Fungi are heterotrophic, meaning they cannot produce their own food like plants do through photosynthesis. Instead, they obtain energy by absorbing nutrients from their surroundings.

Here's how fungi acquire energy:

1. Secreting enzymes: Fungi release digestive enzymes into their environment, breaking down complex organic matter like wood, leaves, or even living organisms.

2. Absorbing nutrients: The broken-down nutrients are then absorbed directly through the fungal cell walls, providing them with the energy and building blocks they need to grow and reproduce.

Fungi can be classified into different groups based on their energy source:

* Saprotrophic fungi: These are the most common type and obtain their nutrients from dead organic matter. Examples include mushrooms, molds, and yeast.

* Parasitic fungi: These live on and feed off living organisms, often causing diseases. Examples include athlete's foot fungus and rust fungi.

* Mutualistic fungi: These fungi live in a symbiotic relationship with another organism, both benefiting from the interaction. Examples include mycorrhizal fungi that live in association with plant roots.

No matter the source, all fungi acquire energy through the process of absorption, breaking down complex molecules and taking in the resulting simpler compounds.