chapter 1 what is life?. all living things exhibit five characteristics in combination

Chapter 1

WHAT IS LIFE?

All living things exhibit five characteristics in combination.

A. Characteristics of Life1. Organization

• chemical (atom -> molecule -> macromolecule)

• organelle• cell• tissue• organ• organ system• multicellular organism

Biological organization beyond individual organisms• Population: two or more members

of the same species living in the same place at the same time

• Community: Populations of different species in a particular area

• Ecosystem: The living and nonliving components of an area

• Biosphere: the parts of the planet that can sustain life and the organisms that live there

Each level of biological organization exhibits emergent properties.

Ex. Capillaries transport blood (property not exhibited by individual endothelial cells).

2. Energy Use & MetabolismMetabolism - biochemical reactions

that acquire & use energy.Why do organisms need energy?• to combat entropy (the tendency

towards disorder)• to build new structures• to repair/break down old

structures• to reproduce

How do organisms obtain energy?

• By extracting energy from the environment• Producers: get energy from non-

living sources• Consumers: get nutrients made

by other organisms• Decomposers: get nutrients from

dead organisms

3. Maintenance of Homeostasis• Homeostasis - the ability of an

organism to maintain its internal environment despite conditions in the external environment.

• Failure to maintain homeostasis can have drastic consequences including death

Ex. Human body temperature is ~98.6ºF• if body temperature rises, you sweat.• if body temperature lowers, you shiver.

4. Reproduction, Growth & DevelopmentAsexual reproduction - involves a

single parent; progeny are genetically identical to the parent.

• Often used in unicellular organisms

Sexual reproduction - involves 2 parents; progeny are genetically diverse.

Is it essential for an individual to reproduce?

• Not necessarily . . . • The population needs to be

maintainedOrganisms that successfully

reproduce over several generations compose a species

5. Irritability & AdaptationIrritability - immediate response to

a stimulus.

Adaptation - an inherited behavior or characteristic that enables an organism to survive & reproduce.

Over time, adaptations are modified by natural selection.

Natural Selection - the enhanced survival & reproductive success of individuals whose inherited traits better adapt them to a particular environment.

Evolution• Genetic change within a

population• Natural selection is one of the

driving forces• Mutations in DNA provide genetic

variation upon which natural selection acts

• An ongoing process

B. BiodiversityLife on earth is diverse, yet similar.

Taxonomists place organisms into groups based upon evolutionary relationships.

Broadest, most inclusive group (taxon) is the domain.

Domain Kingdom Phylum or Division Class Order Family Genus Species

Genus & species refer to the organism’s binomial (name).

The Three Domains:• Bacteria - unicellular prokaryotes• Archaea - unicellular prokaryotes• Eukarya - eukaryotes

• Kingdom Protista• Kingdom Plantae• Kingdom Fungi• Kingdom Animalia

Human classification scheme:Domain EukaryaKingdom AnimaliaPhylum ChordataClass MammaliaOrder Primates Family HominidaeGenus & species Homo sapiens

C. The Study of LifeScientists study life by using the

scientific method.

What is difference between hypothesis, theory & law?

• Hypothesis - “an educated guess”; a tentative explanation of phenomena which is experimentally tested.

• Theory - a widely accepted explanation of natural phenomena; has stood up to thorough & continual testing.

• Law - a statement of what always occurs under certain conditions.

Validity can be influenced by:• Sample size• The appropriate use of controls• A control group is treated like the experimental group except for the one variable being tested• Placebos are a form of control

• Use of double blind studies

Chapter 15

THE EVOLUTION OF EVOLUTIONARY THOUGHT

Biological evolution - genetic change in a population over time.

• Macroevolution - large scale evolutionary changes [speciation, extinction] that occur over relatively long periods of time.

• Microevolution - changes in individual allele frequencies within a population that occur over relatively short periods of time.

Often, accumulating microevolutionary changes lead to macroevolutionary changes.

