Download Hypothesis-Driven Science Hypothesis

4/1/2011
THE PROCESS OF SCIENCE
– What is science?
– The word science is derived from a Latin verb
meaning “to know.”
Discovery Science
Hypothesis-Driven Science
• Science seeks natural
causes for natural
phenomena.
• As a formal process of
inquiry, consists of a
series of steps.
– This limits the scope of
science to the study of
structures and processes
that we can observe and
measure.
– The key element of the
scientific method is
hypothesis-driven
science.
Hypothesis-Driven Science
– As a formal process of inquiry, the scientific method
consists of a series of steps.
• The key element of the scientific method is
hypothesis-driven science.
Revise and repeat
Observation
Question
Hypothesis
Prediction
Experiment
Hypothesis-Driven Science
Observation:
My flashlight
doesn’t work.
Question:
What’s wrong
with my
flashlight?
Hypothesis:
The flashlight’s
Th
fl hli ht’
batteries
are dead.
Prediction:
If I replace the
batteries, the
flashlight will
work.
Experiment:
I replace the
batteries with
new ones.
Experiment
supports
hypothesis;
make additional
predictions
and test them.
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Theories in Science
– What is a scientific theory, and how is it different
from a hypothesis?
• A theory is much broader in scope than a
hypothesis.
• Theories only become widely accepted in science if
they are supported by an accumulation of extensive
and varied evidence.
Chemistry of Life
– Matter is anything that occupies space and has mass.
– Matter is found on the Earth in three physical states:
• Solid
• Liquid
• Gas
Atoms
– Each element consists of one kind of atom.
• An atom is the smallest unit of matter that still retains the
properties of an element.
2
Protons
2
Neutrons
2
Electrons
Nucleus
Nucleus
Cloud of negative
charge (2 electrons)
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Chemistry of Life
– Matter is composed of chemical elements.
• Elements are substances that cannot be broken down
into other substances.
Change the number of PROTONS in the nucleus and you
change the ELEMENT
Chemistry of Life
– Elements differ in the number of subatomic particles
in their atoms.
• The number of protons, the atomic number, determines which
element it is.
• An atom’s mass number is the sum of the number of protons
and neutrons.
j
• Mass is a measure of the amount of matter in an object.
Periodic Table of the Elements
Legend
Solid
Liquid
Gas
Synthetic
Alkali metals
Alkali earth metals
Transition metals
Rare earth metals
Other metals
Noble gases
Halogens
Other nonmetals
Atomic number = number of protons within the nucleus
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Chemistry of Life
– Twenty-five elements are essential to life.
– Four elements make up about 96% of the weight of
Carbon (C): 18.5%
the human body:
• Oxygen
Calcium (Ca): 1.5%
Phosphorus (P): 1.0%
Oxygen (O):
• Carbon
65.0%
Potassium (K): 0.4%
Sulfur (S): 0
0.3%
3%
• Hydrogen
Sodium (Na): 0.2%
Chlorine (Cl): 0.2%
• Nitrogen
Magnesium (Mg): 0.1%
Trace elements: less than 0.01%
Hydrogen (H):
9.5%
Boron (B)
Chromium (Cr)
Cobalt (Co)
Copper (Cu)
Fluorine (F)
Iodine (I)
Iron (Fe)
Nitrogen (N):
3.3%
Manganese (Mn)
Molybdenum (Mo)
Selenium (Se)
Silicon (Si)
Tin (Sn)
Vanadium (V)
Zinc (Zn)
Chemical Properties of Atoms
– Electrons determine how an atom behaves when it encounters
other atoms.
First electron shell
(can hold 2 electrons)
Electron
Outer electron shell
(can hold 8 electrons)
Hydrogen (H)
Carbon (C)
Atomic number = 1 Atomic number = 6
Nitrogen (N)
Atomic number = 7
Oxygen (O)
Atomic number = 8
© 2010 Pearson Education, Inc.
Covalent Bonds
– A covalent bond forms when two atoms share one or
more pairs of outer-shell electrons.
– Atoms held together by covalent bonds form a
molecule.
Name
Electron configuration
(molecular formula)
Hydrogen gas (H2)
Structural formula
Space-filling model
Ball-and-stick model
Single bond
(a pair of shared electrons)
Oxygen gas (O2)
Double bond
(two pairs of shared electrons)
Methane (CH4)
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Ionic Bonds
– When an atom loses or gains electrons, it becomes
electrically charged.
• Charged atoms are called ions.
• Ionic bonds are formed between oppositely charged ions.
Outer shell
has 1 electron
Na
Sodium atom
The outer electron is stripped
from sodium and completes
the chlorine atom’s outer shell
Outer shell
has 7 electrons
Cl
Chlorine atom
Complete
outer shells
Na+
Sodium ion
Cl−
Chlorine ion
The attraction
between the
ions—an ionic
bond—holds
them together
Sodium chloride (NaCl)
Hydrogen Bonds
– Water is a compound in which the electrons in its
covalent bonds are shared unequally.
• This causes water to be a polar molecule, one with opposite
charges on opposite ends.
(slightly +)
(slightly +)
H
H
O
(slightly –)
Hydrogen bonding
• Weak bonds formed
between hydrogen and
another atom
– Surface tension of water
• Important
p
as
intramolecular bonds,
giving shape to proteins
and other biomolecules
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WATER AND LIFE
– Life on Earth began in water and evolved there for 3
billion years.
• Modern life remains tied to water.
• Your cells are composed of 70%–95% water.
Properties of Water
• Numerous properties due to the hydrogen bonding
Properties of Water
– Water molecules stick
together as a result of
hydrogen bonding.
Evaporation from
the leaves
• This is called cohesion.
