This module examines responses to the individual plants and animals, and their populations, to important aspects of terrestrial and aquatic environments that are determinants of distribution and abundance. It investigates in depth the extent to which physiological, metabolic and morphological responses may confer evolutionary fitness, particularly in extreme environments. Some of the environmental constraints covered act by imposing deficiencies of essential resources or conditions (e.g. water, essential ions, oxygen, carbon, light and temperature), whereas others are the result of toxicity, either natural or resulting from human activity (e.g. metal ions, salinity, acidity and organic industrial pollutants). The module will lead you through more fundamental aspects of ecology to consider their application in seeking to meet the multiple challenges of pollution and climate change.