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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