Download dominant organisms

UNIT 6 – HISTORY AND ORGANIZATION OF BIOLOGICAL DIVERSITY
MAIN IDEA: FOSSILS PROVIDE EVIDENCE OF THE CHANGE IN ORGANIZATION OVER TIME
OBJECTIVE 1: DESCRIBE THE LAND ENVIRONMENT AND EARLY ATMOSPHERE OF THE
PRIMITIVE EARTH
A. Early Earth was lifeless for several hundred million years.
1. The crust of the Earth had to cool and solidify before life could exist because before that time the
heat would have been too intense for organisms to survive.
2. The atmosphere of primitive Earth probably contained little free oxygen, and gases that made up
the atmosphere were most likely those spewed from volcanoes, and similar to today’s volcanoes
released water vapor, carbon dioxide, sulfur oxide, hydrogen sulfide, hydrogen cyanide, and
nitrogen and hydrogen
OBJECTIVE 2:
A.
B.
C.
D.
E.
IDENTIFY THE DIFFERENT TYPES OF FOSSILS, HOW THEY ARE FORMED, AND
WHAT INFORMATION THEY MIGHT PROVIDE
By about 3.9 billion years ago, earth cooled enough for water in the atmosphere to condense which
led to millions of years of rainstorms with lightning to fill Earth’s oceans. It is in these oceans some
3.9 to 3.5 billion years ago that some scientists propose that life first appeared.
Rocks cannot provide information about Earth’s infancy, but they are an important source of
information about the diversity of life that has existed on the planet.
About 99 percent of species are extinct – they no longer live on Earth but only a small amount are
preserved as fossils.
Only those organisms that are buried quickly in sediment are readily preserved.
A fossil is evidence of an organism that lived long ago and they can be formed in many ways. (see
fig. 14.1, page 392)
1.
Trace fossils – a marking or indirect evidence left by an animal like a footprint, trail or burrow
2.
Molds and Casts – a mold is an impression of an organism while the cast is a mold filled with
sediment.
3.
Petrified fossils – minerals sometimes penetrate and replace the hard parts of an organism,
producing copies of them
4.
Replacement - the original of an organism is replaced with mineral crystals that can leave
detailed replicas of hard or soft parts.
5.
Amber – insects get caught n sticky resin from trees which hardens to form amber
6.
Original material – mummification freezing preserves original organisms.
OBJECTIVE 3:
A.
B.
C.
D.
EXPLAIN HOW SEDIMENTARY ROCKS ARE FORMED AND WHY FOSSILS ARE
FOUND IN THEM
For fossils to form, organisms usually have to be buried in small particles of mud, sand or clay soon
after they die. (See page fig. 14.2, page 394)
1.
These particles are compressed over time and harden into sedimentary rock.
2.
Fossils continue to from at the bottom of lakes, streams, and oceans.
Sedimentary rock forms layers that prevent damage to the organism. The oldest layers are on the
bottom.
1.
Other type of rock (metamorphic) form when heat, pressure, and chemical reactions change
other rocks. This process would destroy any fossils as would the formation of igneous rock
which is made when magma cools.
Fossils become exposed in the layers of sedimentary rock as erosion occurs or from earth
movements. (The Earth’s surface can rupture during earthquakes and some rock layers fold over
others.
A paleontologist is a scientist who studies fossils. From fossil evidence scientists infer the diet of
the organism and its environment.
OBJECTIVE 4:
A.
DISCUSS THE FOSSIL RECORD AND RELATE IT TO RELATIVE AND
RADIOMETRIC DATING
The oldest layers of sedimentary rock are on the bottom, therefore the oldest fossils are found in the
bottom layers of rock. This is called relative dating. (see fig. 14.3, page 395)
1. Scientists base relative dating on the law of superposition to determine the order of
appearance and extinction of the species that formed fossils in the layers.
1
B.
C.
2.
Relative dating cannot be used to determine the actual age of a fossil.
To determine the specific ages of fossils scientists use radiometric dating techniques utilizing
radioactive isotopes in the fossils or rocks.
1. Radioactive isotopes are unstable nuclei that break down over time forming a new element after
it decays.
2. Each radioactive isotope has a characteristic decay rate called a half-life, or the amount of time
it takes for half of the original isotope to decay.
3. Scientists compare the amount of radioactive isotope to that of the new element it forms.
4. Scientists use Potassium-40 that decays to Argon-40.
a. Potassium (K) –40 has a half life of 1.3 billion years old.
5. Scientists also use Carbon-14 to date fossils less than 60,000 years old. C-14 has a half life of
5,730 years. It is used to date orgainic substances like bone and tissue. (see fig.14.4, pg. 396)
This dating technique may produce inconsistent dates because the initial amount of radioisotope in
the rock can never be known with certainty. For this reason, scientists analyze many samples of
rocks using as many methods as possible to get consistent results.
