Transcript On the Origin of Species

AP Biology
Scientific Inquiry and Unifying
Themes
Seven Unifying Themes in
Biology
1. Emergent Properties
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Atom
Molecule
Organelle
Cell
Tissue
Organ
Organ system
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Population
community
Ecosystem
• Biological processes often involve several levels of
biological organization
– Most biologists specialize in the study of life at a particular
level
• Each step upward, properties emerge that
were not present at the simpler levels of
organization
• Characteristics of life
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Order
Reproduction
Growth and development
Energy utilization
Response to the environment
Homeostasis
Evolutionary adaptation
– Reductionism
• Reducing complex systems to simpler
components that are more manageable to
study
2. The Cell
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Cell is the lowest level of structure
capable of performing ALL the activities
of life.
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All organisms are composed of cells
Basic unit of structure and function
– Cell Theory
• Robert Hooke
– Described and named cells in 1665
– Observed a slice of cork, magnified 30x
• Anton van Leeuwenhoek
– Discovered organisms we now know to be single-celled
– Magnifying glasses at 300x, observed pond water, blood
cells and sperm cells
• 1839 Matthias Schleiden and Theodor Schwann
– Summarized their own microscopic studies and those of
others by concluding that all living things consist of cells
• Two Main Cell types
– Eukaryotic Cells
» Subdivided by internal membranes into many
different functional compartments- membrane bound
organelles
» DNA is organized within a nucleus
» Cytoplasm (thick fluid surrounding nucleus), contains
organelles that perform most of the cell’s functions
» Some have cell walls
– Prokaryotic Cells
» DNA is not separated from the rest of the cell
» Lack cytoplasmic organelles typical of eukaryotic
» Almost all have cell walls
3. Heritable Information
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Heritable information is encoded in DNA
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the substance of genes
the units of inheritance that transmit
information from parents to offspring
Structure
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Double helix
Nucleotides
- Genome- entire “Iibrary” of genetic
instructions that an organism inherits.
4. Structure/Function
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Form fits function
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Analyzing a biological structure gives us
clues about what it does and how it works.
Knowing the function of a structure provides
insight about its construction.
5. Interaction with the Environment
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Organisms are examples of an open
system (entity that exchanges materials
and energy with its surroundings)
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Two main processes
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Cycling of nutrients
Flow of energy
– Exchange of energy between an organisms and
its surroundings involves the transformation of
one form of energy to another
• Photosynthesis• Muscle movement• Cellular work-
6. Regulation
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Enzymes
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Catalysts that speed up reactions
Regulatory mechanisms determine precisely when,
where, and how fast certain reactions occur in the
cell
– Many biological processes are selfregulating,
• operating by feedback
– an output or product of a process regulates the
process
• Negative feedback, feedback inhibition, slows
or stops processes
• Positive feedback speeds a process up
7.
Evolution
- The core theme of biology
- Species that are similar share a common
ancestor that represents a relatively
recent branch point on the tree of life.
– Charles Darwin
• 1859 On the Origin of Species
• Two main concepts
– Contemporary species arose from a succession of
ancestors through a process of “descent with
modification”
– Proposed mechanism of Natural Selection (how
evolution occurs)
» Individual variation
» Struggle for existence
» Differential reproductive success
Scientific Inquiry
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Science is a way of knowing
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Two main types of exploration
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Discovery science
Hypothetico-deductive science
Most scientists practice a combination of
these two forms of inquiry
– Discovery Science and Induction
• Science seeks natural causes for natural
phenomena
– Limits scope of science to the study of structure and
processes that we can observe and measure
(directly or indirectly)
• Verifiable observations and measurements are
the data of discovery science.
– Enables us to describe life at its many levels
– Can lead to important conclusions based
on a type of logic called inductive
reasoning.
• An inductive conclusion is a generalization that
summarizes many concurrent observations.
• Ex. “All organisms are made of cells”
• Hypothesis vs. theory
– Theories are broader in scope
– Theories are only accepted if supported by an
accumulation of extensive and varied evidence
(contradicts everyday usage of the word)
– Science as a Social Process
• Most scientists work as teams
• It is not unusual that several scientists are
asking the same questions
• Build on what has been learned from earlier
research, and pay close attention to
contemporary scientists working in the same
field
• Share information through publications
• Cooperation and competition characterize
scientific culture
– Hypothetico-deductive science
• “Scientific method” or “Nature of Science
(NOS)”
• Hypothetico refers to hypothesis
• Deductive refers to the use of deductive logic
to test hypotheses.
– Reasoning flows from general to specific
– Usually takes the form of predictions about what
outcomes of experiments or observations we should
expect if a particular hypothesis (premise) is correct.
– “If…then” logic
– Then we test the hypothesis by performing an
controlled experiment
– Cultural context of Science
• Science is embedded in the culture of its
times.
• Some philosophers argue that scientists are so
influenced by cultural and political values that
science is no more objective than other ways
of “knowing nature”.
• Other extreme are people who speak of
scientific theories as though they were natural
laws instead of human interpretations of
nature.