Class 11th Biology Biological Classification Notes

Introduction

Biological classification helps in organizing organisms systematically. It is necessary for:
✔️ Understanding evolutionary relationships.
✔️ Easier identification and nomenclature.

🌿 Aristotle classified organisms into plants and animals.
📜 Carl Linnaeus proposed the two-kingdom classification.
🔬 R.H. Whittaker introduced the five-kingdom classification in 1969.
🧬 Carl Woese proposed the three-domain system based on RNA sequencing.

Five-Kingdom Classification (Whittaker, 1969)

🦠 Monera – Prokaryotic, unicellular organisms without a nucleus (e.g., Bacteria, Cyanobacteria).
🦠 Protista – Eukaryotic, mostly unicellular organisms living in water (e.g., Amoeba, Euglena).
🍄 Fungi – Eukaryotic, multicellular (except yeast), with a chitin cell wall (e.g., Yeast, Mushrooms).
🌳 Plantae – Eukaryotic, multicellular, autotrophic (e.g., Algae, Angiosperms).
🦁 Animalia – Eukaryotic, multicellular, heterotrophic, no cell wall (e.g., Insects, Mammals).

Kingdom Monera (Bacteria & Cyanobacteria)

🦠 Prokaryotic, unicellular, and lacking a true nucleus.
🔬 Cell Wall: Made of peptidoglycan.
🧫 Reproduction: Binary fission, spore formation.

💡 Types of Bacteria (Based on Shape):
🔵 Cocci – Spherical (e.g., Streptococcus).
🟦 Bacilli – Rod-shaped (e.g., Escherichia coli).
🌀 Spirilla – Spiral-shaped (e.g., Spirillum).
✔️ Vibrio – Comma-shaped (e.g., Vibrio cholerae).

🔥 Archaebacteria (Ancient Bacteria):

• 🌱 Methanogens – Found in cow intestines, help in biogas production.
• 🧂 Halophiles – Live in salty environments.
• 🌋 Thermoacidophiles – Live in hot springs.

Kingdom Protista (Single-Celled Eukaryotes)

🔬 Eukaryotic, unicellular organisms living in aquatic habitats.

💡 Types of Protists:

• Protozoans – Heterotrophic (e.g., Amoeba, Paramecium).
• Diatoms – Photosynthetic with a silica cell wall (e.g., Navicula).
• Dinoflagellates – Photosynthetic and bioluminescent (e.g., Gonyaulax).
• Euglenoids – Both autotrophic & heterotrophic (e.g., Euglena).
• Slime Moulds – Saprophytic (e.g., Physarum).

💨 Locomotion in Protists:
🦠 Amoeba moves using pseudopodia.
🦠 Paramecium moves using cilia.
🦠 Euglena moves using flagella.

Kingdom Fungi (Heterotrophic Decomposers)

🍄 Eukaryotic, multicellular (except yeast), with a cell wall made of chitin.
🍂 Heterotrophic – Feeds on dead organic matter (saprophytes) or live organisms (parasites).

💡 Types of Fungi:
✔️ Moulds – Rhizopus (bread mould).
✔️ Yeast – Saccharomyces (used in baking).
✔️ Mushrooms – Agaricus (edible mushrooms).
✔️ Parasitic Fungi – Puccinia (causes rust in wheat).

🧬 Reproduction:

• Asexual – Spores, budding (in yeast).
• Sexual – Fusion of hyphae.

Kingdom Plantae (Autotrophic Multicellular Organisms)

🌿 Eukaryotic, multicellular, autotrophic (perform photosynthesis).
🌱 Cell Wall: Made of cellulose.

💡 Types of Plants:

• Algae – Aquatic, photosynthetic (e.g., Spirogyra, Chlorella).
• Bryophytes – Non-vascular, require moist environments (e.g., Moss, Liverworts).
• Pteridophytes – Vascular, reproduce via spores (e.g., Ferns).
• Gymnosperms – Seed-producing plants without flowers (e.g., Pine, Cycas).
• Angiosperms – Flowering plants (e.g., Mango, Rose).

Kingdom Animalia (Multicellular Heterotrophs)

🦁 Eukaryotic, multicellular, heterotrophic, no cell wall.
🧠 Nervous system present for coordination.

👶 Modes of Reproduction:

• Oviparous – Lay eggs (e.g., Birds, Reptiles).
• Viviparous – Give birth to live young (e.g., Mammals).

Viruses, Viroids, and Prions

🦠 Viruses – Acellular organisms containing DNA or RNA, cannot reproduce outside a host.
✔️ Examples: DNA Virus (Smallpox), RNA Virus (HIV, Coronavirus).

🦠 Viroids – Smaller than viruses, contain RNA only (e.g., Potato spindle tuber disease).

🦠 Prions – Infectious proteins causing brain diseases (e.g., Mad Cow Disease).

Conclusion

✔️ Biological classification is essential for understanding life’s diversity.
✔️ The five-kingdom system categorizes organisms based on characteristics.
✔️ Helps scientists study evolutionary history and relationships.