1. Radioactive isotopes that can be used for radiometric dating are found only in igneous and
metamorphic rocks, not sedimentary. Igneous rocks that are found in layers closely associated
with fossil bearing sedimentary rocks can be used for assigning relative dates to fossils.
OBJECTIVE 5: SUMMARIZE THE MAJOR EVENTS OF THE GEOLOGIC TIME SCALE
A. The Geologic Time Scale is a calendar of Earth’s history based on evidence found in rocks and
shows the major geological and biological events. (see fig. 14.5, page 397)
B. The Geologic Time Scale is divided into the Precambrain time and the Phanerozoic eon. An era is
the next largest division of the geologic time scale.
1. The Phanerozoic eon includes the Paleozoic, Mesozoic, and Cenozoic eras.
2. Each era is divided into one or more periods.
TIME
Now – 55.8 m.y.a
55.8 – 251 m.y.a
251 – 542 m.y.a
542 m.y.a – 4.6 b.y.a
ERA
Cenozoic
Mesozoic
Paleozoic
Precambrian
DOMINANT ORGANISMS
Mammals, Humans
Reptiles, first mammals
Amphibians, Fish, Invertebrates, Ferns
Bacteria, Sponges, Jellyfish
C. The fossil record shows that there were several occurrences of mass extinction that fall between
explosive radiation of life.
D. Precambrian
1. Makes up nearly 90% of Earth’s history, stretching from the formation of the Earth to the
beginning of the Paleozoic era about 542 million years ago.
2. First life prokaryotic heterotrophs, followed by autotrophic prokaryotes (cyanobacteria) which
provided atmospheric oxygen. Eukaryotic cells emerged and by the end of the Precambrian, life
included animals.
3. Extensive glaciation marked the second half of the Precambrian. This may have delayed
evolution until the Ediacaran period where food chains remained short.
E. Paleozoic
1. Fossil record shows an enormous increase in the diversity of life during the Cambrian period of
this era. The ancestors of most major animal groups diversified at this time. This is called the
Cambrian explosion.
2. Life in the oceans flourished, and swampy forests covered much of the land surface. Insects
dominated the air and tetrapods (first land vertebrates) thrived in freshwater pools.
3. Largest mass extinction recorded by the fossil record marked the end of this era. About 90% of
the marine species and 70% of the land species disappeared at this time.
F. Mesozoic
1. Early mammals and dinosaurs appeared as did flowering plants and birds. Reptiles were the
dominant organisms.
2. The mass extinction of the dinosaurs and an estimated 2/3 of all living species marked the end of
this era.
2
3. A large crater off the coast of eastern Mexico might suggest the collision of a large meteorite filled
the atmosphere with toxic dust and changed the climate to one that many species could no longer
survive.
a. Evidence for the meteorite is found in the layer of rock between the Cretaceuos period and
the Paleogene period.
b. These layers contain a high amount of the element called iridium; an element rare on Earth,
but common in meterorites.
4. Pangaea split as a result of plate tectonics which likely influenced the course of evolution.
G. Cenozoic
1. Original mammals were small, and shrew-like but after the mass extinction at the end of the
Mesozoic era, mammals began to diversify including primates.
H. The study of biological diversity from the fossil record is generally limited to the study of the
differences among species. Biological diversity within a species is difficult to study because the rarity
of preserved organic material as a source of DNA in fossils.
MAIN IDEA: EVIDENCE INDICATES THAT A SEQUENCE OF CHEMICAL EVENTS PRECEDED THE
ORIGIN OF LIFE ON EARTH AND THAT LIFE HAS EVOLVED CONTINUOUSLY SINCE THAT TIME.
OBJECTIVE 6: ANALYZE EARLY EXPERIMENTS THAT SUPPORT THE CONCEPT OF
BIOGENESIS
A. An early belief of the origin of life was spontaneous generation; the idea that nonliving material
can produce life such as flies from rotting meat, fish and frogs from muddy water.
B. Spontaneous generation was disproved by Francesco Redi and Louis Pasteur
1. Redi showed that you needed something from the environment in order for the maggots to form
on decaying meat (see fig. 14.11, page 401). He disproved the spontaneous generation of large
organisms.
2. Pasteur showed that microorganisms that developed in broth came from spores in the air (see
fig. 14.12 page 402)
C. Following Pasteur’s experiment the theory of biogenesis, the idea that living organisms only come
from other living organisms, became the cornerstone of biology.
OBJECTIVE 7: COMPARE AND CONTRAST MODERN THEORIES OF THE ORIGIN OF LIFE
A. Scientists hypothesize that two developments must have preceded the appearance of life on Earth.
1. Simple organic molecules, or molecules that contain carbon, must have formed.
2. These molecules must have been organized into complex organic molecules such as proteins,
carbohydrates, and nucleic acids that are essential to life.
B. The early atmosphere contained water vapor, carbon dioxide, nitrogen, methane and ammonia, but
no oxygen.
