AP Biology

Scientific Inquiry and Unifying Themes

Seven Unifying Themes in Biology

1. Emergent Properties- Atom- Molecule- Organelle- Cell - Tissue- Organ- Organ system

- 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– 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- Cell is the lowest level of structure

capable of performing ALL the activities of life.- 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- Heritable information is encoded in DNA

- the substance of genes- the units of inheritance that transmit

information from parents to offspring

- Structure- Double helix- Nucleotides

- Genome- entire “Iibrary” of genetic instructions that an organism inherits.

4. Structure/Function- Form fits function

- 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- Organisms are examples of an open

system (entity that exchanges materials and energy with its surroundings)- Two main processes

- 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- Enzymes

- Catalysts that speed up reactions- Regulatory mechanisms determine precisely

when, where, and how fast certain reactions occur in the cell

– Many biological processes are self-regulating,

• 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

- Science is a way of knowing- Two main types of exploration

- 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.