SSC CGL - Detailed Guide 2025
Self-Paced Course
Cell - The Basic Unit of Life
Reference: Lucent GK, NCERT Class 6–12
Cell Structure & Organelles
Cells are the structural and functional units of all living organisms. They can be:
- Unicellular (e.g., Amoeba)
- Multicellular (e.g., Humans)
All cells have three main parts: Plasma membrane, Cytoplasm, and Nucleus.
Cell Structure Overview
| Component | Description |
|---|---|
| Plasma Membrane | Semi-permeable membrane controlling entry and exit of substances |
| Cytoplasm | Gel-like substance containing organelles and enzymes for metabolic activities |
| Nucleus | Control center of the cell; contains DNA, chromatin, and nucleolus |
Major Cell Organelles
| Organelle | Structure & Function |
|---|---|
| Cell Wall | Rigid outer covering in plant cells (made of cellulose); provides protection and shape |
| Nucleus | Double membrane; controls all cell activities; contains genetic material |
| Mitochondria | Double membrane; powerhouse of cell; site of ATP production (aerobic respiration) |
| Endoplasmic Reticulum | Two types: Rough ER (with ribosomes -- protein synthesis) and Smooth ER (lipid synthesis, detoxification) |
| Ribosomes | Non-membranous; site of protein synthesis; found in cytoplasm or on RER |
| Golgi Apparatus | Stacked membranes; modifies, packages, and transports proteins and lipids |
| Lysosomes | Membrane-bound sacs with enzymes; digest old organelles and foreign substances ("suicidal bags") |
| Vacuoles | Storage sacs for water, nutrients, and waste; large and central in plant cells, small in animal cells |
| Plastids | Found only in plant cells; types: Chloroplast (photosynthesis), Chromoplast (color), Leucoplast (storage) |
| Centrosome/ Centrioles | Present in animal cells; help in spindle formation during cell division |
| Cytoskeleton | Network of fibers; provides shape, support, and helps in intracellular transport |
Difference between Plant and Animal Cells
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present (made of cellulose) | Absent |
| Shape | Usually fixed (rectangular) | Usually irregular or round |
| Plastids | Present (e.g., chloroplasts) | Absent |
| Vacuoles | Large central vacuole | Small and many (if present) |
| Centrioles | Absent (except in lower plants) | Present |
| Lysosomes | Rare | Common |
| Energy Storage | Stored as starch | Stored as glycogen |
| Mode of Nutrition | Autotrophic (photosynthesis) | Heterotrophic |
| Golgi Apparatus | Present (scattered units called dictyosomes) | Present (compact stack) |
Developed By Jan Mohammad
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