C. Many scientists worked to explain the appearance of organic molecules
1. Alexander Oparin hypothesized that early life began in the oceans.
a. He suggested that energy from the sun, lightning, and Earth’s heat triggered chemical
reactions to produce small organic molecules.
b. Rain washed the molecules into the ocean creating the “primordial soup”.
2. In 1953 American scientists Miller and Urey’s experiments showed that under the proposed
conditions on early Earth, small organic molecules, like amino acids, could form. (See fig.
14.13, page 403).
D. Some scientists think that the organic reactions that occurred before the formation of life occurred in
the hydrothermal volcanic vents of the deep sea, where sulfur forms the base of a unique food chain.
Others believe that meteorites brought the first organic molecules.
E. The next step in the origin of life, as proposed by some scientists, was the formation of complex
organic compounds, especially proteins.
1. In the Miller-Urey experiment, amino acids could bond together but they also separated quickly.
Proteins may have been formed if amino acids were bound to a clay particle, which was a
common sediment in the oceans.
2. American biochemist Sydney Fox showed how short chains of amino acids could cluster to form
protocells, a large, ordered structure, enclosed by a membrane, that carries out some life
activities, such as growth and division.
3
F.
G.
Another requirement for life is a coding system. Many biologists consider RNA to have been life’s
first coding system since RNA sequences have changed very little over time. Additionally, RNA is
capable of evolution by natural selection, and some RNAs behave like enzymes.
Another important step in the evolution of life is the formation of membranes. The connection
between the various chemical reactions and the overall path from molecules to cells is unsolved.
OBJECTIVE 8:
A.
B.
C.
D.
E.
RELATE THE HYPOTHESIS ABOUT THE ORIGIN OF CELLS TO THE
ENVIRONMENTAL CONDITIONS OF THE EARLY EARTH.
The first forms of life were probably prokaryotes, anaerobic and heterotrophs that evolved from
protocells.
1.
Overtime, these heterotrophs would use up the food supply.
Organisms that could make their own food (autotrophs) evolved by the time the food was gone.
1. These organisms were probably similar to present day archaeobacteria; those that live in harsh
environments like deep ocean vents or hot springs. Like present day archaeobacteria these first
autotrophs were probably chemosynthetic not photosynthetic as they don’t get energy from the
sun and they don’t need or make oxygen.
The next organisms to evolve may have been photosynthetic prokaryotes.
1. These organisms began producing oxygen found in Earth’s atmosphere
2. Aerobic organisms would have evolved and thrived.
3. Lightning could have converted the oxygen into ozone. Ozone shielded organisms from harmful
effects of ultraviolet radiation, enabling the evolution of eukaryotes.
The proposes that eukaryotes evolved through a symbiotic relationship between prokaryotes.
endosymbiont theory (see fig. 14.17, page 407)
1. evidence exists to support this hypothesis
a. Both mitochondria and chloroplasts resemble certain types of bacteria.
b. Both chloroplasts and mitochondria contain DNA that is very similar to the DNA found in
prokaryotes and very unlike the DNA found in eukaryotic nuclei
c. Chloroplasts and mitochondria have their own ribosomes, similar to ribosomes of
prokaryotes
d. Chloroplasts and mitochondria reproduce by fission independently of the cells that contain
them.
2. Though the endosymbiont theory is widely endorsed, there are no traces of early life to prove
this theory.
In review, the sequence of HYPOTHESIZED events that led from a lifeless Earth to the presence of
Eukaryotic cells is:
1. simple organic molecules complex organic molecules protocells genetic material
prokaryotic cells symbiosis of prokaryotic cells eukaryotic cells
CHARLES DARWIN DEVELOPED A THEORY OF EVOLUTION BASED ON NATURAL SELECTION
OBJECTIVE 9: DISCUSS THE EVIDENCE THAT CONVINCED DARWIN THAT SPECIES COULD
CHANGE OVER TIME
A.
As a naturalist on the HMS Beagle, Darwin surveyed the coast of South America. During the five
year voyage, Darwin saw marine fossils, experienced earthquakes, observed animals on the
Galapagos Islands and read a book by Charles Lyell called the Principles of Geology, which
proposed that the Earth was millions of years old.
B.
Darwin observed that the different islands seemed to have their own, slightly different varieties of
animals.
1. The birds were identified as new species and not found to live anywhere else in South America
although they closely resembled those found on the mainland.
2. The mainland and the islands had very different environments so they should not have looked
so much alike unless, Darwin suspected, populations from the mainland changed after reaching
the Galapagos.
C.
Darwin hypothesized that new species gradually appear through small changes in ancestral
species.
1. Darwin studied selective breeding in pigeons and called the process artifical selection. He
observed that individuals are variable and that the variations are heritable. He also realized
that selection could lead to changes over time.
4
D. Darwin was also influenced by an essay by Thomas Malthus, an economist. Darwin realized that in
nature there is a struggle for existence. Those less equipped die.
OBJECTIVE 10:
LIST THE FOUR PRINCIPLES OF NATURAL SELECTION AND SHOW HOW THIS
PROCESS COULD CHANGE A POPULATION.
