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Biological Classification
Biology · Class 11NCERT pp. 10–212 sets × 25 questionsFree
Key facts and formulas for Biological Classification, three worked sample questions, and two full practice sets. Every question has a hint, a reason for every option and a step-by-step solution, with a calculator or animation where one helps. English and Hinglish.
Key facts for this chapter
| Idea | Rule or fact |
|---|
| Five kingdoms (Whittaker 1969) | Monera, Protista, Fungi, Plantae, Animalia; criteria: cell structure, nutrition, body organisation, reproduction, phylogeny |
| Cell walls | Monera: peptidoglycan; Fungi: chitin (N-acetylglucosamine); Plantae: cellulose; Diatoms: silica; Animalia: none |
| Bacterial shapes | Coccus sphere, bacillus rod, vibrio comma, spirillum spiral; ribosomes 70S; reproduce by fission |
| Archaebacteria | Halophiles in salty areas, thermoacidophiles in hot springs, methanogens in marshes; special membrane lipids |
| Cyanobacteria and nitrogen cycle | Heterocysts fix N2; Rhizobium in legume nodules; Nitrosomonas NH3 to nitrite, Nitrobacter nitrite to nitrate |
| Protista groups | Diatoms: silica walls, diatomaceous earth; dinoflagellates: marine, red tides; Euglena: photosynthetic in light, heterotrophic in dark; slime moulds: saprophytes |
| Protozoans | Amoeba pseudopodia; Trypanosoma sleeping sickness (tsetse); Paramoecium cilia, two nuclei; Plasmodium malaria; Entamoeba amoebic dysentery |
| Fungal reproduction | Plasmogamy, karyogamy, then meiosis in zygote; ascospores inside asci, basidiospores outside basidium; Deuteromycetes only conidia |
| Fungi examples | Rhizopus bread mould, Ustilago smut, Puccinia rust, Agaricus mushroom, Amanita muscaria hallucinogenic, Claviceps ergot |
| Viruses | Ivanowsky 1892, Beijerinck 1898, Stanley 1935; Diener viroids 1971; capsid helical, icosahedral or complex; HIV has ssRNA |
Three sample questions
Q1. Aristotle's early scientific attempt at classification sorted plants into
- monocots and dicots
- trees, shrubs and herbs
- algae, mosses and ferns
- cellular and acellular groups
Hint and solution
Hint: Aristotle used simple outer features that anyone can see, such as the size and woodiness of a plant.
- Aristotle → simple external features — The question asks how Aristotle sorted plants. He used only visible features.
- Plants: trees, shrubs, herbs — He grouped plants by size and woodiness into trees, shrubs and herbs. Animals he grouped as red-blooded or not.
- Monocot/dicot = later system — Monocots and dicots depend on internal seed structure, so they are not his scheme.
- Answer: trees, shrubs, herbs — So the correct choice is trees, shrubs and herbs. Option B.
Answer: B. Aristotle used simple external features: plants as trees, shrubs and herbs; animals as red-blooded or not.
Q2. Consider the Two Kingdom system.
I. It did not separate prokaryotes from eukaryotes.
II. It did not separate unicellular from multicellular organisms.
III. It did not separate photosynthetic from non-photosynthetic forms.
Which are correct?
- I and II only
- II and III only
- I and III only
- I, II and III
Hint and solution
Hint: The Two Kingdom system had only Plantae and Animalia. Ask which kinds of organisms had no separate place.
- Two Kingdoms: Plantae + Animalia — Only two kingdoms existed, so many organisms were forced into one of them.
- Statement I: prokaryote = eukaryote group — Bacteria, which are prokaryotes, were placed with eukaryotes. So I is true.
- Statements II and III also true — Unicellular and multicellular forms were mixed, and so were photosynthetic and non-photosynthetic ones such as fungi. So II and III are true.
- All three correct — Since every statement is true, the answer is I, II and III. Option D.
Answer: D. All three were gaps, which is why the system was judged inadequate.
Q3. Whittaker's five kingdom classification (1969) used which criteria?
- Cell structure, mode of nutrition, body organisation, reproduction and phylogenetic relationships
- Only the presence of a cell wall
- Only habitat and size
- Only external form
Hint and solution
Hint: Whittaker combined several features, not just one. Think of cell, food, body and reproduction.
- Five kingdoms → many criteria — The question asks about the criteria of the five kingdom system. Whittaker used more than one.
- Cell structure + nutrition + body — He looked at cell type, how the organism gets food, and how its body is organised.
- Reproduction + phylogeny — He also added mode of reproduction and evolutionary relationships.
- Answer: all five criteria — Only the first option lists all of these. Option A.
Answer: A. Several criteria were combined, not outer form alone.
How to use this chapter
Read the NCERT pages first, then attempt Set 1 without the hints. Note every wrong answer in a mistake list, read the reason for each option, and retry Set 2 two days later. A topic is solid when you can say why each wrong option is wrong.