2.2 Features of Organisms

Cambridge O Level Biology (5090)

2026 📋 Syllabus Objectives

By the end of this topic, you should be able to:

  1. State the main features used to place all organisms into one of the five kingdoms: Animal, Plant, Fungus, Prokaryote, Protoctist
  2. State the main features used to place organisms into groups within the animal kingdom — including the main vertebrate groups (mammals, birds, reptiles, amphibians, fish) and the main arthropod groups (myriapods, insects, arachnids, crustaceans)
  3. State the main features used to place organisms into groups within the plant kingdom — limited to ferns and flowering plants (dicotyledons and monocotyledons)
  4. Classify organisms using the features from objectives 1, 2, and 3
  5. State the main features of viruses — limited to protein coat and genetic material
  6. Understand that viruses can only replicate inside living cells

📖 Main Content

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SECTION 1: The Five Kingdoms

All living things on Earth are sorted into five major groups called kingdoms. A kingdom is the largest and most general level of classification — think of it as the biggest "drawer" into which you sort living things.

The five kingdoms are:

  • Animal
  • Plant
  • Fungus
  • Prokaryote
  • Protoctist

Each kingdom has a unique set of features that makes it different from the others. Let's look at each one.

🐅 Kingdom: Animal

Animals are the most familiar living things to most of us — think of dogs, fish, insects, and humans.

Key features of animals:

  • Their cells have a nucleus (a control centre inside the cell that contains genetic information)
  • Their cells have no cell walls (unlike plants and fungi)
  • Their cells have no chloroplasts (so they cannot make their own food using sunlight)
  • They feed on organic substances — this means they eat other living things or things made by other living things (organic substances are carbon-containing molecules made by living organisms)

💡 In simple terms: Animals are living things that eat other organisms for food and have cells without cell walls.

🌿 Kingdom: Plant

Plants are the green, rooted organisms you see in gardens, forests, and fields.

Key features of plants:

  • Their cells have a nucleus
  • Their cells have cell walls made of cellulose (cellulose is a tough carbohydrate that gives plant cells their firm shape)
  • Their cells often contain chloroplasts — structures that hold a green pigment called chlorophyll
  • Chlorophyll absorbs energy from sunlight so the plant can make its own food through photosynthesis (the process of turning sunlight, water, and carbon dioxide into sugar)
  • They feed by photosynthesis — they make their own food and do not need to eat other organisms
  • They may have roots, stems, and leaves (though not all plants have all of these — mosses, for example, do not have true roots)
  • Because plants make food from sunlight, they do not need to move around — they stay in one place

💡 In simple terms: Plants are green, stay in one place, make their own food from sunlight, and have cell walls made of cellulose.

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