A. Darwin’s theory about the origin of species has four basic principles:
1. Individuals in a population show variations among others of the same species.
2. Variations are inherited.
3. Animals have more young than can survive on the available resources.
4. Variations that increase reproductive success will be more common in the next generation.
B. Darwin called his theory natural selection. He reasoned that given enough time, natural selection
could modify a population enough to produce a new species. (see fig. 15.3, page 420 to see how
natural selection can change a population)
1. Natural selection is the framework for evolution, the cumulative changes in groups of organisms
through time. Populations evolve, not the individual.
C. Theory of Evolution
1. In nature there is an overproduction of offspring
2. There is a struggle for survival as offspring compete for food, shelter, space, mates and not all
will survive
3. Variations exist among offspring
4. Offspring that are best adapted to the environment (best fit) survive
5. Natural selection occurs
6. Over time, evolution of a new species can occur: a great diversity of species increases the
chance that at least some organisms survive large changes to the environment.
MAIN IDEA: MULTIPLE LINES OF EVIDENCE SUPPORT THE THEORY OF EVOLUTION
OBJECTIVE 11: DISTINGUISH AMONG THE TYPES OF EVIDENCE FOR EVOLUTION
A. A theory explains available data and suggests further areas of experimentation. The theory of
evolution states that all organisms on Earth have descended from a common ancestor. There is
evidence that supports the theory of evolution by natural selection:
1. Variations do exist in populations
2. Fossils
3. Traits that allow organisms to thrive in particular environments.
Since the time of Darwin, his theory has been constantly tested.
B. Fossils offer some of the most significant evidence of evolutionary change.
1. Fossils show that ancient species share similarities with species now living on our planet.
2. The fossil record shows that not all extinct species have a modern counterpart and that some
species have remained unchanged for millions of years.
3. Scientists have found hundreds of thousands of transitional fossils that contain features shared by
different species. (see fig. 15.5, page 424) They provide detailed patterns of evolution for the
ancestors of many modern animals including mollusks, horses, whales and humans.
4. Researchers consider two major classes of traits when studying transitional fossils:
a. Derived traits – newly evolved features and do not appear in the fossils of the common
ancestors
b. Ancestral traits – more primitive features that do appear in ancestral forms.
C. Comparative Anatomy – studying the structural differences and similarities between organisms (see
fig. 15.6, page 425 and table 15.2, page 425)
1. homologous structures – same anatomy (like having a radius and an ulna), maybe different
function, but probably they have a common ancestor and similar evolutionary origin.
2. Analogous structures – same function (flying), but do not have a common evolutionary
ancestor
3. Vestigial structure – remnants of structures that are no longer functional; forelimbs of an
ostrich or eyes of blind cave-fish. Since vestigial structures have the same evolutionary origins
as fully functional features in related species, they are also considered homologous.
D. Comparative Embryology – the more closely related the longer the embryos will remain similar
throughout development (see fig. 15.8, page 426)
E. Comparative Biochemistry – the more closely related two organisms are, the more similar the base
sequences in the DNA or amino acids of their proteins. (see fig.15.9, page 427)
5
1.
Cytochrome C is an enzyme found in the metabolic systems of many different and seemingly
unrelated species. Because this molecule is complex, it probably did not evolve separately in
each of the species. The similarities in structure indicate common ancestry and the amount of
difference in sequence is an index divergence since the last shared ancestor.
F. Geographic distribution suggests evolution as Darwin observed that animals of the South American
mainland were more similar to other South American animals than they were to animals living in
similar environments in Europe.
1. Patterns of migration are important and are explained in a field of study called biogeography.
2. Evolution is linked with climate and geological forces, especially plate tectonics, which helps
explain many ancestral relationships and geographic distributions seen in fossils and living
organisms today.
G. Summary: the more closely related organisms will have homologous structures, similar anatomy and
biochemistry and may have vestigial structures of a common ancestor.
OBJECTIVE 12: EXPLAIN HOW THE STRUCTURAL AND PHYSIOLOGICAL ADAPTATIONS RELATE
TO NATURAL SELECTION AS WELL AS SOME CONSEQUENCES OF
ADAPTATIONS
A. Review: Adaptations are traits shaped by natural selection that increase an organism’s reproductive
success. Darwin’s theory of evolution explains how adaptations may develop in species.
1. Fitness is a measurer of the relative contribution an individual trait makes to the next generation.
It is often measured as the number of reproductively viable offspring that an organism produces
in the next generation.
B. The better an organism is adapted to its environment the better its chances of survival and
reproductive success.
C. Adaptations that may be structural or morphological
1. examples are thorns on a rose plant, fins of a fish, quills on a porcupine
2. mimicry – Occurs when natural selection favors a behavior or appearance in one species that is
similar to that of a harmful species. Predators avoid both.
a. Mimicry often increases an organisms fitness.
