Biology (Holt)

38 CHAPTER 2Chemistry of Life

Section 4 Energy and Chemical

Reactions

Energy for Life Processes

You are surrounded by energy. Energy is in food, in the motion of a

speeding car, in the sound of a guitar, and in the warmth of a blazing

fire. is the ability to move or change matter. Energy exists in

many forms—including light, heat, chemical energy, mechanical

energy, and electrical energy—and it can be converted from one form

to another. If you kick a ball, for example, the energy of your kick

makes the ball move. If you cook an egg in a hot skillet, heat causes

the egg to change color and solidify, as shown in Figure 12. The

energy transferred to the egg by heat rearranges the atoms and mol-

ecules in the egg. The bioluminescent click beetle, also shown in

Figure 12, uses energy to produce light.

Energy can be stored or released by chemical reactions. A chem-

ical reaction is a process during which chemical bonds between

atoms are broken and new ones are formed, producing one or more

different substances. At any moment, thousands of chemical reac-

tions are occurring in every cell of your body. The starting materials

for chemical reactions are called reactants.The newly formed sub-

stances are called products.Chemical reactions are summarized by

chemical equations, which are written in the following form:

Reactants →Products

The arrow is read as “changes to” or “forms.” For example, dissolv-

ing sodium chloride in water causes the following reaction:

NaCl →Na++ Cl–

Energy

Objectives

Evaluatethe importance
of energy to living things.

Relateenergy and chemical
reactions.

Describethe role of
enzymes in chemical
reactions.

Identifythe effect of enzymes
on food molecules.

Key Terms

energy

activation energy

enzyme

substrate

active site

An egg becomes solid when it is heated. A chemical reaction causes the bioluminescent click beetle, Pyrophorus

noctilucus,to give off light energy.

Figure 12 Evidence of chemical reactions

9C

9C

12A

4B