Class 9 Biology – Cell Notes, PYQs & Important Questions

 Class 9 Biology – Cell Notes, PYQs, and Important Questions for School Exams

Introduction

The cell is the fundamental unit of life — every living organism, from tiny bacteria to large animals, is made up of cells. Understanding the structure, functions, and types of cells forms the base of all biological studies in higher classes.
This chapter, “The Fundamental Unit of Life”, is a key topic in CBSE Class 9 Biology, carrying high weightage in both school exams and board-internal assessments.

In this article, you will find well-organized notes, important short and long questions, and previous year questions (PYQs) to help you score full marks in your exams.

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1. What is a Cell?

A cell is the smallest structural and functional unit of life.
It performs all essential functions like growth, respiration, and reproduction.

Discovery of Cell

• Robert Hooke (1665): Discovered cells while observing cork slices under a microscope.
• Anton van Leeuwenhoek: First observed living cells.
• Theodor Schwann and Matthias Schleiden (1838–39): Proposed Cell Theory —

“All living organisms are made of cells, and the cell is the basic unit of life.”

• Rudolf Virchow (1855): Added the idea that “all cells arise from pre-existing cells.”

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2. Types of Organisms

• Unicellular Organisms: Made up of a single cell (e.g., Amoeba, Paramecium, Bacteria).
• Multicellular Organisms: Made up of many cells (e.g., Plants, Animals, Humans).

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3. Structure of a Cell

A cell is made up of three main parts:

a. Cell Membrane (Plasma Membrane)

• Thin, flexible boundary that controls the entry and exit of substances.
• Selectively permeable — allows only certain materials to pass through.

b. Cytoplasm

• Jelly-like fluid inside the cell where all cell organelles are suspended.
• Site for most metabolic activities.

c. Nucleus

• Controls all cellular activities.
• Contains chromosomes that carry genes — the hereditary material.
• Enclosed by a nuclear membrane.

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4. Cell Organelles and Their Functions

Cell Organelle	Structure	Function
Endoplasmic Reticulum (ER)	Network of membranes	Transport of materials
Golgi Apparatus	Stack of flattened sacs	Packaging and secretion
Mitochondria	Double membrane, inner folded (cristae)	Powerhouse of cell – releases energy
Lysosomes	Small vesicles with enzymes	Digests worn-out parts (suicidal bags)
Plastids (in plants)	Contains pigments	Photosynthesis and color
Vacuoles	Fluid-filled sacs	Storage of food, water, and waste
Ribosomes	Small round bodies	Protein synthesis
Centrioles (in animals)	Cylindrical bodies	Help in cell division

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5. Differences Between Plant and Animal Cells

Feature	Plant Cell	Animal Cell
Cell Wall	Present	Absent
Vacuole	Large and central	Small or absent
Plastids	Present (chloroplasts)	Absent
Shape	Regular (rectangular)	Irregular (round)

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6. Important Diagrams to Practice

1. Plant Cell (Labelled diagram)
2. Animal Cell (Labelled diagram)
3. Structure of Nucleus

Tip: Practice drawing and labeling neatly — diagrams often carry 2–3 marks in school exams.

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7. Important Terms

• Prokaryotic Cell: Cell without a well-defined nucleus (e.g., Bacteria).
• Eukaryotic Cell: Cell with a defined nucleus (e.g., Plants, Animals).
• Organelle: Specialized structure inside the cell performing specific functions.
• Chromosomes: Thread-like structures carrying genetic information.

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8. Important Questions for School Exams

Very Short Answer Questions (1 Mark)

1. Who discovered the cell?
   Answer: Robert Hooke in 1665.
2. What is the function of mitochondria?
   Answer: It produces energy — called the powerhouse of the cell.
3. What are ribosomes?
   Answer: Sites of protein synthesis.
4. Name one organelle found only in plant cells.
   Answer: Chloroplast.
5. What is the basic unit of life?
   Answer: Cell.

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Short Answer Questions (2–3 Marks)

1. State the differences between plant and animal cells.
2. What are the functions of Golgi apparatus and lysosomes?
3. Explain the importance of the nucleus in a cell.
4. What is cell theory? Who proposed it?
5. How do prokaryotic and eukaryotic cells differ?

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Long Answer Questions (4–5 Marks)

1. Describe the structure and function of various cell organelles.
2. Explain the discovery and development of cell theory.
3. Draw a neat labelled diagram of a plant cell and mention its main parts.
4. Explain the differences between prokaryotic and eukaryotic cells with examples.

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9. Previous Year Questions (PYQs) – CBSE and School Exams

1. What is the function of the plasma membrane? (CBSE 2022)
2. Name the organelle known as the powerhouse of the cell. (CBSE 2023)
3. Define the term “cell.” (School Exam 2023)
4. Explain the functions of the Golgi apparatus. (CBSE 2021)
5. Draw a labelled diagram of a plant cell. (Frequent question)

Tip: Questions on “Cell organelles” and “Differences between plant and animal cells” are repeated almost every year in school exams.

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10. Study Tips for Class 9 Students

• Make short notes: Write points for each organelle and revise daily.
• Practice diagrams: These are easy marks if drawn correctly.
• Learn by examples: Relate cell organelles to real-life analogies (e.g., Mitochondria = Powerhouse).
• Solve PYQs: Helps you understand the pattern of recurring questions.
• Revise definitions: Many 1-mark questions come directly from definitions.

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Summary

The cell is the foundation of life, and mastering this chapter ensures a strong base for higher classes like Class 11 and 12 Biology.
By revising notes, practicing labelled diagrams, and solving previous year questions, students can easily score full marks in this chapter.
Focus on functions of organelles, differences between plant and animal cells, and definitions — they form the backbone of most question papers.