single-celled organisms

• Need for exchange

  • Single-celled organisms need to obtain substances from their environment to be used in processes inside the cell (e.g. oxygen for respiration).
  • Waste substances also need to be removed from the cell (e.g. carbon dioxide) to avoid harming the cell.
• Body surface exchange

  • Single-celled organisms can exchange gases and other substances using their cell membrane.
  • The rate of gas exchange is increased by a larger surface area to volume ratio.
  • Single-celled organisms can be adapted to increase their surface area to volume ratio (e.g. by making themselves wide, flat or with multiple folds).
• Diffusion rate

  • Diffusion rate is rapid for single-celled organisms because the substances only have to move across one cell-surface membrane.