Consider the characteristics of a living and a nonliving thing



TIPS FOR MASTERING KEY CONCEPTS

Living is hard work; energy must be expended to perform all the processes that occur in organisms. Chemical reactions, cellular functioning, running, growing, and reproducing all require energy. Work must be done if an organism or cell is to stay alive, and energy must be expended for work to be done. All organisms-from prokaryotes and protists to fungi, plants, and animals-obtain energy by carrying out cellular respiration. They break down energy-rich food molecules and then use the released energy to synthesize ATP, the universal energy currency for organisms. The food molecules are oxidized, and ADP is reduced to ATP.

In obtaining and processing energy, the cells of organisms follow the laws of thermodynamics, use catalysts to speed up chemical reactions, and employ regulated, multistep pathways that have evolved over time.

The laws of thermodynamics describe how energy changes.

• If energy is present, work can be done.

• Moving objects have kinetic energy, whereas stored energy is called potential energy.

• The electrons of atoms have potential energy; when they are transferred from one atom to another, energy is transferred; when electrons are shared in covalent bonds, energy is stored in the bond.

• Oxidation involves the removal of an electron from an atom or molecule; reduction involves the addition of an electron to an atom or molecule; the two processes are always linked.

• Energy can be neither created nor destroyed, but can be converted from one form to another (first law of thermodynamics).

• The amount of useful energy in a system constantly decreases, while disorder (entropy) constantly increases (second law of thermodynamics).

• The amount of energy actually available to do work in a system is called free energy; in a chemical reaction, the free energy of the products may be greater or less than the free energy of the reactants, depending on the type of reaction.

• Enzymes speed up biochemical reactions by lowering the amount of activation energy needed.

ATP is the energy currency of life.

• The high-energy bonds of ATP (adenosine triphosphate) are easily broken, and cells use these bonds as the immediate source of energy for almost all their work.

Metabolism is the chemical life of the cell.

• All of the chemical reactions carried out by a cell or organism are part of its metabolism.

• The chemical reactions are often arranged in specific sequences or biochemical pathways that have specific feedback regulation mechanisms.

• These pathways have evolved slowly, one step at a time, working backward from the end result.

• Much of metabolism is devoted to making ATP and then breaking down ATP, a requirement of life.

1. Skim the titles, boldfaced words, pictures, figures, and captions in Section 1. Write three facts you discovered about how organisms obtain energy.

a.

b.

c.

2. Define the following terms:

metabolism

adenosine triphosphate

cellular respiration

energy

photosynthesis

thermodynamics

3. List at least seven of your body’s cell processes that require energy.

a.

b.

c.

d.

e.

f.

g.

4. Complete the following table to compare the laws governing the flow of energy.

| |1st Law of Thermodynamics |2nd Law of Thermodynamics |

|Defined | | |

|Example | | |

6. Sequence the flow of energy from the sun to heterotrophs

7. How does you body use ATP?

8. Label the three parts of the ATP molecule shown below.

7. Compare and contrast catabolic and anabolic pathways by writing a characteristic of each in the following Venn diagram.

-----------------------

Both

Anabolic

Catabolic

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