A perspective is how a particular situation is viewed and understood by an individual.

Systems are sets of interacting or interdependent components.

The biosphere is an ecological system composed of individuals, populations, communities, ecosystems.

Ecosystems are sustained by supplies of energy and matter.

Biodiversity is the total diversity of living systems and it exists at several levels.

Biological diversity is being adversely affected by both direct and indirect influences.

Movements of water in the hydrosphere are driven by solar radiation and gravity.

Water security is having access to sufficient amounts of safe drinking water.

Soil is a dynamic system within the larger ecosystem that has its own inputs, outputs, storages and flows.

Land is a finite resource, and the human population continues to increase and require feeding.

The atmosphere forms the boundary between Earth and space.

Climate describes the typical conditions that result from physical processes in the atmosphere.

Natural resources are the raw materials and sources of energy used and consumed by society.

Energy sources are both renewable and non-renewable.

Births and immigration are inputs to a human population.

Urban areas contain urban ecosystems.