Class 11 Chapter 8

Test your Knowledge

question 1 of 5

Which organelle is known as the powerhouse of the cell?

1.Nucleus

2.Ribosome

3.Golgi apparatus

4.Mitochondria

Cell Structure and Function

The cell is the basic structural and functional unit of life. All living organisms, from the smallest bacteria to complex multicellular organisms like humans, are made up of cells. Cells can exist as independent units of life (in unicellular organisms) or as building blocks of more complex structures (in multicellular organisms).

1.0Cell: The Unit of Life

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

Cell Theory

Proposed by Schleiden and Schwann Schleiden
All plants are made up of different types of cells, which form cells.
Schwann: The bodies of animals are composed of cells and cell products.
Schleiden and Schwann were not able to describe how new cells were formed.

Shape of Eukaryotic Cell

Prokaryotic Cells

The prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO (Pleuro Pneumonia Like Organisms).
They are generally smaller and multiply more rapidly than the eukaryotic cells.
They may vary greatly in shape and size.
The four basic shapes of bacteria are bacillus (rod like), coccus (spherical), vibrio (comma shaped) and spirillum (spiral).

Eukaryotic Cells

The eukaryotes include all the protists, plants, animals and fungi.
In eukaryotic cells there is an extensive compartmentalisation of cytoplasm through the presence of membrane bound organelles.
,s possess an organised nucleus with a nuclear envelope.
In addition, eukaryotic cells have a variety of complex locomotory and cytoskeletal structures. Their genetic material is organised into chromosomes.

Also check: Structure of prokaryotic and eukaryotic cells

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NEET Biology

Class 11 Chapter 8

Class 11 Chapter 8: Cell – The Unit of Life

The Cell – The Unit of Life chapter introduces the cell as the basic structural, functional, and biological unit of all living organisms. It explains the discovery of cells, cell theory, prokaryotic and eukaryotic cells, cell envelope, and the structure and functions of various cell organelles such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, plastids, ribosomes, vacuoles, and the cytoskeleton. This chapter builds the foundation for understanding cell biology and is one of the highest-weightage chapters in NEET Biology, with numerous questions directly based on NCERT diagrams, organelle functions, and cellular comparisons.

At ALLEN, these revision notes simplify Cell – The Unit of Life through concise explanations, NCERT-based facts, labelled diagrams, comparison tables, and exam-oriented revision points. These notes help students develop conceptual clarity and prepare effectively for NEET and CBSE Board examinations.

1.0Chapter Snapshot

Parameter	Details
Chapter Type	Cell Biology
Difficulty Level	Moderate
Revision Time	4–5 Hours

2.0Related Supporting Resources

Resource	Status
Chapter Mock Test Paper
Chapter Mock Test Paper Solutions
Cell The Unit of Life Practice Paper with Solution
Cell Cycle and Cell Division Practice Paper with Solution

Test your Knowledge

question 1 of 5

Which organelle is known as the powerhouse of the cell?

1.Nucleus

2.Ribosome

3.Golgi apparatus

4.Mitochondria

Must-Revise Concepts

Cell membrane

Cell organelles structure and function

Cell Structure and Function

Centrioles (Ultrastructure and Function)

Cilia

Cytoskeleton

Endomembrane system

Endoplasmic reticulum

Plant cell and animal cell

Plasma membrane structure

Sequence of developmental processes in a plant cell

Structure of prokaryotic and eukaryotic cells

Cell Structure and Function

The cell is the basic structural and functional unit of life. All living organisms, from the smallest bacteria to complex multicellular organisms like humans, are made up of cells. Cells can exist as independent units of life (in unicellular organisms) or as building blocks of more complex structures (in multicellular organisms).

1.0Cell: The Unit of Life

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

Cell Theory

Proposed by Schleiden and Schwann Schleiden
All plants are made up of different types of cells, which form cells.
Schwann: The bodies of animals are composed of cells and cell products.
Schleiden and Schwann were not able to describe how new cells were formed.

Shape of Eukaryotic Cell

Prokaryotic Cells

The prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO (Pleuro Pneumonia Like Organisms).
They are generally smaller and multiply more rapidly than the eukaryotic cells.
They may vary greatly in shape and size.
The four basic shapes of bacteria are bacillus (rod like), coccus (spherical), vibrio (comma shaped) and spirillum (spiral).

