AY Honors/Ecology - Advanced/Answer Key

2. State the first and second laws of thermodynamics and explain how they are important to ecology.

First Law

”In any process, the total energy of the universe remains constant.”

More simply, the First Law states that energy cannot be created or destroyed; rather, the amount of energy lost in a steady state process cannot be greater than the amount of energy gained.

This is the statement of conservation of energy for a thermodynamic system. It refers to the two ways that a closed system transfers energy to and from its surroundings - by the process of heating (or cooling) and the process of mechanical work. The rate of gain or loss in the stored energy of a system is determined by the rates of these two processes. In open systems, the flow of matter is another energy transfer mechanism, and extra terms must be included in the expression of the first law.

In an ecological sense, the first law shows that a creature's energy must come from somewhere, and it must go somewhere as well. Primary producers transfer energy from the sun to primary consumers to secondary consumers at the top of the food chain. All along the way, some of the energy is dissipated in the form of heat.

Second Law

“The entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium.”

One can look at entropy as a measure of chaos or disorder. A high level of entropy means a high level of disorder. A low level of entropy means a high level of order. So, for example, a broken cup has less order and more chaos than an intact one. Likewise, solid crystals, the most organized form of matter, have very low entropy values; and gases, which are highly disorganized, have high entropy values.

The second law states that the disorder of an isolated system increases, or that the order in that system decreases. It becomes more chaotic over time.

An easily understood example of the second law in action would be a sandcastle. When it is first built, it is highly organized, so it has a low entropy level. Unless someone is there tending the sandcastle, it begins to fall apart. Wind blows sand from from the walls, the windows become less and less defined until they disappear, its height decreases over time, and eventually, one would not be able to tell that there was a sandcastle there at all.

An ecological system is dependent on energy input from an external source, namely, the sun. Without the sun, the system would be isolated, and life would cease to exist. Without energy input from the sun, plants would die, followed by the herbivores, followed by the carnivores and scavengers (including bacteria that break down the tissues of dead organisms). When all the organisms have died, the system can be said to ave reached equilibrium.

3. Explain the three basic trophic (feeding) levels and give a good example of a plant or animal for each.

The three basic trophic levels are primary producers, primary consumers, and secondary consumers.

In land-based ecosystems, plants such as grass are the primary producers and form the first trophic level (primary producers). Next are herbivores (primary consumers) that eat the grass, such as rabbits. Next are carnivores (secondary consumers) that eat the rabbits, such as a bobcats.

Keep in mind that trophic relationships are rarely this simple. Very often they are more of a "web" than a "chain." For example, mountain lions may eat both rabbits and bobcats. The trophic categorization of the mountain lion exists on two levels, possibly more.

11. Find a Spirit of Prophecy quotation and a Bible text pertinent to ecology and explain their relevance and application to our day.

Adventist Youth Honors Answer Book/Ecology quotations