What is a Cell?

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When you look around, you see both living and non-living things. You must have wondered and asked yourself – ‘what is it that makes an organism living, or what is it that an inanimate thing does not have which a living thing has’? The answer to this is the presence of the basic unit of life – the cell in all living organisms.

What makes something living?

Look around you. You may see plants, animals, people, books, tables, and stones. Some of these are living things, while others are non-living things.

Living things, such as humans, animals, and plants, carry out life activities. They grow, use energy, and respond to changes around them. Non-living things, such as rocks and chairs, do not carry out these life activities on their own.

What is a cell?

Imagine building a house with many small bricks. Just as bricks are the basic building blocks of a house, cells are the basic building blocks of living organisms.

The cell is the basic unit of life.

All living organisms are made up of cells. Some organisms, like bacteria, consist of just one cell. Others, like humans, have trillions of cells.

Examples to understand

Plant: It has cells that help it grow and make food.
Human: Our bodies contain many different kinds of cells that help us breathe, digest food, and move.
Stone: It is non-living and does not consist of living cells.

Remember

Cells are the basic structural and functional units of life. They build living organisms and perform essential life activities.

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All organisms are composed of cells. Some are composed of a single cell and are called unicellular organisms while others, like us, composed of many cells, are called multicellular organisms.

Organisms Based on the Number of Cells

All living organisms are made up of cells. But did you know that some organisms have only one cell, while others have millions or even trillions of cells?

1. Unicellular Organisms

The word “uni” means one. Therefore, unicellular organisms are living things made up of just one cell. This single cell performs all the activities needed for the organism to survive, such as obtaining food, using energy, and removing waste.

Examples of unicellular organisms

Amoeba
Paramecium
Bacteria
Yeast

Imagine a tiny living organism doing everything necessary to stay alive using just one cell!

2. Multicellular Organisms

The word “multi” means many. Multicellular organisms are living things made up of many cells. Different cells perform different jobs, working together to keep the organism alive.

Examples of multicellular organisms

Humans
Dogs
Birds
Trees

For example, in the human body, muscle cells help us move, nerve cells carry messages, and red blood cells carry oxygen.

Difference Between Unicellular and Multicellular Organisms

Feature	Unicellular	Multicellular
Number of cells	One	Many
Examples	Amoeba, bacteria	Humans, trees
Cell activities	One cell performs all essential life activities	Different cells perform specialised jobs

Remember for NEET

Unicellular organisms consist of a single cell, whereas multicellular organisms consist of many cells. In multicellular organisms, cells may become specialised to perform different functions.

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Unicellular organisms are capable of (i) independent existence and (ii) performing the essential functions of life. Anything less than a complete structure of a cell does not ensure independent living. Hence, cell is the fundamental structural and functional unit of all living organisms.

Why Is the Cell the Fundamental Unit of Life?

Imagine a tiny organism called Amoeba. It consists of just one cell, but that single cell can obtain food, produce energy, remove waste, grow, and reproduce. It can live independently without needing to be part of a larger organism.

1. Independent Existence

Independent existence means being able to live on your own. Unicellular organisms, such as Amoeba and Paramecium, can survive independently because their single cells carry out all the essential activities needed for life.

Example: Amoeba

Amoeba is made up of only one cell. That cell obtains food, digests it, removes waste, and performs other essential life functions.

2. Essential Functions of Life

Every living organism must perform certain activities to stay alive. These include:

Nutrition: Obtaining and using food.
Respiration: Releasing energy from food.
Excretion: Removing waste materials.
Growth: Increasing in size or developing.
Reproduction: Producing new organisms.

A complete living cell has the structures needed to carry out essential life processes. A smaller part of a cell, such as a cell organelle, cannot normally live independently and perform all these functions.

Why Must a Cell Be Complete?

Think of a cell as a small factory. Different parts perform different jobs, such as producing energy and making proteins. These parts work together to keep the cell alive.

If we take only one part of the factory, it cannot perform every job needed to run the entire factory. Similarly, an individual cell part generally cannot perform all the functions required for independent life.

Fundamental Structural and Functional Unit

Structural unit: Cells form the bodies of all living organisms.

Functional unit: Cells carry out the essential activities necessary for life.

Remember for NEET

The cell is called the fundamental structural and functional unit of life because it forms the basic building block of living organisms and carries out essential life processes.

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Antonie Von Leeuwenhoek first saw and described a live cell. Robert Brown later discovered the nucleus. The invention of the microscope and its improvement leading to the electron microscope revealed all the structural details of the cell.

Discovery of Cells and the Development of Microscopes

Have you ever wondered how scientists discovered something as tiny as a cell when we cannot see most cells with our naked eyes? The answer is the microscope! Scientists developed better microscopes over time, allowing them to observe cells and their internal structures in greater detail.

1. Antonie van Leeuwenhoek

Antonie van Leeuwenhoek was a scientist who used a simple microscope to observe living microorganisms. He was the first to observe and describe living cells and tiny living organisms using a microscope.

Remember

Antonie van Leeuwenhoek — first to observe and describe living cells.

2. Robert Brown

Robert Brown was a botanist who discovered the nucleus in plant cells in 1831. The nucleus is an important cell structure that contains most of the genetic material in eukaryotic cells and helps control cellular activities.

Remember

Robert Brown — discovered the nucleus in 1831.

3. Development of the Microscope

Early microscopes allowed scientists to see cells, but many internal structures were too small to observe clearly. As microscopes improved, scientists could study cells in greater detail.

The electron microscope was a major advancement. It uses a beam of electrons instead of visible light and can reveal much smaller structures than a conventional light microscope.

Light Microscope vs Electron Microscope

Light microscope: Uses visible light to observe cells and some of their structures.
Electron microscope: Uses electrons to reveal much finer details of cellular structures.

How These Discoveries Helped Biology

These scientific discoveries helped us understand that cells contain different structures, each performing particular functions. Modern microscopes have made it possible to study organelles such as mitochondria, ribosomes, and the endoplasmic reticulum in much greater detail.

Important Facts for NEET

Antonie van Leeuwenhoek: First to observe and describe living cells.
Robert Brown: Discovered the nucleus in 1831.
Electron microscope: Reveals fine details of cellular structures because of its high resolving power.