a single large chloroplast, two flagella, and a stigma (eyespot); it is important in molecular biology research (Figure
5.37).
Figure 5.37 Chlamydomonasis a unicellular green alga.
Chlorellais a nonmotile, large, unicellular alga, andAcetabulariais an even larger unicellular green alga. The size of
theseorganismschallenges theideathatallcellsaresmall,andtheyhavebeenusedingeneticsresearchsinceJoachim
Hämmerling (1901–1980) began to work with them in 1943.Volvoxis a colonial, unicellular alga (Figure 5.37).
A larger, multicellular green alga isUlva, also known as the sea lettuce because of its large, edible, green blades.
The range of life forms within the Chlorophyta—from unicellular to various levels of coloniality to multicellular
forms—has been a useful research model for understanding the evolution of multicellularity. The red algae are mainly
multicellular but include some unicellular forms. They have rigid cell walls containing agar or carrageenan, which
are useful as food solidifying agents and as a solidifier added to growth media for microbes.
Which groups of algae are associated with harmful algal blooms?5.5 Lichens
Learning Objectives
- Explain why lichens are included in the study of microbiology
- Describe the unique characteristics of a lichen and the role of each partner in the symbiotic relationship of a
lichen - Describe ways in which lichens are beneficial to the environment
No one has to worry about getting sick from a lichen infection, but lichens are interesting from a microbiological
perspective and they are an important component of most terrestrial ecosystems. Lichens provide opportunities for
study of close relationships between unrelated microorganisms. Lichens contribute to soil production by breaking
down rock, and they are early colonizers in soilless environments such as lava flows. The cyanobacteria in some
lichens can fix nitrogen and act as a nitrogen source in some environments. Lichens are also important soil stabilizers
in some desert environments and they are an important winter food source for caribou and reindeer. Finally, lichens
222 Chapter 5 | The Eukaryotes of Microbiology
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