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1
CHAPTER 1
AN INTRODUCTION
TO BIOLOGY
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Properties of Life
UnityAll modern forms of life display a common set
of characteristicsBased on biological evolution
DiversityMany types of environments with diverse
organisms
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Seven Characteristics of Life
1. Cells and organization
2. Energy use and metabolism
3. Response to environmental changes
4. Regulation and homeostasis
5. Growth and development
6. Reproduction
7. Biological evolution
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Levels of Organization
1. Atoms2. Molecules and macromolecules3. Cells4. Tissues5. Organs6. Organism7. Population8. Community9. Ecosystem10. Biosphere
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Evolutionary History
Life began on Earth as primitive cells
3.5-4 bya Those primitive cells underwent evolutionary
changes that gave rise to the species we see today
Understanding evolutionary history helps us understand the structure and function of an organism’s body
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Example
Evolutionary change involves modifications of existing structures
Structures may be modified to serve new purposes
Legs used for walking were modified into a dolphin’s flipper or a bat’s wing
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Two mechanisms of evolutionary change
1. Vertical descent with modification Progression of changes in a lineage New species evolve from pre-existing
species by the accumulation of mutations Natural selection takes advantage of
beneficial mutations
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2. Horizontal gene transfer Genetic exchange between different species Relatively rare Genes that confer antibiotic resistance are
sometimes transferred between different bacteria species
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Tree or web of life?
Horizontal gene transfer was an important part of the process that gave rise to modern species
Tree of life focuses on vertical evolution Web of life includes the contribution of
horizontal gene transfer
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Classification
Taxonomy is the grouping of species based on common ancestry
3 domainsBacteria- unicellular prokaryoteArchaea- unicellular prokaryoteEucarya- unicellular to multicellular eukaryotes
4 kingdoms Protista, fungi, plantae and animalia
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A species is placed into progressively smaller groups that are more closely related evolutionarily
Approach emphasizes the unity and diversity of different species
Jaguar example
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Genomes and Proteomes
GenomeThe complete genetic makeup of an organism
Evolutionary history and relatedness of all living organisms can be illuminated by genome analysis
GenomicsTechniques used to analyze DNA sequences
in genomes
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ProteomesThe complete complement of proteins that a
cell or organism can make The genome carries the information to
make its proteome Proteomics
Techniques used to analyze the proteome of a single species and the comparison of proteomes of different species
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Biology as a scientific discipline
Science is the observation, identification, experimental investigation, and theoretical explanation of natural phenomena
The scientific method is used to test theories
Some scientists also gather information
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Investigate life at different levels
Different branches of biology study life at different levels using a variety of tools.
As new tools become available, they allow scientists to ask new questions
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Hypothesis or theory?
HypothesisProposed explanation for a natural
phenomenonEducated guess based on previous
observations or experimental studies Example
Maple trees drop their leaves in autumn because of shortened amount of sunlight
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Hypothesis must make predictions that can shown to be correct or incorrect
Additional observations or experiments support or reject a hypothesis
A hypothesis is never really provenWe may not have found the true explanation
for a phenomenon
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Theory Broad explanation of some aspect of the natural world
that is substantiated by a large body of evidence Allows us to make many predictions Also can never be proved true
Due to overwhelming evidence, extremely likely to be true
Example The theory that DNA is the genetic material Overwhelming body of evidence supports this theory
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Two key attributes of a theory
1. Consistency with a vast amount of known data
2. Ability to make many correct predictions
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Understanding biology
Curiosity is the key Not a rigid set of steps 2 general approaches
1. Discovery-based science
2. Hypothesis testing
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Discovery-based science
Collection and analysis of data without the need for a preconceived hypothesis
Goal is to gather informationTest drugs to look for action against diseaseSequence genomes and proteomes
Often leads to hypothesis testing
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Hypothesis Testing/Scientific Method Five stages
1. Observations are made regarding natural phenomena.
2. These observations lead to a hypothesis that tries to explain the phenomena. As mentioned, a useful hypothesis is one that is testable because it makes specific predictions.
3. Experimentation is conducted to determine if the predictions are correct.
4. The data from the experiment are analyzed.
5. The hypothesis is accepted or rejected.
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Common features
Data are often collected in two parallel manners Control and experimental sample Differ by only one factor
Data analysis Statistically significant differences Apply statistical analyses to determine if the control
and experimental samples are likely to be different from each other because of the single variable that is different between the two samples
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If the two sets of data are found not to be significantly different, we would reject our hypothesis.
Alternatively, if the differences between the two sets of data are significant, we would accept our hypothesis, though it is not proven
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Cystic Fibrosis
Affects about 1 in every 3,500 Americans Persons with CF produce abnormally thick
and sticky mucus that obstructs the lungs and pancreas
Average lifespan for people with CF is currently in their mid- to late 30s
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1945, Dorothy Anderson determined that cystic fibrosis is a genetic disorder
Discovery-based sciences used to find CF gene
1989, research groups headed by Lap-Chi Tsui, Francis Collins, and John Riordan identified the CF gene
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CF Gene and Hypothesis
Researchers hypothesize that the CF gene encodes a protein that transports chloride ions (Cl-) across the membrane of cells
Led to experiments to test normal cells and cells from CF patients for their ability to transport Cl- CF cells were found to be defective in chloride
transport Transferring a normal CF gene into cells in the lab
corrects this defect
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Results support the hypothesis that the CF gene encodes a protein that transports Cl- across the plasma membrane
A mutation in this gene causes it to encode a defective transporter protein, leading to a salt imbalance
This imbalance affects water levels outside the cell, which explains the thick and sticky mucus in CF patients
In this example, hypothesis testing has provided a way to accept or reject an idea regarding how a disease is caused by a genetic change
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