Download Principles of Biology Lake Tahoe Community College

Botany – Bio 201
Lake Tahoe Community College
Fall 2008
Instructor: Ralph Sinibaldi
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Chapter 18
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I. The current diversity of life is a reflection of 3.5 billion years of life on earth
There are maybe 10 million species on earth; some say up to 30 million (rainforest beetle study )
A. Taxonomy, the science of classification, provides a system to name different groups of organisms
B. Evolution is the process by which change occurs, and new forms arise
C. Systematics is the effort to analyze modern organisms relationships; try to deduce the history of
change that led to modern life.
D. Phylogeny is the study of evolutionary steps leading from past life forms to modern life forms; this term
literally mean “origin of groups”.
II.
A population consists of organisms of a species in a given area; most areas have many populations of difft
species.
A. A species is a group of organisms having traits not found in other organisms; e.g. oranges = Citrus
sinensis; lemons = Citrus limon, and grapefruits = Citrus paradisi;
B. How do we decide whether a partic. organism belongs to any species? Type specimens allow comparison of
new species to a sample placed on file when the species was first named. But still there are difficulties- age and
maturity, and individual differences must be accounted for, therefore there are many type specimens. So the
similarities btn these fruits are noted; biologists have classed them all as citrus, yet their differences are
acknowledged by having individual species determinations.
C. Mating tests resolve the difficulty of defining a species; but some fungus are asexual. Also there are
hybrids. Others are weakly fertile. Often there are arguments about species boundaries.
III.
Taxonomy is grouping of species in a hierarchy, as well as the formal system for assigning new names;
scientific names are important because there is no ambiguity as with common names. Plantains (Plantago
major) have at least 300 common names; in English it is called Plantain major, broad-leaved Plantain, and has
45 other English names, 74 Dutch names, 106 German names, and as many as several hundred more in other
languages.
A. Modern taxonomy began with Carolus Linnaeus (1707 – 1778), who published Species Plantarum in 1753
1. Linnaeus assigned 6000 species into 1000 groups called genera, wrote a descriptive name for them,
and used a single word combined with the genus name to provide a shortened name. He used flowers
to characterize most plants bc most variety and least subject to environmental influence. Today, every
species gets a binomial. Always underlined or printed in italics.
2. The binomial system of taxonomy is based on the system Linnaeus developed
a. first name of the binomial is the genus name
b. second name of the binomial is the specific epithet
c. the species name is a combination of the genus and specific epithet
3. Genera are grouped into families, families into orders, orders into classes, classes into divisions,
divisions into kingdoms and kingdoms into domains. Sometimes there are additional groupings –
sub or super class, or varieties.
a. the Domain is the least specific description
b. the species is the most specific description
c. we use the word taxon to refer to one or more of the hierarchical designations.
1. Herbaria keep type specimens and botanical gardens maintain living specimens
2. Keys can be used to identify organisms
d. For example, onions can be classified like this:
Kingdom: Plantae
Division: Magnoliophyta
Class: Liliopsida
Order: Liliales
Family: Liaceae
Genus: Allium
Species: Allium cepa L.
4. The Plant Kingdom is divided into a number of Divisions – liverworts, hornworts, mosses,
Whiskferns, club mosses, horsetails, ferns, gymnosperms, and flowering plants
IV.
Evolution is the mechanism that explains both the historical and future origins of biological diversity
A.
V.
Charles Darwin and Alfred Wallace proposed that species could change or evolve over many
generations. Darwin studied theology as a young man, getting a C avg. In 1831 King William IV of
England commissioned a sailing vessel, the HMS Beagle to chart coastlines, esp S. America. Darwin
was recommended by his teachers.
1. Darwin published “Origin of Species” in 1859, in which his tenets of change were described,
along with a detailed argument with supporting evidence
2. Today, the theory of evolution underlies the science of biology
B. Darwin surmised that hereditary change occurred randomly and was passed on to succeeding
generations
C. The major sources of variation are recombination’s of DNA in the formation of gametes; mutation’s in
the base sequences of DNA; and bringing gametes together from two parents
D. Endosymbiosis may have joined very dissimilar organisms together
1. Evidence suggests that chloroplasts were once free living cyanobacteria – cyanobacteria
engulfed by a eukaryotic host.
2. Evidence suggests that mitochondria were once free living heterotrophic respiring bacteria
that either invaded or were engulfed by a host. Energy allowed increases in size and complexity
and activity.
3. Eventually, most DNA merged with nuclear DNA in host. Merging DNA from different
sources provides innovative opportunities to increase the diversity of life. Molecular evidence
supports this theory.
E. The environment plays a role in determining which changes in DNA will pass from one generation to the
next
1. Darwin proposed that natural selection was the way in which adaptation of organisms could
make it easier to reproduce and survive. Adaptations are traits that make it easier for an
organism to survive in a given environment.
2. Natural selection can alter, through differential reproduction, and organisms reproductive
success
3. Natural selection can influence the composition of a population by
a. Directional selection – a shift in the type of individuals leaving offspring
b. disruptive or diversifying selection: when selection favors the extreme types of
individuals in a population
c. stabilizing selection, where the most common types are selected, creating a more
homogeneous population
speciation is the mechanism by which diversity can increase over time
A. the most common mechanism of speciation requires geographic and reproductive isolation and
subsequent selection
B. Polyploidy and hybridization are two speciation processes requiring only reproductive isolation to be
effective
C. Adaptive radiation allows an ancestral species to exploit numerous new environments and create
numerous and diverse new species. The origins of flowering plants follow this pattern