What is the fundamental unit of life?

The cell is the fundamental unit of life found in all living organisms responsible for structure and function.

What are the main types of cells?

The two main types of cells are prokaryotic and eukaryotic cells.

Who proposed the cell theory?

The cell theory was proposed by Schleiden and Schwann, and later modified by Rudolf Virchow.

What does the cell theory state?

It states that all living organisms are made of cells and new cells arise from pre-existing ones.

Define prokaryotic cell.

Prokaryotic cells are simple cells without a true nucleus or membrane-bound organelles, like bacteria.

Define eukaryotic cell.

Eukaryotic cells have a well-defined nucleus and membrane-bound organelles like plant and animal cells.

What is the function of the plasma membrane?

The plasma membrane is selectively permeable and controls material movement in and out of the cell.

Cytoplasm is the jelly-like substance between the nucleus and cell membrane containing organelles.

What are cell organelles?

Cell organelles are specialized structures like mitochondria, Golgi apparatus, and ribosomes that perform specific functions.

The nucleus contains chromosomes composed of DNA and proteins, controlling heredity and cell activities.

In prokaryotic cells, nucleoid is an undefined region containing genetic material without a membrane.

What is the function of mitochondria?

Mitochondria produce energy in the form of ATP, through the process of cellular respiration.

Why is mitochondria called the powerhouse of the cell?

Because it generates energy needed for metabolic processes in the form of ATP.

Ribosomes are organelles responsible for protein synthesis.

NCERT Class 9 Science Chapter 5 The Fundamental Unit of Life Notes

Q: Who discovered the cell?

Robert Hooke discovered the cell in 1665 while observing cork cells under a microscope.

10 CBSE Marks

★★★★★ Difficulty

10 Topics

Very High Board Weight

Topics Covered

10 key topics in this chapter

Who Discovered the Cell?

Cell Theory

Why is Cell the Basic Unit?

Prokaryotic vs Eukaryotic Cell

Plant Cell vs Animal Cell

Cell Wall & Cell Membrane

Nucleus & Chromosomes

Cytoplasm

Cell Organelles

Mitochondria, Plastids & Vacuole

Study Resources

📖 NCERT Notes ✏️ MCQ Practice 📝 Exercise Solutions ✅ True / False Quiz

Key Concepts

01. Discovery & Cell Theory

Robert Hooke (1665) first observed cells in cork. Leeuwenhoek saw living cells. Cell Theory (Schleiden & Schwann, 1838–39): all living organisms are made of cells; the cell is the basic structural and functional unit of life.

02. Prokaryotic vs Eukaryotic

Prokaryotic cells (bacteria, blue-green algae) lack a membrane-bound nucleus. Eukaryotic cells (plants, animals, fungi) have a true membrane-bound nucleus and membrane-bound organelles.

03. Cell Wall & Cell Membrane

Cell wall is present in plants, fungi, and bacteria — made of cellulose in plants. It gives rigidity and shape. The cell membrane (plasma membrane) is present in all cells — selectively permeable, controls passage of substances.

04. Nucleus

The nucleus is the control centre — contains DNA (hereditary material) in chromosomes. The nuclear envelope has pores. The nucleolus inside synthesises ribosomal RNA. Prokaryotes have a nucleoid instead.

05. Cell Organelles

Mitochondria — power house (ATP synthesis). Chloroplasts — photosynthesis (only in plant cells). Ribosome — protein synthesis. Endoplasmic Reticulum (ER) — transport. Golgi apparatus — packaging. Lysosomes — digestion (suicide bags).

06. Osmosis & Plasmolysis

Osmosis is the movement of water across a semi-permeable membrane from high water potential to low water potential. Turgid: swollen cell. Flaccid: limp cell. Plasmolysis: cell shrinks in hypertonic solution.

Formulas at a Glance

#	Name	Expression	Notes
01	Organisation Level	`Cell → Tissue → Organ → Organ System → Organism`	Hierarchy of biological organisation
02	Osmosis Direction	`Water moves: low solute conc. → high solute conc.`	Across semi-permeable membrane
03	Hypertonic Solution	`External solute > cell solute → cell shrinks`	Plasmolysis occurs
04	Hypotonic Solution	`External solute < cell solute → cell swells`	Turgidity occurs

Important Notes

Plant cells differ from animal cells: have cell wall, chloroplasts, and a large central vacuole. Animal cells have centrioles instead.

Lysosomes contain hydrolytic enzymes — they digest worn-out organelles (autophagy) and are called "suicide bags" because they can burst and destroy the cell.

Mitochondria and chloroplasts have their own DNA and ribosomes — supporting the endosymbiotic theory.

The nuclear membrane is absent during cell division — this is a key feature of mitosis/meiosis.

Exam Tips & Common Mistakes

Draw a labelled diagram of a plant cell and an animal cell — diagrams are worth 3–5 marks in CBSE.

"Suicide bags of cell" = Lysosomes. "Power house of cell" = Mitochondria. "Kitchen of plant cell" = Chloroplast. These one-liners appear every year.

Osmosis vs diffusion: osmosis only involves water; diffusion involves any substance. Both require no energy.

For plasmolysis questions, state: "cell placed in hypertonic solution → water exits → cytoplasm shrinks away from cell wall".

Prokaryote vs Eukaryote — always mention: membrane-bound nucleus (absent/present), size (smaller/larger), membrane organelles (absent/present).

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The Fundamental Unit of Life