Invitation to Biology

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Invitation to Biology

• Chapter 1

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Lifes Levels of Organization

• The world of life shows levels of organization,
  from the simple to the complex, which extend
  through
• cells
• populations
• communities
• ecosystems
• the biosphere

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Lifes Levels of Organization
Fig. 1-1, p.4
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Lifes Levels of Organization
tissue
atom
cell
organ
organ system
molecule
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Molecules of Life

• All things are made up of the same units of
  matter
• atoms, molecules
• Living things are made of up of a certain subset
  of molecules
• nucleic acids, proteins, carbohydrates, lipids

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DNA (deoxyribonucleic acid)

• The signature molecule of life
• Molecule of inheritance
• Directs assembly of amino acids

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Heritability of DNA

• Inheritance
• Acquisition of traits by way of transmission of
  DNA from parent to offspring
• Reproduction
• Mechanisms by which an organism produces
  offspring
• Governed by instructions in DNA

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DNA Guides Development

• Development
• Transformation from fertilized egg to adult
• Series of stages
• Instructions for each stage in DNA

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Energy Is the Basis of Metabolism

• Energy Capacity to do work
• Metabolism Reactions by which cells acquire
  and use energy to grow, survive, and reproduce

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Interdependencies among Organisms

• Producers
• Make their own food
• Consumers
• Depend on energy stored in tissues of
  producers
• Decomposers
• Break down remains and wastes

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Energy Flow

• Usually starts with energy from sun
• Transfer from one organism to another
• Energy flows in one direction
• Eventually, all energy flows back to the
  environment

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Sensing and Responding

• Organisms sense changes in their environment and
  make responses to them
• Receptors detect specific forms of energy
• The form of energy detected by a receptor is a
  stimulus

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Homeostasis

• Maintenance of internal environment within range
  suitable for cell activities
• Pancreas maintains level of sugar in blood by
  secreting hormones

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Unity of Life

• All organisms
• Are composed of the same substances
• Engage in metabolism
• Sense and respond to the environment
• Have the capacity to reproduce based on
  instructions in DNA

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Diversity of Life

• Millions of living species
• Additional millions of species now extinct
• Classification scheme attempts to organize this
  diversity

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Scientific Names

• Two-part naming system
• Devised by Carolus Linnaeus
• First name is genus (plural, genera)
• Homo sapiens - genus is Homo
• Second name is species within genus

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Three-Domain Classification

• Bacteria
• Archaea
• Eukarya (includes protists, plants, fungi, and
  animals)

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Lifes Diversity
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Prokaryotes

• Archaea and Bacteria
• Single-celled
• No nucleus or organelles
• Include producers, consumers, decomposers

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Eukaryotes

• Eukarya (plants, fungi, animals, protists)
• DNA is inside a nucleus
• Most are larger and more complex than the
  prokaryotes

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Plants

• All are multicelled
• Most are photosynthetic producers
• Make up the food base for communities, especially
  on land

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Fungi

• Most are multicelled
• Consumers and decomposers
• Extracellular digestion and absorption

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Animals

• Multicelled consumers
• Herbivores
• Carnivores
• Parasites
• Scavengers
• Move about during at least
• some stage of their life.
• Your couch-potatoe roommate
• doesnt count!)

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Mutation Source of Variation

• Mutation change in structure of DNA
• Basis for the variation in heritable traits
• Most are harmful

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Adaptive Trait

• A trait that gives the individual an advantage
  in survival or reproduction, under a given set of
  circumstances

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Evolution

• Genetically based change in a line of descent
  over time
• Population changes, not individuals

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Natural Selection

• The outcome of differences in survival and
  reproduction among individuals that vary in
  details of heritable traits
• This process helps explain evolution - changes in
  a line of descent over generations

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Artificial Selection

• Breeders favor some form of traits over others
• Individuals exhibiting favored traits are bred
• Favored traits increase in the population

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Observations, Hypotheses, and Tests

• Observe phenomenon
• Develop hypotheses
• Make predictions
• Devise test of predictions
• Carry out test and analyze results

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Scientific Theory

• A hypothesis that has been tested for its
  predictive power many times and has not yet been
  found incorrect
• Has wide-ranging explanatory power
• Darwins Theory of Evolution by Natural Selection

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Role of Experiments

• Procedures used to study a phenomenon under known
  conditions
• Allows you to predict what will happen if a
  hypothesis is not wrong
• Can never prove a hypothesis 100 correct (always
  seems to be an exception)

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Experimental Design

• Control group
• A standard for comparison
• Identical to experimental group except for
  variable being studied
• Sampling error
• Non-representative sample skews results
• Minimize by using large samples

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Field Experiment
Experimental Group 46 H. cydno individuals with
white markings
Control Group 34 H. cydno individuals with
yellow markings

• Study of Heliconius butterflies
• Example of mimicry!

