Class 9 Biology: The Fundamental Unit of Life – Cell
IntroductionThe cell is the basic structural and functional unit of life. Every living organism is made up of cells. Some organisms, such as bacteria, consist of a single cell, while plants and animals are made up of millions of cells.In this chapter, we will learn about the structure of a cell, different cell organelles, their functions, and the differences between plant and animal cells.
Discovery of the Cell
The cell was first observed by Robert Hooke in 1665.He observed a thin slice of cork under a microscope and noticed many small box-like structures. He called these structures cells because they looked like small rooms.Important PointRobert Hooke → Discovered and named the cell in 1665.
Types of Organisms Based on Number of Cells
Living organisms can be divided into two groups:
1. Unicellular Organisms
Organisms made up of only one cell are called unicellular organisms.Examples:AmoebaParameciumBacteriaYeastA single cell performs all the necessary life processes.
cell, in biology, the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed. A single cell is often a complete organism in itself, such as a bacterium or yeast. Other cells acquire specialized functions as they mature. These cells cooperate with other specialized cells and become the building blocks of large multicellular organisms, such as humans and other animals.
Although cells are much larger than atoms, they are still very small. The smallest known cells are a group of tiny bacteria called mycoplasmas; some of these single-celled organisms are spheres as small as 0.2 μm in diameter (1μm = about 0.000039 inch), with a total mass of 10−14 gram—equal to that of 8,000,000,000 hydrogen atoms. Cells of humans typically have a mass 400,000 times larger than the mass of a single mycoplasma bacterium, but even human cells are only about 20 μm across. It would require a sheet of about 10,000 human cells to cover the head of a pin, and each human organism is composed of more than 30,000,000,000,000 cells.
This article discusses the cell both as an individual unit and as a contributing part of a larger organism. As an individual unit, the cell is capable of metabolizing its own nutrients, synthesizing many types of molecules, providing its own energy, and replicating itself in order to produce succeeding generations. It can be viewed as an enclosed vessel, within which innumerable chemical reactions take place simultaneously. These reactions are under very precise control so that they contribute to the life and procreation of the cell. In a multicellular organism, cells become specialized to perform different functions through the process of cell differentiation. In order to do this, each cell keeps in constant communication with its neighbors. As it receives nutrients from and expels wastes into its surroundings, it adheres to and cooperates with other cells. Cooperative assemblies of similar cells form tissues, and a cooperation between tissues in turn forms organs, which carry out the functions necessary to sustain the life of an organism.
‘Illegal, unauthorised’: Election Commissioners objected to Form 6 change
The section itself was not marked mandatory, but applicants could not proceed to submit the form without answering it.Written by: Ritika Chopra5 min readNew DelhiUpdated: Sep 25, 2026 11:15 AM ISTOn July 12, The Indian Express first reported on the new declaration in Form 6 on the Commission's ECINet portal. (File photo)Make us preferred source on Google5The change is “illegal,” “unauthorised,” it needs to be sent to the Government…it must be removed immediately so that young, first-time voters are not harassed. The warning by the two Election Commissioners couldn’t have been clearer — and yet it was ignored.The change brought questions related to SIR into Form 6, the form new voters have to fill. It asked applicants to choose one of three statements: whether their name appeared in electoral roll during the last SIR held in the early 2000s, whether the name of a parent or grandparent appeared in that roll, or whether neither their name nor that of their parents appeared in it.
On July 12, The Indian Express first reported on the new declaration in Form 6 on the Commission’s ECINet portal. On August 13, referring to The Indian Express report, Sandhu wrote to the Deputy Election Commissioner and the Director General in charge of IT, with Chief Election Commissioner Gyanesh Kumar and Joshi copied on the note.Also read | What Election Commission rift reveals: Cloud over its conductSandhu recalled Joshi’s May 16 note, with which he had agreed, that Form 6 was a statutory form embedded in the rules and could not be changed without approval from the competent authority — meaning, the Government.“In spite of these very clear views expressed by two Election Commissioners,” Sandhu wrote, the “unauthorised/ illegal changes in Form-6 on the portal” had not been removed and the original form had not been restored. The changes “must be removed immediately so that young and would-be first time voters, who are otherwise eligible, can register themselves as voters as per law, without any harassment”, he wrote.What the addition meansThe right to vote belongs to the individual: a person qualifies by age, citizenship and residence, not by whether their parents made it through the last revision. And, in a deeply contested SIR where over 13 crore people have already been dropped from the list, inserting such a question puts a shadow on their children as well.
Sandhu recalled Joshi’s May 16 note, with which he had agreed, that Form 6 was a statutory form embedded in the rules and could not be changed without approval from the competent authority — meaning, the Government.“In spite of these very clear views expressed by two Election Commissioners,” Sandhu wrote, the “unauthorised/ illegal changes in Form-6 on the portal” had not been removed and the original form had not been restored. The changes “must be removed immediately so that young and would-be first time voters, who are otherwise eligible, can register themselves as voters as per law, without any harassment”, he wrote.What the addition meansThe right to vote belongs to the individual: a person qualifies by age, citizenship and residence, not by whether their parents made it through the last revision. And, in a deeply contested SIR where over 13 crore people have already been dropped from the list, inserting such a question puts a shadow on their children as well.