Single-Celled Organisms
Biology: AQA A Level, topic 3.2.1
Single-Celled Organisms
Single-celled organisms exchange directly with their external environment.
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.
- Substances are exchanged by all organisms for this reason.
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.
Test yourself on Single-Celled Organisms
Which of the following statements about substance exchange are true?
Which of these is NOT an adaptation of single-celled organisms to increase their surface area to volume ratio?