Tennessee Wastewater Operator Practice Exam

In a biofilm, which layer has the greatest access to resources and grows the fastest?

1. Innermost layer

2. Middle layer

3. Outermost layer

4. Layer of dead cells

The correct answer is: Outermost layer

In a biofilm, the outermost layer has the greatest access to resources and therefore experiences the fastest growth. This is primarily because the outer layer is in direct contact with the surrounding environment, allowing it to efficiently utilize available nutrients, oxygen, and other essential resources. Biofilms are complex structures made up of microbial communities that adhere to surfaces. They typically exhibit stratification, where layers of cells have different access to resources. The innermost layer is often shielded from the flow of nutrients and oxygen, and the layer of dead cells lacks the capacity for growth or resource accumulation. The middle layer, while still receiving some resources, is not as exposed as the outermost layer. In contrast, the outermost layer benefits from optimal conditions, such as light in phototrophic biofilms or nutrients in other types, facilitating rapid cell division and growth compared to the other layers. Thus, the dynamic nature of resource availability in a biofilm strongly favors the growth of the outermost layer.