2.1

• Essential characteristics that define a living organism:

  • MRS GREN: Matter, Respiration, Stimuli, Gases, Reproduction, Energy, Nutrients
  • Living organisms require energy (light or chemical energy), Matter (e.g., water), Gases, Nutrients, Ions, ability to respond to Stimuli, removing waste (excretion)
• Cells obtain and convert energy for their metabolic activities through:

  • METABOLISM: sum of chemical reactions in cells
  • Converting chemical energy (cellular respiration)
  • Converting light energy (photosynthesis)
• Organisms acquire and utilise nutrients in different ways:

  • Autotrophs: Chemosynthesis + Photosynthesis
  • Heterotroph: Cellular Respiration
• Organisms reproduce through various methods:

  • Unicellular organisms reproduce asexually by duplicating DNA and forming 2 identical daughter cells
  • Multicellular organisms may reproduce sexually, asexually, or by both methods
• Elimination of waste products is crucial for the health and functioning of cells and organisms because:

  • Cells require inputs (energy and matter) and produce outputs (wastes) for function, reproduction, response to stimuli, and growth
  • Metabolic processes produce potentially toxic wastes (e.g., carbon dioxide, urea) that need removal for cells to remain healthy and functional
• Distinguishing between Matter and Energy:

  ENERGY:

  • Light energy from the sun
  • Chemical energy stored in complex molecules
  • Wastes

  MATTER:

  • Gases such as O2 and CO2
  • Simple nutrients, ions, and water
• Three principles of cell theory:

  • The cell is the basic unit of life
  • Cells arise from pre-existing cells
  • All living things are composed of cells or cell products