The major distinguishing characteristic of fungi is their heterotrophic mode of nutrition. This means they obtain their food from other organisms, unlike plants which produce their own food through photosynthesis.

Here's a breakdown:

* Heterotrophic: Fungi cannot make their own food, so they must obtain it from other sources, either living or dead.

* Saprophytic: Many fungi decompose dead organic matter, playing a vital role in nutrient cycling.

* Parasitic: Some fungi live on and obtain nourishment from living organisms, sometimes causing disease.

* Mutualistic: Some fungi form symbiotic relationships with other organisms, benefiting both parties.

This unique way of obtaining food is what sets fungi apart from plants, animals, and bacteria.