This document discusses key concepts in ecology including: 1) Ecology is the study of interactions among organisms and between organisms and their environment. The biosphere is made up of different levels of organization from individuals to the entire planet. 2) Energy flows through ecosystems in one direction from producers to consumers while matter cycles through ecosystems as it moves between organisms and the non-living environment through processes like the carbon, nitrogen, and phosphorus cycles. 3) Nutrients are required by all organisms and cycle through ecosystems, with their availability impacting ecosystem productivity. Certain nutrients can become limiting if scarce.

1. Chapter 3 The Biosphere Chapter 3 The Biosphere Chapter 3 The Biosphere

5. 3-1 What is Ecology

17. 3 – 2 Energy Flow

43. 3 – 3 Cycles of Matter