The Chemical Basis of Life Chemical Basis of Life? What are we made of? What are we made of?

2.1 Living organisms are composed of about 25 chemical elements Describe the importance of chemical elements to living organisms Chemicals are at the base level of biological hierarchy Arrangement of these elements eventually leads to formation of living organisms Copyright © 2009 Pearson Education, Inc.

2.3 Elements can combine to form compounds Explain the formation of compounds Compound—a substance consisting of two or more different elements combined in a fixed ratio Many of the compounds in living organisms contain C, H, N, and O. –DNA, for example, contains all four of these elements Different arrangements of elements provide unique properties for each compound Copyright © 2009 Pearson Education, Inc.

2.4 Atoms consist of protons, neutrons, and electrons Describe the structure of an atom An atom is the smallest unit of matter that still retains the properties of a element –Proton—has a single positive electrical charge –Electron—has a single negative electrical charge –Neutron—is electrically neutral Demonstration on charge – Do opposites really attract? Copyright © 2009 Pearson Education, Inc.

Electron cloud Protons 2e – Nucleus Electrons Mass number = 4 Neutrons 2 2 2

2.4 Atoms consist of protons, neutrons, and electrons Although all atoms of an element have the same atomic number, some differ in mass number –Isotopes have the same numbers of protons and electrons but different numbers of neutrons –Unlike 12 C, 14 C is an unstable (radioactive) isotope that gives off energy Copyright © 2009 Pearson Education, Inc.

Healthy brain Alzheimer’s patient PET scan used to image the brain

2.6 Electron arrangement determines the chemical properties of an atom Only electrons are involved in chemical activity Atoms want to fill their outer electron shells –To accomplish this, the atom can share, donate, or receive electrons –This results in attractions between atoms called chemical bonds Distinguish between ionic, hydrogen, and covalent bonds Copyright © 2009 Pearson Education, Inc.

Ionic bonding – transfer of electrons Electron transfer creates ions (charged atoms) Cation (positive ion); Anion (negative ion) Ex: Salts (sodium chloride) file:///C:/Users/Pringle/AppData/Local/Temp/02_07AIonicBonds _A%20%282%29.html

Covalent Bonding – sharing pairs of electrons Number of electrons required to complete an atom’s valence shell determines how many bonds will form Ex: Hydrogen & oxygen bonding in water; methane

Polar/nonpolar covalent bonds Electronegativity-attraction for electrons Nonpolar covalent -electrons shared equally Ex: diatomic H-H Polar covalent-one atom more electronegative than the other (charged) Ex: water H-O-H

Hydrogen bonds In water, bond formed by charge differential between hydrogen and oxygen(electronegativity)

2.11 Hydrogen bonds make liquid water cohesive List and define the life-supporting properties of water Hydrogen bonding causes molecules to stick together, a property called cohesion –This is useful in plants that depend upon cohesion to help transport water and nutrients up the plant Activities with water to demonstrate cohesion, surface tension, and cohesion. Copyright © 2009 Pearson Education, Inc.

2.14 Water is the solvent of life A solution is a liquid consisting of a uniform mixture of two or more substances –The dissolving agent is the solvent –The substance that is dissolved is the solute Demonstration of a solution Copyright © 2009 Pearson Education, Inc.

2.15 The chemistry of life is sensitive to acidic and basic conditions A few water molecules can break apart into ions –Some are hydrogen ions (H + ) –Some are hydroxide ions (OH – ) –A balance between the two is critical for chemical processes to occur in a living organism Copyright © 2009 Pearson Education, Inc.

2.15 The chemistry of life is sensitive to acidic and basic conditions Chemicals other than water can contribute H + to a solution –They are called acids –An example is hydrochloric acid (HCl) An acidic solution has a higher concentration of H + than OH – Copyright © 2009 Pearson Education, Inc.

2.15 The chemistry of life is sensitive to acidic and basic conditions Some chemicals accept hydrogen ions and remove them from solution –These chemicals are called bases –For example, sodium hydroxide (NaOH) provides OH – that combines with H + to produce H 2 O (water) Copyright © 2009 Pearson Education, Inc.

2.15 The chemistry of life is sensitive to acidic and basic conditions Explain the pH scale and the formation of acid and base solutions A pH scale (pH = potential of hydrogen) is used to describe whether a solution is acidic or basic –pH ranges from 0 (most acidic) to 14 (most basic) –A solution that is neither acidic or basic is neutral (pH = 7) Activity -testing the pH of various solutions Copyright © 2009 Pearson Education, Inc.

Acidic solution pH scale Battery acid Lemon juice, gastric juice Grapefruit juice, soft drink, vinegar, beer Tomato juice Rain water Human urine Saliva Pure water 6 7 Human blood, tears Seawater Milk of magnesia Household ammonia Household bleach Oven cleaner Neutral solution Basic solution NEUTRAL [H + ]=OH – ] Increasingly ACIDIC (Higher concentration of H + ) 14 Increasingly BASIC (Lower concentration of H + )

2.18 Chemical reactions make and break bonds, changing the composition of matter Define a chemical reaction and explain how it changes the composition of matter The formation of water from hydrogen and oxygen is an example of a chemical reaction The reactants (H 2 and O 2 ) are converted to H 2 O, the product –Photosynthesis is an example where plants drive a sequence of chemical reactions that produce glucose Copyright © 2009 Pearson Education, Inc.

Resources for Chapter 2 Using your disc that came with your text, go to Student Home, Chapter 2: The Chemical Basis of Life 1.Take the pre test 2.Complete activities. 3.Test yourself 4.Extend your knowledge 5.Current events -On line article New Glimpses of Life’s Puzzling Origins - go to and answer questions – hand in