Biology Chapter 1

Biology Scientific study of life Lays the foundation for asking basic questions about life and the natural world

Why Study Biology? To learn how organisms are constructed, how they function, where they live, and what they do To help develop, modify, and refine ideas about life

Molecules of Life All things are made up of the same units of matter Living things are made up of a certain subset of molecules: –Nucleic acids –Proteins –Carbohydrates –Lipids

DNA (deoxyribonucleic acid) Signature molecule of life Molecule of inheritance Directs assembly of amino acids

DNA and Inheritance Inheritance –Acquisition of traits by way of transmission of DNA from parent to offspring Reproduction –Mechanism by which an organism produces offspring –Governed by instructions in DNA

Nothing Lives without Energy Energy = Capacity to do work Metabolism = Reactions by which cells acquire and use energy to grow, survive, and reproduce

Sensing and Responding Organisms sense changes in their environment and make responses to them Receptors detect specific forms of energy (stimuli) Allows maintenance of homeostasis

Levels of Organization Cell Multicelled Organism Population Community Ecosystem Biosphere

Interdependencies among Organisms Producers Make their own food Consumers Depend on energy stored in tissues of producers Decomposers Break down remains and wastes

Decomposers Decomposers break down dead organisms and wastes and release the nutrients they contain into the soil, where they are again available to the roots of plants (producers). In this way, decomposers play an important role in recycling nutrients and getting rid of waste.

Energy Flow Usually starts with energy from sun Transfer from one organism to another Energy flows in one direction Eventually, all energy flows back to the environment

Producers Consumers, Decomposers NUTRIENT CYCLING ONE-WAY FLOW OF ENERGY In time, all energy flows back to the environment. ENERGY FROM SUN

Unity of Life All organisms: –Are composed of the same substances –Engage in metabolism –Sense and respond to the environment –Have the capacity to reproduce based on instructions in DNA

Diversity of Life Millions of living species Millions more now extinct Classification schemes attempt to organize diversity

Scientific Names Devised by Carolus Linnaeus First name is genus (plural, genera) –Homo sapiens - genus is Homo Second name is species within genus

Eubacteria (Bacteria) Archaebacteria (Archaea) Eukaryota (Eukaryotes) 3 Domains

Origin of life Eubacteria Archaebacteria Eukaryotes ProtistansPlantsFungiAnimals 6 Kingdoms

Single cells No nucleus or organelles Smaller, less complex Prokaryotic Organisms Eukaryotic Organisms Single- or multi- celled Nucleus and other organelles Larger, more complex

Mutation: Source of Variation Mutation = change in structure of DNA Basis for the variation in heritable traits Most are harmful

Adaptive Trait A trait that gives the individual an advantage in survival or reproduction, under a given set of circumstances

Evolution Genetically based change in a line of descent over time Population changes, not individuals

Antibiotic Resistance Antibiotics are used to kill bacteria Mutations for antibiotic resistance exist or arise Antibiotic-resistant bacteria survive and reproduce better than nonresistant Over time, proportion of antibiotic- resistant bacteria increases

Scientific Method Observe phenomenon Develop hypotheses Make predictions Devise test of predictions Carry out test and analyze results

Role of Experiments Used to study a phenomenon under known conditions Allows you to predict what will happen if a hypothesis is not wrong Can never prove a hypothesis 100% correct

Experimental Design Control group –A standard for comparison –Identical to experimental group except for variable being studied Sampling error –Nonrepresentative sample skews results –Minimize by using large samples

Scientific Theory A hypothesis that has been tested for its predictive power many times and has not yet been found incorrect Has wide-ranging explanatory power –Darwin’s theory of evolution by natural selection

Biological Therapy Experiments Can we use viruses that attack bacteria (bacteriophages) to fight infections?

Experiment 1 Hypothesis - Bacteriophages can protect mice against infectious bacteria Prediction - Mice injected with bacteriophages will not die as a result of bacterial injection

Experiment 1 - Test Experimental group Inject with bacteria and bacteriophage Control group Inject with bacteria and saline

Experiment 1 - Results & Conclusion Experimental group All mice lived Control group All mice died Conclusion - Bacteriophage injections protect mice against bacterial infections

Experiment 2 Prediction - Bacteriophage injections will be more effective treatment than single dose of the antibiotic streptomycin Test - Mice injected with bacteria, then with saline, streptomycin, or bacteriophage

Experiment 2 - Results With 2nd injection: –Bacteriophage - 11 of 12 mice lived –60 mg/gm streptomycin - 5 of 12 lived –100 mg/gm streptomycin - 3 of 12 lived –Saline - all mice died Conclusion - Bacteriophage treatment can be as good or better than antibiotic

Minimizing Variables All mice were same age and sex, reared under same conditions Each mouse in each test group received exact same treatment All mice in control group received same amount of saline Variable tested was antibiotic treatment versus bacteriophage treatment

Limits of Science Scientific approach cannot provide answers to subjective questions Cannot provide moral, aesthetic, or philosophical standards

Scientists Raise Questions The external world, not internal conviction, must be the testing ground for scientific beliefs