Definitions From Fundamental Unit Of Life

Key definitions from the Class 9 NCERT Science Chapter "The Fundamental Unit of Life" (Chapter 5), listed clearly for easy reference:

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🔹 Key Definitions

1. Cell:
   The basic structural and functional unit of life.

2. Plasma Membrane / Cell Membrane:
   The outermost covering of the cell that separates the contents of the cell from its external environment.

3. Diffusion:
   The movement of substances from an area of higher concentration to an area of lower concentration.

4. Osmosis:
   The movement of water molecules through a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.

5. Selectively Permeable Membrane:
   A membrane that allows only certain substances to pass through it.

6. Cell Wall:
   A rigid outer covering found in plant cells, made up of cellulose, that provides structural support and protection.

7. Nucleus:
   A membrane-bound organelle that contains genetic material (DNA) and controls the activities of the cell.

8. Cytoplasm:
   The fluid content inside the plasma membrane, excluding the nucleus, where most cell organelles are suspended.

9. Prokaryotic Cell:
   Cells that do not have a well-defined nucleus or membrane-bound organelles.

10. Eukaryotic Cell:
    Cells that have a well-defined nucleus and membrane-bound organelles.

11. Nucleoid:
    An irregularly-shaped region in a prokaryotic cell where the genetic material is located.

12. Cell Organelles:
    Specialized structures within the cell that perform specific functions.

13. Endoplasmic Reticulum (ER):
    A network of membranes involved in the synthesis and transport of proteins (rough ER) and lipids (smooth ER).

14. Golgi Apparatus:
    An organelle that modifies, sorts, and packages proteins and lipids for storage or transport.

15. Lysosomes:
    Membrane-bound sacs filled with digestive enzymes that help in breaking down waste materials and cellular debris.

16. Mitochondria:
    Organelles known as the powerhouse of the cell because they release energy during cellular respiration.

17. Plastids:
    Organelles found in plant cells, including chloroplasts (for photosynthesis), chromoplasts, and leucoplasts.

18. Chloroplasts:
    Green plastids containing chlorophyll that carry out photosynthesis.

19. Vacuoles:
    Storage sacs within the cell that store substances like water, nutrients, and waste products.

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20. Chromosomes:
    Thread-like structures made of DNA and protein present in the nucleus, which carry genetic information.

21. Genes:
    Units of inheritance made up of DNA, which control the traits or characteristics of an organism.

22. Ribosomes:
    Small, non-membrane-bound organelles responsible for protein synthesis. They may be free-floating or attached to the endoplasmic reticulum.

23. Smooth Endoplasmic Reticulum (SER):
    A type of ER that lacks ribosomes and is involved in lipid synthesis and detoxification.

24. Rough Endoplasmic Reticulum (RER):
    A type of ER studded with ribosomes, which plays a key role in protein synthesis and transport.

25. Tissue (briefly introduced or referred to):
    A group of cells having similar structure and function.

26. Organelle:
    A specialized subunit within a cell that performs a specific function, usually membrane-bound in eukaryotes.

27. Multicellular Organism:
    An organism made up of more than one cell, with cells specialized to perform different functions.

28. Unicellular Organism:
    An organism made up of a single cell that performs all life processes.

29. Cell Division (brief reference):
    The process by which a parent cell divides into two or more daughter cells.

30. Cell Theory:
    A scientific theory which states that all living organisms are made up of cells, and all cells arise from pre-existing cells.

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