A. Pre-Darwinian Views1. Aristotle (384-322 B.C.) & others

• Species are fixed & unchanging.• Earth is relatively young (only a few

thousand years old).• Species could not become extinct.

2. Georges Buffon (1707-1788)• Individuals within a species

change.• The earth is very old.

3. James Hutton (1726-1797)• Forces that formed the earth

acted in a gradual, yet uniform, way. [uniformitarianism]

4. Georges Cuvier (1769-1832)• Fossils represent extinctions.

• Older, simpler fossils appeared in the lower layers of rock. [superposition]

5. Jean-Baptiste de Lamarck (1744-1829)• Strong advocate of evolution.• Proposed that species evolve from

existing species as a result of interactions with their environment.

• Mechanism for evolution – “progeny inherit acquired characteristics from parents”.

6. Charles Lyell (1797-1875)• Renewed idea of uniformitarianism.

B. Charles Darwin (1809-1882)

Received degree in Theology (1831); embarked on a 5-year voyage (1831-1836) as a naturalist aboard the HMS Beagle.

Throughout his voyage, Darwin developed his theory of evolution on basis of:• observations during the voyage• ideas of Hutton, Cuvier, Buffon,

Lamarck, Lyell & MalthusDarwin published On the Origin of

Species by Means of Natural Selection in 1859 - 22 years after his voyage!

Almost scooped by Alfred Russell Wallace in 1858.

Darwin’s main ideas:• Populations include individuals

that vary for inherited traits.• More individuals are born than

survive to reproduce.• Individuals compete with each

other for limited resources.

• Within populations, the characteristics of some individuals make them more able to survive a particular environmental challenge.

• The mechanism of evolution is natural selection.

Natural selection is the differential survival & reproduction of organisms whose genetic traits better adapt them to a particular environment.• The direction of natural selection

can change.• Natural selection does not lead to

perfection.

Sexual selection is a form of natural selection that directly affects traits that increase an individual’s chance of reproducing.

Evolution by means of natural selection explains both the unity & diversity of life on earth.• Shared ancestry (descent from

a common ancestor) explains similarities among species.

• Natural selection accounts for much of the diversity.

C. Evolution Today - EpidemiologyBiological evolution is a continual

and ongoing process.

1. Emerging Infectious Diseases• resurgence of some diseases

(measles, cholera, diphtheria & tuberculosis)

• appearance of “new” diseases (toxic shock syndrome, Legionnaires’ disease, AIDS & Ebola)

2. Rise of Antibiotic ResistanceResistant bacteria appeared just 4

years after the medical community started prescribing antibiotics.

Antibiotics kill susceptible bacteria, but leave behind those that can resist it - creating a situation where they can flourish.

• This is a case of artificial selection

Today, some laboratory strains of Staphylococcus are resistant to ALL known antibiotics.

Chapter 16

THE FORCES OF EVOLUTIONARY CHANGE -

MICROEVOLUTION

Evolution occurs at the population level as allele frequencies change.

A. Hardy-Weinberg EquilibriumA theoretical state in which allele

frequencies of a population do not change from one generation to the next.

H-W equilibrium is only possible if:• mating population is large• mating is entirely random• there is NO migration, mutation,

or natural selection

Hardy-Weinberg Equationp2 + 2pq + q2 = 1

p2 = frequency of homozygous dominant individuals

2pq = frequency of heterozygotesq2 = frequency of homozygous

recessive individualsp = frequency of dominant alleleq = frequency of recessive allele

NOTE: p + q = 1

H-W example #1:In a certain population, 36% have

sickle cell anemia. What is the frequency of the dominant allele?

What do we know? (p2, 2pq, q2, p or q)q2 = 36% or 0.36

What do we want to find? p

Calculations:q2 = q 0.36 = 0.6 q = 0.6p + q = 1 Thus, p = 1 - 0.6 or 0.4

H-W example #2:In a certain population, the frequency

of the dominant allele is 0.7. What is the frequency of heterozygous individuals?

