Download Case study: spider mimicry

Pounce rate (% of trials in
which spider jumped on fly)
• Case study: spider mimicry
Control group
(untreated flies)
Experimental group
(wing markings masked)
Pounce rate (% of trials in
which spider jumped on fly)
Control group
(untreated flies)
Experimental group
(wing markings masked)
What are alternate explanations for these results??
Number of stalk and
attack responses
by spiders
• Another test of the spider mimic hypothesis: wing transplants
Wing
markings
Wing
waving
Normal
spider
mimic
Mimic with
mimic wing
transplant
Controls
Mimic with
housefly
wing
transplant
Housefly
with
mimic wing
transplant
Experimentals
Normal
housefly
• "Good" scientific hypotheses are testable, falsifiable and
suggest new experiments.
• Science is based on observations of measurable things.
• Scientists strive for "objectivity".
• The scientific method assumes that our perceptions
are objective–unbiased, independent of mind,
personality, feelings.
• Ideas are based on evidence, not authority.
• But science is a human endeavor. Look for
examples of subjectivity, bias, spin, and the influence
of personality.
• Science is a process.
• It is never done.
• Never proven.
• All conclusions are tentative.
“Seek simplicity but distrust it”
Lecture 3
CHAPTER ONE
THE SCIENCE OF BIOLOGY
1.2 Properties of Life
• Biology is the STUDY OF LIFE
– But what does it mean to be alive?
– Are viruses alive?
1.2 All living organisms share five basic properties
– 1. Cellular Organization
• All living organisms are composed of at least one cell
– 2. Metabolism
• All living organisms use energy
– 3. Homeostasis
• All living organisms maintain stable internal conditions
– 4. Growth and reproduction
• All living organisms grow and reproduce
– 5. Heredity
• All living organisms possess a genetic system that is based on DNA
1.3 The Organization of Life
• Living organisms function and interact with
each other at many levels
• These levels are organized in a hierarchy of
increasing complexity
– Cellular Level
– Organismal Level
– Populational Level
Fig. 1.4
Fig. 1.4
biosphere
Fig. 1.4
1.3 Emergent Properties
• The living world has a hierarchy of organizational
levels - from molecules to ecosystems
• Each higher level contains novel properties not
present at the simpler level of organization
• Emergent properties - with each level, new
properties EMERGE as a result of interactions
among components at the lower level.
1.4 Five general themes unify and explain biology
• 1.
–
–
–
See Table 1.1
Evolution
The genetic change in a species over time
It is a result of a process termed natural selection
Variation may also be caused by artificial selection
• 2.
–
–
–
The Flow of Energy
All living organisms require energy
The sun is the source of energy for ecosystems
Plants capture energy via photosynthesis
• They then act as an energy source for other organisms
• 3. Cooperation
– Cooperation between organisms is critical for evolution
– Symbiosis occurs when two organisms of different species live in
direct contact
1.4 Five general themes unify and explain biology
• 4. Structure Determines Function
– Biological structures are well suited to their function
• This is true at every level of organization
• 5. Homeostasis
– All living organisms act to maintain a relatively stable internal
environment
– Maintaining homeostasis requires a lot of signaling back-and-forth
between cells
1.5 How Scientists Think
• Deductive
Reasoning
– Using accepted
general principles
as a “guide” to
explain specific
observations
D
Fig. 1.5
•Inductive Reasoning
–Discovering general
principles through
examination of specific
cases
–It is used by scientists
to develop hypotheses
about how the world
works
I
Fig. 1.5
1.6 Science in Action: A Case Study
•
•
•
•
•
In 1985, a scientist discovered a hole in the ozone above Antarctica
The culprit was later revealed to be chlorofluorocarbons (CFCs)
– Coolants in air conditions; propellants in aerosols
CFCs condense into tiny ice crystals
– Warmed by the sun, they attack and destroy ozone
The ozone layer protects us from the sun’s ultraviolet (UV) rays
–1% drop in ozone 6% increase in skin cancers
There is now a worldwide reduction in CFC production
–The ozone layer will recover by mid-21st century
1.7 The Scientific Method
Observation
Question
Hypothesis 1
Hypothesis 2
Hypothesis 3
Hypothesis 4
Hypothesis 5
Potential
hypotheses
Experiment
Hypothesis 5
Hypothesis 3
Hypothesis 2
Remaining
possible
hypotheses
Reject
hypotheses
1 and 4
Experiment
Hypothesis 5
Reject
hypotheses
2 and 3
Last remaining
possible hypothesis
Predictions
Experiment 1
Fig. 1.7
Experiment 2
Experiment 3
Predictions
confirmed
Experiment 4
1.8 Theory and Certainty
• A theory is a set of hypotheses that have been tested many
times and not rejected
• It indicates a higher degree of certainty
• However, there is no absolute truth in science
– So the acceptance of a theory is provisional
• The source of misunderstandings
– To the general public, a theory represents lack of
knowledge or a guess
– To scientists, a theory represents the models which
are most certain
• The scientific “method”
– A series of logical “either/or” predictions tested by experiments to
reject alternative hypotheses
– Insight and imagination are necessary to good scientific examination
• The limitations of science
– It is limited to organisms and processes that can be observed and
measured
• Supernatural and religious phenomena are beyond the scope of
science
– There are also practical limits
• Science cannot make value judgments
• Science cannot be relied upon to solve all problems
1.9 Four Theories Unify Biology
• 1. The Cell Theory
• 2. The Gene Theory
• 3. The Theory of Heredity
• 4. The Theory of Evolution
1. The Cell Theory: Organization of Life
• Robert Hooke, 1665
– Discovered cells
• Anton van Leeuwenhoek, 1670s
– Discovered single-celled life
• Matthias Schleiden & Theodor Schwann, 1839
– All living organisms are composed of cells
– Cells are the basic units of life
• Rudolf Virchow, 1866
– All cells come from other cells
Still called a theory
(don’t memorize this!)
2. The Gene Theory: Molecular Basis of Inheritance
• The information that determines what an organism is like
is encoded in its genes
• Genes are located along DNA molecules
• The entire set of DNA instructions that specifies a cell is
termed its genome
The gene
theory
Fig 1.12
3. The Theory of Heredity: Unity of Life
• This theory was first advanced by Gregor Mendel in 1865
– It basically states that genes of an organism are inherited
as discrete units
• Later, other biologists proposed the chromosomal theory of
inheritance
– Genes are physically located on chromosomes
The Central DOGMA
DNA
RNA
protein
4. The Theory of Evolution: Diversity of Life
• This theory was first advanced by Charles Darwin in 1859
– It attributes the diversity of the living world to natural
selection
• An essential component of this theory is that evolution
involves “descent by modification”
– All living organisms are related to one another in a
common tree of life
4. The Theory of Evolution: Diversity of Life
• Biologists divide all living organisms into
three domains
&
two types of cells
– Bacteria
PROKARYOTES
– Archaea
– Eukarya
EUKARYOTES
Eukarya
4. The Theory of Evolution: Diversity of Life
• The domain Eukarya is divided into four kingdoms
Protista
Plantae
Fungi
Eukarya
Fig. 1.1
Animalia
Fig. 1.15
The tree
of life
Crocodiles are
more closelyrelated to birds
than to other
reptiles
A phylogenic tree indicates evolutionary relationships
Prokaryotes
Eukaryotes
PROTISTS are the simplest
and most diverse of the
eukaryotes and gave rise to
the other three eukaryotic
kingdoms
Fig. 1.16