Cell: Structural and Functional Unit of Life

All living things are made up of cells, which are the smallest building blocks of life. Just like a book is made up of letters, words, and sentences, living things are organised in levels: cells → tissues → organs → organ systems → organism. Every living thing uses cells to carry out all the activities that keep it alive.

Organelles together constitute the basic unit called the cell. The cell is the basic structural, functional, and biological unit of all known organisms and the study of cells is called cell biology. A cell is the smallest unit of life. Robert Hooke was the first to discover cells.

• All organisms are composed of cells, either unicellular (one cell) or multicellular (many cells). Mycoplasmas are the smallest known cells.
• Cells act as the building blocks of all living beings, providing structure and converting nutrients into energy.
• Cells vary in complexity, shape, and size, performing various functions in organisms. Different shapes and sizes of cells are similar to the way bricks form buildings.
• Cells are the lowest level of organisation in all life forms. The number of cells varies from organism to organism; humans have more cells than bacteria.
• Cells contain various organelles that carry out specialised life processes. Each cell organelle has a specific structure and function. Hereditary material is also contained within cells.

The smallest cell in the human body is the sperm cell. The largest cell in the human body is the egg cell (ovum). The longest cell is the nerve cell. The largest cell is the egg cell of the ostrich.

1. Robert Hooke (1665): He looked at a thin piece of cork under a microscope and saw small compartments that looked like a beehive. He called these "cells," which comes from the Latin word meaning “small room.”
2. Anton Van Leeuwenhoek later used a more advanced microscope with higher magnification and observed cell motility, concluding these entities were alive and naming them "animalcules."
3. In 1833, Robert Brown, a Scottish botanist, described the nucleus in orchid cells, providing initial insights into cell structure.
4. M.J. Schleiden & Theodore Schwann (1838): They said that all living things are made of cells, and cells are the basic building blocks of life.
5. Rudolph Virchow (1885): He stated that new cells come from existing cells, meaning cells divide to make new ones.