Case study: spider mimicry

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2 Pounce rate (% of trials in which spider jumped on fly) Case study: spider mimicry Control group (untreated flies) Experimental group (wing markings masked)

3 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??

4 Another test of the spider mimic hypothesis: wing transplants Number of stalk and attack responses by spiders Wing markings Wing waving Normal spider mimic Mimic with mimic wing transplant Mimic with housefly wing transplant Housefly with mimic wing transplant Normal housefly Controls Experimentals

5 "Good" scientific hypotheses are testable, falsifiable and suggest new experiments. Science is based on observations of measurable things. Scientists strive for "objectivity".

6 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.

7 Science is a process. It is never done. Never proven. All conclusions are tentative.

8 Seek simplicity but distrust it

9 Lecture 3 CHAPTER ONE THE SCIENCE OF BIOLOGY

10 1.2 Properties of Life Biology is the STUDY OF LIFE But what does it mean to be alive? Are viruses alive?

11 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

12 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

13 Fig. 1.4

14 Fig. 1.4

15 Fig. 1.4 biosphere

16 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.

17 1.4 Five general themes unify and explain biology 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 See Table 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

18 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

19 1.5 How Scientists Think Deductive Reasoning Using accepted general principles as a guide to explain specific observations D Fig. 1.5

20 Inductive Reasoning Discovering general principles through examination of specific cases It is used by scientists to develop hypotheses about how the world works Fig. 1.5 I

21 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-21 st century

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23 1.7 The Scientific Method Observation Question Hypothesis 1 Hypothesis 2 Hypothesis 3 Hypothesis 4 Hypothesis 5 Experiment Reject hypotheses 1 and 4 Potential hypotheses Hypothesis 5 Hypothesis 3 Hypothesis 2 Experiment Reject hypotheses 2 and 3 Remaining possible hypotheses Hypothesis 5 Last remaining possible hypothesis Predictions Experiment 1 Experiment 2 Experiment 3 Experiment 4 Fig. 1.7 Predictions confirmed

24 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

25 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

26 1.9 Four Theories Unify Biology 1. The Cell Theory 2. The Gene Theory 3. The Theory of Heredity 4. The Theory of Evolution

27 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!)

28 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

29 The gene theory Fig 1.12

30 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

31 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

32 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

33 4. The Theory of Evolution: Diversity of Life The domain Eukarya is divided into four kingdoms Protista Plantae Fungi Animalia Eukarya Fig. 1.1

34 Fig The tree of life Crocodiles are more closelyrelated to birds than to other reptiles

35 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