Cambridge IGCSE Biology 1 Characteristics and Classification of Living Organisms Exam Questions

About Cambridge IGCSE Biology 1 Characteristics and Classification of Living Organisms

This is the opening topic of Cambridge IGCSE Biology and sets out what makes something alive and how biologists sort organisms into groups. You need the seven characteristics of living organisms, the binomial system of naming species, and how to use and construct dichotomous keys. Core content covers the main features of vertebrate classes and arthropod groups; Extended candidates also learn the five kingdoms, ferns and flowering plants (monocots and dicots), and the structure of viruses. Examiners like key-construction questions, identifying organisms from drawings, and explaining why classification increasingly uses DNA base sequences. The ideas link forward to cell structure, variation and evolution.

What you need to know

• 1.1 Characteristics of life All living organisms show movement, respiration, sensitivity, growth, reproduction, excretion and nutrition (often remembered as MRS GREN). Learn the full syllabus definition of each, for example excretion is the removal of waste products of metabolism and substances in excess of requirements.
• 1.2 Species and binomial names A species is a group of organisms that can reproduce to produce fertile offspring. The binomial system gives each species a genus and species name, for example Homo sapiens, with the genus written with a capital letter.
• 1.2 Classification and DNA Organisms are classified by shared features. Extended candidates must explain that classification reflects evolutionary relationships, and that organisms with more similar DNA base sequences (and amino acid sequences in proteins) share a more recent common ancestor.
• 1.2 Dichotomous keys Each step of a key splits organisms into two groups using a single visible feature, such as presence of wings. When constructing a key, use observable features rather than size or colour alone where possible, and make each question answerable with yes or no.
• 1.3 Animal groups Vertebrates: mammals (fur, external ears, mammary glands), birds (feathers, beak), reptiles (dry scales), amphibians (moist skin) and bony fish (wet scales, fins, gills). Arthropods: insects (three pairs of legs, three body sections), arachnids (four pairs of legs), crustaceans (more than four pairs of jointed legs, two pairs of antennae) and myriapods (many segments, legs on each).
• 1.3 Kingdoms and plants (Extended) The five kingdoms are animal, plant, fungus, prokaryote and protoctist. Ferns have leaves called fronds and reproduce by spores; flowering plants reproduce by seeds and are split into monocotyledons (parallel leaf veins, flower parts in threes) and dicotyledons (branching veins, parts in fours or fives).
• 1.3 Viruses (Extended) Viruses are not part of any kingdom. They have a protein coat surrounding genetic material and can only reproduce inside host cells.

Common mistakes in 1 Characteristics and Classification of Living Organisms

• Writing the binomial name with a capital letter for the species name. Only the genus has a capital, for example Panthera leo.
• Using vague features in a key such as 'big' or 'dark'. Use clear, observable features, for example 'has six legs' or 'leaf has a smooth edge'.
• Saying excretion is the removal of faeces. Faeces are egested, not excreted, because most of their content was never part of metabolism.
• Calling viruses prokaryotes. Viruses are not cells and are not placed in any of the five kingdoms.
• Confusing arachnids and insects. Spiders have four pairs of legs and two body sections; insects have three pairs of legs and three body sections.

Try three 1 Characteristics and Classification of Living Organisms exam-style questions