1. Symbiotic Relationships Mutualism: both species benefit from the relationship Commensalism: one organisms benefits and the other is neither helped nor harmed Parasitism: one organism lives on or inside another organisms and harms it

2. Role of Microorganisms in Ecosystems Microorganisms are organisms that are too small to see with the unaided eye. Microorganisms can either maintain the health of an ecosystem or disrupt the health of an ecosystem

3. Examples of microorganisms maintaining the health of an ecosystem 1. Some microorganisms are decomposers, which means they can recycle organic matter. Decomposers free up carbon, hydrogen, phosphorus, nitrogen, and other nutrients so that they can be re- used in the ecosystem.

4. Nitrogen Fixation 2. Microorganisms fix nitrogen, which is the process of changing N 2 into NH 3. This is done so that plants can use the nitrogen for growth and development.

5. Mycorrhizae 3. Mycorrhizae is a type of fungus that forms a mutualistic relationship with a plant. – The plant supplies the mycorrhizae with carbohydrates. The mycorrhizae allows the plant to absorb more nutrients. – For example, some plants cannot absorb phosphorus. The mycorrhizae can access this nutrient and make it available to the plant.

6. Examples of microorganisms disrupting the health of an ecosystem 1.When a lot of nutrients come into an aquatic ecosystem, algal blooms sometimes form. The algae hogs the sunlight, causing most of the plants in the area to die. Bacteria enter the area to decompose the dead plants, which reduces the amount of oxygen available for the other organisms.

7. Dead Zones 2. The lack of oxygen caused by the algal bloom creates an hypoxic (low-oxygen) area. This is called a dead zone.