Yeasts are eukaryotic micro-organisms classified in the Fungi kingdom. 1500 species are described but that is estimated to be only 1% of all yeast species. Most require oxygen for aerobic cellular respiration, or are anaerobic, using aerobic methods of energy production.
Yeast are unicellular, Saccharomyces cerevisiae has been used in baking and fermenting alcoholic beverages for thousands of yeats. Living yeast ferment alcohol. The use organic compounds as a source of energy and do not require sunlight to grow.
Other yeasts like Candida albicans are opportunistic pathogens and can cause infections in people.
Recently, yeast has been used to generate electricity in microbial fuel cells, and produce ethanol for the biofuel industry.
Amoebae: are single cell life forms with an irregular shape. "Amoeba" and "Amoeboid" are interchangeable, and refer to a creatue moving by use of pseudopods. There are at least 97 different genera.
The superclass Rhizopoda has naked and shelled amoebas. They tend to ingest food and creep toward food. Amoebas breathe using their entire cell membrane that is constantly immersed in water. Some consume bacteria, others, like yeast, consume dead organic material, others eat protists
