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Chapter 2
Are We Alone in the Universe?
Water, Biochemistry, and Cells
Fourth Edition
BIOLOGY
Science for Life | with Physiology
Colleen Belk • Virginia Borden Maier
© 2013 Pearson Education, Inc.
Copyright © 2009 Pearson Education, Inc.
PowerPoint Lecture prepared by
Jill Feinstein
Richland Community College
2.1 What Does Life Require?
A Definition of Life
 There is no simple definition of life. Instead there is
a list of characteristics.
1. movement
2. responsiveness
3. growth
4. reproduction
5. respiration
6. digestion
7. absorption
8. circulation
9. excretion
© 2013 Pearson Education, Inc.
2.1 What Does Life Require?
A Definition of Life
 But, all Earth organisms…
 have a common set of biological molecules
 are composed of cells
 can maintain homeostasis
 can evolve
 require liquid water
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Life: Levels of Organization
•Atoms
•Molecules
•Macromolecules
•Organelles
•Cells
•Tissues
•Organs
•Organ systems
•Organism
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2.1 What Does Life Require?
 Elements: fundamental forms of matter
 Atoms: the smallest units of an element
 Atoms are composed of
 Protons (positive charge) and neutrons in the nucleus of the atom
 Electrons (negative charge) are found in an “electron cloud”
 Ions are atoms with an electrical charge.
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Atom = smallest unit of an element that still retains the
chemical & physical properties of that element
i.e. really, really, really tiny thing!
-composed of: protons = one positive charge, 1 atomic
mass unit
electrons = one negative charge, no
mass
neutrons = no charge, 1 atomic mass
unit
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Periodic Table of Elements
-elements are grouped on a Periodic Table of Elements
-the elements are grouped according to physical and chemical characteristics
-on the chart each element is associated with a letter, an atomic number
& an atomic mass
IA
IIA
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IIIA IVA VA VIA VIIA VIII
atomic
symbol
atomic
mass (weight)
12
6
C
e.g. # protons (e-) = 6
# pr+6 + #No 6 = 12
atomic
number
7
3
Li
e.g. # protons (e-) = 3
# pr+3 + #No 4 = 7
Atomic mass = number of protons + neutrons
Atomic number = number of protons when the element is electrically
neutral
** when neutral, the number of protons and electrons are equal
© 2013 Pearson Education, Inc.
© 2013 Pearson Education, Inc.
Atoms and Disease: Cystic Fibrosis
Cystic fibrosis is the most common lethal genetic disease in the United States

one out of every 2,500 people of European descent
loss of three NT’s from a gene coding for a transporter of chloride ions

results in the loss of one amino acid within the protein sequence of the
transporter

