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

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

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

About 25 different chemical elements are essential to life

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

(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

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

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

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

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