5.1: Introduction

Learning Objectives

• Observe the ubiquity of fungi in the environment.
• Describe the microscopic structures of fungi by examining samples of molds, mushrooms and yeast.

Fungi are a diverse and important group of eukaryotes. As saprobes they play a critical role in decomposing dead organic matter and returning essential nutrients to our environment. Most fungi do this by excreting enzymes into their environment to break down organic material and then subsequently absorb the breakdown products of those nutrients across their cell walls and cell membranes. Many fungi also form important symbiotic relationships with other organisms such as the case with mycorrhizae and lichens. In the case of mycorrhizae, fungal organisms associate with the roots of plants forming a mutualistic relationship. The nature of this relationship is that the fungi function as extensions to the root systems, increasing the surface area of nutrient and water absorption. In return, the plants deliver some of their photosynthetic products back to the fungus. Similarly, lichens are an example of mutualism between a fungal organism and a unicellular photosynthetic organism such as an algae or cyanobacteria. The role of the fungi in this relationship is to help to support and anchor the photosynthetic partner while receiving organic nutrients from that partner in return. We will observe samples of both symbiotic relationships as part of this lab.

There are approximately 1.5 million fungal species dispersed into seven major groups including: Basidiomycota, Ascomycota, Blastocladiomycota, Neocallismastigamycota, Chytridiomycota, Glomerulomycotina, and Zygomycota. Each of these groups has distinguishing characteristics such as their methods of reproduction, habitat or structural features that allow us to differentiate between them. You will be observing specimens selected from the most prominent of these groups of fungi including Basidiomycota, Ascomycota and Zygomycota. A combination of live and prepared specimens will be available for you to gain familiarity with the distinguishing features of each group.

Fungi have a variety of different means of reproduction but often rely on the dissemination of spores to disperse organisms to new locations. These spores are easily airborne and are, therefore, prevalent in the air that we breathe. Thus, in addition to your observations of the various types of fungi, you will perform an experiment to evaluate the prevalence of fungi in your environment. You will do this using an assay known as the Settle Plate Method. This method requires that you leave plates exposed to the environment for a period to collect any fungal spores that might be present. After several days of incubation, the growth on these plates will help you to determine how many fungal organisms were able to settle onto the plate during the period of exposure.

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