On first observation, fungi tend to resemble plants. They cannot move on their own and their cells have rigid cell walls. However, fungi do not contain chloroplasts and so cannot carry out photosynthesis. Instead, fungi obtain the energy needed for life by absorbing complex organic material from other organisms or their remains. Some fungi are parasites and feed off organisms that were once alive.
Yeast are in the fungi kingdom.
Like other fungi, yeast have no chlorophyll but get their energy from a process called fermentation , a chemical process where sugars and starches are changed to alcohol and carbon dioxide in the absence of oxygen. Yeast is added to bread to make it rise by producing millions of tiny bubbles of carbon dioxide. Remember, not all fungi are unicellular and so not all are considered microorganisms. Other larger fungi include mushrooms and bread molds. The last group of microorganisms are currently the subject of scientific debate.