Exploring Life Chapter 1

Unifying Themes of Biology A hierarchy of organization The cellular basis of life Heritable information The correlation between structure and function The interaction of organisms with their environment Unity in diversity Evolution Scientific process Biology is an enormous scope—it is your job to identify how the information we discuss fits into these themes.

Life’s Hierarchical Order Atoms ↓ Biological molecules Organelles Cells Tissues Organs Organ systems Complex organisms (Beyond the individual organism) Population Community Ecosystem Biomes Biosphere The living world is a hierarchy, with each level of biological structure building on the level below it. Each level of biological organization has emergent propertiesproperty that emerges as a result of interactions between components

Holism and Reductionism Because properties of life emerge from complex organization, it is impossible to fully explain a higher level of order by breaking it into its partsHolism Reductionismthe principle that a complex system can be understood by studying its component parts Watson and Crick used reductionism to understand how DNA is inherited by studying its molecular structure.

Cell Theory Cells are an organism’s basic units of structure and function Lowest level of structure capable of performing all activities of life All organisms are composed of cells May be unicellular or multicellular

Cell Theory Microscopes and the discovery of the cell helped form the cell theory: Robert Hookelooked at dead cells—cork Antonie van Leeuwenhoklooked at living cells Schleiden and Schwannreasoned that all living things are made of cells Electron microscopes have revealed the complex ultrastructure of cells.

Cell Theory Two major kinds of cells Prokaryotic Eukaryotic Bacteria All other kingdoms No membrane bound nucleus Membrane bound nucleus Lacks membrane bound organelles Subdivided by internal membranes into functional compartments called organelles Almost all have tough external walls Some cells have tough cell walls, animal cells lack cell walls

Continuity of life is based on heritable information in the form of DNA Biological instructions are encoded in DNA DNA is made of nucleotides Phosphate │ Sugar—Base (A,G,C,T) Inheritance is based on mechanism for copying DNA and the passing of this information from the parent to offspringheredity All forms of life essentially use the same genetic codedifferences in organisms reflect differences in nucleotide sequence

Structure and function are correlated at all levels of biological organization Structure gives clues about what it does and how it works Apparent at many levels of biological organization If you know the function, this can help to understand the structure

Includes other organisms as well as abiotic factors Organisms are open systems that interact continuously with their environments Includes other organisms as well as abiotic factors Abioticnot living

Homeostasis Regulation of biological processes is critical for maintaining the ordered state of life Feedback Positive feedback speeds up a process Increased uterine contractions, increases childbirth Negative feedback slows a process down Constriction of blood vessels, decreased heat loss

Evolution, Unity and Diversity Biological diversity is enormous To make this diversity more comprehensible, biologist classify species into categoriestaxonomy Taxonomy is constantly changing— 5 Kingdoms— Monera, Protista, Fungi, Plantae, Animalia 6 Kingdom— breaks Monera down into two groups Eubacteria and Archaebacteria

Evolution, Unity and Diversity At the lower levels of diversity and at the lower levels of organization Universal genetic code Similar metabolic pathways Cell structure

Evolution, Unity and Diversity Evolution is the core theme of biology Life evolves—can be described as a branching tree of life Species that are very similar share a common ancestor at a recent branch point on the phylogenetic tree Less closely related organisms share a more ancient common ancestor All life is connected and can be traced back to primeval prokaryotes that existed more than three billion years ago

Evolution, Unity and Diversity Evolution accounts for both the unity and diversity of life Similarities between two species may be a reflection of their descent from a common ancestor Differences between species may be the result of natural selection

Scientific Process Scientific Methodprocess which outlines a series of steps used to answer questions

Scientific Process Hypothesiseducated guess proposed as a tentative answer to a specific question or problem Inductive reasoningmaking an inference from a set of specific observations to reach a general conclusion Deductive reasoningmaking an inference from general premises to specific consequences usually takes the form of if…then logic deductive reasoning usually involves predicting experimental results that are expected if the hypothesis is true.

Scientific Process Useful hypotheses have the following characteristics: Hypotheses are possible causes Hypotheses reflect past experience with similar questions Multiple hypotheses should be proposed whenever possible Hypotheses must be testable Hypotheses can be eliminated, but not confirmed with absolute certainty

Scientific Process Controlled experiment Control groupgroup in which all variables are held constant Variablecondition of an experiment that is subject to change and that may influence an experiment’s outcome Experimental groupthe group in which one factor or treatment is varied

Scientific Process Collect data Make observations Take measurements

Scientific Process Analyze dataPutting data into a usable form Graph Interpret the datarecognize trends

Scientific Process Make a conclusion Support or disprove your hypothesis ↓ modify experiments test again conclusion

Science and Technology Technology extends our ability to observe and measure, which enables scientists to work on new questions that were previously unapproachable