Class 9th Chapter 1 :- The fundamental unit of life : cell

 Class 9th  

Chapter 1 :- The fundamental unit of life : cell

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📘 Chapter: The Fundamental Unit of Life — Cell

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🔹 Introduction:

• The cell is the basic structural, functional, and biological unit of all living organisms.

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

• Anton van Leeuwenhoek was the first to observe living cells.

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🔹 Cell Theory:

Formulated by Schleiden and Schwann:

1. All living organisms are made up of cells.

2. The cell is the basic unit of life.

3. Rudolf Virchow added: "All cells arise from pre-existing cells."

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🔹 Types of Organisms:

• Unicellular: Single-celled organisms (e.g., Amoeba, Paramecium)

• Multicellular: Made of many cells (e.g., humans, plants)

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🔹 Types of Cells:

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No true nucleus	True nucleus with membrane
Cell size	Small (1–10 µm)	Larger (10–100 µm)
Examples	Bacteria	Plants, animals, fungi
Organelles	No membrane-bound organelles	Membrane-bound organelles

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🔹 Structure of a Cell:

1. Plasma Membrane / Cell Membrane

• Outer covering of cell.

• Selectively permeable: Allows certain substances to pass.

• Made of lipid bilayer with proteins.

2. Cell Wall (only in plant cells)

• Rigid outer layer made of cellulose.

• Provides support and protection.

3. Cytoplasm

• Jelly-like fluid inside the cell.

• Holds organelles in place.

4. Nucleus

• Control center of the cell.

• Contains DNA (genetic material).

• Has nuclear membrane, nucleoplasm, nucleolus, and chromatin.

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🔹 Cell Organelles:

Organelle	Function
Mitochondria	"Powerhouse of the cell"; site of respiration & energy (ATP) production
Endoplasmic Reticulum (ER)

• Rough ER: Has ribosomes; makes proteins

• Smooth ER: No ribosomes; makes lipids

| Golgi Apparatus | Modifies, stores, and packages proteins and lipids |

| Lysosomes | Contains digestive enzymes; "Suicide bags" of the cell |

| Ribosomes | Site of protein synthesis (found in cytoplasm or on Rough ER) |

| Plastids (in plants only) |

• Chloroplasts: Photosynthesis (contain chlorophyll)

• Leucoplasts: Store starch

• Chromoplasts: Give color to fruits/flowers

| Vacuoles | Storage of water, waste, etc. (Large in plant cells, small in animal cells) |

| Centrosome | Found only in animal cells; helps in cell division |

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🔹 Differences Between Plant and Animal Cells:

Feature	Plant Cell	Animal Cell
Cell Wall	Present	Absent
Chloroplast	Present	Absent
Vacuole	Large central vacuole	Small or absent
Shape	Usually rectangular	Usually round or irregular
Centrioles	Absent	Present

🔹 Key Concepts:

• Cells → Tissues → Organs → Organ Systems → Organism

• All life functions occur at the cellular level: growth, metabolism, reproduction, etc.

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