Define biodiversity.

Biodiversity refers to the variety of life forms on Earth, encompassing not only the sheer number of different species but also the genetic diversity within those species and the ecosystems they form. It reflects the complexity of interactions between organisms and their environments, making it a critical concept in understanding ecological health and resilience.

The phrase "variety of life" points to the multitude of species, genetic variations among them, and the diverse ecosystems they collectively inhabit. Biodiversity is essential for ecosystem services, such as pollination, nutrient cycling, and climate regulation, which sustain life on Earth.

The other options present narrower or incomplete interpretations of biodiversity. For instance, focusing solely on the number of species in a population misses the broader ecological relationships and genetic diversity that contribute to overall biodiversity. Similarly, the distribution of species across ecosystems, while important in ecological studies, doesn’t fully encapsulate the concept of biodiversity’s richness. Finally, the rate of extinction is a critical issue related to biodiversity, but it reflects a consequence of diminishing biodiversity rather than a definition of it itself. Therefore, the definition that emphasizes the variety of life comprehensively captures the essence of what biodiversity entails.