What defines the biosphere?

The biosphere is defined as the part of the planet containing living organisms. It encompasses all ecosystems and regions of the Earth where life exists, including land (terrestrial ecosystems), water (aquatic ecosystems), and the atmosphere. The biosphere integrates various habitats—ranging from forests and deserts to oceans and rivers—where diverse organisms interact with each other and their environment. This definition captures the essence of life on Earth, highlighting the interconnectedness of all living beings and their habitats.

While options like the area on land where plants grow or the underwater region of the Earth describe specific habitats, they do not fully encapsulate the entire biosphere. Similarly, defining the biosphere solely based on biodiversity misses important aspects, as it is not just the region with the most biodiversity, but rather the entirety of the Earth’s systems that support life. Therefore, the definition focusing on the part of the planet containing living organisms is the most comprehensive and accurate representation of the biosphere.