Introduction to Science and the Scientific Method

What is Science?

• Process for understanding the natural, observable world
• Physicist William Lawrence Bragg said the important thing is to find new ways of thinking about things, not obtain new facts

How to Study Science

• Scientists ask questions which are answered by collecting data
• The scientific method is iterative

Scientific Method

• Consists of making observations and formulate general theories
• Refine, expand, or reject existing hypothesis and develop predictions
• Gather data to test predictions

Theory vs Hypothesis

• A hypothesis is a testable explanation for something observed
• A theory is an explanation for a very general class of phenomena or observations

Theories

• Explanation for a general class of phenomena or observations with two components
• Pattern: Something that occurs in the natural world
• Process: Responsible for creating the pattern
• Two theories form the framework for modern biological science: cell theory and evolution by natural selection

Characteristics of Life

• All living organisms share five fundamental characteristics
• Cells
• Replication
• Evolution
• Information
• Energy

Cell Theory

• Proposed by Robert Hooke and Anton van Leeuwenhoek in the late 1660s
• It states that all organisms are made of cells
• All cells come from preexisting cells
• A cell is a highly organized compartment bounded by a plasma membrane with concentrated chemicals in the solution

Origin of Cells

• Cell Theory: All organisms are made of cells (pattern) and all cells come from preexisting cells (process).
• Spontaneous Generation (historical belief): organisms could arise spontaneously, even from nonliving things
• Pasteur's experiment of using different flasks helped prove that the all-Cells theory is what happens

Implications of Cell Theory

• All individuals in a population of single-celled organisms are related by common ancestry
• In multicellular organisms, all cells are connected by common ancestry

Theory of Evolution by Natural Selection

• Charles Darwin and Alfred Russel Wallace, in 1858, made two claims regarding the natural world
• All species are related by common ancestry, and species can change through time
• A species is a distinct, identifiable type of organism
• Characteristics of species can be modified from generation to generation; called descent with modification

Evolution

• Change in the characteristics of a population over time
• A population is a group of the same species which live in the same area and time
• Natural selection explains how evolution occurs

Natural Selection Conditions

• Two conditions must be met for natural selection to occur in a population
• Individuals must vary in characteristics that are heritable
• Certain versions of these heritable traits help individuals reproduce more than other versions

Evolution by Natural Selection

• Heritable traits that lead to increased reproductive success become more common
• Characteristics change as a result of natural selection acting on individuals
• Natural selection acts on individuals and evolutionary change occurs in populations
• Speciation occurs when populations diverge to form new species

Artificial Selection

• Changes in populations occur when humans select which individuals will produce the most offspring Repeating this process leads to changes in a domesticated population over time

Fitness vs Adaptation

• Fitness is the ability of an individual to produce offspring
• Individuals with high fitness produce many surviving offspring
• Adaptation is a trait that increases the fitness of an individual in a particular environment

Life Processing Information

• The chromosome theory of inheritance provides the foundation to answering questions about the source of heritable traits
• Third unifying idea of biology

Chromosomal Theory of Inheritance

• Proposed in 1902 by Walter Sutton and Theodor Boveri
• Hereditary information is encoded in genes
• Genes are units located on chromosomes
• 1950s: chromosomes are molecules of deoxyribonucleic acid, or DNA

DNA

• Basic unit is chromosomes, molecules of deoxyribonucleic acid, or DNA
• DNA is the hereditary material
• Genes are segments of DNA that code for cell products
• Each strand of its double helix is made up of four building blocks (A, T, C, G)
• It encodes the needed information for growth and reproduction.

DNA Structure

• James Watson and Francis Crick proposed that DNA is a double-stranded helix
• Two strands are connected by building blocks
• A pairs with T
• C pairs with G
• This pairing is preserved, which allows DNA to be copied

Central Dogma

• DNA codes for ribonucleic acid, or RNA, which codes for proteins
• Proteins determine physical traits

Life Requires Energy

• Chemical reactions take place inside cells and require energy
• Organisms have two fundamental nutritional needs:
• Chemical energy in the form of adenosine triphosphate, or ATP
• Molecules that build DNA, RNA, and proteins

Tree of Life (Phylogenetic Tree)

• Darwin and Wallace also stated natural selection can lead to changes within species, as well as between species
• The tree depicts a divergence process in which natural selection has caused populations of one species to diverge and change

Tree of Life

• A family tree of organisms that describes relationships with a single ancestral species at its base
• Phylogeny is the actual genealogical relationships among all organisms
• It's built using computer programs looking for the connections between species

Molecules and the Tree of Life

• Biologists study RNA and DNA from different organisms to uncover the genetic connections
• Carl Woese used the small unit rRNA in looking evolutionary relationships among organisms
• Comparing the sequences may indicate a closer relationship

Analyzing Genetic Variation

• Genetic analysis can be useful for determining how closely the species are related
• A-T-A-T-G-G-A-G is an example of green algae DNA

Phylogenetic Trees

• Diagrams that show the relationships between species
• The branches that share ancestors show that they are related
• What is more closely related: A & B or A & E?

Tree of Life Estimation

• Constructed through complex branching arrangements consistent with existing genetic data
• Universal tree or tree of life that includes a diverse array of species
• Nodes represent common ancestors
• Can show how species are related, three main group of organisms: Eukaryotes in the domain eukarya and prokaryotes in the domains bacteria and archea

Naming Branches

• Taxonomy is the practice of naming and classifying organisms
• A taxon refers to a named group
• Carl Linnaeus established the classification system in 1735
• Each organism has unique two-part name
• Made scientific classification levels

Hypothesis Testing

• Science tests ideas about how the natural world works by testing the predictions made by hypotheses
• Hypothesis testing is a two-step process
• State the hypothesis as precisely as possible and list the predictions it makes
• Design an observational or experimental study capable of testing those predictions
• Food competition hypothesis: Giraffes evolved long necks by natural selection because those reach food unavailable to others
• Simmons and Scheepers tested the food competition, and one of the three was incorrect
• The sexual competition states that winner ones have higher success and sire more offspring

Good Experimental Designs

• Include a reference or control group to check for influential factors
• Conditions must be constant or as equivalent as possible to eliminate other variables
• Must repeat test with larger sample sizes

Explore the nature of science as a process for understanding the natural world. Learn how scientists formulate theories by asking questions, collecting data, and refining hypotheses. Understand the difference between a hypothesis and a theory, and how theories explain patterns and processes in the world.