Eukaryotic Cells

The eukaryotes include all the protists, plants, animals and fungi.
In eukaryotic cells there is an extensive compartmentalisation of cytoplasm through the presence of membrane bound organelles.
,s possess an organised nucleus with a nuclear envelope.
In addition, eukaryotic cells have a variety of complex locomotory and cytoskeletal structures. Their genetic material is organised into chromosomes.

Also check: Structure of prokaryotic and eukaryotic cells

Plasma Membrane/Cell Membrane

Selective permeable
Structure of cell membrane : For study of cell membrane, mature RBCs of mammals are used
Fluid mosaic model : By singer and Nicolson Irregular (mosaic) arrangement of proteins
Lipid : Quasi fluid nature

Cell wall : Non living, rigid structure Outer covering in plant, fungi and bacteria

Functions :

Provide shape to the cell
Protection from mechanical damage and infection
Barrier to undesirable macromolecules
Cell-to-cell interaction

Endomembrane System

Organelle	Structure	Function
Endoplasmic Reticulum (ER)	Network of membranes (Rough & Smooth)	Rough ER: protein synthesis; Smooth ER: lipid synthesis, detoxification
Golgi Apparatus	Stack of flattened membrane sacs	Modifies, sorts, packages proteins and lipids into vesicles
Lysosomes (mainly animal cells)	Membrane-bound vesicles with enzymes	Break down waste, damaged organelles, and foreign substances
Vacuoles	Fluid-filled sacs	Store nutrients, waste products; large central vacuole in plant cells

Mitochondria

Number, shape, size and structure are variable
Sausage like or cylindrical shape
Site of aerobic respiration
Produce ATP, power house of cell
Divide by fission

Plastids

Plastids are found in all plant cells and in euglenoides.
These are easily observed under the microscope as they are large.
They bear some specific pigments, thus imparting specific colours to the plants.
Based on the type of pigments, plastids can be classified into chloroplasts, chromoplasts and leucoplasts.

Ribosomes

Ribosomes are the granular structures first observed under the electron microscope as dense particles by George Palade (1953).
They are composed of ribonucleic acid (RNA) and proteins and are not surrounded by any membrane.

Cytoskeleton

An elaborate network of filamentous proteinaceous structures consisting of microtubules, microfilaments and intermediate filaments present in the cytoplasm is collectively referred to as the cytoskeleton.
The cytoskeleton in a cell are involved in many functions such as mechanical support, motility, maintenance of the shape of the cell

Nucleus - Robert Brown : Discovery of the nucleus

Flemming : Gave the chromatin term, staining of nuclear material by basic dyes
Nuclear envelope : Two parallel discontinuous membranes with a perinuclear space of 10-50 nm
Barrier in between the cytoplasm and the nucleoplasm
Nuclear pore : Passage for movement of proteins and mRNA in both directions between the nucleus and the cytoplasm.
Nucleolus : Content of nucleolus is continuous with rest of the nucleoplasm because it is a membrane-less structure
Nucleoplasm : Nuclear matrix Contains Nucleolus and chromatin Site of active rRNA synthesis
Chromatin : Extended and elaborate network of nucleoprotein fibres in interphase nucleus.

1.0Biomolecules

Biomolecules are the organic and inorganic molecules present in living organisms that are essential for life.
They are mostly carbon-based compounds.

Types of Biomolecules

Biomolecules are classified into 4 major types:

Carbohydrates (Sugars)

Elements: C, H, O
Function: Provide energy and structural support.
Monosaccharides: Simple sugars (e.g., glucose, fructose)
Disaccharides: Two monosaccharides joined (e.g., sucrose = glucose + fructose)
Polysaccharides: Many monosaccharides (e.g., starch, cellulose, glycogen)

Proteins

Proteins are polypeptides
They are linear chains of amino acids linked by peptide bonds. Each protein is a polymer of amino acids.
As there are 20 types of amino acids (e.g., alanine, cysteine, proline, tryptophan, lysine, etc.), a protein is a heteropolymer and not a homopolymer.
A homopolymer has only one type of monomer repeating ‘n’ number of times.
Hence, dietary proteins are the source of essential amino acids.
Therefore, amino acids can be essential or non-essential. The latter are those which our body can make, while we get essential amino acids through our diet/food.