3. camouflage – enables a species to blend with their surroundings for protection or predation and
occurs when natural selection favors a species’ resemblance to an object in the environment like
a twig or leaf.
D. Physiological adaptations are changes in an organism’s metabolic processes and can occur more
rapidly than structural adaptations.
1. Species of bacteria that originally were killed by penicillin and other antibiotics have developed
drug resistance. Some diseases have now reemerged in more harmful forms.
E. Not all features of an organism are necessarily adaptive. Some features might be consequences of
other evolved features.
1. Spandrel example – spaces between arches set in a square to support a dome are called
spandrels and are often decorative. Some features might be like spandrels – a consequence of
another adaptation.
2. A biological example is the helplessness of human babies. Some scientists feel it is a
consequence of the evolution of big brains and upright posture and not an adaptive process that
leads to increased parenting and more learning.
MAIN IDEA: THE THEORY OF EVOLUTION CONTINUES TO BE REFINED AS SCIENTISTS LEARN
NEW INFORMATION
OBJECTIVE 13: EXPLAIN EVOLUTION IN TERMS OF POPULATION GENETICS AND RELATE BOTH
TO THE HARDY-WEINBERG PRINCIPLE
A. Scientists now know that natural selection is not the only mechanism of evolution. Evolution occurs
at the population level, with genes as the raw material.
B. Although it has been long understood that alleles are a form of an inherited character trait, scientists
did not always understand why dominant alleles wouldn’t overwhelm recessive alleles in a population.
C. In 1908, hardy and Weinberg came up with a solution independently of one another. According to
their idea, the Hardy-Weinberg principle, when allelic frequencies remain constant, a population is
in genetic equilibrium. (see fig. 15.14, page431)
6
D. Using MATH ‫ ײַ‬allele frequencies and equilibrium frequencies can be determined.
1. Example 1: determine allele frequencies
100 people in a population (must be a REALLY small town!)
40 people EE (earlobes attach to their heads)
40 people Ee
20 people ee (earlobes are free…unattached)
So in the population there are……
80 E alleles (2 E alleles X 40) + 40 E alleles = 120 E alleles
40 e alleles (2 e alleles X 20) + 40 e alleles = 80 e alleles
E allele frequency  120/200 or 0.6
e allele frequency  80/120 or 0.4
The Hardy –Weinberg principle says that the allele frequencies in populations should be constant.
This is expressed as p + q = 1 where p represents the E allele and q the e allele.
2.
Example 2: determine the equilibrium frequency of each genotype in the population, using the
equation p2 + 2pq + q2 = 1 where,
p2 = homozygous dominant (EE)
2pq = heterozygous (Ee)
q2 = homozygous recessive (ee)
(0.6)(0.6) + 2(0.6)(0.4) + (0.4)(0.4) = 1 SO………
equilibrium frequency for EE = .36
equilibrium frequency for Ee = .48
equilibrium frequency for ee = .16
F.
According to the Hardy-Weinberg principle, a population in genetic equilibrium must meet five
conditions:
1. The population must be very large
2. There is no immigration or emigration
3. Mating is random
4. Mutations do not occur
5. natural selection does not occur.
If a population is not in genetic equilibrium, at least one of the five conditions has been violated. All
five conditions are known mechanisms for evolutionary change. Of these, natural selection is
thought to provide adaptive advantages to a population, and only natural selection acts on an
organism’s phenotype.
OBJECTIVE 14: EXPLAIN HOW GENETIC DRIFT, GENE FLOW, NONRANDOM MATING, MUTATION
AND NATURAL SELECTION VIOLATE THE HARDY WEINBERG PRINCIPLE
A. Any change in allele frequencies in a population due to chance is called genetic drift. Alleles are
selected randomly through independent assortment and in large populations, enough alleles “drift” to
ensure that the entire allele frequency of the entire population remains pretty constant from one
generation to the next. Genetic drift can introduce new genes and variety into a population.
B. In small populations the effects of genetic drift become more pronounced, and the chance of losing
an allele becomes greater.
C. There are two extreme examples of genetic drift.
1. The founder affect occurs when a small population settles in a place separated from the rest of
the population. This sample population carries a random subset of the population’s genes.
Alleles that were uncommon might become common and offspring in the new generation will
carry these genes.
a. In the Amish, have a frequency of six finger dwarfism.
2. Bottleneck occurs when a population declines to a very low number and then rebounds. The
gene pool of the rebound population is often genetically similar to that of the population at its
7
D.
E.
F.
G.
lowest level; at its reduced diversity. This genetic similarity mimics inbreeding which decreases
fertility and could be factor in the potential extinction of a species. (see fig. 15.15, page 433).
Gene flow – Only when there is no gene flow is a population in genetic equilibrium. That means it’s a
closed system with no genes entering or leaving the population. In reality, few populations are
isolated.
Rarely is mating completely random in a population. Organisms mate with those that are in close
proximity, and inbreeding can lead to changes in allele frequencies.
