An Introduction to Human Anatomy and Physiology
Chapter Five: Cellular (Aerobic) Respiration
Introduction:
As you no-doubt recall, some organisms, known as
autotrophs, can manufacture their own food. Most do this by using the molecule
chlorophyll to absorb solar energy, which is then used to manufacture glucose from carbon dioxide and water. This is
photosynthesis; almost all plants and algae, and many bacteria are capable of manufacturing food in this way.
Other organisms are
heterotrophs, because they cannot manufacture their own food. Instead, they must eat other organisms.
As you also know, organisms need food for two reasons. Food provides the raw materials organisms need in order to build body tissues, and it provides the energy organisms need for growth, maintenance, and repair of body tissues. Mostly, this energy is provided by the chemical breakdown of carbohydrate molecules; as molecular bonds are broken, the energy they store is released, and ATP molecules are used to transport the energy to wherever it’s needed.
The process in which organisms break down high-energy molecules (glucose, in particular) to produce energy that is stored and transported by ATP molecules takes place inside cells and is known as
cellular respiration. Because the complete breakdown of glucose into CO
2 and H
2O requires oxygen to proceed, cellular respiration is often referred to as
aerobic respiration – though strictly speaking, aerobic respiration is the second half of cellular respiration.
Respiration, by the way, is one of those confusing words that’s used in several different ways. Most people think of “respiration” as the moving of air in and out of the lungs, but strictly speaking, that’s “breathing” – or more properly,
ventilation. “Respiration” is the metabolic breakdown of organic molecules for energy. If oxygen is used in the breakdown process (as it usually is), then it’s aerobic respiration; otherwise, it’s anaerobic respiration.
Introduction
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