Chapter 2: Characteristics of Life

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Diversity of living organisms: refers to the large variety of organisms on Earth

Life: describes an organic-based object  that possesses the characteristics of metabolism and continuity of life

Metabolism: the sum of all the chemical reactions in a living organism

Continuity of life: describes how living organisms arise from living organisms of the same type

The five characteristics of life:

1. Organisation
2. Nutrition
3. Homeostasis/Excretion
4. Response
5. Reproduction


Organisation refers to different levels of complexity in living organisms

Cell → tissue → organ → organ system → organism → population

  • The cell is the building block of life
  • Molecules (proteins, fats, carbohydrates) organised into organelles, organised into cells, organised into tissues, organised into organs, organised into systems, organised into an organism
  • Disruption of organisation leads to malfunction of metabolism and/or continuity of life


Nutrition is the way in which living organisms obtain and use food

  • All our energy ultimately comes from the Sun
  • Plants create glucose from carbon dioxide and water using the energy in sunlight – photosynthesis
  • Herbivores eat the plants and the flow of energy begins – the food chain
  • Carnivores eat the herbivores
  • The chemical energy in the bonds of glucose is converted by a cell’s machinery to other forms of energy so the organism can do work


Excretion refers to the getting rid of waste products of metabolism from the body

  • An organism’s body has ways to maintain its internal environment (homeostasis)
  • Excretion is one way in which an organism maintains its internal environment
  • Excretion in animals occurs via lungs, kidneys and skin
  • Excretion in plants occurs via stomata (leaves) and lenticels (stem)
  • Excretion in single-celled organisms (e.g. bacteria) occurs via diffusion


Response refers to the way in which living organisms react to their environment

  • A living organism responds to environmental changes thereby maintaining a favourable metabolic environment
  • In animals the stimulus is detected by sense organs that respond to light, sound, temperature, chemical equilibrium, touch, movement and direct mainly muscles to produce movement
  • In plants responses are usually very slow – they respond to light and water by altering the direction of growth – tropisms (e.g. phototropism and geotropism)


Reproduction refers to the way in which an organism or organisms interact to create a new individual

  • Every living organism has the inherent ability and need to reproduce, and occurs by usually by one of two methods:
    1. Asexual reproduction: formation of offspring by one individual organism (all offspring are genetically identical to the parent)
    2. Sexual reproduction: formation of offspring from  two parents (male and female)