BIOLOGY Volume 1 - A Guide to General Biology - 2004

9. UTILIZATION OF ENERGY

In Ch. 7, we already touched upon what energy is and why it is essential for All living organisms. The Examples given there show that energy exists in various forms—chemical, electrical, mechanical, light, and thermal. The reader should be familiar with how these different forms of energy are utilized in living organisms and be able to provide examples (if unable to do so, it is helpful to review sec. 7.1).

Questions concerning energy are among the most fundamental in biology. All living systems—from The Cell to ecosystems—require energy to perform work. Just as any cell will perish very quickly if deprived of its energy supply (as we shall see below, this is easily demonstrated in aerobic Cells by treating them with cyanide), so too will any ecosystem collapse if the continuous influx of solar energy is interrupted.

9.1. Explain how animals depend on light energy.

Nutrition is the process that supplies a living Organism with the energy it needs. Food also provides the raw Materials required for building and repairing cellular structures. However, the energy bound in nutrients must be converted into a form that cells can readily utilize. This function is performed by Respiration—the process to which this chapter is dedicated. We discussed the interrelationship between autotrophic nutrition, heterotrophic nutrition, and respiration in Ch. 7 (see Fig. 7.1). Fig. 9.1 provides a somewhat different perspective on energy exchange between the environment and living cells.

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Fig. 9.1. Energy Flow from the Sun to the cell (part of the energy is dissipated as heat). The carbon cycle is also shown.

9.1. What is Respiration?

Respiration is the process by which energy is released through The oxidation of Organic compounds. This energy becomes available to living cells in the form of ATP. When this biochemical process takes place within cells, it is called cellular respiration. If oxygen is required, it is termed aerobic respiration; if the reactions proceed in the absence of oxygen, it is referred to as Anaerobic respiration.

The substrates for cellular respiration are mostly CARBOHYDRATES (such as glucose) or fats. They are broken down step-by-step through a series of enzymatic reactions. In each such reaction, a small amount of energy is released, part of which is stored in molecules of a substance called adenosine triphosphate (ATP), while the remainder is dissipated as heat. ATP acts as the energy currency within cells. The energy trapped in its molecules is then utilized to drive energy-requiring reactions.