1️⃣ Discovery of Cell
Key Definitions
- Cell: The basic structural and functional unit of life.
- Cell Theory: Proposed by Schleiden and Schwann.
Explanation (Point-wise)
-
Robert Hooke (1665)
- Observed thin slice of cork under microscope.
- Saw small compartments.
- Named them “cells” (means little rooms).
-
Leeuwenhoek
- Observed living cells for the first time.
-
Schleiden (1838)
- All plants are made of cells.
-
Schwann (1839)
- All animals are made of cells.
-
Virchow (1855)
- Stated: “All cells arise from pre-existing cells.”
Cell Theory
- All living organisms are made up of cells.
- Cell is the basic structural and functional unit of life.
- All cells arise from pre-existing cells.
Important Points / Exam Tips
✔ Smallest living unit = Cell
✔ Father of cell = Robert Hooke
✔ Living cell first seen by = Leeuwenhoek
2️⃣ Types of Organisms Based on Number of Cells
Key Definitions
- Unicellular organisms: Organisms made of single cell.
- Multicellular organisms: Organisms made of many cells.
Explanation
1. Unicellular Organisms
- Single cell performs all functions.
- Example: Amoeba, Paramecium, Bacteria
2. Multicellular Organisms
- Many cells.
- Division of labour present.
- Example: Human beings, Plants
Diagram Description
Draw two diagrams:
- Amoeba (single cell)
- Human body (many cells)
Important Points
✔ In unicellular organisms, one cell = whole organism
✔ Multicellular organisms show specialisation of cells
3️⃣ Shape and Size of Cells
Key Definitions
- Cells vary in shape, size, and number.
Explanation
Size of Cells
- Smallest cell: Mycoplasma
- Largest cell: Ostrich egg
- Longest cell: Nerve cell
Shape of Cells
Depends on function:
- Nerve cell → Long (transmit messages)
- RBC → Round and biconcave
- Muscle cell → Spindle-shaped
Important Points
✔ Shape depends on function
✔ Size measured in micrometre (µm)
4️⃣ Cell Structure
Cell has three main parts:
- Plasma Membrane
- Cytoplasm
- Nucleus
4.1️⃣ Plasma Membrane
Key Definition
- Thin outer covering of cell.
- Also called Cell Membrane.
Explanation
Functions:
- Protects the cell.
- Allows entry and exit of substances.
- Selectively permeable in nature.
Important Processes
1. Diffusion
Movement of molecules from high concentration to low concentration.
2. Osmosis
Movement of water through semi-permeable membrane.
Osmosis Conditions
- Hypotonic solution → Cell swells
- Hypertonic solution → Cell shrinks
- Isotonic solution → No change
Diagram Description
Draw plant cell in:
- Hypotonic solution (turgid)
- Hypertonic solution (plasmolysis)
Important Points
✔ Plasma membrane is flexible
✔ Osmosis only involves water
4.2️⃣ Cell Wall (Plant Cell Only)
Key Definition
- Rigid outer layer outside plasma membrane.
- Made of cellulose.
Functions
- Provides shape.
- Protects plant cell.
- Prevents bursting.
Important Points
✔ Present only in plant cells
✔ Made of cellulose
4.3️⃣ Cytoplasm
Key Definition
- Jelly-like substance between nucleus and cell membrane.
Explanation
- Contains organelles.
- Site of many chemical reactions.
4.4️⃣ Cell Organelles
Definition
Specialised structures inside cytoplasm performing specific functions.
5️⃣ Nucleus
Key Definition
- Control centre of cell.
Structure
- Nuclear membrane
- Nucleolus
- Chromatin
Chromatin → forms chromosomes
Functions
- Controls cell activities.
- Carries hereditary information (DNA).
Important Points
✔ Without nucleus → cell cannot survive long
✔ Nucleus contains genetic material
6️⃣ Prokaryotic and Eukaryotic Cells
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | Not well defined | Well defined |
| Organelles | Absent | Present |
| Example | Bacteria | Plants, Animals |
Important Points
✔ Prokaryotes → Primitive
✔ Eukaryotes → Advanced
7️⃣ Endoplasmic Reticulum (ER)
Definition
Network of membranes.
Types:
- Rough ER (RER) – Ribosomes present
- Smooth ER (SER) – Ribosomes absent
Functions
- RER → Protein synthesis
- SER → Lipid synthesis
8️⃣ Ribosomes
- Site of protein synthesis.
- Present on RER or free in cytoplasm.
9️⃣ Golgi Apparatus
Function
- Packaging and secretion of materials.
Diagram Description
Stacked flattened sacs.
🔟 Lysosomes
Definition
- Suicidal bags of cell.
Function
- Digest waste material.
1️⃣1️⃣ Mitochondria
Definition
Powerhouse of cell.
Function
- Produces energy (ATP).
Structure
- Double membrane.
- Inner membrane folded → Cristae
- Inner space → Matrix
1️⃣2️⃣ Plastids (Plant Cells Only)
Types:
- Chloroplast → Photosynthesis
- Chromoplast → Colour
- Leucoplast → Storage
Important Points
✔ Chloroplast contains chlorophyll
1️⃣3️⃣ Vacuoles
Definition
Storage sacs.
In plant cells:
- Large central vacuole.
In animal cells:
- Small and temporary.
🌟 Difference Between Plant and Animal Cell
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell wall | Present | Absent |
| Plastids | Present | Absent |
| Vacuole | Large | Small |
| Shape | Fixed | Irregular |
📌 Quick Revision Summary
✔ Cell = Basic unit of life
✔ Cell theory → Schleiden & Schwann
✔ Plasma membrane → Selectively permeable
✔ Osmosis → Movement of water
✔ Nucleus → Control centre
✔ Mitochondria → Powerhouse
✔ Ribosomes → Protein synthesis
✔ Golgi → Packaging
✔ Lysosomes → Digestion
✔ Plastids → Plant cells only
✔ Prokaryotes vs Eukaryotes → Based on nucleus
