Meaning Of A Cell, History And Theory

Hi, welcome to this blog on the meaning of a cell, history and theory.

Table Of Contents

1. Meaning of a cell
2. Classification of living organisms based on the number of cells
3. History of the cell
4. The cell theory.
5. Revision question.

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Cell As Living Unit Of An Organism

Meaning of a cell: The cell is defined as a structural and functional unit of a living organism. In other words, the cell is the simplest, the smallest and basic unit of life. All living things (plants and animals) are made of cells.

The cell is regarded as the basic unit of all living things because it can carry out all life activities such as feeding, reproduction, excretion, growth, adaptation, respiration, definite lifespan, sensitivity and movement. All these activities possessed by a cell are Characteristics of living things.

Classification of living organisms based on the number of cells

Living organisms are classified into two major groups based on the number of cells. These groups are:

1. Unicellular or accelular organisms: These are organisms which consists of only one cell.

Examples of unicellular organisms are:

• Amoeba
• Chlamydomonas
• Euglena
• Paramecium

2. Multicellular organism: These are organisms which consists of two or more cells. In other words, these organisms have many cells.

Examples of multicellular organisms are:

• Volvox
• Hydra
• Spirogyra
• Flowering plants
• Fish
• Bird
• Man.

History Of The Cell

Many scientist contributed to the history of the cell. Among the scientists are:

1. Robert Hooke, An English scientist could be seen as the father of cells. He was the first human being to discover honey-comb structure of the cell in 1665. In his book, micrographia, he described his observations of a magnified thin slice of a cork of an oak tree. He established that the cork is made up of thin component or rooms. He then named the component cells.
2. Felix Dujarding, A French biologist in 1835 discovered that the cell was made up of living substance. He however name the Living substance protoplasm.
3. Matthias Schleiden, A German botanist in 1838 revealed that the bodies of plants are made up of cells which were described as units of life.
4. Theodore Schwann, Another German zoologist in 1839 also discovered that the body of all animals are composed of cells. The discoveries of Schleiden and Schwann led to the postulation of the cell theory in 1839.
5. Rudolph Von Virchow, A German biologist in 1855 concluded in his research that all cells come from previous existing cells.

The Cell Theory

The cell theory states that:

• The cell is the structural and functional unit of life.
• All living organisms are made up of cells.
• All cells come from previously existing cells.
• There is no life apart from the life of cells.
• All living things are either single cell (unicellular) or group of cells (multicellular).

Revision Questions

1. What is the meaning of a cell?
2. Explain the forms in which living cells exist and give an example in each case.
3. Briefly describe the history of the cell.
4. (a) Explain briefly the cell theory (b) Name two scientist who contributed to the development of the set theory.