Lipids

Fats: Glycerol + Fatty acids (saturated or unsaturated)
Phospholipids: Found in cell membranes
Steroids: Hormones like testosterone, cholesterol

Nucleic Acids

Types: DNA and RNA
Building Blocks: Nucleotides (Sugar + Phosphate + Nitrogenous base)
DNA: A, T, G, C
RNA: A, U, G, C

Enzymes

Enzymes are biocatalysts.
Almost all enzymes are proteins.
Some enzymes are nucleic acids (RNA), called Ribozymes.
Enzymes can be depicted by a line diagram.
Any enzyme like any protein has the primary, secondary & tertiary structure.
The catalytic structure of most of the enzymes is tertiary.
Inorganic catalysts work efficiently at high temperatures and high pressures

Factors Affecting Enzyme Activity

2.0Cell Cycle and Cell Division

The cell cycle and cell division are fundamental processes by which cells grow, replicate their DNA, and divide to produce new cells.
These processes are essential for growth, development, repair, and reproduction in living organisms.

Phases of Cell Cycle

A typical eukaryotic cell cycle is illustrated by human cells in culture.
These cells divide once every 24 hours.
However, this duration of cell cycle can vary from organism to organism and also from cell type to cell type.
Yeast, for example, can progress through the cell cycle in only about 90 minutes.
The cell cycle is divided into two basic phases:
Interphase
M Phase (Mitosis phase)
G₁ phase (Gap 1)
S phase (Synthesis)
G₂phase (Gap 2)

3.0Mitosis – Cell Division in Somatic (Body) Cells

Definition:
Mitosis is a type of cell division that results in two identical daughter cells, each having the same number of chromosomes as the parent cell.

Stages of Mitosis

Stage	Events
Prophase	Chromosomes become visible as they condense. The nuclear envelope disappears. Spindle fibers start to form.
Metaphase	Chromosomes line up in the middle (metaphase plate). Spindle fibers attach to centromeres.
Anaphase	Sister chromatids are pulled apart to opposite poles of the cell.
Telophase	Two new nuclei form. Chromosomes de-condense. The nuclear envelope reappears.

Cytokinesis

Division of the cytoplasm.
In animal cells: cell membrane pinches in.
In plant cells: a cell plate forms.

Meiosis – Cell Division in Sex Cells (Gametes)

Meiosis is a type of cell division that reduces the chromosome number by half and produces 4 genetically different haploid cells (gametes like sperm and egg). It's used for:
Sexual reproduction
Maintaining chromosome number across generations
Genetic variation

Meiosis Happens in Two Parts

Meiosis I – Reduction division (chromosome number is halved)

Stage	Events
Prophase I	Chromosomes condense. Homologous chromosomes pair up and exchange genetic material (crossing over) → genetic variation.
Metaphase I	Homologous pairs line up at the center.
Anaphase I	Homologous chromosomes are pulled to opposite poles.
Telophase I + Cytokinesis	2 haploid cells form. Each has half the original chromosome number (but with duplicated chromosomes).

Meiosis II – Like mitosis, but with haploid cells

Stage	Events
Prophase II	Chromosomes condense again.
Metaphase II	Chromosomes line up at the centre.
Anaphase II	Sister chromatids are pulled apart.
Telophase II + Cytokinesis	4 haploid gametes are formed. Each is genetically unique.

Also Read:

Locomotion and Movement	Structural Organisation in Animals and Plants	Genetic Engineering
Biotechnology and its Applications	Ecology and Environment	Plant Kingdom
Morphology in flowering plants	Plant Physiology	Human Physiology

1.0Learning Outcomes

After completing this chapter, you will be able to:

Understand the structure and functions of cells.
Differentiate between prokaryotic and eukaryotic cells.
Explain the structure and functions of major cell organelles.
Understand the fluid mosaic model of the plasma membrane.
Compare plant and animal cells.
Identify important cellular structures through labelled diagrams.
Solve NCERT and NEET-based conceptual and diagram-based questions confidently.

