Functions of Life (DP IB Biology: HL): Revision Note

Functions of Life

• Unicellular (single-celled) and multicellular (many cells) organisms must carry out the following functions to stay alive:

  • Metabolism - all the enzyme-catalysed reactions occurring in a cell, including cell respiration

  • Reproduction - the production of offspring. It may be sexual or asexual

  • Homeostasis - the ability to maintain and regulate internal conditions within tolerable limits, including temperature

  • Growth - the permanent increase in size

  • Response - (or sensitivity), the ability to respond to external or internal changes (stimuli) in their environment. Thus improving their chance of survival

  • Excretion - the disposal of metabolic waste products, including carbon dioxide from respiration

  • Nutrition - the acquisition of energy and nutrients for growth and development, either by, absorbing organic matter or by synthesising organic molecules (e.g. photosynthesis)

• Unicellular organisms have adapted unique ways to carry out these functions compared to multicellular organisms

  • Mitochondria are present to provide energy through respiration

  • The cell membrane controls movement of materials in and out of the cell to maintain homeostasis

  • Ribosomes are present to produce proteins for growth and repair, in addition enzymes for vital cell functions

  • Vacuoles are used for digestion purposes and also to store waste substance

  • Cilia or flagella are used for movement of the organism in response to changes in the environment