What do we know? (p2, 2pq, q2, p or q)p = 0.7

What do we want to find? 2pq

Calculations:p + q = 1 Thus, q = 1 - 0.7 or 0.32pq = 2 x 0.7 x 0.3 or 0.42

From the previous example we know:p = 0.7 q = 0.3 2pq = 0.42

Calculate the frequency of homozygous dominant individuals.

0.49Calculate the frequency of homozygous

recessive individuals. 0.09If there are 1000 individuals in this

population, how many are:• heterozygous? 420• homozygous dominant? 490• homozygous recessive? 90

H-W equilibrium provides a background against which microevolution can be detected.• If allele & genotype frequencies

change from one generation to the next, then evolution is occurring with respect to that particular gene.

• If frequencies remain unchanged, then evolution is not occurring.

B. Factors That Cause Microevolution in Natural Populations

1. Nonrandom MatingNonrandom mating causes certain

alleles to become more common in future generations (some individuals leave more offspring than others).

Ex. Albinism among Arizona’s Hopi Indians

2. MigrationIndividuals migrate between

populations.• Immigrating individuals introduce

new alleles and migrating individuals remove alleles.• Gene flow is the movement of alleles

between populationsEx. New York City’s waves of immigration

3. Genetic DriftA change in the gene pool of a small

population due to chance.

Genetic drift in human populations may be caused by the founder effect or a population bottleneck.

• Founder effect – genetic drift due to a few individuals leaving a large population to found a new group.• Unlikely that gene pool of founding

population is representative of original population.

Ex. Ellis-van Creveld syndrome among Pennsylvania Amish.

• Population bottleneck – genetic drift due to high mortality in a population.• Unlikely that gene pool of the

remaining population is representative of original population.

Ex. Pingelapese blindness among Pingelapese people of the eastern Caroline islands.

Decreased genetic diversity among Cheetahs.

4. MutationA change in the DNA - introduces

‘new’ alleles into the population.

Mutations can be beneficial, “silent”, or harmful.

5. Natural SelectionThe differential survival and

reproduction of organisms whose genetic traits better adapt them to a particular environment.

Considered to be the major driving force of evolution.

Types of Natural Selection• Directional Selection

Environment selects against one phenotypic extreme, allowing the other to become more prevalent.

• Disruptive SelectionEnvironment selects

against intermediate phenotype, allowing both extremes to become more prevalent.

• Stabilizing SelectionEnvironment selects

against two extreme phenotypes, allowing the intermediates to become more prevalent.

Balanced PolymorphismA form of stabilizing selection that

maintains deleterious recessive alleles in a population because heterozygotes resist an infectious disease.• Sickle cell anemia is maintained

because heterozygotes are resistant to malaria.

• Cystic fibrosis is maintained because heterozygotes are resistant to cholera & typhoid fever.

Chapter 44

COMMUNITIES AND ECOSYSTEMS

EcosystemAll the biotic (living) and abiotic

(nonliving) components in a defined area.

• Ecosystems interact.• All ecosystems require a constant

input of energy.• Chemicals are cycled within

ecosystems.

1. Energy FlowEnergy flows in one direction

through an ecosystem.Route of energy flow is determined by an

ecosystem’s trophic structure.

photo- or chemoautotrophs

animals that eat producers

animals that eat herbivores

animals that eat carnivores

Food web - several species function at more than one trophic level.

The Antarcticweb of life

Food web – severalspecies function at morethan one trophic level.

Is all of the energy stored by individuals at one trophic level available to the next?No - energy needs of individual, second law of thermodynamics.

On average, ~10% (2-30%) is transferred.

Energy transfer in Cayuga Lake:

algae store 1,500 kcal

aquatic herbivores store 150 kcalsmelt fish store 15 kcalhumans store 1.5 kcal

Food chains rarely extend beyond 4 trophic levels.

Other types of pyramids can be used to describe ecosystems.

• pyramid of numbers - shows number of organisms at each trophic level.

• pyramid of biomass - shows total weight of organisms at each trophic level.