2.05-Minute Quick Revision

Must-Revise Concepts

Cell Theory
Prokaryotic Cell
Eukaryotic Cell
Plasma Membrane
Cell Wall
Nucleus
Endoplasmic Reticulum
Golgi Apparatus
Lysosomes
Mitochondria
Plastids
Ribosomes
Vacuoles
Cytoskeleton

Important NCERT Facts

Robert Hooke discovered cells in cork in 1665.
Schleiden and Schwann proposed the Cell Theory, which was later modified by Rudolf Virchow.
Singer and Nicolson proposed the Fluid Mosaic Model of the plasma membrane.
Mitochondria and chloroplasts possess their own DNA and ribosomes.
Ribosomes are the sites of protein synthesis.
Lysosomes contain hydrolytic enzymes and are known as the "suicidal bags" of the cell.

Diagram Recall

Prokaryotic Cell
Animal Cell
Plant Cell
Plasma Membrane
Nucleus
Endoplasmic Reticulum
Golgi Apparatus
Mitochondrion
Chloroplast
Ribosome

Quick Revision Tips

Memorize the functions of every cell organelle.
Compare prokaryotic and eukaryotic cells using a table.
Practice all labelled NCERT diagrams regularly.
Revise important scientists and their discoveries.
Focus on membrane-bound organelles and their functions.

3.0High Weightage Topics

Topic	NEET Importance	Difficulty Level
Cell Theory	High	Easy
Prokaryotic vs Eukaryotic Cells	Very High	Moderate
Plasma Membrane	High	Moderate
Cell Organelles	Very High	Moderate
Mitochondria & Chloroplast	Very High	Moderate
Ribosomes & Lysosomes	High	Easy–Moderate
Plant Cell vs Animal Cell	High	Easy

4.0NCERT Fact Box

Concept	Important Fact
Cell Theory	Proposed by M.J. Schleiden and T. Schwann, later modified by Rudolf Virchow, who stated that all cells arise from pre-existing cells.
Fluid Mosaic Model	Proposed by Singer and Nicolson (1972) to explain the structure of the plasma membrane.
Powerhouse of the Cell	Mitochondria produce ATP through cellular respiration and contain their own DNA and ribosomes.
Protein Synthesis	Ribosomes are the sites of protein synthesis and are non-membrane-bound organelles.
Cell Wall	Plant cell walls are mainly composed of cellulose, providing rigidity and protection.
Semi-Autonomous Organelles	Mitochondria and chloroplasts possess their own DNA and ribosomes and can replicate independently.
Important NCERT Diagrams	Prokaryotic Cell, Plant Cell, Animal Cell, Plasma Membrane, Nucleus, Mitochondrion, Chloroplast, Golgi Apparatus

5.0Common Mistakes & NEET Tips

Common Mistake	Correct Approach
Confusing prokaryotic and eukaryotic cells	Compare nucleus, organelles, ribosomes, DNA, and cell size using a table.
Mixing organelle functions	Prepare a one-line function chart for every cell organelle.
Forgetting membrane-bound organelles	Revise which organelles are membrane-bound and which are non-membrane-bound.
Confusing rough ER and smooth ER	Rough ER contains ribosomes and synthesizes proteins, whereas smooth ER synthesizes lipids and detoxifies drugs.
Ignoring NCERT diagrams	Practice labelled diagrams of plant cells, animal cells, mitochondria, chloroplasts, and Golgi apparatus.
Memorizing discoveries without scientists	Learn important scientists along with their discoveries from NCERT.
Mixing plant and animal cell features	Revise cell wall, plastids, centrioles, vacuoles, and lysosomes through comparison tables.

6.0ALLEN Faculty Tips

Prepare a comparison table of all cell organelles and their functions.
Memorize important scientists and their contributions to cell biology.
Practice labelled diagrams from NCERT regularly.
Revise differences between prokaryotic and eukaryotic cells.
Focus on membrane structure and organelle functions.
Solve Previous Years' Questions (PYQs) and NCERT-based MCQs to improve conceptual understanding.

7.0PYQ Trend Analysis

Cell – The Unit of Life is one of the highest-weightage chapters in NEET Biology. Questions are frequently asked on cell organelles, membrane structure, prokaryotic and eukaryotic cells, and cell theory.

