Scars can be seen on the surface of the yeast cell where buds have broken off. Yeasts such as Saccharomyces, play an important role in the production of bread and in brewing. Yeasts are also one of the most widely used model organisms for genetic studies, for example in cancer research. Other species of yeast such as Candida are opportunistic pathogens and cause infections in individuals who do not have a healthy immune system.