INTRODUCTION

An impressive achievement in biology in the twentieth century was gaining a comprehensive understanding of respiration. All living things respire. Still, the knowledge that most people have of what is involved often begins and ends with: “we inhale air rich in oxygen and exhale it enriched with carbon dioxide.” But there is much more to it than that.

The foods we eat are slowly burned or “combusted,” as Lavoisier described it more than 250 years ago (see Chapter 1). Using the O2 from the air, we slowly convert carbohydrates, fats, proteins, and other substances, finally, to CO2 and water. This releases the energy contained in foods, some of it in the form of chemical energy, which is useful to us; the rest is given off to our surroundings as heat. We put the useful energy to work to sustain our life support systems – to drive our muscles and other organs, keep us warm, feed our brains, and build our complex molecules (Figure 2).

PLANTS NEED RESPIRATION AS WELL AS PHOTOSYNTHESIS

We might suppose that because plants have access to an endless supply of energy from the sun they do not need any other source – not so. Not all parts of a plant photosynthesize, only those that are green; however, non-green parts also need energy. In addition, photosynthesis occurs only during the day but plants grow round the clock.