Teacher resources and professional development across the curriculum

Teacher professional development and classroom resources across the curriculum

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Life Science: Session 7

Energy and Life

What is energy?

In the video for Session 1 (What is Life?), the need for a constant supply of new energy was defined as one of the five characteristics used to define life. But what is energy? In many dictionaries, energy is defined as “the capacity to do work.” One way to apply this definition to the living world is to recognize that living things are both highly organized and constantly active. Energy does the work that sustains these things. Without energy, life disorganizes and comes to a halt.

How is energy connected to life?

cereal box
Calories indicate the amount
of chemical energy in food

There are several properties of energy that characterize its connection to life.

Energy exists in different forms: Electricity, light, sound, heat, and the movement of large objects are all forms of energy. The energy stored in molecules, called chemical energy, is another form. The forms of energy that are most significant to life are light, the chemical energy in food, and heat, which is a by-product of all energy reactions.

Energy can change forms: In the living world, photosynthesis changes light energy into chemical energy that is stored as sugar. The energy in sugar is released when it is “burned” during the process of cell respiration. Some of this energy is transferred to other molecules, and some of it is released as heat.

Energy is conserved: Energy has been found to follow the laws of thermodynamics. The first law states that energy is conserved. What this means is that in any system, the total amount of energy remains the same, even though it may change form or place. In the video, Dr. Les Kaufman burns a marshmallow. The first law of thermodynamics dictates that the amount of chemical energy stored in the marshmallow will be the same as the amount released as light and heat in the flames.

Energy tends toward disorder: The second law of thermodynamics states that when one form of energy is converted to another, the amount of useful energy tends to decrease. Put another way, in energy reactions, energy spontaneously changes from higher-quality forms to lower-quality forms. In the case of the marshmallow, what was once highly organized energy in the chemical bonds of food changed to light and ultimately heat — a very disorganized form of energy.

G. Evelyn Hutchinson said: “Disorder spreads through the universe, and life alone battles against it.” A constant supply of new energy is what keeps life organized and makes life’s activities possible.

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