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between a cell’s watery internal and external environments.
They also include signaling molecules and familiar fats that
store energy and make up part of our diet. Lipids will be dis-
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cussed along with carbohydrates in more detail in Module 3.

✓ Concept Check

11. Identify the four most common atoms in organic
molecules.
12. Describe how the number of valence electrons in
a carbon atom is responsible for carbon’s ability to
form a large diversity of molecules.
13. Identify the four major types of organic molecules.
14. Describe a polymer.
FIGURE 1.15 Lipids
15. Describe the property of lipids that allows them
When oil, which is a lipid, is mixed in water, it forms droplets to to function as a barrier between a cell’s interior and
minimize its contact with water. Oil, like all lipids, is hydrophobic. external environments.
Photo: ThomasVogel/Getty Images

Module 1 Summary

®
PREP FOR THE AP EXAM • The periodic table organizes all of the elements in a way
REVISIT THE BIG IDEAS that describes their properties. Page 31
ENERGETICS: Using the content in this module, identify the LG 1.3 Atoms combine to form molecules linked by

key elements that all organisms obtain from the environment chemical bonds.
and exchange with the environment.

• Valence electrons are the electrons in an atom’s outer-
most energy shell and determine the ability of an
LG 1.1 Matter and energy govern the properties of life. atom to combine with other atoms to form molecules.
• All organisms are made up matter and require energy to Page 31

sustain life. Page 26 • Covalent bonds arise when two elements share one or

• Organisms obtain matter from other organisms and the more pairs of electrons. Page 33

environment, and matter therefore moves in a cycle, with • Covalent bonds may be either nonpolar or polar. Page 34

the same atoms used and reused. Page 26 • Ionic bonds result from the attraction of oppositely
• Energy from the sun or chemical compounds is used by charged ions. Page 34

organisms to do work but cannot be reused. Page 27 • Chemical reactions involve the breaking and forming of
chemical bonds, forming new molecules. Page 35

LG 1.2 The atom is the fundamental unit of matter.
• Atoms consist of protons, neutrons, and electrons. Page 30 LG 1.4 Carbon is the backbone of organic

• The atomic number is the number of protons an element molecules.
contains, and it determines the identity of the element. • Carbon’s electron configuration allows it to form four

Page 30 covalent bonds. Page 36
• The atomic mass is the number of protons and neutrons • Carbon’s bonding allows a diversity of molecules to be

an element contains. Page 30 formed. Page 37

• Isotopes are elements with the same number of protons • The four major classes of organic molecules are proteins,
but different numbers of neutrons. Page 30 nucleic acids, carbohydrates, and lipids. Page 37

• Electrons occupy energy shells or levels that move • Proteins play a role in the structure of cells and can speed
around the nucleus. Page 31 up the rate of chemical reactions. Page 37
MODULE 1 ELEMENTS OF LIFE 39
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