Cell Theory – Definition , History, Principles, Scientists

Cell Theory - Definition , History, Principles, Scientists , importance explained with example

Define Cell Theory

The cell theory states that the basic unit of structure and function of all living organisms is the cell. All cells arise from pre-existing cells by cell division.

History of Cell theory 

  • In 1838, Matthias Schleiden, a German Botanist, announced that every plant is made up of a large number of cells. He added that each of these cells performed various life processes. 
  • A year later, Theodor Schwann, a German zoologist, made similar discoveries in animals. He declared that all animals and plants are composed of cells, which serve as the units of structure and function. This, in short, is called the Cell Theory, having been proposed by Schwann and Schleiden in the year 1839. 
  • Rudolf Virchow in 1858 made an addition to the cell theory by saying that all cells arise from pre-existing cells.

Also Check – Cell – Structure and Functions

What are the 3 principles of Cell Theory?

According to the cell theory there are 3 Important Principles

  1. The cell is the smallest unit of structure of all living things.
  2. All living organisms are composed of one or more cells.
  3. The cell is the unit of function of all living things.All cells arise from pre-existing cells.

What does The Cell Theory mean?

  • All living things are made up of cells, just as a wall is made up of bricks. 
  • Hence, cells are the basic building blocks of living organisms. They are complex living structures.
  • All cells are similar in their basic structure and function but are not identical. They differ in size and structure.
  • New cells are formed due to division in old cells. The organization of cells in the body of a living organisms determine its structure.
  • The way an organism functions depends on the way the cells work.

Also Check – Parts of Plant Cell – Location , Structure and Functions

Cell Theory Explanation 

To explain Cell Theory  we will take two examples, a Tree such as Peach and an Animal such as a Mouse.

Structural Unit 

  • If we take any part of the body of a Mouse or any part of a Peach tree and examine it under a microscope, it will show a cellular structure.

Functional Unit

  • Any function in the body of the Mouse or in the Peach tree is due to the activity in its cells. For example, movement of the Mouse is due to the contractions of muscle cells, food is digested by the enzymes which the cells of the gut secrete, digested food is absorbed by the cells and absorbed food is used up in cells for various metabolic activities. 
  • In a Peach tree, photosynthesis occurs in the cells of leaves, the root cells absorb water from the soil, and so on. 

Cells Die and are Replaced. 

  • The body of the Mouse, or of the Peach tree, is composed of millions and millions of cells. Many of these cells continuously die and are replaced by new ones which are formed by the division of younger cells. Formation of cells from pre-existing cells is a never-ending chain.

Most life starts as a Single cell

  • The life of the Mouse and the life of the Peach tree started as a fertilized egg and as a seed respectively. The egg was a single cell produced by the cells of the ovary of the mother Mouse. The Peach seed had an embryo (formed after pollination and fertilization) which also started as a single cell in the ovary of the flowers of the parent Peach tree.

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