell.
- It protects the living protoplasm
- It gives strength and rigidity to the plant cell.
- As it is permeable therefore it helps in the transport of materials across the membrane.
2. Cell membrane:
It is also known as Plasma membrane. It is found in all cells. It surrounds the cytoplasm and is thin, elastic and semi-permeable in nature. According to the fluid mosaic model, Cell membrane is composed of lipids and proteins. A cell membrane is a lipid bilayer membrane as two lipid layers are found at the center.
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| Cell membrane |
Fluid Mosaic Model:
S.J Singer and G.L Nicolson in 1972 proposed a model to explain the structure of the plasma membrane. This model is accepted today and is called Fluid mosaic model.
This model states that cell membrane is composed of Lipid bilayer in which proteins molecules float in the sea of lipids. While some stay embedded in the membrane.
The proteins are confined to the surface of the membrane but are distributed in a mosaic pattern. There are two types of proteins in the Plasma membrane.
Extrinsic proteins: Present on the surface.
Intrinsic Proteins: Located within the lipid bilayer.
Function Of Plasma Membrane:
- Cell membrane gives shape to the cell.
- It gives protection and mechanical strength to the cell.
- It helps in the inflow and outflow of materials.
- It acts as a receptor to recognize hormones, neurotransmitter, and chemicals.
3. Cytoplasm:
Cytoplasm lies between the plasma membrane and the nuclear membrane. It is viscous and translucent. It contains a number of cell organelles, Insoluble waste products, and storage products.
The soluble part of the cytoplasm is called cytosol. Chemically cytosol is composed of about 90% water. Cytosol may be in the form of sol or gel.
Sol is a nonviscous state while Gel is vicious.
Functions Of Cytoplasm:
Cytoplasm has the following main functions.
- Cytoplasm acts as a storehouse of vital chemicals.
- Glycolysis occurs in the cytoplasm of a cell.
- It contains cytoplasmic organelles which are important for the proper function of a cell.
4. Nucleus:
A nucleus is also called Heart of the cell. It is surrounded by a double nuclear membrane. The protoplasm of the nucleus is called Nucleoplasm. The nuclear membrane is semipermeable in nature.
The Eukaryotic cell has two distinct structures in the nucleus.
Chromosomes:
Waldyer in 1876 discovered chromosomes. The chromosomes are elongated thread-like structures visible clear during cell division.
Chromosomes are composed of DNA and Proteins(Histones). Gene which is the hereditary units is located on chromosomes. A number of chromosomes are constant for each species.
For example, Chromosomes number in chicken is 78, In horses is 64, in tobacco is 48, inhuman is 46 and fruit fly is 8.
Nucleolus:
The nucleolus is dark-staining bodies one or more nuclei per nucleus. They are composed of DNA and Proteins. They are concerned with the synthesis of ribosomal RNA.
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| Cell nucleus |
Function Of Nucleus:
- The nucleus contains Hereditary information in the form of genes.
- Nucleus control all the activities of the cell.
- A cell without a nucleus has a very short lifespan. For example, RBCs live only about 120 days.
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Cell Theory:
Cell theory was formulated by T. Schwann and M.Schleiden in 1838.
The main point of cell theory are:
- All living organism is composed of one or more cells.
- The cell is the basic structural and functional unit of life.
- New cell arises from pre-existing cells by division.
Emergence Of Cell Theory:
Discovery of a cell is directly related to the invention of the microscope. In 1965 Robert Hooke examined the piece of cork made up of oak bark under a microscope. He published his research in his famous publication "Micrographia". He examined small chambers in the piece of Croke and named these chambers as Cells.
A French Botanist H.Dutrochel in 1824 confirmed Hook's observations. Another biologist Robert Brown discovered Nucleus in the cell of orchids in 1831. And then two German biologists Schwan and Schleiden put forward the Cell Theory.
A German pathologist Rudolf Virchow in 1855 gave the statement that " Every cell comes from a cell ". The word cellula was used.
Louis Pasture in 1862 gave experimental proof for Virchow's hypothesis. He used that bacteria could be formed only from existing bacteria.
These results lead to the emergence of cell theory.
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