⚡ Quick Revision: The Discovery & Cell Theory
The cell is the basic structural and functional unit of all living organisms.
Robert Hooke: The scientist who first observed "cells" in a thin slice of cork in 1665.
Core Cell Theory
- ✔ All living things are composed of one or more cells.
- ✔ The cell is the basic unit of life.
- ✔ New cells arise from pre-existing cells through cell division.
⚡ Quick Revision: Cell Organelles (Part 1)
Protoplasm: The entire living substance of a cell, consisting of the cytoplasm and the nucleus.
The Main Components
- ✔ Cell Membrane: Semi-permeable outer layer that controls the entry/exit of substances.
- ✔ Cell Wall: Rigid outer layer (plants only) made of cellulose; provides shape and protection.
- ✔ Cytoplasm: Jelly-like substance where most chemical reactions and metabolic activities occur.
The Cell Membrane with the Cell Wall. The membrane is living and present in all cells; the wall is non-living and present only in plants/fungi.
⚡ Quick Revision: The Control Center & Energy
Nucleus: The brain of the cell that contains genetic material (DNA) and coordinates all cellular activities.
Vital Organelles
- ✔ Mitochondria: Known as the "Powerhouse of the Cell"; site of cellular respiration and ATP (energy) production.
- ✔ Vacuoles: Storage sacs for water, food, or waste; very large in plant cells to maintain turgidity.
- ✔ Nucleolus: A small dense spherical structure inside the nucleus responsible for making ribosomes.
⚡ Quick Revision: Specialized Organelles
Plastids are unique organelles found only in plant cells, responsible for color and food manufacture.
Types of Plastids
| Plastid | Color/Feature | Function |
|---|---|---|
| Chloroplasts | Green (Chlorophyll) | Photosynthesis. |
| Chromoplasts | Red, Orange, Yellow | Coloring flowers/fruits. |
| Leucoplasts | Colorless | Storage of starch/oils. |
Other Important Structures
- ✔ Endoplasmic Reticulum (ER): Network of membranes for protein and lipid synthesis.
- ✔ Ribosomes: Tiny granular structures that are the sites of protein synthesis.
- ✔ Golgi Bodies: Flat sacs involved in the packaging and secretion of cell products.
⚡ Quick Revision: Plant Cell vs. Animal Cell
While both cells share common organelles, they have distinct differences based on their nutritional and structural needs.
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present (made of cellulose). | Absent. |
| Plastids | Present (Chloroplasts, etc.). | Absent. |
| Vacuoles | One large central vacuole. | Small, temporary vacuoles. |
| Centrosome | Absent. | Present (helps in division). |
Shape: Plant cells are usually fixed/rectangular due to the cell wall, whereas animal cells are irregular or oval.
⚡ Quick Revision: Levels of Organization
Living organisms show a hierarchy of organization, from the simplest unit to a complex individual.
The Biological Hierarchy
- 1 Cell: The basic building block (e.g., Nerve cell).
- 2 Tissue: A group of similar cells performing a specific function (e.g., Muscle tissue).
- 3 Organ: Different tissues working together (e.g., Heart, Stomach, Leaf).
- 4 Organ System: A group of organs working for a common goal (e.g., Digestive system).
- 5 Organism: The complete living being (e.g., Human, Mango tree).
Division of Labour: The distribution of different functions among various cells, tissues, or organs for better efficiency.