- ALL fungi are CHEMOHETEROTROPHIC (chemo-organotrophic) - synthesising the organic compounds they need for growth and energy from pre-existing organic sources in their environment, using the energy from chemical reactions.
- Since their protoplasm is protected by a rigid wall, fungi must obtain their nutrients by the process of ABSORPTION.
- SMALL MOLECULES (e.g. simple sugars, amino acids) in solution can be absorbed directly across the fungal wall and plasma membrane.
- LARGER, MORE COMPLEX MOLECULES (e.g. polymers such as polysaccharides and proteins) must be first broken down into smaller molecules, which can then be absorbed. This degradation takes place outside the fungal cell or hypha and is achieved by enzymes which are either released through or are bound to the fungal wall. Because these enzymes act outside the cell they are called EXTRACELLULAR ENZYMES.
- Since water is essential for the diffusion of extracellular enzymes and nutrients across the fungal wall and plasma membrane, actively growing fungi are usually restricted to relatively moist (or humid) environments.