Members of the kingdom Fungi are eukaryotic, heterotrophic, multicelled organisms (except for yeasts).  Examples of fungi are "mushrooms," puffballs, bracket fungi, molds, and mildews.  Fungi cell walls contain chitin, which is the same material found in the exoskeletons of arthropods.  Fungi are important decomposers in ecosystems as they break down organic materials such as dead organisms, leaves, old wood, and feces.

The body of the multicellular fungi consists of long, slender hyphae, some of which can specialize to hold spores, to anchor its body, to secrete enzymes, and to absorb decomposing material.  Fungi break down potential food sources by excreting strong hydrolytic enzymes (exoenzymes).  Once the food is broken down into smaller molecules, the fungi then absorb them into their bodies. 
 
Fungi are generally described and grouped according to the way they reproduce.  Reproduction can be both sexual and asexual, producing spores that disperse by wind or water.

The term "yeast" is used to described any single-celled fungus species, including Baker's yeast (Saccharomyces cerevisiae). Most fungi, such as mushrooms, molds and rusts, are multicellular and are not microbes. Members of the Fungus group are eukaryotes (their cells contain membrane-enclosed nuclei and organelles) that feed by absorption. The cell walls of fungi are composed of chitin, the material that gives hardness to the exoskeletons of insects.

Baker's yeast cells are larger than bacteria cells, usually about 10µm in diameter. Students will not be able to observe many internal details of yeast cells using a typical classroom microscope set-up. However, they may notice some dividing or budding yeast cells. Yeasts are able to reproduce asexually by simple cell division or by pinching off bud cells from a parent cell. Baker's yeast has many uses, including in the production of beer and bread, and as a model organism for the study of processes inside cells.

Viewing this presentation fulfills part of the requirements for completing the short course on The Science of Microbes, offered on BioEd Online for professional development contact hours. The Science of Microbes Teacher's Guide may be obtained in its entirety from the Center for Educational Outreach, Baylor College of Medicine (1-800-798-8244).

You can download a PDF of this lesson, including the pre-assessment, from BioEd Online or K8 Science.

The Science of Microbes and accompanying online professional development were supported, in part, by Science Education Partnership Award number 5R25RR018605 from the National Center for Research Resources of the National Institutes of Health (NIH) to Baylor College of Medicine. The unit was developed in partnership with the Baylor-UT Houston Center for AIDS Research, an NIH-funded program (AI036211). The opinions, findings, and conclusions expressed in this presentation are solely those of the authors and do not necessarily reflect the views of Baylor College of Medicine or the sponsoring agencies.