Lesson 5 - Basics of Energy Exchange Review

Which of the following demonstrates the second law of thermodynamics?

• Unplugging a lamp turns the light off because energy cannot be created from nothing.

• Most of the water rushing down a river flows around a boat rather than pushing it.

• Consumers eat plants and other organisms to obtain chemical energy for use by their cells.

• Plants require sunlight to grow by converting light energy into chemical energy.

Answer explanation

According to the second law of thermodynamics, the total ordered and usable energy of a system decreases with every energy conversion because some energy is wasted or lost. When water flows down a river, some of the energy can be harnessed to move a boat or rotate a turbine, but much of the energy released by the downstream flow is wasted.

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The water at the top of a waterfall has _____.

• potential energy

• kinetic energy

• electrical energy

• nuclear energy

Answer explanation

Water at the top of a waterfall possesses energy of position. Because gravity pulls objects toward Earth, an object in a high position has potential energy that can become kinetic energy (energy of motion) when the force of gravity causes the object to fall.

When a car runs out of gasoline, the engine turns off and will not restart unless new gasoline is provided. This effect demonstrates _____.

• the first law of thermodynamics

• the second law of thermodynamics

• potential energy

• kinetic energy

Answer explanation

Because energy cannot be created, the energy to perform work must be obtained from an external source. Automobile engines depend on the energy released by the burning of gasoline molecules.

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The transfer of energy in our biosphere is _____.

• unidirectional

• heterotrophic

• cyclical

• autotrophic

Answer explanation

Some energy is lost as heat when energy is transferred from one organism to the next. This heat is not transferred back into a useable form of energy for the organisms on our planet. Therefore, energy moves unidirectionally from the sun to organisms that can convert sunlight to chemical energy and then to herbivores, omnivores, and carnivores.

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Which of the following correctly demonstrates the flow of energy through an ecosystem?

• a producer absorbing sunlight

• a consumer absorbing sunlight

• an herbivore absorbing sunlight

• a carnivore absorbing sunlight

Answer explanation

Producers, such as plants, absorb and convert light energy into chemical energy. Consumers eat the plants or animals who have eaten plants.

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Which of the following is the best definition of an autotroph?

• An organism that uses light energy to make food.

• An organism that must consume other organisms to get energy.

• An organism that can make its own food.

• An organism that breaks down dead and decaying matter.

Answer explanation

Using inorganic molecules and alternative energy sources, autotrophs are producers and create biomolecules that store chemical energy. Organisms that convert light energy are photoautotrophs, a type of autotroph.

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Humans are _____.

• autotrophs

• heterotrophs

• photoautotrophs

• producers

Answer explanation

Humans are consumers and cannot create their own food or convert alternative energy sources into chemical energy.

Which of the following is true about endergonic reactions?

• The reactants have more potential energy than the products.

• The reactants have less potential energy than the products.

• Cellular respiration is an example of an endergonic reaction.

• Energy is released when an endergonic reaction occurs.

Answer explanation

Because the products possess more potential energy than the reactants, energy must be added to endergonic reactions to convert the lower energy reactants to higher products.

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Which of the following characteristics describes an exergonic reaction?

• The reactants have more potential energy than the products.

• The reactants have less potential energy than the products.

• Photosynthesis is an example of an exergonic reaction.

• Energy is gained when an exergonic reaction occurs.

Answer explanation

Reactants release energy during an exergonic reaction, resulting in products that contain less energy.

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NGSS.HS-PS1-4

If we could observe the reactions occurring inside a living cell, some reactions would be exergonic and others would be endergonic. The sum of all these chemical reactions is the cell’s _____.

• pool of enzymes

• catabolism

• energy cycle

• metabolism

Answer explanation

To carry out life processes, cells perform functions that include both exergonic and endergonic reactions.

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