What does biodiversity refer to?

Biodiversity encompasses the variety and variability of life forms within a given ecosystem, region, or the entire planet. It includes the different species of plants, animals, fungi, and microorganisms, as well as the genetic diversity within those species and the ecosystems they form. Biodiversity is integral to functioning ecosystems, as it contributes to resilience, ecological balance, and provides a range of services including food supply, disease regulation, and climate stabilization.

The other options focus on specific aspects of the environment but do not capture the comprehensive nature of biodiversity. For example, the number of water sources in an area pertains to hydrology rather than the diversity of life forms. The presence of ecosystems in urban areas may indicate fragmentation but does not speak to the variety of species within those ecosystems. Lastly, the geographical distribution of resources addresses the spatial aspect of natural resources rather than the diversity of life itself. Thus, the definition provided in the correct answer is the most accurate representation of what biodiversity entails.