Chapter 2: Biological Classification
NCERT Biology | NEET-UG Preparation | Chapter Summary
Learning objective: Understand the development of biological classification, the five-kingdom system, the major characteristics of different kingdoms, and the differences between viruses, viroids, prions and lichens.
Kingdom Protista
Kingdom Protista includes mainly unicellular eukaryotic organisms. They are commonly found in aquatic environments or places with moisture.
General characteristics
- They possess a true nucleus and membrane-bound organelles.
- Some are photosynthetic, while others are heterotrophic.
- Movement, where present, may occur through cilia, flagella or pseudopodia.
- Reproduction may be asexual or sexual, depending on the group.
Major groups
- Chrysophytes: Include diatoms and golden algae. Diatoms have silica-rich cell walls, and their accumulated remains contribute to diatomaceous earth.
- Dinoflagellates: Mostly marine and photosynthetic. Many have two flagella. Some species cause red tides.
- Euglenoids: Usually occur in freshwater. They have a protein-rich pellicle instead of a typical cell wall and may show mixotrophic nutrition.
- Slime moulds: Saprophytic protists that feed on decaying organic matter. Under suitable conditions, they form reproductive structures that produce spores.
- Protozoans: Heterotrophic protists commonly divided into amoeboid, flagellated, ciliated and sporozoan forms in traditional classifications.
| Group | Key feature |
|---|---|
| Diatoms | Silica-rich cell walls |
| Dinoflagellates | Two flagella in many species; some cause red tides |
| Euglenoids | Pellicle and mixotrophic nutrition in examples such as Euglena |
| Ciliated protozoans | Cilia help in movement and food collection |
| Amoeboid protozoans | Pseudopodia help in movement and food capture |