Note: The trend below is based on the analysis of previous years' NEET question papers. The exact number of questions may vary each year.

Topic	Questions Asked (Last 5 Years)	Average Difficulty
Cell Theory	1	Easy
Prokaryotic vs Eukaryotic Cells	1–2	Moderate
Plasma Membrane	1	Moderate
Cell Organelles	2–3	Moderate
Mitochondria & Chloroplast	1–2	Moderate
Plant Cell vs Animal Cell	1	Easy–Moderate

8.0Most Common Question Types

Comparing prokaryotic and eukaryotic cells.
Identifying the structure and functions of cell organelles.
Differentiating plant and animal cells.
Solving questions on the fluid mosaic model of the plasma membrane.
Identifying scientists associated with cell biology discoveries.
Solving organelle-based match-the-following and assertion-reason questions.
Answering NCERT-based diagram and case-based questions.
Solving Previous Years' NEET conceptual questions.

9.0Smart Revision Strategy

Revise cell theory and the contributions of important scientists.
Compare prokaryotic and eukaryotic cells using summary tables.
Memorize the structure and functions of every cell organelle.
Practice labelled diagrams of plant cells, animal cells, and organelles.
Revise membrane structure and the fluid mosaic model.
Read all NCERT diagrams, tables, and highlighted facts carefully.
Solve Previous Years' Questions (PYQs) and NCERT-based MCQs.
Complete revision with a chapter-wise NEET mock test.

Class 11 Biology Chapters List:- JEE & NEET Revision Notes

Chapter 1 The Living World

Chapter 2 Biological Classification

Chapter 3 Plant Kingdom

Chapter 4 Animal Kingdom

Chapter 5 Morphology of Flowering Plants

Chapter 6 Anatomy of Flowering Plants

Chapter 7 Structural Organisation in Animals

Chapter 8 Cell: The Unit of Life

Chapter 9 Biomolecules

Chapter 10 Cell Cycle and Cell Division

Chapter 11 Photosynthesis in Higher Plants

Chapter 12 Respiration in Plants

Chapter 13 Plant Growth and Development

Chapter 14 Breathing and Exchange of Gases

Chapter 15 Body Fluids and Circulation

Chapter 16 Excretory Products and their Elimination

Chapter 17 Locomotion and Movement

Chapter 18 Neural Control and Coordination

Chapter 19 Chemical Coordination and Integration

Frequently Asked Questions

Join ALLEN!

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Class

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I authorise ALLEN Career Institute Pvt Ltd to send me regular updates via Phone calls, Whatsapp, SMS, Robocalls (Automated Calls), Emails, or on postal address.

Class 11 Chapter 8: Cell – The Unit of Life

The Cell – The Unit of Life chapter introduces the cell as the basic structural, functional, and biological unit of all living organisms. It explains the discovery of cells, cell theory, prokaryotic and eukaryotic cells, cell envelope, and the structure and functions of various cell organelles such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, plastids, ribosomes, vacuoles, and the cytoskeleton. This chapter builds the foundation for understanding cell biology and is one of the highest-weightage chapters in NEET Biology, with numerous questions directly based on NCERT diagrams, organelle functions, and cellular comparisons.

At ALLEN, these revision notes simplify Cell – The Unit of Life through concise explanations, NCERT-based facts, labelled diagrams, comparison tables, and exam-oriented revision points. These notes help students develop conceptual clarity and prepare effectively for NEET and CBSE Board examinations.

1.0Chapter Snapshot

Parameter	Details
Chapter Type	Cell Biology
Difficulty Level	Moderate
Revision Time	4–5 Hours

2.0Related Supporting Resources

Resource	Status
Chapter Mock Test Paper
Chapter Mock Test Paper Solutions
Cell The Unit of Life Practice Paper with Solution
Cell Cycle and Cell Division Practice Paper with Solution

Must-Revise Concepts

Cell membrane

Cell organelles structure and function

Cell Structure and Function

Centrioles (Ultrastructure and Function)

