The Fundamental Unit of Life Class 9, part of CBSE Class 9 Science Chapter 5, introduces students to the structure and function of cells, the basic building blocks of life. This chapter explores the discovery of cells, types of cells, cell organelles and their functions, and critical processes like osmosis, diffusion, and cell division: mitosis and meiosis. By understanding these concepts, students gain a solid foundation in biology.
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Discovery of Cells in Biology
Who Discovered the Cell?
Robert Hooke discovered cells in 1665 by observing cork under a microscope.
Later, Anton van Leeuwenhoek observed living cells using an advanced microscope.
Cell Theory
Proposed by: Schleiden and Schwann.
Key Points:
All living organisms are made of cells.
The cell is the basic structural and functional unit of life.
All cells arise from pre-existing cells (added by Rudolf Virchow).
Types of Cells
Prokaryotic Cells
Simple and primitive cells without a well-defined nucleus.
Genetic material is present as a nucleoid (not membrane-bound).
Example: Bacteria.
Eukaryotic Cells
Complex cells with a well-defined nucleus enclosed by a nuclear membrane.
Contain membrane-bound organelles.
Examples: Plant and animal cells.
Structure and Function of Cells
Cells consist of three main components:
Plasma Membrane (Cell Membrane)
Function: Acts as a selectively permeable barrier, controlling the movement of substances in and out of the cell.
Processes:
Diffusion: Movement of molecules (e.g., gases like oxygen) from higher to lower concentration.
Osmosis: Movement of water molecules across a selectively permeable membrane.
Cytoplasm
A jelly-like substance between the plasma membrane and the nucleus.
Contains cell organelles such as mitochondria, ribosomes, and endoplasmic reticulum.
Nucleus
Controls cell activities and contains genetic material (DNA).
Components:
Nuclear Membrane: Encloses the nucleus.
Chromosomes: Carry hereditary information.
Nucleolus: Plays a role in ribosome production.
Cell Organelles and Their Functions
Mitochondria
Known as the "powerhouse of the cell".
Produce energy in the form of ATP (Adenosine Triphosphate) through cellular respiration.
Endoplasmic Reticulum (ER)
Rough ER: Helps in protein synthesis (has ribosomes).
Smooth ER: Synthesizes lipids (lacks ribosomes).
Ribosomes
Responsible for protein synthesis.
Found in the cytoplasm or attached to the rough ER.
Golgi Apparatus
Modifies, packages, and transports proteins and lipids.
Lysosomes
Called the "suicidal bags" of the cell.
Contain digestive enzymes that break down waste materials and cellular debris.
Plastids (Found only in plant cells)
Chloroplasts: Contain chlorophyll for photosynthesis.
Chromoplasts: Provide color to fruits and flowers.
Leucoplasts: Store food like starch, proteins, and oils.
Vacuoles
Storage sacs for water, nutrients, and waste products.
Larger in plant cells compared to animal cells.
Difference Between Plant and Animal Cells
|
Feature |
Plant Cells |
Animal Cells |
|
Cell Wall |
Present (made of cellulose) |
Absent |
|
Plastids |
Present (e.g., chloroplasts) |
Absent |
|
Vacuoles |
Large and central |
Smaller and scattered |
|
Shape |
Rectangular |
Irregular or round |
Important Processes: Osmosis and Diffusion
Diffusion
Movement of molecules (e.g., oxygen, carbon dioxide) from higher to lower concentration.
Osmosis
Movement of water molecules across a selectively permeable membrane from a region of higher water concentration to lower concentration.
Endocytosis
The process by which cells engulf food or other substances from their surroundings.
Cell Division: Mitosis and Meiosis
Mitosis
Occurs in somatic (body) cells.
Results in two identical daughter cells.
Meiosis
Occurs in reproductive cells.
Results in four non-identical daughter cells, each with half the number of chromosomes.
Key Terms to Remember
Prokaryotic and Eukaryotic Cells: Basic types of cells.
Plasma Membrane: Regulates the entry and exit of substances.
Nucleus: Controls cell activities and stores genetic material.
Mitochondria: Powerhouse of the cell.
Osmosis and Diffusion: Processes for the movement of molecules.
Mitosis and Meiosis: Types of cell division.
FAQs on the Fundamental Unit of Life Class 9
What is the fundamental unit of life?
The cell is the fundamental unit of life.
Who discovered the cell?
Robert Hooke discovered the cell in 1665.
What is the difference between prokaryotic and eukaryotic cells?
Prokaryotic cells lack a well-defined nucleus, while eukaryotic cells have a nucleus and membrane-bound organelles.
What is the function of the plasma membrane?
It acts as a selectively permeable barrier, regulating the movement of substances.
Why are mitochondria called the powerhouse of the cell?
They produce energy in the form of ATP through cellular respiration.
What is the role of lysosomes?
Lysosomes contain enzymes that digest waste and cellular debris.
What is the difference between diffusion and osmosis?
Diffusion involves the movement of molecules, while osmosis specifically involves water molecules.
What are plastids?
Organelles found in plant cells that store food or pigments, such as chloroplasts for photosynthesis.
What is the nucleus, and what are its functions?
The nucleus controls cell activities and stores genetic information.
What is the difference between mitosis and meiosis?
Mitosis produces identical cells, while meiosis produces non-identical cells with half the chromosome number.
