Concepts of Biology 2nd Edition

1. Chapter 2
Basic Chemistry and Cells

2. Matter is composed of atoms
• Six types of atoms are basic to life = 95% of body weight
– C carbon
– H hydrogen
– N nitrogen
– O oxygen
– P phosphorus
– S sulfur
• Element
– Substance that cannot be broken down by chemical means into
a simpler substance (periodic table of elements shows all known
elements)
• Atom
– Smallest unit of an element that still retains the chemical and
physical properties of the element

3. • Atomic symbol
– One or two letters that represent the name of an
element (Au, C, O, N)
• Subatomic particles
– Protons
• Positively charged (+)
• Within nucleus
– Neutrons (0)
• Uncharged
• Within nucleus
– Electrons (-)
• Negatively charged
• Orbit about nucleus

4. • Electron shells
– Inner shell
• Lowest energy level
• Holds 2 electrons
– All shells beyond
inner shell
• Holds 8 electrons
– Outer shell
• Highest energy level
• Holds 8 electrons

5. • Atomic number
– Number of protons of an element
– Also tells number of electrons when electronically
neutral

6. • Mass number
– Number of protons plus neutrons
• Isotopes
– Atoms of a single element that differ in their number
of neutrons
• Atomic mass
– Average mass of all isotopes

7. The many medical uses of
radioactive isotopes
• Low levels of radiation
– Tracer to detect tumors
• High levels of radiation
– Sterilize medical and dental products
– Sterilize mail to free it of possible pathogens
(anthrax)
– Treatment for cancer

8. Atoms react with one another to
form molecules
• After atoms react, they have a completed
outer shell
• Periodic table
– Arranges elements based on characteristics
• Periods
– Horizontal row
– How many shells an atom has
• Groups
– Vertical column
– How many electrons an atom has in its outer shell

9. Periods – how many shells
Groups – how many electrons in outer shell

10. • Octet rule
– Atoms will give up, accept, or share electrons in order to have 8
electrons in the outer shell
• Group 8
– Stable
– All other groups readily react
• Compound
– When atoms of two or more elements bond together in fixed
proportions
• Molecule
– Smallest part of a compound that still has the properties of that
compound
– Molecule is union of two or more atoms of the same or different
elements
• Naturally occurring molecules
– O2, H2, N2, H2O
• Naturally occurring compound
– H2O

11. An ionic bond occurs when
electrons are transferred
• One atom can take
electron(s) from another
atom
• Ions result
– Ions that lost electrons are
positively charged
– Ions that gained electrons
are negatively charged
• Ionic bonds result
– An attraction between
negatively and positively
charged ions

12. A covalent bond occurs when
electrons are shared
• Atoms want to fill their outer shell
• Bond notations
– H – H share one pair of electrons
– O = O share two pairs of electrons
– N = N share three pairs of electrons
• Molecular – omits the bond line
– H2
– O2
– N2
• Common bonds required
– H – 1 bond
– O – 2 bonds
– C – 4 bonds

14. Chemical reactions
• Some bonds are broken while others are formed
• Reactants
– Participate in reaction
• Products
– Formed by reaction
• Photosynthesis
– Balanced equation
– Same number of each type of atom occurs on both sides of
arrow

15. A covalent bond can be nonpolar or
polar
• Nonpolar
– Sharing of electrons between two atoms is fairly
equal

16. • Electronegativity
– Attraction of an atom for the electrons in a covalent
bond
• H2O
– O
• Larger atom
• more electronegative
• Slightly negative
– H
• Smaller atom
• Less electronegative
• Slightly positive
• Polar
– Unequal sharing of electrons in a covalent bond
The polarity of water molecules leads to the
formation of hydrogen bonds

17. Hydrogen bonds can occur
between polar molecules
• Hydrogen atoms in
one molecule are
attracted to oxygen
atoms in another
molecule
• Weaker than ionic or
covalent bonds
• Hydrogen bonds also
hold the two strands
of DNA together

18. The properties of water benefit life
Water molecules stick together and to other
materials
• Due to hydrogen bonding
– Water can be liquid at most temperatures found on
earth
– Water molecules exhibit cohesion (stick together)
– Water molecules exhibit adhesion (stick to other polar
material)
• Cohesion and adhesion
– Create surface tension
– Allows water to rise to the top of plants
– Allows blood to flow through a body

19. Water warms up and cools down
slowly
• This allows organisms to maintain internal
temperatures (homeostasis)
• Cooling slowly aids organisms in winter
• To vaporize water, hydrogen bonds must
be broken, this requires a large amount of
energy

20. Water dissolves other polar
substances
• Solutions are composed of
– Solute
• What is being dissolved
– Solvent
• What does the dissolving
Creating sugar water
solute – sugar
solvent – water

21. • When ionic salt (NaCl) is put in water, the
atoms dissociate and the Na+ and Cl- dissolve
into the water
Hydrophilic – molecule that
can attract water
Hydrophobic – molecule
that canon attract water (oil
and water do not mix)

22. Frozen water is less dense than
liquid
Water expands as it
freezes
Ice floats, allowing
bodies of water to freeze
from the surface down
and they usually do not
freeze solid, allowing
organisms to survive the
winter

23. Living things require a narrow pH
range
• When water dissociates, hydrogen ions (H+) and hydroxide ions
(OH-) result in equal concentrations
• Acids
– Excess hydrogen (H+) ions
• Bases
– Excess hydroxide (OH-) ions

25. • The pH scale measures acidity and basicity
• pH scale ranges from 0 to 14
• Neutral = 7
– This is when H+ concentration equals OH- concentration
• Acidic <7
• Basic >7

26. Buffers help keep the pH of the
body fluids relatively constant
• Buffer
– Resists changes in pH
• Blood pH needs to stay between 7.35 and 7.45
• Carbonic acid (H2CO3) and bicarbonate (HCO3) are present in blood
• Carbonic acid can dissociate to release bicarbonate and H+
– This lowers pH
• When a base is added (OH-) the carbonic acid dissociates and releases
H+, these combine to form water (H2O)
• When there is excess H+, carbonic acid reforms

27. • Breathing releases CO2, which reduces
the amount of carbonic acid in the blood
• Kidneys also filter acids and bases from
the body but act more slowly, although
powerfully. A malfunction of the kidneys
could cause blood pH to go higher or
lower than required levels.

28. Harmful effects of acid rain
• Rainwater pH = 5.6
– Low due to CO2 in the air forming carbonic
acid
• Acid rain pH < 5
– Contains sulfuric and/or nitric acid
– Sulfur dioxide and nitrogen oxides come from
burning fossil fuels
• Acid rain affects lakes in areas with little to
no limestone (a buffer) CaCO3

29. • Acid rain
– Causes mercury to accumulate in fish
– Can make bodies of water lifeless
– Damages plants
– Increases respiratory illness in humans
– Breaks down limestone and marble buildings
and monuments
– Degrades paint on homes and cars