diffusion of chloride ions out of epithelial cells is blocked

results in the thickening of the extracellular fluid outside epithelial cells
symptoms include mucus buildup in some internal organs (blocks passages),
pancreatic damage (build up of digestive enzymes) and abnormal absorption of
nutrients in the small intestine
average life span in US – 37.4 yrs
average life span in Canada – 47.7 yrs
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Isotope:
• all atoms of an element have the same number of protons
but may differ in number of neutrons
•
the number of protons defines what the element is
•
e.g. 6 protons = carbon and only carbon
• isotopes are two atoms of an element that differ in
number of neutrons
• in nature an element is a mixture of its isotopes
pr+:
e-:
No:
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12C
13C
6
6
6
6
6
7
14C
6
6
8** radioactive
Radioactive isotope uses:
1. carbon dating - 14C
2. radioactive imaging - e.g. PET scanning
-use of FDG – radioactive glucose tracer
-18F radioactive isotope (2-fluoro-deoxy-glucose)
3. radiotherapy in cancer treatment - 60Co
Cancerous
throat
tissue
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Radioactive Iodine:
-Iodine-131
-high doses specifically enter and kill thyroid tissues
-lower doses are more dangerous and not used
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Radioactivity
• the protons and neutrons are held together in the nucleus by
a kind of nuclear “glue”
• when the number of neutrons increase – the nucleus
becomes unstable
• the breakup of the nucleus releases particles with energy in
the form of radioactivity
•
•
also known as radioactive decay
three different kind of particles released – each with different energy
levels
•
•
alpha (helium atom), beta and gamma
the decay can eventually change the # protons – transform one atom
into another
pr+:
e-:
No:
© 2013 Pearson Education, Inc.
12C
13C
6
6
6
6
6
7
14C
6
6
8** radioactive
Molecules of Life:
• the chemicals used in metabolic reactions or those
that are produced by them can be classified into
2 groups:
1. Inorganic
2. Organic
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Organic Chemistry
 All life on Earth is based on organic chemistry: the
chemistry of the complex carbon containing molecules.
 organic molecules must contain: oxygen, hydrogen and carbon
 Carbon makes up most of the mass of living organisms.
 Carbon: a molecular TinkerToy
 Can bond to 4 different atoms at once
 Carbon can make hydrocarbons
 Simple organic molecules
 Carbon can make macromolecules
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How do you make a molecule? Bonding and Electron
Configurations
 Chemical bonds are dependent on the atom’s
electron configuration.
First shell
Second shell
 Electrons are arranged in energy levels or
electron shells
 1st electron shell holds up to 2 electrons
 made of a subshell called the s orbital
1s orbital 2s orbital

2nd
3rd
and
electron shells holds up to 8
electrons each
 each are made up two subshells called
the s and p orbitals
 4th shell holds up to 18 electrons
 made up of s, p and d orbitals
 The outer shell that holds electrons is
called the valence shell
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y
x
z
Three 2p orbitals
(b) Separate electron orbitals
1s, 2s, and
2p orbitals
(c) Superimposed electron orbitals
How do you make a molecule? Bonding and Electron
Configurations
The Bohr Model: Bed check for
electrons
forming bonds depends on how are
electrons organized around the
nucleus of an atom
Nils Bohr proposed electrons orbit
around the atom’s nucleus in specific
energy levels or orbits (shells)

1st shell – closest to the nucleus only
holds 2 electrons

2nd shell can hold 8

3rd holds 18 – only 8 are involved in
bonding reactions

4th holds 18 – only 8 are involved in
bonding reactions
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First shell
Neon, with two filled
Shells (10 electrons)
Second shell
(a) Electron distribution diagram
•an atom will always try to complete its outermost shell
•basis for bonding reactions
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VIII
I
Hydrogen
1H
Electron
distribution
diagram
First
shell
II
Lithium
3Li
Beryllium
4Be
III
Boron
5B
IV
Helium
2He
V
VI
VII
Carbon
6C
Nitrogen
7N
Oxygen
8O
Fluorine
9F
Neon
10Ne
Silicon
14Si
Phosphorus
15P
Sulfur
16S
Chlorine
17Cl
Argon
18Ar
Second
shell
Sodium Magnesium Aluminum
11Na
12Mg
13Al
Third
shell
•
the periodic table of the elements tells you the electron distribution for each
element
•
•
•
•
•
by its row and column position
1st row – valence electrons in the first electron shell
2nd row – valence electrons in the second electron shell
1st column – 1 valence electron
3rd column – 3 valence electrons
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How do you make a molecule? Bonding and Electron
Configurations
atoms with incomplete valence shells can share or transfer
valence electrons with certain other atoms to form molecules
molecule - particle formed by the union of more than one
atom