Microscopic tubes
SEM
Cohesion due to
hydrogen bonds
between water
molecules
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Properties of Water
– Heat and temperature are related, but different.
• Heat is the amount of energy associated with the movement of
the atoms and molecules in a body of matter.
• Temperature measures the intensity of heat.
– Water can absorb and store large amounts of heat
while only changing a few degrees in temperature.
– Water can moderate temperatures.
Properties of Water
– Surface tension is the measure of how difficult it is to
stretch or break the surface of a liquid.
• Hydrogen bonds give water an unusually high surface tension.
Water is the solvent of life
*solution
*solvent
*solute
*aqueous solution
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Acids, Bases and pH
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Increasingly basic
(lower H+ concentration)
Oven cleaner
Basic
solution
Increasingly acidic
(greater H+ concentration)
Neutral
[H+] = [OH–]
Neutral
solution
Acidic
solution
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Household
12 bleach
Household ammonia
11
Milk of magnesia
10
9
Seawater
8
Human blood
7 Pure water
6 Urine
5
4 Tomato juice
3 Grapefruit juice,
soft drink
2 Lemon juice,
gastric juice
1
0
pH scale
Carbon and Organic Chemistry
– Carbon is a versatile atom.
– Carbon forms large, complex, and diverse molecules
necessary for life’s functions.
– Organic compounds are carbon-based molecules.
Structural
formula
Ball-and-stick
model
Space-filling
model
Carbon and Organic Chemistry
• Variations in Carbon
skeletons
Carbon skeletons vary in length
Carbon skeletons may be unbranched or branched
Carbon skeletons may have double bonds,
which can vary in location
Carbon skeletons may be arranged in rings
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Hydrocarbons
– Larger hydrocarbons form fuels for engines.
– Hydrocarbons of fat molecules fuel our bodies.
Carbon and Organic Chemistry
• The unique properties of an organic compound
depend not only on its carbon skeleton but also on the
atoms attached to the skeleton
– These atoms are called functional groups
– Some common functional groups include:
Hydroxyl group
Carbonyl group
Amino group
Carboxyl group
Found in alcohols
and sugars
Found in sugars
Found in amino acids
and urea in urine (from
protein breakdown)
Found in amino acids,
fatty acids, and some
vitamins
Macromolecules
– On a molecular scale, many of life’s molecules are
gigantic, earning the name macromolecules.
– Three categories of macromolecules are
• Carbohydrates
• Proteins
• Nucleic acids
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Macromolecules
*most macromolecules are polymers
polymer
monomer
The making and breaking of polymers:
Dehydration reaction:
Hydrolysis:
Carbohydrates
• Carbohydrates include
– Small sugar molecules in soft drinks
• Monosaccharides & Disaccharides
– Long starch molecules in pasta and potatoes
• Polysaccharides
Monosaccharides
• Monosaccharides are simple sugars
– Glucose, found
in sports drinks
– Fructose, found
in fruit
• Honey
H
contains
t i
both glucose and
fructose
Glucose
Fructose
Isomers
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Monosaccharides
• In aqueous solutions, monosaccharides form
rings
(b) Abbreviated ring
structure
(a) Linear and ring
structures
Disaccharides
• A disaccharide is a double sugar
• Disaccharides are joined by the process of dehydration
synthesis
Glucose
Glucose
Maltose
Disaccharides
• The most common disaccharide is sucrose,
common table sugar
– It consists of a glucose
linked to a fructose
– Sucrose is extracted
from sugar cane and the
roots of sugar beets
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Polysaccharides
– They are long chains of sugar units
– They are polymers of monosaccharides
Glucose
monomer
Starch granules in
potato tuber cells
(a) Starch
Glycogen
Granules
In muscle
tissue
(b) Glycogen
Cellulose fibril in
a plant cell wall
Cellulose molecules
(c) Cellulose
Polysaccharides
• Most animals cannot derive nutrition from
fiber
– How do grazing animals survive
on a diet of cellulose?
Proteins
• Proteins perform most of the tasks the body
needs to function
– They are the most elaborate of life’s molecules
MAJOR TYPES OF PROTEINS
Structural Proteins
Storage Proteins
Contractile Proteins
Transport Proteins
Enzymes
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The Monomers: Amino Acids
• All proteins are constructed from a common
set of 20 kinds of amino acids
Amino Carboxyl
group
group
Side
group
Proteins as Polymers
Carboxyl
group
• Cells link amino acids
together by
dehydration synthesis
– The resulting bond
between them is
called a peptide
bond
Amino
group
Side
group
Side
group
Amino acid
Amino acid
Dehydration
synthesis
Side
group
Side
group
Peptide bond
Protein Structure
– The arrangement of
amino acids makes
each protein different
5
1
15
10
30
35
40
• Primary
structure
– Th
The specific
ifi
sequence of amino
acids in a protein
20
25
45
50
55
65
60
70
85
80
75
95
90
100
110
105
115
120
125
129
Amino acid
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Protein Structure
• A slight change in the primary structure of a protein
affects its ability to function
– The substitution of one amino acid for another in
hemoglobin causes sickle-cell disease
1
2
6
7. . . 146
4
5
Normal hemoglobin
(a) Normal red blood cell
1
3
2
3
6
7. . . 146
4
5
Sickle-cell hemoglobin
(b) Sickled red blood cell
Protein Structure
• Proteins have four levels of structure
Hydrogen bond
Pleated sheet
Polypeptide
(single subunit)
Amino acid
(a) Primary structure
Complete
protein,
with four
polypeptide
subunits
Hydrogen bond
Alpha helix
(b) Secondary
structure
(c) Tertiary
structure
(d) Quaternary structure
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