1.1 Characteristics of Living Organisms

2026 Syllabus Objectives

  1. Describe the characteristics of living organisms by describing:
    • (a) movement as an action by an organism or part of an organism causing a change of position or place
    • (b) respiration as the chemical reactions in cells that break down nutrient molecules and release energy for metabolism
    • (c) sensitivity as the ability to detect and respond to changes in the internal or external environment
    • (d) growth as a permanent increase in size and dry mass
    • (e) reproduction as the processes that make more of the same kind of organism
    • (f) excretion as the removal of the waste products of metabolism and substances in excess of requirements
    • (g) nutrition as the taking in of materials for energy, growth and development

What is an Organism? 🧬

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An organism is a complete living thing. Examples include humans, bacteria, plants like mango trees, and animals like the platypus.

Biology is the study of organisms. Despite the incredible diversity of life on Earth, all organisms share seven fundamental characteristics that distinguish them from non-living things.

Key Principle: Some non-living things may exhibit one or two of these characteristics, but no non-living thing possesses all seven characteristics. This is what makes something truly alive.

The Seven Characteristics of Living Organisms 📋

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All living organisms exhibit seven characteristics, commonly remembered by the acronym MRS GREN:

1. Movement 🏃

Definition: Movement is an action by an organism or part of an organism causing a change of position or place.

Key Points:

  • Movement is easily observable in animals (walking, running, swimming, flying)
  • Plant movement is less obvious but still present
  • Some plants can move parts of themselves quite quickly (e.g., Venus flytrap snapping shut)
  • At the cellular level, chloroplasts can be observed moving inside plant cells under a microscope

Examples:

  • Animals: Running, swimming, flying
  • Plants: Turning flowers to face the sun, internal movement of chloroplasts
  • Venus flytrap: Rapid closing of trap leaves to catch prey

2. Respiration ⚡

Definition: Respiration is the chemical reactions in cells that break down nutrient molecules and release energy for metabolism.

Key Points:

  • Respiration is a chemical reaction that occurs inside every living cell
  • It is the way organisms obtain energy from nutrients (usually glucose)
  • Energy released from respiration is used to drive other chemical reactions in cells
  • All chemical reactions in cells (including respiration) are collectively called metabolism

Important: Respiration is NOT the same as breathing. Respiration is a cellular process that releases energy from glucose.

The Process:

Nutrient molecules (glucose)→RespirationEnergy for metabolism\text{Nutrient molecules (glucose)} \xrightarrow{\text{Respiration}} \text{Energy for metabolism}

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