Mutations are a random change in genetic material and their cumulative affect could change allele
frequencies, thus violating equilibrium. Many mutations cause harm or are lethal, but sometimes a
mutation might provide an advantage and would be selected for.
The Hardy Weinberg principle requires that all individuals in a population be equally adapted to their
environment and thus equally contribute to the next generation. This rarely happens as natural
selection favors those best adapted for survival and reproduction. Since natural selection is
determined by environmental conditions it definitely is not random.
OBJECTIVE 15: DESCRIBE THE THREE DIFFERENT TYPES OF NATURAL SELECTION THAT ACT
ON AN ORGANISMS PHENOTYPE AND EXPALIN SEXUAL SELECTION
A. Allelic frequencies in a population’s gene pool will change over generations due to the natural
selection of variations. (see fig. 15.16, page 434)
B. There are three different types of natural selection
1. Stabilizing selection – favors average individuals and reduces variation in a population. This is
the most common as it leads to higher fitness.
2. Directional selection – favors one of the extreme variations of a trait and can lead to rapid
evolution of a population. (see fig. 15.17, page 435)
3. Disruptive selection – favors both extreme variations of a trait, resulting eventually in no
intermediate forms of the trait and leading to the evolution of two new species.(see fig. 15.18,
page 436)
C. Significant changes to the gene pool can lead to the evolution of a new species over time.
D. Sexual selection operates in populations where male and females differ in appearance. Darwin
was unclear as to why some qualities of sexual attractiveness appeared to be the opposite of what
might enhance survival.
1. It is debated by modern scientists if sexual reproduction is a form of natural selection. Some feel
it is as the bigger and brighter bodies of some male species enhance reproductive success.
OBJECTIVE 16: DESCRIBE TWO TYPES OF REPRODUCTIVE ISOLATING MECHANISMS THAT
PREVENT GENE FLOW AND RELATE THESE TO SPECIATION
A. Most scientists define speciation as the process whereby some members of sexually reproducing
population change so much that they can no longer produce fertile offspring with members of the
original population.
B. Two types of reproductive isolation prevent gene flow, one occurring before fertilization and one
occurring after fertilization.
C. Prezygotic isolating mechanisms prevent reproduction by making fertilization unlikely. These
mechanisms prevent genotypes from entering a population’s gene pool through ecological,
geographic, behavioral, or other differences.
1. Closely related birds have different mating songs to prevent reproduction
2. Closely related insects might mate at different times during the night
3. Some closely related species of fish in the same stream breed during different times of the year.
D. Postzygotic isolation mechanisms occurs when an infertile hybrid has been produced.
1. a liger!
OBJECTIVE 17: DIFFERENTIATE BETWEEN ALLOPATRIC SPECIATION AND SYMPATRIC
SPECIATION
A. In allopatric speciation a physical barrier divides one population into two or more populations. The
separate populations will eventually have organisms that, if enough time has passed, will no longer
be able to breed successfully with one another.
1. Most scientists think this is the most common form of speciation and small subpopulations have a
better chance of diverging than those living within it.
8
B. In sympatric speciation, a species evolves into a new species without a physical barrier. The
ancestor species and the new species live side by side.
1. This is seen in several insect species and is common in plants due to polyploidy.
OBJECTIVE 18: DISCUSS EVIDENCE OF SPECIATION IN THREE VISIBLE PATTERNS OF
EVOLUTION AND COMPARE THE RATE OF SPECIATION DURING GRADUALISM
AND PUNCTUATED EQUILIBRIUM
A. Adaptive radiation, also called divergent evolution, occurs when species that were once similar to
an ancestral species become increasingly distinct. This occurs when populations adapting to different
environmental conditions change, becoming less alike as they adapt, eventually resulting in new
species.
1. Darwin’s finches on the Galapagos Islands and Honeycreepers of the Hawaiian Islands are
examples of adaptive radiation and divergent evolution as is possibly the wide variety of
mammals after the extinction of dinosaurs.
2. Adaptive radiation can occur in a relatively short amount of time. (14,000 years).
B. Coevolution is seen as many species evolve in close relationship with another species.
1. Mutualism is an example…go back and look at unit 6!
2. Coevolution can be described as an arms race as seen in some insects and plants, where the
insects depend upon the plant for food. The plant develops a chemical defense against the
insect and the insects, in turn, evolve biochemistry to resist the defense.
C. Convergent evolution occurs when unrelated species resemble one another due to natural selection
(organisms share similar ecology and climate) (see Table 15.4, page 440)
D. There are two hypotheses to explain the time required for speciation as evolution is a dynamic
process.
