Class 8 Science – Cell Structure and Functions: Basics of Life

1. Introduction

• Cells are the basic structural and functional units of life.

• All living organisms are made up of one or more cells.

• Cells perform vital life processes like nutrition, respiration, growth, and reproduction.

Key Concept:

• Understanding cells helps explain how organisms live, grow, and respond to the environment.

2. Discovery of Cells

• Discovered by Robert Hooke in 1665 when observing cork under a microscope.

• Term “cell” comes from the Latin word meaning “small room”.

• Microscope revealed internal structures in living organisms.

3. Types of Cells

1. Prokaryotic Cells

   • Simple structure, no distinct nucleus.

   • Example: Bacteria.

   • DNA floats in the cytoplasm.

2. Eukaryotic Cells

   • Complex structure with nucleus and membrane-bound organelles.

   • Example: Plant and animal cells.

   • DNA is enclosed in the nucleus.

4. Structure of a Typical Cell

Key Parts and Functions:

1. Cell Membrane

   • Thin covering around the cell.

   • Controls entry and exit of substances.

2. Cytoplasm

   • Jelly-like substance inside the cell.

   • Holds cell organelles and facilitates chemical reactions.

3. Nucleus

   • Controls cell activities.

   • Contains genetic material (DNA).

4. Mitochondria

   • Powerhouse of the cell.

   • Provides energy for cell activities.

5. Endoplasmic Reticulum (ER)

   • Network for transport of materials within the cell.

6. Golgi Apparatus

   • Packages and transports substances inside and outside the cell.

7. Ribosomes

   • Sites of protein synthesis.

8. Lysosomes

   • Contain digestive enzymes to break down waste and unwanted materials.

9. Chloroplasts (in plant cells)

   • Site of photosynthesis to produce food using sunlight.

10. Cell Wall (in plant cells)

    • Provides strength and rigidity.

5. Key Concepts about Cells

• Cell is the unit of life: All functions of life occur within cells.

• Different cells have specialized functions: e.g., nerve cells transmit signals, red blood cells carry oxygen.

• Living organisms can be unicellular (single cell) or multicellular (many cells).

• Organelles are specialized structures within cells that perform specific functions.

6. Key Points to Remember

• Cells are the basic building blocks of life.

• Two main types: Prokaryotic (simple) and Eukaryotic (complex).

• Cell membrane, cytoplasm, nucleus, and organelles are vital for cell functions.

• Plant cells have cell wall and chloroplasts, animal cells do not.

• Studying cells helps understand growth, reproduction, and life processes.