Cell Biology: Complete Notes for NEET by PW

The cell is the basic structural and functional unit of life, making it one of the fundamental concepts in Biology. Understanding cell structure, cellular functions, the history of cell discovery, and the differences between unicellular and multicellular organisms helps build a foundation for further topics in Class 11 Biology.

PW brings you the  Cell Biology One Shot Video, which introduces the Botany preparation plan and syllabus before moving into cell biology. The session covers the introduction to the cell and cell theory, helping you begin your Biology preparation with the fundamental concepts required for further learning. Use these notes alongside the video to revise the basics, remember important contributions and strengthen your understanding of the topics covered.

Cell: The Structural And Functional Unit Of Life

A cell is defined as the basic structural and functional unit of life.

Cell As A Structural Unit

Cells form the body structure of living organisms. A simple comparison is:

Brick is to house as cell is to living organism.

A house is made by arranging many bricks. Similarly, the body of a multicellular organism is formed by the organisation of many cells. The human body contains trillions of cells and approximately 200 different cell types.

Examples include cells of the:

• Eye

• Skin

• Buccal cavity

• Liver

• Kidney

• Lungs

• Stomach

• Intestine

Cell As A Functional Unit

Cells are called functional units because metabolic reactions and other body functions occur within them. Digestion, energy production, chemical conversion, and other cellular activities depend on cell function.

A complete cell is required for independent life. Anything smaller than a complete cell cannot be called living under this framework.

Unicellular And Multicellular Organisms

Organisms are classified according to the number of cells in their bodies.

In a unicellular organism, one cell performs nutrition, digestion, energy production, reproduction, and other life processes. Therefore, the organism can survive independently.

In multicellular organisms, specialised cells and organs perform different tasks. For example, the stomach helps in digestion, the kidneys help in excretion, and the heart supports circulation. This arrangement is called division of labour.

Discovery Of The Cell

Robert Hooke

Robert Hooke observed cork from an oak plant in 1665 using a simple microscope. He saw empty, box-like compartments and named them cellulae. The modern term cell was derived from this word.

Hooke observed dead cells because the cork tissue had lost its protoplasm. The cell walls remained visible.

He also described his observations in the book Micrographia.

Anton Van Leeuwenhoek

Anton van Leeuwenhoek later observed living and motile microscopic forms. He used a combination of lenses and observed organisms such as protozoans, sperm cells, and motile bacteria.

He called these moving, animal-like forms animalcules.

Robert Brown

In 1831, Robert Brown discovered the nucleus. The nucleus is called the brain of the cell because it controls cellular activities.

Memory Tip: Hooke means cell, Leeuwenhoek means living cell, and Brown means the brain of the cell, or nucleus.

Microscopy And Electron Microscopy

Microscopy developed through several stages:

1. Simple microscopy

2. Compound microscopy

3. Light microscopy

4. Phase-contrast microscopy

5. Electron microscopy

Electron microscopy uses an electron beam and provides greater magnification and detail. Its major advancement after 1950 made structures such as ribosomes, the endoplasmic reticulum, and the cell membrane easier to study.

Metabolism: An Important Biological Process

Metabolism refers to the chemical reactions occurring inside the body.

For example:

• Starch in potato is digested into glucose.

• Glucose is oxidised.

• Oxidation produces ATP.

• ATP supplies energy for body functions.

Memory Tip: Starch, glucose, oxidation, ATP, and energy form the basic sequence.

Metabolic reactions are of two types:

Types of Organisms Based on the Number of Cells

Organisms are classified into two categories based on the number of cells present in their bodies.

Unicellular Organisms

Unicellular organisms have bodies made up of only one cell.

Examples

• Bacteria

• Amoeba

• Paramecium

• Yeast

Characteristics:

• Their entire body consists of a single cell.

• The single cell performs all essential functions of life.

• They can perform these functions and survive independently.

Multicellular Organisms

Multicellular organisms have bodies made up of more than one cell.

Examples 

• Humans

• Cockroaches

• Complex plants

• Other animals

Characteristics:

• Their bodies contain multiple cells.

• Different cells perform different functions.

• They show a division of labour, in which work is distributed among different cells, organs and organ systems.

For example, the digestive system performs digestion, the respiratory system performs respiration, and the circulatory system supports blood circulation.

Difference Between Unicellular and Multicellular Organisms

Electron Microscopy and Its Importance

Electron microscopy is an advanced microscopic technique that uses electron beams to magnify objects and reveal fine structural details.

Major advancements in electron microscopy occurred during the 1950s, allowing scientists to observe cellular structures in greater detail.

Important points:

• Electron microscopy provides greater magnification and reveals finer details of cells.

• Its advancement helped scientists understand cellular structures that were not clearly visible earlier.

• Consider the following structures as examples:

• Ribosomes

• Endoplasmic reticulum

• Cell membrane

Quick Revision: Important Scientists and Their Contributions

Important Points for NEET Revision

• The cell is the structural and functional unit of life.

• Robert Hooke observed dead cells in cork in 1665.

• Micrographia was written by Robert Hooke.

• Anton van Leeuwenhoek is credited with the first observation of living cells.

• Animalcules is the term associated with Anton van Leeuwenhoek.

• Robert Brown discovered the nucleus in 1831.

• Unicellular organisms consist of one cell and can perform all essential life functions through that cell.

• Multicellular organisms show a division of labour among different cells.

• Electron microscopy uses electron beams and helps reveal fine cellular structures.

• The 1950s were an important period of advancement in electron microscopy.

Watch the first free Botany class from PW Arjuna NEET 2.0 2027 to understand the preparation plan, get introduced to the syllabus and begin learning about cells and cell theory.

Topics covered in the video:

• Botany preparation plan

• Introduction to the syllabus

• Introduction to the cell

• Cell theory

A clear understanding of the Botany preparation plan and syllabus can help you start your NEET 2027 journey with greater confidence. Revising foundational concepts such as the cell and cell theory will also prepare you for further Biology topics. Watch the first free Botany class from PW Arjuna NEET 2.0 2027 and use PW's learning resources to support your NEET preparation.

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