Experiment Both yellow and white forms of H.
cydno butterflies are introduced into
isolated rain forest habitat of yellow H.
eleuchia butterflies. Numbers of
individuals resighted recorded on a daily basis
for two weeks.
Results Experimental group (H.
cydno individuals without yellow wing markings)
is selected against. 37 of the original group of
46 white butterflies disappear (80), compared
with 20 of the 34 yellow controls (58).
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Limits of Science

• Scientific approach cannot provide answers to
  subjective questions
• Cannot provide moral, aesthetic, or philosophical
  standards

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Science vs. Supernatural

• Science has run up against religious belief
  systems
• Copernicus suggested Earth-centered universe
  (proved incorrect)
• Darwin proposed evolution instead of creation
  (still debated!)

Nicolaus Copernicus (1473-1543)
Charles Darwin (1809-1882)
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Asking Questions

• Scientists still ask questions that challenge
  widely held beliefs, religious or otherwise (and
  vice versa!)
• However, the external world, not internal
  conviction, is the testing ground for scientific
  beliefs

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Lifes Chemical Basis

• Chapter 2

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Elements

• Fundamental forms of matter
• Cant be broken apart by normal means
• 92 occur naturally on Earth

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Most Common Elements in Living Organisms

• Oxygen
• Hydrogen
• Carbon
• Nitrogen

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What Are Atoms?

• Smallest particles that retain properties of an
  element
• Made up of subatomic particles
• Protons ()
• Electrons (-)
• Neutrons (no charge)

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Representing the Hydrogen Atom
Shell model
Ball model
Electron density cloud
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Atomic Number

• Number of protons
• All atoms of an element have the same atomic
  number
• Atomic number of hydrogen 1
• Atomic number of carbon 6

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Mass Number

• Number of protons
• Number of neutrons
• Isotopes vary in mass number

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Isotopes

• Atoms of an element with different numbers of
  neutrons (different mass numbers)
• Carbon 12 has 6 protons, 6 neutrons
• Carbon 14 has 6 protons, 8 neutrons

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Radioisotopes

• Have an unstable nucleus that emits energy and
  particles
• Radioactive decay transforms radioisotope into a
  different element
• Decay occurs at a fixed rate

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Radioisotopes as Tracers

• Tracer is substance with a radioisotope attached
  to it
• Emissions from the tracer can be detected with
  special devices
• Following movement of tracers is useful in many
  areas of biology

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Radioisotopes in Medicine

• Positron-Emission Tomography (PET) uses
  radioisotopes to form images of body tissues
• Patient is injected with tracer and put through a
  PET scanner
• Body cells absorb tracer at different rates
• Scanner detects radiation caused by energy from
  decay of the radioisotope, and radiation then
  forms an image
• Image can reveal variations and abnormalities in
  metabolic activity

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Other Uses of Radioisotopes

• Drive artificial pacemakers
• Radiation therapy
• Emissions from some radioisotopes can destroy
  cells. Some radioisotopes are used to kill small
  cancers.

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What Determines Whether Atoms Will Interact?

• The number and arrangement of their electrons

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Electrons

• Carry a negative charge
• Repel one another
• Are attracted to protons in the nucleus
• Move in orbitals - volumes of space that surround
  the nucleus

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Electron Orbitals

• Orbitals can hold up to two electrons
• Atoms differ in the number of occupied orbitals
• Orbitals closest to nucleus are lower energy and
  are filled first

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Shell Model

• First shell
• Lowest energy
• Holds 1 orbital with up to 2 electrons
• Second shell
• 4 orbitals hold up to 8 electrons

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Electron Vacancies

• Unfilled shells make atoms likely to react
• Hydrogen, carbon, oxygen, and nitrogen all have
  vacancies in their outer shells

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Chemical Bonds, Molecules, Compounds

• Bond is union between electron structures of
  atoms
• Atoms bond to form molecules
• Molecules may contain atoms of only one element -
  O2
• Molecules of compounds contain more than one
  element - H2O

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Chemical Bookkeeping

• Use symbols for elements when writing formulas
• Formula for glucose is C6H12O6
• 6 carbons
• 12 hydrogens
• 6 oxygens

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Chemical Bookkeeping

• Chemical equation shows reaction
• Reactants ---gt Products
• Equation for photosynthesis

REACTANTS
PRODUCTS
sunlight energy
6CO2
12H2O

C6H12O6
6H2O

6O2

CARBON DIOXIDE
WATER
WATER
OXYGEN
GLUCOSE
12 hydrogens 6 oxygens
12 oxygens
6 carbons 12 hydrogens 6 oxygens
6 carbons 12 oxygens
24 hydrogens 12 oxygens
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Important Bonds in Biological Molecules?
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Important Bonds in Biological Molecules?
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Important Bonds in Biological Molecules

