The Chemistry of Life
Chapter 6 Outline
Section 6.1: Atoms and Their Interactions
A. Elements
An element is a substance that can’t be broken down into simpler chemical
substances. Everything is made of elements. The periodic table is a chart of all of
the known elements on Earth.
1) Natural elements in living things
Only about 25 of the naturally occurring elements on Earth are essential to
living organisms.
2) Trace elements
Elements that are present in living things in very small amounts such as
copper and iron are called trace elements and they are vital to maintenance of
healthy cells.
B. Atoms: The Building Blocks of Elements
An atom is the smallest particle of an element that has the characteristics of that
element. Atoms are the basic building blocks of all matter.
1) The structure of an atom
The center of an atom is called the nucleus and it contains protons which are
positively charged and neutrons which have no charge. The space around the
nucleus known as the electron cloud contains negatively charged electrons.
2) Electron energy levels
Electrons exist around the nucleus in regions known as energy levels. The
first level can only hold 2 electrons, the second level can hold 8 electrons, and
the third level can hold 18 electrons.
C. Isotopes of an Element
Atoms of the same element that have the same number of protons and electrons
but a different number of neutrons are called isotopes of that element.
D. Compounds and Bonding
A compound is a substance that is composed of atoms of two or more different
elements that are chemically combined. (NaCl is a compound composed of the
elements sodium and chlorine.)
1) How covalent bonds form
A bond in which two or more atoms share their out shell electrons to gain
stability is known as a covalent bond. A molecule is a group of atoms held
together by a covalent bond. (Water is a molecule composed of two hydrogen
atoms and one oxygen atom.)
2) How ionic bonds form
An atom or group of atoms that loses or gains electrons becomes charged and
is called an ion. Positively charged ions are called cations and negatively
charged ions are called anions. The attractive force between two ions of
opposite charge is known as an ionic bond.
E. Chemical Reactions
In living organisms, chemical reactions occur inside cells. Some of the chemical
reactions build up molecules and other reactions break down molecules. All of
the chemical reactions that occur within an organism are referred to as that
organism’s metabolism.
1) Writing chemical equations
A chemical reaction shows how substances are broken apart and rearranged to
form new substances. The original substances shown on the left side of a
chemical reaction are called the reactants and the new substances shown on
the right side of a chemical reaction are called the products.
F. Mixtures and Solutions
A mixture is a combination of substances in which the individual components
retain their own properties. An example would be like a combination of sand and
sugar. A solution is a mixture in which one or more substance (solutes) are
distributed evenly in another substance (solvent). An example would be like
crystal light powder (solute) being mixed in water (solvent).
1) Acids and bases
The pH is a measure of how acidic or basic a solution is and the pH scale
ranges from 0 to 14. Acids are any substances that form hydrogen ions
(H+) in water and have a pH value which is less than 7. Bases are any
substances that form hydroxide ions (OH-) in water and have a pH value
which is greater than 7. Neutral substances have a pH of 7.
Section 6.2: Water and Diffusion
A. Water and Its Importance
Water makes up 70-95% of most organisms. Most life processes can occur only
when molecules and ions are free to move and collide with one another and this
occurs when the molecules are dissolved in water.
1) Water is polar
A polar molecule is a molecule with an unequal distribution of charge. The
molecule will have a positive end and a negative end. Attractions between the
negative end of one water molecule and the positive end of another water
water molecule forms a weak bond called a hydrogen bond.
2) Water resists temperature changes
Water is like an insulator that helps maintain a steady environment when
conditions fluctuate.
3) Water expands when it freezes
Most substances contract as they cool down. Water actually expands as it
freezes and this is why ice floats and lakes freeze from the top down instead
of from the bottom up.
B. Diffusion
All objects in motion have energy of motion called kinetic energy and moving
particles will travel in a straight line until it collides with another particle.
1) Early observations: Brownian motion
Brownian motion is the random motion of atoms and molecules in solids,
liquids and gases.
2) The process of diffusion
Diffusion is the net movement of particles from an area of higher
concentration to an area of lower concentration. Concentration, temperature,
and pressure are 3 key factors that affect the rate of diffusion.
3) The results of diffusion
Diffusion results in dynamic equilibrium which is a condition where there is
continuous movement of particles but no overall change in concentration of
particles.
4) Diffusion in living systems
When a living cell is is in dynamic equilibrium with its environment,
materials move into and out of the cell at equal rates. As a result, there is no
net change in concentration of materials inside or outside the cell.
Section 6.3: Life Substances
A. The Role of Carbon in Organisms
Carbon atoms can make four bonds with other carbon atoms as well as other
elements. Due to this characteristic of carbon, a multitude of various carbonbased compounds can be formed.
1) Molecular chains
Carbon compounds vary greatly in size - - from 1 carbon atom to thousands of
carbon atoms. Large organic compounds are called biomolecules and there are
4 main categories: carbohydrates, lipids, proteins, and nucleic acids. A
polymer is a large molecule formed when many smaller molecules bond
together.
2) The structure of carbohydrates
A carbohydrate is a biolmolecule composed of carbon, hydrogen, and oxygen
with a ratio of about 2 hydrogen atoms and 1 oxygen atom for each carbon
atom. Carbohydrates are used by cells to provide energy. Examples of
carbohydrates are: starch, glycogen, and cellulose.
3) The structure of lipids
Lipids are large biomolecules that are made mostly of carbon and hydrogen
with a small amount of oxygen. Examples of lipids are: fats, oils, waxes, and
steroids.
4) The structure of proteins
A protein is a large, complex polymer composed of carbon, hydrogen, oxygen,
nitrogen and sometimes sulfur. Amino acids are the building blocks of
proteins. When one amino acid connects to another, a peptide bond is formed.
An enzyme is a protein that changes the rate of a chemical reaction. Examples
of proteins are: enzymes, hair, fingernails, horns, and hoofs of animals.
5) The structure of nucleic acids
A nucleic acid is a complex biomolecule that stores cellular information in
the form of a code. Nucleic acids are made up of carbon, hydrogen, oxygen,
nitrogen, and phosphorus atoms arranged in three groups: a nitrogenous base,
a simple sugar, and a phosphate group. Nucleotides are the building blocks of
nucleic acids. Examples of nucleic acids are DNA (deoxyribonucleic acid)
and RNA (ribonucleic acid). DNA and RNA work together to direct the
formation of proteins which have vital roles such as directing cellular activity
and repair.