Cilia

Cytoskeleton

Endomembrane system

Endoplasmic reticulum

Plant cell and animal cell

Plasma membrane structure

Sequence of developmental processes in a plant cell

Structure of prokaryotic and eukaryotic cells

Plasma Membrane/Cell Membrane

Selective permeable
Structure of cell membrane : For study of cell membrane, mature RBCs of mammals are used
Fluid mosaic model : By singer and Nicolson Irregular (mosaic) arrangement of proteins
Lipid : Quasi fluid nature

Cell wall : Non living, rigid structure Outer covering in plant, fungi and bacteria

Functions :

Provide shape to the cell
Protection from mechanical damage and infection
Barrier to undesirable macromolecules
Cell-to-cell interaction

Endomembrane System

Organelle	Structure	Function
Endoplasmic Reticulum (ER)	Network of membranes (Rough & Smooth)	Rough ER: protein synthesis; Smooth ER: lipid synthesis, detoxification
Golgi Apparatus	Stack of flattened membrane sacs	Modifies, sorts, packages proteins and lipids into vesicles
Lysosomes (mainly animal cells)	Membrane-bound vesicles with enzymes	Break down waste, damaged organelles, and foreign substances
Vacuoles	Fluid-filled sacs	Store nutrients, waste products; large central vacuole in plant cells

Mitochondria

Number, shape, size and structure are variable
Sausage like or cylindrical shape
Site of aerobic respiration
Produce ATP, power house of cell
Divide by fission

Plastids

Plastids are found in all plant cells and in euglenoides.
These are easily observed under the microscope as they are large.
They bear some specific pigments, thus imparting specific colours to the plants.
Based on the type of pigments, plastids can be classified into chloroplasts, chromoplasts and leucoplasts.

Ribosomes

Ribosomes are the granular structures first observed under the electron microscope as dense particles by George Palade (1953).
They are composed of ribonucleic acid (RNA) and proteins and are not surrounded by any membrane.

Cytoskeleton

An elaborate network of filamentous proteinaceous structures consisting of microtubules, microfilaments and intermediate filaments present in the cytoplasm is collectively referred to as the cytoskeleton.
The cytoskeleton in a cell are involved in many functions such as mechanical support, motility, maintenance of the shape of the cell

Nucleus - Robert Brown : Discovery of the nucleus

Flemming : Gave the chromatin term, staining of nuclear material by basic dyes
Nuclear envelope : Two parallel discontinuous membranes with a perinuclear space of 10-50 nm
Barrier in between the cytoplasm and the nucleoplasm
Nuclear pore : Passage for movement of proteins and mRNA in both directions between the nucleus and the cytoplasm.
Nucleolus : Content of nucleolus is continuous with rest of the nucleoplasm because it is a membrane-less structure
Nucleoplasm : Nuclear matrix Contains Nucleolus and chromatin Site of active rRNA synthesis
Chromatin : Extended and elaborate network of nucleoprotein fibres in interphase nucleus.

1.0Biomolecules

Biomolecules are the organic and inorganic molecules present in living organisms that are essential for life.
They are mostly carbon-based compounds.

Types of Biomolecules

Biomolecules are classified into 4 major types:

Carbohydrates (Sugars)

Elements: C, H, O
Function: Provide energy and structural support.
Monosaccharides: Simple sugars (e.g., glucose, fructose)
Disaccharides: Two monosaccharides joined (e.g., sucrose = glucose + fructose)
Polysaccharides: Many monosaccharides (e.g., starch, cellulose, glycogen)

Proteins

Proteins are polypeptides
They are linear chains of amino acids linked by peptide bonds. Each protein is a polymer of amino acids.
As there are 20 types of amino acids (e.g., alanine, cysteine, proline, tryptophan, lysine, etc.), a protein is a heteropolymer and not a homopolymer.
A homopolymer has only one type of monomer repeating ‘n’ number of times.
Hence, dietary proteins are the source of essential amino acids.
Therefore, amino acids can be essential or non-essential. The latter are those which our body can make, while we get essential amino acids through our diet/food.