1. gradualism is the idea that species originate through gradual change of adaptations. Most
scientists do think that evolution proceeds in small gradual steps.
a. fossil record of camel supports this idea
2. punctuated equilibrium argues speciation occurs relatively quickly (10,000 years or less), in
rapid bursts, with long periods of genetic equilibrium in between.
a. environmental changes, or introduction of a competitive species lead to rapid changes in a
populations gene pool
b. supported by the fossil record of the elephant
MAIN IDEA: BIOLOGISTS USE A SYSTEM OF CLASSIFICATION TO ORGANIZE INFORMATION
ABOUT THE DIVERSITY OF LIVING THINGS
OBJECTIVE 19: EVALUATE THE HISTORY, PURPOSE, AND METHODS OF TAXONOMY
A. To better understand organisms, biologists organize them into groups
1. Classification – the grouping of organisms based on similarities
2. Taxonomy – the branch of biology that groups and names organisms based on studies of their
different characteristics.
B. Many have tried to classify organisms
1. Aristotle (394 – 322 B.C.)
a. Classified organisms into two groups: plants and animals
b. Plants were grouped according to structure: herbs, shrubs, and trees
c. Animals were classified according to the presence or absence of red blood and those with
red blood were further grouped according to where they lived: land, air, or water
d. Useful, but did not group organisms according to evolutionary relationships and viewed
species as distinct, separate and unchanging.
2. Carolus Linnaeus ( 1707 – 1778)
a. Broadened Aristotle’s classification method and formalized it into a scientific system.
b. Based on physical and structural similarities of organisms so it revealed relationships as
well as the behavior of the organisms.
c. His system is the basis of modern classification systems and was the first system of
taxonomic organization.
C. Today’s taxonomists try to identify the underlying natural relationships and compare external and
internal structures, as well as the organism’s geographical distributions and chemical makeup.
D. Taxonomy provides a framework in which to study the relationships among living organisms. The
most useful systems of classification show evolutionary relationships among species.
9
E.
Classifying organisms is a useful tool for scientists who work in agriculture, forestry, and medicine.
1. May lead to the discovery of new species or useful substances.
OBJECTIVE 20: EXPLAIN THE MEANING OF A SCIENTIFIC NAME AND DESCRIBE THE
ORGANIZATION OF TAXA IN THE BIOLOGICAL CLASSIFICATION SYSTEM
A. Modern classification systems use a two-word naming system called binomial nomenclature
developed by Linnaeus.
B. The first word identifies the genus, a group of similar species that are closely related and share a
common ancestor.
C. The second word identifies the specie and usually describes a characteristic of the organism.
1. Homo sapiens – genus Homo, species sapien which means wise.
D. Latin is the language of scientific names. Latin is a language that is no longer used in conversation,
and, therefore it doesn’t change. Latin also historically has been the language of scientists.
1. Prevents confusion of common names and many different languages.
2. See page 486 on how to write scientific names
3. You cannot identify an organism by the species name alone.
E. As biologists group organisms they subdivide the groups on the basis of more specific criteria
F. A named group of organisms is called a taxon (plura, taxa)
G. The broader the taxa, the more general its characteristics, the more species it contains.
H. Within the classification hierarchy there are four larger taxa: kingdom, phylum, class, order, and
three smaller subdivisions: family, genus, species.
I. See figure 17.4 on page 488
J. Sometimes the word domain is used instead of phylum when discussing plants and bacteria.
K. A domain contains one or more kingdoms like Eukarya.
L. Systematics is the study of past and present biological diversity with an emphasis on evolutionary
relationships. Systematists work to identify species and relationships among known species.
Through classification of organisms it is possible to find possible treatments and cures for diseases.
MAIN IDEA: CLASSIFICATION SYSTEMS HAVE CHANGED OVER TIME AS INFORMATION HAS
INCREASED
OBJECTIVE 21: COMPARE AND CONTRAST SPECIES CONCEPTS
A. Typological species concept – Aristotle and Linnaeus used this concept which is based on the idea
that species are distinct and unchanging. The type specimen was an individual of the species that
best displayed the characteristics of that species. If another specimen was found with variations it
was labeled as a new species.
1. Using the typological concept may have classified organisms together that did not share a close
evolutionary relationship.
2. Because we know species change over time, this concept has been replaced but some of its
traditions, such as reference to type specimens remain.
B. Biological species concept – 60-70 years ago the definition of species was changed to a group of
organisms that can interbreed and produce fertile offspring in a natural setting. This concept works
in most everyday experiences and is used often although limitations for this concept do exist:
1. Some organisms can interbreed and produce fertile offspring although they are classified as
separate species, ex. Wolves and dogs.
2. This concept does not account for extinct species.
3. This concept does not account for species that reproduce asexually (bacteria)
C. Phylogenetic species concept – Phylogeny is the evolutionary history of a species. This concept
defines a species as a cluster of organisms that is distinct from other clusters and shows evidence of
a pattern of ancestry and descent. When a phylogenetic species branches, it becomes two different
phylogentic species. (recall geographic isolation).
1. This concept solves some of the problems found with the other concepts because it applies to
extinct species and species that reproduce asexually.
