1. Matter is made of elements
CHAPTER 2 The Chemical Basis of Life
Life depends on Chemistry
Organisms are composed of matter
Matter is made of elements
Elements are made of atoms

2. Rattlebox moths release a chemical that spiders don’t like
This spider caught a rattlebox moth and then let it go

5. D. Organ: Flight muscle of a moth
Molecules and ecosystems are at opposite ends of the biological hierarchy
Rattlebox moth
C. Cell and tissue: Muscle cell within muscle tissue
Each level of organization in the biological hierarchy builds on the one below it
At each level, new properties emerge
Myofibril (organelle)
B. Organelle: Myofibril (found only in muscle cells)
Actin
Myosin
Figure 2.1
Atom
A. Molecule: Actin

6. About 25 different chemical elements are essential to life

7. Carbon, hydrogen, oxygen, and nitrogen make up the bulk of living matter, but there are other elements necessary for life
Table 2.2

8. Goiters are caused by iodine deficiency
Nitrogen deficiency in corn
Figure 2.2

9. 2.3 Elements can combine to form compounds
Chemical elements combine in fixed ratios to form compounds
Example: sodium + chlorine  sodium chloride

10. 2.4 Atoms consist of protons, neutrons, and electrons
The smallest particle of an element is an atom
Different elements have different types of atoms
An atom is made up of protons and neutrons located in a central nucleus
The nucleus is surrounded by electrons 2
Protons
Nucleus 2
Neutrons 2
Electrons
A. Helium atom

11. Sodium and chloride ions bond to form sodium chloride, common table salt
Na+
Cl–
Figure 2.7B

12. 2.9 Water is a polar molecule
THE PROPERTIES OF WATER
2.9 Water is a polar molecule
Atoms in a covalently bonded molecule may share electrons equally, creating a nonpolar molecule
If electrons are shared unequally, a polar molecule is created

13. In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen
This makes the oxygen end of the molecule slightly negatively charged
The hydrogen end of the molecule is slightly positively charged
Water is therefore a polar molecule
(–)
(–) O H H
(+)
(+)
Figure 2.9

14. 2.10 Overview: Water’s polarity leads to hydrogen bonding and other unusual properties
The charged regions on water molecules are attracted to the oppositely charged regions on nearby molecules
This attraction forms weak bonds called hydrogen bonds
Hydrogen bond
Figure 2.10A

15. Like no other common substance, water exists in nature in all three physical states:
as a solid
as a liquid
as a gas
Figure 2.10B

16. Cohesion – water sticking to itself
2.11 Hydrogen bonds make liquid water cohesive and adhesive
Cohesion – water sticking to itself
Adhesion – water sticking to other molecules
Cohesion among water molecules plays a key role in the transport of water against gravity in plants
Adhesion, clinging of one substance to another, contributes too, as water adheres to the wall of the vessels.

17. Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion.
Water has a greater surface tension than most other liquids of cohesion.
Water behaves as if covered by an invisible film.
Some animals can stand, walk, or run on water without breaking the surface.
Fig. 3.3

18. 2.12 Water’s hydrogen bonds moderate temperature
It takes a lot of energy to disrupt hydrogen bonds
Therefore water is able to absorb a great deal of heat energy without a large increase in temperature
Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for:
Prevention of temperature fluctuations that are outside the range suitable for life.
Coastal areas having a mild climate
A stable marine environment

19. This leads to evaporative cooling
A water molecule takes a large amount of energy with it when it evaporates
This leads to evaporative cooling
Figure 2.12

20. 2.13 Ice is less dense than liquid water
Molecules in ice are farther apart than those in liquid water
Hydrogen bond
ICE
Hydrogen bonds are stable
LIQUID WATER
Hydrogen bonds constantly break and re-form
Figure 2.13

21. Ice is therefore less dense than liquid water, which causes it to float
If ice sank, it would seldom have a chance to thaw
Ponds, lakes, and oceans would eventually freeze solid

22. 2.14 Water is a versatile solvent
Solutes whose charges or polarity allow them to stick to water molecules dissolve in water
Solution – when all of the solvent is evenly distributed in the solvent. (evenly mixed)
Solute –the item being dissolved or mixed in. Usually in lower concentration
Solvent – the substance that the solute is dissolved in.
Suspension – the materials mixed on the solute are not dissolved completely and are instead suspended in the solution.
Na+ – –
Na+ + +
Cl–
Cl– – – + + –
Ions in solution
Salt crystal
Figure 2.14

23. 2.15 The chemistry of life is sensitive to acidic and basic conditions
A compound that releases H+ ions in solution is an acid, and one that accepts H+ ions in solution is a base
Acidity is measured on the pH scale:
0-7 is acidic
8-14 is basic
Pure water and solutions that are neither basic nor acidic are neutral, with a pH of 7

24. (Higher concentration of H+) (Lower concentration of H+)
pH scale
The pH scale H+
OH–
Lemon juice; gastric juice
(Higher concentration of H+)
Increasingly ACIDIC
Grapefruit juice
Acidic solution
Tomato juice
Urine
NEUTRAL
[H+] = [OH–]
PURE WATER
Human blood
Seawater
Neutral solution
(Lower concentration of H+)
Increasingly BASIC
Milk of magnesia
Household ammonia
Household bleach
Oven cleaner
Basic solution
Figure 2.15

25. Cells are kept close to pH 7 by buffers
Buffers are substances that resist pH change
They accept H+ ions when they are in excess and donate H+ ions when they are depleted
Buffers are not foolproof

26. 2.16 Connection: Acid precipitation threatens the environment
Some ecosystems are threatened by acid precipitation
Acid precipitation is formed when air pollutants from burning fossil fuels combine with water vapor in the air to form sulfuric and nitric acids
Figure 2.16A

27. 2.17 Chemical reactions rearrange matter
REARRANGEMENTS OF ATOMS
2.17 Chemical reactions rearrange matter
In a chemical reaction:
reactants interact
atoms rearrange
products result
Figure 2.17A
2 H2 + O2 
2 H2O

28. Living cells carry out thousands of chemical reactions that rearrange matter in significant ways
Beta-carotene
Vitamin A
(2 molecules)
Figure 2.17B