Lipids

Fats: Glycerol + Fatty acids (saturated or unsaturated)
Phospholipids: Found in cell membranes
Steroids: Hormones like testosterone, cholesterol

Nucleic Acids

Types: DNA and RNA
Building Blocks: Nucleotides (Sugar + Phosphate + Nitrogenous base)
DNA: A, T, G, C
RNA: A, U, G, C

Enzymes

Enzymes are biocatalysts.
Almost all enzymes are proteins.
Some enzymes are nucleic acids (RNA), called Ribozymes.
Enzymes can be depicted by a line diagram.
Any enzyme like any protein has the primary, secondary & tertiary structure.
The catalytic structure of most of the enzymes is tertiary.
Inorganic catalysts work efficiently at high temperatures and high pressures

Factors Affecting Enzyme Activity

2.0Cell Cycle and Cell Division

The cell cycle and cell division are fundamental processes by which cells grow, replicate their DNA, and divide to produce new cells.
These processes are essential for growth, development, repair, and reproduction in living organisms.

Phases of Cell Cycle

A typical eukaryotic cell cycle is illustrated by human cells in culture.
These cells divide once every 24 hours.
However, this duration of cell cycle can vary from organism to organism and also from cell type to cell type.
Yeast, for example, can progress through the cell cycle in only about 90 minutes.
The cell cycle is divided into two basic phases:
Interphase
M Phase (Mitosis phase)
G₁ phase (Gap 1)
S phase (Synthesis)
G₂phase (Gap 2)

3.0Mitosis – Cell Division in Somatic (Body) Cells

Definition:
Mitosis is a type of cell division that results in two identical daughter cells, each having the same number of chromosomes as the parent cell.

Stages of Mitosis

Stage	Events
Prophase	Chromosomes become visible as they condense. The nuclear envelope disappears. Spindle fibers start to form.
Metaphase	Chromosomes line up in the middle (metaphase plate). Spindle fibers attach to centromeres.
Anaphase	Sister chromatids are pulled apart to opposite poles of the cell.
Telophase	Two new nuclei form. Chromosomes de-condense. The nuclear envelope reappears.

Cytokinesis

Division of the cytoplasm.
In animal cells: cell membrane pinches in.
In plant cells: a cell plate forms.

Meiosis – Cell Division in Sex Cells (Gametes)

Meiosis is a type of cell division that reduces the chromosome number by half and produces 4 genetically different haploid cells (gametes like sperm and egg). It's used for:
Sexual reproduction
Maintaining chromosome number across generations
Genetic variation

Meiosis Happens in Two Parts

Meiosis I – Reduction division (chromosome number is halved)

Stage	Events
Prophase I	Chromosomes condense. Homologous chromosomes pair up and exchange genetic material (crossing over) → genetic variation.
Metaphase I	Homologous pairs line up at the center.
Anaphase I	Homologous chromosomes are pulled to opposite poles.
Telophase I + Cytokinesis	2 haploid cells form. Each has half the original chromosome number (but with duplicated chromosomes).

Meiosis II – Like mitosis, but with haploid cells

Stage	Events
Prophase II	Chromosomes condense again.
Metaphase II	Chromosomes line up at the centre.
Anaphase II	Sister chromatids are pulled apart.
Telophase II + Cytokinesis	4 haploid gametes are formed. Each is genetically unique.

Also Read:

Locomotion and Movement	Structural Organisation in Animals and Plants	Genetic Engineering
Biotechnology and its Applications	Ecology and Environment	Plant Kingdom
Morphology in flowering plants	Plant Physiology	Human Physiology

1.0Learning Outcomes

After completing this chapter, you will be able to:

Understand the structure and functions of cells.
Differentiate between prokaryotic and eukaryotic cells.
Explain the structure and functions of major cell organelles.
Understand the fluid mosaic model of the plasma membrane.
Compare plant and animal cells.
Identify important cellular structures through labelled diagrams.
Solve NCERT and NEET-based conceptual and diagram-based questions confidently.

2.05-Minute Quick Revision

Must-Revise Concepts

Cell Theory
Prokaryotic Cell
Eukaryotic Cell
Plasma Membrane
Cell Wall
Nucleus
Endoplasmic Reticulum
Golgi Apparatus
Lysosomes
Mitochondria
Plastids
Ribosomes
Vacuoles
Cytoskeleton

Important NCERT Facts

Robert Hooke discovered cells in cork in 1665.
Schleiden and Schwann proposed the Cell Theory, which was later modified by Rudolf Virchow.
Singer and Nicolson proposed the Fluid Mosaic Model of the plasma membrane.
Mitochondria and chloroplasts possess their own DNA and ribosomes.
Ribosomes are the sites of protein synthesis.
Lysosomes contain hydrolytic enzymes and are known as the "suicidal bags" of the cell.