D. See table 17.2, page 491
OBJECTIVE 22: DESCRIBE METHODS USED TO DESCRIBE PHYLOGENY
A. To classify a species, scientists often construct patterns of descent or phylogenies, by using
characters – inherited features that vary among species. Characters can be morphological or
biochemical.
10
B. Morphological characters that are shared suggest species evolved from a recent common ancestor.
1. Homologous characters, although performing different functions, show an anatomical similarity
inherited from a common ancestor.
2. Morphological similarities, like bones with hollow spaces, show that birds are most closely related
to dinosaurs than other reptiles. Even the possibility of feathers might reveal a close relationship.
(see fig. 17.7, page 493).
C. Biochemical characters, like amino acids and nucleotides, are used to help determine evolutionary
relationships among species. Chromosome number and structure are also used as clues for
determining species similarities. DNA and RNA analysis are powerful tools for reconstructing
phylogenies.
1. The greater number of shared DNA sequences between species, the greater number of shared
genes and therefore the greater the evidence that there is a common ancestor.
2. Molecular data has changed traditional taxonomic organization. (see fig. 17.9, page 494)l
3. A molecular clock uses comparisons of DNA sequences to estimate phylogeny and rate of
evolution. The differences between the genes indicate the presence of mutations. The more
mutations that have accumulated, the more time that has passed since divergence.
a. The rate of mutation is affected by many factors, including the type of mutation, where it is in
the genome, the type of protein the mutation affects, and the population in which the mutation
occurs.
OBJECTIVE 23: EXPLAIN HOW CLADOGRAMS AND REVEAL PHYLOGENETIC RELATIONSHIPS
A. The most common systems of classification today are based on a method of analysis called
cladistics, which classifies organisms according to the order that they diverged from a common
ancestor.
B. Scientists consider both ancestral characters, those that are found within the entire line of descent of
a group of organisms, and derived characters, those that are present in members of one group of the
line but not in the common ancestor.
C. A cladogram is a branching diagram that represents the proposed phylogeny or evolutionary history
of a species or a group. The groups used in the cladograms are called clads. A clad is one branch
of the cladogram. See pages 496-497
1. When constructing a cladogram the outgroup is the species or group of species that has more
ancestral characteristics with respect to the other organisms being compared.
2. The cladogram is then constructed by sequencing the order in which derived characteristics
evolved with respect to the outgroup.
3. When making a cladogram a primary assumption is that the greater the number of derived
characters shared by groups, the more recently the groups share a common ancestor.
MAIN IDEA: THE MOST WIDELY USED BIOLOGICAL CLASSIFICATION SYSTEM HAS SIX
KINGDOMS WITHIN THREE DOMAINS
OBJECTIVE 24: COMPARE MAJOR CHARACTERISTICS OF THE THREE DOMAIN AND
DIFFERENTIATE AMONG THE SIX KINGDOMS
A. The broadest category in the classification system used by most biologists is the domain. Currently
there are three domains. Within these domains there are six kingdoms. (see Table 17.3, page 502)
B. Domain Bacteria – Eubacteria, members of Domain Bacteria and Kingdom Eubacteria are unicellular
prokaryotes, with strong cell walls containing peptidoglycan, a polymer that has two kinds of sugars
that alternate in the chain. They survive in many different environments. While some are aerobic,
others are anaerobic. Some are autotrophic but most are heterotrophic.
C. Domain Archea are species classified in this domain and Kingdom and are thought to be more
ancient than bacteria and yet more closely related to our eukaryotic ancestors. There cell walls do
not have peptidoglycan and they are diverse in shape and nutrition requirements. Some are
autotrophic but most are heterotrophic. They are called extremophiles because they can live in
extreme environments like boiling hot springs, salty lakes, mu marshes, thermal vents on the ocean
floor; places where there is no oxygen.
D. Domain Eukarya – These organisms have a membrane bound nucleus and other membrane bound
organelles and they are called eukaryotes. This domain has 4 kingdoms.
1. Protista – eukaryote, lacks complex organ systems, most are unicellular, may be autotrophs
(plant –like protests are called algae) or heterotrophs (animal like protists are called protozoans)
11
Others may be parasitic or saprobe, while some exhibit characteristics of both plants and
animals. All protests live in moist environments.
2. Fungi – eukaryote, absorptive heterotroph, unicellular or multicellular, immobile. They have no
cell walls. Fungus consist of a threadlike mass of filaments called hyphae. Hyphae are
responsible for the growth, feeding and reproduction of the fungus. Fungus play an important role
in decomposing organic matter and recycling the nutrients on the earth. Some can cause
disease, others have symbiotic relationships.
3. Plantae – multicellular eukaryotes that are photosynthetic, immobile, have cell walls made of
cellulose, contain cells, tissues, and organs. Examples of organs are roots, stems, and leaves.
These organisms form the base of all land habitats.
4. Animalia – eukaryote, multicellular, ingestive heterotroph, no cell walls, cells organized into
tissues and tissues into complex organs, and they into complex organ systems. Animals live in
the water, on land, and in the air. Most are mobile.
12