scientific method why is it used? when is it used? what is it?

Scientific method

• Why is it used?

• When is it used?

• What is it?

Why is the scientific method important?

• to distinguish between valid research and propaganda

• 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

Figure 2.10x


• 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


• 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


– 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


• 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


• 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


• O, C, H, N , and Ca

Table 2.2


• Isotopes have a different number of neutrons

Table 2.4

– Some isotopes are radioactive


• Radioactive isotopes can be useful tracers for medical diagnosis

Figure 2.5BFigure 2.5A


• 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)


Atoms can join with other atoms

• Ionic bonds

• Covalent bond: polar and nonpolar

• Hydrogen bonds


• 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

+–


• Sodium and chloride ions bond to form sodium chloride, common table salt

Figure 2.7B

Na+

Cl–


• 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


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


• 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?


• 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


• surface tension created by cohesive water molecules

Hydrogen bonds make liquid water cohesive

Figure 2.11


• Trees move water because of H-bonds

Figure 2.11x


• 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


– A water molecule takes a large amount of energy with it when it evaporates

– evaporative cooling

Figure 2.12


• 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


• Frozen water floats (left) and frozen benzene sinks (right)

Figure 2.13x2


- 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


• 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+

+

+

+

+


• Like no other common substance, water exists in nature in all three physical states:

Figure 2.10B

– solid

– liquid

– gas


– Which element did this damage?

Figure 2.16B


• 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


• 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–


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


• Acid precipitation damage to trees

Figure 2.16x1


Figure 2.10Bx

scientific method why is it used? when is it used? what is it?

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