Diagram Recall

Prokaryotic Cell
Animal Cell
Plant Cell
Plasma Membrane
Nucleus
Endoplasmic Reticulum
Golgi Apparatus
Mitochondrion
Chloroplast
Ribosome

Quick Revision Tips

Memorize the functions of every cell organelle.
Compare prokaryotic and eukaryotic cells using a table.
Practice all labelled NCERT diagrams regularly.
Revise important scientists and their discoveries.
Focus on membrane-bound organelles and their functions.

3.0High Weightage Topics

Topic	NEET Importance	Difficulty Level
Cell Theory	High	Easy
Prokaryotic vs Eukaryotic Cells	Very High	Moderate
Plasma Membrane	High	Moderate
Cell Organelles	Very High	Moderate
Mitochondria & Chloroplast	Very High	Moderate
Ribosomes & Lysosomes	High	Easy–Moderate
Plant Cell vs Animal Cell	High	Easy

4.0NCERT Fact Box

Concept	Important Fact
Cell Theory	Proposed by M.J. Schleiden and T. Schwann, later modified by Rudolf Virchow, who stated that all cells arise from pre-existing cells.
Fluid Mosaic Model	Proposed by Singer and Nicolson (1972) to explain the structure of the plasma membrane.
Powerhouse of the Cell	Mitochondria produce ATP through cellular respiration and contain their own DNA and ribosomes.
Protein Synthesis	Ribosomes are the sites of protein synthesis and are non-membrane-bound organelles.
Cell Wall	Plant cell walls are mainly composed of cellulose, providing rigidity and protection.
Semi-Autonomous Organelles	Mitochondria and chloroplasts possess their own DNA and ribosomes and can replicate independently.
Important NCERT Diagrams	Prokaryotic Cell, Plant Cell, Animal Cell, Plasma Membrane, Nucleus, Mitochondrion, Chloroplast, Golgi Apparatus

5.0Common Mistakes & NEET Tips

Common Mistake	Correct Approach
Confusing prokaryotic and eukaryotic cells	Compare nucleus, organelles, ribosomes, DNA, and cell size using a table.
Mixing organelle functions	Prepare a one-line function chart for every cell organelle.
Forgetting membrane-bound organelles	Revise which organelles are membrane-bound and which are non-membrane-bound.
Confusing rough ER and smooth ER	Rough ER contains ribosomes and synthesizes proteins, whereas smooth ER synthesizes lipids and detoxifies drugs.
Ignoring NCERT diagrams	Practice labelled diagrams of plant cells, animal cells, mitochondria, chloroplasts, and Golgi apparatus.
Memorizing discoveries without scientists	Learn important scientists along with their discoveries from NCERT.
Mixing plant and animal cell features	Revise cell wall, plastids, centrioles, vacuoles, and lysosomes through comparison tables.

6.0ALLEN Faculty Tips

Prepare a comparison table of all cell organelles and their functions.
Memorize important scientists and their contributions to cell biology.
Practice labelled diagrams from NCERT regularly.
Revise differences between prokaryotic and eukaryotic cells.
Focus on membrane structure and organelle functions.
Solve Previous Years' Questions (PYQs) and NCERT-based MCQs to improve conceptual understanding.

7.0PYQ Trend Analysis

Cell – The Unit of Life is one of the highest-weightage chapters in NEET Biology. Questions are frequently asked on cell organelles, membrane structure, prokaryotic and eukaryotic cells, and cell theory.

Note: The trend below is based on the analysis of previous years' NEET question papers. The exact number of questions may vary each year.

Topic	Questions Asked (Last 5 Years)	Average Difficulty
Cell Theory	1	Easy
Prokaryotic vs Eukaryotic Cells	1–2	Moderate
Plasma Membrane	1	Moderate
Cell Organelles	2–3	Moderate
Mitochondria & Chloroplast	1–2	Moderate
Plant Cell vs Animal Cell	1	Easy–Moderate