This lesson is about how scientists organize the millions of different living things into groups. This process is called classification. Understanding the main groups and their key features is essential.

1. Short Notes: Core Concepts

A. Why Classify?

• To make organisms easier to study.

• To understand the evolutionary relationships between different life forms.

• To easily identify organisms.

B. The Three Domains All life is first divided into three super-kingdoms or Domains:

1. Archaea: Prokaryotes (no nucleus) that live in extreme environments (hot springs, very salty water).

2. Bacteria: The more common prokaryotes. Found everywhere. Some cause disease, many are useful. Includes Cyanobacteria.

3. Eukarya: All organisms with a true nucleus in their cells. This domain is divided into four kingdoms.

C. The Four Eukaryotic Kingdoms

1. Protista: Simple eukaryotes. Mostly unicellular. Includes algae and protozoa (like Amoeba).

2. Fungi: Have cell walls made of chitin. They are heterotrophs (get food from others), often by decomposing dead matter. Includes mushrooms and yeast.

3. Plantae: Multicellular, have cell walls made of cellulose, and are autotrophs (make their own food via photosynthesis).

4. Animalia: Multicellular, no cell walls, and are heterotrophs.

D. Kingdom Plantae - Key Divisions

• Non-flowering Plants: Reproduce without flowers.

  • Seedless Plants: (e.g., Ferns, Moss). Reproduce with spores.

  • Seeded Plants (Gymnosperms): Have "naked" seeds, often in cones (e.g., Pinus, Cycas).

• Flowering Plants (Angiosperms): Produce flowers and seeds are enclosed in a fruit.

  • Monocots: One cotyledon, fibrous roots, parallel leaf veins, flower parts in 3s (e.g., Paddy, Coconut, Grass).

  • Dicots: Two cotyledons, tap root system, reticulate (net-like) leaf veins, flower parts in 4s or 5s (e.g., Mango, Beans, Rose).

E. Kingdom Animalia - Key Divisions

• Invertebrates (No backbone):

  • Cnidaria: Soft bodies, tentacles with stinging cells (e.g., Jellyfish, Hydra).

  • Annelida: Segmented (ringed) bodies (e.g., Earthworm, Leech).

  • Mollusca: Soft body, often with a shell, have a muscular foot (e.g., Snail, Octopus).

  • Arthropoda: Exoskeleton and jointed legs. The largest phylum (e.g., Insects, Spiders, Crabs, Centipedes).

  • Echinodermata: Spiny skin, marine animals, often with five-part symmetry (e.g., Starfish, Sea Urchin).

• Vertebrates (Have a backbone):

  • Pisces (Fish): Live in water, breathe with gills, have scales and fins. Cold-blooded.

  • Amphibia (Amphibians): Start life in water (gills), move to land as adults (lungs). Have moist skin. Cold-blooded (e.g., Frog, Salamander).

  • Reptilia (Reptiles): Have dry, scaly skin. Lay eggs with leathery shells. Cold-blooded (e.g., Snake, Lizard, Crocodile).

  • Aves (Birds): Have feathers and wings. Lay eggs with hard shells. Warm-blooded.

  • Mammalia (Mammals): Have hair/fur, give birth to live young, and produce milk. Warm-blooded (e.g., Human, Elephant, Bat, Whale).

F. Binomial Nomenclature

• The scientific, two-part naming system (invented by Carolus Linnaeus).

• Format: Genus species (e.g., Human is Homo sapiens).

• Rules:

  1. The Genus name is capitalized.

  2. The species name is lowercase.

  3. The whole name is written in italics or is underlined.

2. Tips & Tricks for the Exam

• Focus on Comparison Tables: The best way to study classification is by comparing groups. The Monocot vs. Dicot table and the characteristics of the 5 Vertebrate classes are extremely important.

• Learn One Example: For every group (phylum or class), learn one clear example. This helps you remember the features.

• Spot the Keyword: In questions, look for keywords. "Jointed legs" -> Arthropoda. "Feathers" -> Aves. "Cellulose cell wall" -> Plantae.

3. Important Points & Common Exam Questions

• Monocot vs. Dicot Differences: You will almost certainly be asked to list differences.

• Classify an Animal: "A butterfly has an exoskeleton and jointed legs. To which phylum does it belong? State your reason."

  • Answer: Phylum Arthropoda, because it has an exoskeleton and jointed legs.

• Identify a Vertebrate Class: "An animal has dry scales and is cold-blooded. To which vertebrate class does it belong?"

  • Answer: Class Reptilia.

• Scientific Names: "Write the scientific name for a human correctly."

  • Answer: Homo sapiens (or Homo sapiens underlined).