• Ionic Bonds
• Covalent Bonds
• Hydrogen Bonds

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Ion Formation

• Atom has equal number of electrons and protons -
  no net charge
• Atom loses electron(s), becomes positively
  charged ion
• Atom gains electron(s), becomes negatively
  charged ion

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Ionic Bonding

• One atom loses electrons, becomes positively
  charged ion
• Another atom gains these electrons, becomes
  negatively charged ion
• Charge difference attracts the two ions to each
  other

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Formation of NaCl

• Sodium atom (Na)
• Outer shell has one electron
• Chlorine atom (Cl)
• Outer shell has seven electrons
• Na transfers electron to Cl forming Na and Cl-
• Ions remain together as NaCl (salt)

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Formation of NaCl
electron transfer
chlorine atom 17 p 17 e-
sodium atom 11 p
chlorine ion 17 p 18 e-
sodium ion 11 p 10 e-
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Covalent Bonding

• Atoms share a pair or pairs of electrons to fill
  outermost shell

• Single covalent bond
• Double covalent bond
• Triple covalent bond

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Nonpolar Covalent Bonds

• Atoms share electrons
• Nuclei of atoms have equal number of protons
• Example Hydrogen gas (H-H)

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Polar Covalent Bonds

• Number of protons in nuclei of participating
  atoms is not equal
• Electrons spend more time near nucleus with most
  protons
• Water - Electrons more attracted to O nucleus
  than to H nuclei

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Hydrogen Bonding

• Molecule held together by polar covalent bonds
  has no net charge
• However, atoms of the molecule carry different
  charges
• Atom in one polar covalent molecule can be
  attracted to oppositely charged atom in another
  such molecule

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hydrogen bond
Examples of Hydrogen Bonds
water molecule
ammonia molecule
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Properties of Water

• Polarity
• Temperature-Stabilizing
• Solvent
• Cohesive

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Water Is a Polar Covalent Molecule

• Molecule has no net charge
• Oxygen end has a slight negative charge
• Hydrogen end has a slight positive charge

O
H
H


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Liquid Water
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Hydrophilic HydrophobicSubstances

• Hydrophilic substances
• Polar
• Hydrogen bond with water
• Example sugar
• Hydrophobic substances
• Nonpolar
• Repelled by water
• Example oil

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Temperature-Stabilizing Effects

• Liquid water can absorb much heat before its
  temperature rises
• Why?
• Much of the added energy disrupts hydrogen
  bonding rather than increasing the movement of
  molecules

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Evaporation of Water

• Large energy input can cause individual molecules
  of water to break free into air
• As molecules break free, they carry away some
  energy (lower temperature)
• Evaporative water loss is used by mammals to
  lower body temperature

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Why Ice Floats

• In ice, hydrogen bonds lock molecules in a
  lattice (matrix)
• Water molecules in lattice (ice) are spaced
  farther apart then those in liquid water
• Ice is less dense than water
• (When is H20 most dense?)

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Water Is an Excellent Solvent

• Ions and polar molecules dissolve easily in water
  
• When solute dissolves, water molecules cluster
  around its ions or molecules and keep them
  separated

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Water Cohesion

• Hydrogen bonding holds molecules in liquid water
  together
• Creates surface tension
• Allows water to move as continuous column upward
  through stems of plants

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Spheres of Hydration
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The pH Scale

• Measures H concentration of fluid
• Change of 1 on scale means 10X change in H
  concentration
• Highest H Lowest H
• 0---------------------7-------------------14
• Acidic Neutral Basic

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Examples of pH

• Pure water is neutral with pH of 7.0
• Acidic
• Stomach acid pH 1.0 - 3.0
• Lemon juice pH 2.3
• Basic
• Seawater pH 7.8 - 8.3
• Baking soda pH 9.0

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The pH Scale
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Acids Bases

• Acids
• Donate H when dissolved in water
• Acidic solutions have pH lt 7
• Bases
• Accept H when dissolved in water
• Acidic solutions have pH gt 7

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Weak and Strong Acids

• Weak acids
• Reluctant H donors
• Can also accept H after giving it up
• Carbonic acid (H2CO3) is example
• Strong acids
• Completely give up H when dissolved
• Hydrochloric acid (HCl) is example

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Salts

• Compounds that release ions other than H and OH-
  when dissolved in water
• Example NaCl releases Na and Cl
• Many salts dissolve into ions that play important
  biological roles

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Buffer Systems

• Minimize shifts in pH
• Partnership between weak acid and base it forms
  when dissolved
• Two work as pair to counter shifts in pH

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Carbonic Acid-Bicarbonate Buffer System

• When blood pH rises, carbonic acid dissociates to
  form bicarbonate and H
• H2C03 -----gt HC03- H
• When blood pH drops, bicarbonate binds H to form
  carbonic acid
• HC03- H -----gt H2C03