They can be both. Some are even able to switch between the two.
A fungi is a multi-cell but can be a single cell
Yeast is a single-celled fungi.
Fungi:Fungi is multi celled but can also be single celled. Fungi is not a plant, either. Fungi cant make its own food. Fungi absorbs food from the material they live on. An example of a Fungi is : Mushrooms, Yeast.
The five main kingdoms in nature are: Animalia (organisms with complex cells and tissues), Plantae (organisms that photosynthesize), Fungi (organisms that absorb nutrients), Protista (mostly single-celled organisms), and Monera (prokaryotic organisms).
Multi cellular
Yeast is a single-cell fungus. I'm pretty sure all single-celled fungi are classified as yeast,but don't hold me to that.
Certain types of fungi happen to be uni-cellular. Others are multicellular, but I don't know the names of multi cellular fungi.
Bacteria tend to be single celled organisms.
Sac Fungi are both unicellular and multicellular
Yeast
Fungi and Protista.
Is a arachnids a single or multi celled