1. Nutrient Cycling: Organisms depend on the nonliving environment for essential nutrients. Plants take in water and minerals from the soil, and animals obtain these nutrients by consuming plants or other animals. When organisms die, they decompose, returning nutrients back to the soil, air, and water, where they can be used by other organisms. This cycle of nutrient movement between living things and the nonliving environment is crucial for maintaining life on Earth.

2. Energy Flow: The ultimate source of energy for most life on Earth is the sun. Plants capture sunlight through photosynthesis and convert it into chemical energy in the form of sugars. Animals then obtain this energy by eating plants or other animals. This flow of energy from the sun through living organisms and back to the nonliving environment (as heat) is a fundamental principle of ecology.