Scientific method Why is it used? When is it used? What is it?
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Transcript of Scientific method Why is it used? When is it used? What is it?
• The main steps of the scientific method
• Feedback• falsifiable
Observation
Question
Hypothesis
Prediction
Test:Experiment or
additionalobservation
Test does notsupport hypothesis; revise hypothesis or
pose new one
Test supports hypothesis; make
additional predictions and test them
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Biosphere
• Ecosystem- abiotic factors- all organisms
• Community
• Population
• Organism
ECOSYSTEM LEVELEucalyptus forest
COMMUNITY LEVELAll organisms ineucalyptus forest
POPULATION LEVELGroup of flying foxes
ORGANISM LEVELFlying fox
ORGAN SYSTEM LEVELNervous system
ORGAN LEVELBrain
Brain Spinal cord
Nerve
TISSUE LEVELNervous
tissue
CELLULAR LEVELNerve cell
MOLECULAR LEVELMolecule of DNA
Figure 1.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Organisms are made up of:
– organ systems
– organs
– tissues
– cells
– molecules
ECOSYSTEM LEVELEucalyptus forest
COMMUNITY LEVELAll organisms ineucalyptus forest
POPULATION LEVELGroup of flying foxes
ORGANISM LEVELFlying fox
ORGAN SYSTEM LEVELNervous system
ORGAN LEVELBrain
Brain Spinal cord
Nerve
TISSUE LEVELNervous
tissue
CELLULAR LEVELNerve cell
MOLECULAR LEVELMolecule of DNA
Figure 1.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
– Each level of organization builds on the one below it
– At each level, new properties emerge
biological function starts at the chemical level
ATOMS AND MOLECULES
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• Atom is smallest particle of an element; each element has unique number of protons
• Electrical charges of particles
Atoms consist of protons, neutrons, and electrons
Figure 2.4A A. Helium atom
2
2
2
Protons
Neutrons
Electrons
Nucleus
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• An element is a substance that cannot be broken down to other substances by ordinary chemical means
• Molecules are combinations of atoms of the same or different elements
• Life requires about 25 chemical elements
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• O, C, H, N , and Ca
Table 2.2
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• Isotopes have a different number of neutrons
Table 2.4
– Some isotopes are radioactive
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• Radioactive isotopes can be useful tracers for medical diagnosis
Figure 2.5BFigure 2.5A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Electrons are arranged in shells
– The outermost shell determines the chemical properties of an atom
Figure 2.6
HYDROGEN (H)Atomic number = 1
CARBON (C)Atomic number = 6
NITROGEN (N)Atomic number = 7
OXYGEN (O)Atomic number = 8
Electron
Outermost electron shell (can hold 8 electrons)
First electron shell (can hold 2 electrons)
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Atoms can join with other atoms
• Ionic bonds
• Covalent bond: polar and nonpolar
• Hydrogen bonds
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• Ions = atoms that gained or lost electrons
– An electrical attraction between ions = ionic bond
Figure 2.7A
NaSodium atom
ClChlorine atom
Na+
Sodium ionCl–
Chloride ion
Sodium chloride (NaCl)
Na Cl Na Cl
+–
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• Sodium and chloride ions bond to form sodium chloride, common table salt
Figure 2.7B
Na+
Cl–
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• atoms share outer shell electrons with other atoms and form molecules
• Nonpolar - electrons are shared equally by the atoms
• Polar - electrons are unequally shared
Covalent bonds
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Free radicals - reversed fountain of youth
• Unpaired electron, very reactive
• damages DNA in mitochondria, causes artery damage, cancer, speeds aging process
• Source: metabolism, sunlight, alcohol, smoking
• Neutralized by Vit E, carotenoids, Vit C
• Eat your fruits and veggies
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen
Figure 2.9
(–)
O
(–)
(+)(+)
H H
Water: What does it have to do with life?
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The slightly negative O is attracted to the positive H, creating a hydrogen bond
Water’s polarity leads to hydrogen bonding and other unusual properties
Figure 2.10A
Hydrogen bond
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• surface tension created by cohesive water molecules
Hydrogen bonds make liquid water cohesive
Figure 2.11
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• Trees move water because of H-bonds
Figure 2.11x
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• It takes a lot of energy to disrupt hydrogen bonds
– Water absorbs a lot of heat energy with only a small increase in temperature
– As water cools, a slight drop in temperature releases a large amount of heat
Water’s hydrogen bonds moderate temperature
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– A water molecule takes a large amount of energy with it when it evaporates
– evaporative cooling
Figure 2.12
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Molecules in ice are farther apart than those in liquid water
Ice is less dense than liquid water
Figure 2.13
Hydrogen bond
ICEHydrogen bonds are stable
LIQUID WATERHydrogen bonds constantly
break and re-form
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Frozen water floats (left) and frozen benzene sinks (right)
Figure 2.13x2
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- Lower water is protected by the surface layer of ice.
– Life can survive in cold water underneath ice.
– Spring thaw pushes nutrient-rich bottom water to surface
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• Many solutes will stick to polar water molecules and dissolve in water
Water is a versatile solvent
Figure 2.14
Ions in solution
Salt crystal
Cl–
Na+
Cl–
–
– –
–
–Na+
+
+
+
+
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Like no other common substance, water exists in nature in all three physical states:
Figure 2.10B
– solid
– liquid
– gas
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– Which element did this damage?
Figure 2.16B
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• A compound that releases H+ ions in solution is an acid, and one that accepts H+ ions in solution is a base.
The chemistry of life is sensitive to acidic and basic conditions
Acid Acid- + H+
Base- + H+ Base
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• Acidity is measured on the pH scale:
– 0-7 is acidic
– 8-14 is basic
– neutral, pH of 7
Figure 2.15
pH scale
Acidic solution
Neutral solution
Basic solution
Incr
easi
ng
ly A
CID
IC(H
igh
er c
on
cen
trat
ion
of
H+)
Incr
easi
ng
ly B
AS
IC(L
ow
er
con
cen
trat
ion
of
H+)
NEUTRAL[H+] = [OH–]
Lemon juice; gastric juice
Grapefruit juice
Tomato juice
Urine
PURE WATER
Seawater
Milk of magnesia
Household ammonia
Household bleach
Oven cleaner
Human blood
H+
OH–
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Acid rain is formed when air pollutants from burning fossil fuels combine with water vapor in the air to form sulfuric and nitric acids
Connection: Acid rain threatens the environment
Figure 2.16A
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• Acid precipitation damage to trees
Figure 2.16x1