e.g. same kind of atom - O2

e.g. different types of atoms - H20
• formed by held by attractions called chemical bonds
• two types of chemical bonds
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Molecular Bonds: Covalent and Ionic
 Ionic bonds: occurs when there is a transfer of electrons between
atoms
 sodium atom has 1 valence electron
 chloride has 7 valence electrons
 chloride “steals” sodium’s electron to become a more negatively charged ion
 sodium loses its electron to become a more positively charged ion
© 2013 Pearson Education, Inc.
Molecular Bonds: Covalent and Ionic
 Covalent bonds: stronger bond from sharing electrons
 usually forms when a valence shell needs to lose or gain
more than 3 electrons
 Single bonds indicate sharing of one pair of electrons
 Double bonds share two pairs of electrons
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Polar and Non-Polar Covalent Bonds
• in a nonpolar covalent bond - the atoms share their electron equally
• in a polar covalent bond - one atom is more electronegative
•
the atoms do not share the electron equally
• unequal sharing of electrons causes a partial positive or negative
charge for each atom or molecule
•
annotated with the greek letter delta
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Polar and Non-Polar Covalent Bonds
• oxygen is very electronegative – creates polar bonds
• so does nitrogen (N)
–
O
+
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H
H
H2O
+
Requirements for Life:
1. water
2. food
3. oxygen
4. heat
5. pressure
© 2013 Pearson Education, Inc.
Animation: Chemistry and Water
Right-click slide / select “Play”
© 2013 Pearson Education, Inc.
2.1 What Does Life Require? WATER
The Properties of Water
 Molecule: two or more atoms held
together by chemical bonds
 Water molecule: two hydrogen atoms
bonded to one oxygen atom
 Water is a good solvent (helps chemical
reactions).
–
 Solute: what is being dissolved in the
solvent
O
 Solution: solutes added to a solvent+
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H
H
H2O
+
2.1 What Does Life Require?
The Properties of Water
 Water is a polar molecule:
 Oxygen side is
slightly negative
 because it is more
electronegative than hydrogen
 Hydrogen side is slightly positive
 When molecules have no charges, they
are nonpolar.
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The Properties of Water
 Hydrogen bond: the weak attraction between the
hydrogen atom of one water molecule and the
oxygen atom of another
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The Properties of Water
 Water can dissolve
salts and hydrophilic
(water–loving) molecules
because it is polar.
 Nonpolar molecules such
as oil are hydrophobic
(water-fearing) and do not
easily dissolve in water
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The Properties of Water
 Water facilitates chemical reactions
 Solutes in the mixture are called reactants
 End result of the chemical reaction are called
products
 Water molecules tend to stick together:
cohesion
 Water moderates temperature
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The Properties of Water
 Water can dissolve acids and bases and
liberate their ions
 acid = proton (H+) donor

e.g. HCl  the H+ ion is donated
 base = proton (H+) acceptor

can also be considered an OH- acceptor

e.g. NaOH
 when acids and bases are mixed together –
water an a salt is produced

HCl + NaOH  NaCl and H2O
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The Properties of Water
 The pH scale is a measure of
the relative amounts of acids
and bases in a solution.
 pH greater than 7 = basic
 pH lower than 7 = acidic
 Pure water = 7 – neutral
 pH 7 means 10-7 moles of H+ ions/liter of
solution
 pH 10 means 10-10 moles of H+ ions/liter
 pH 4 means 10-4 moles of H+ ions/liter of
solution
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Which of the following would not be considered an
element?

oxygen

iron

water

nitrogen
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Which of the following would not be considered an
element?

oxygen

iron

water

nitrogen
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An atom’s atomic number refers to its _________.

electrons

nucleus

protons

neutrons
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An atom’s atomic number refers to its _________.

electrons

nucleus

protons

neutrons
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What type of bond occurs when electrons are
transferred between atoms?

covalent bonds

hydrogen bonds

ionic bonds

double bonds
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What type of bond occurs when electrons are
transferred between atoms?

covalent bonds

hydrogen bonds

ionic bonds

double bonds
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Glucose and sucrose are both examples of which
category of macromolecules?

polysaccharides

proteins

nucleic acids

lipids
© 2013 Pearson Education, Inc.
Glucose and sucrose are both examples of which
category of macromolecules?

polysaccharides

proteins

nucleic acids

lipids
© 2013 Pearson Education, Inc.