Fungi are considered by most biologists to form a kingdom of their own, parallel to those of animals, plants, bacteria, etc. The Kingdom of Fungi includes a great diversity of organisms occupying a great variety of habitats. They are fundamentally different from plants, which are autotrophic and obtain their energy from light.
Nutrition is by absorption.
Nutrients are absorbed directly into the cell from the external environment. Most animals obtain nutrients by ingestion, taking food into their bodies where it is digested and absorbed. Plants, being autotrophs, produce their food internally. A few fungi, such as yeasts and chytrids, may be single-celled, but these represent a very small percentage of the estimated 1.5 million species. Plant cell walls contain cellulose, not chitin.