Invitation to Biology Chapter 1

Life’s Levels of Organization The world of life shows levels of organization, from the simple to the complex, which extend through: –cells –populations –communities –ecosystems –the biosphere

Molecules of Life All things are made up of the same units of matter: –atoms, molecules Living things are made of up of a certain subset of molecules: –nucleic acids, proteins, carbohydrates, lipids

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

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

DNA Guides Development Development –Transformation from fertilized egg to adult –Series of stages –Instructions for each stage in DNA

Energy Is the Basis of Metabolism Energy = Capacity to do work Metabolism = Reactions by which cells acquire and use energy to grow, survive, and reproduce

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

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

energy input (mainly sunlight) producers (plants and other self-feeding organisms; they make their own food from simple raw materials) nutrient cycling consumers, decomposers (animals, most fungi, many protists, many bacteria that can’t make their own food) energy output (mainly metabolic heat)

Sensing and Responding Organisms sense changes in their environment and make responses to them Receptors detect specific forms of energy The form of energy detected by a receptor is a stimulus

Homeostasis Maintenance of internal environment within range suitable for cell activities Pancreas maintains level of sugar in blood by secreting hormones

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 Additional millions of species now extinct Classification scheme attempts to organize this diversity

Scientific Names Two-part naming system devised by Carolus Linnaeus First name is genus (plural, genera) –Homo sapiens - genus is Homo Second name is species within genus

Bacteria Archaea Eukarya (includes protists, plants, fungi, and animals) Three-Domain Classification Bacteria (EUBACTERIA) Archaea (ARCHAEBACTERIA) Eukarya (EUKARYOTES)

Life’s Diversity

Prokaryotes Archaea and Bacteria Single-celled No nucleus or organelles Include producers, consumers, decomposers

Eukaryotes Eukarya (plants, fungi, animals, protists) DNA is inside a nucleus Most are larger and more complex than the prokaryotes

Plants All are multicelled Most are photosynthetic producers Make up the food base for communities, especially on land

Fungi Most are multicelled Consumers and decomposers Extracellular digestion and absorption

Animals Multicelled consumers –Herbivores –Carnivores –Parasites –Scavengers Move about during at least some stage of their life

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

Natural Selection The outcome of differences in survival and reproduction among individuals that vary in details of heritable traits This process helps explain evolution - changes in a line of descent over generations

Artificial Selection Breeders favor some form of traits over others Individuals exhibiting favored traits are bred Favored traits increase in the population

Observations, Hypotheses, and Tests Observe phenomenon Develop hypotheses Make predictions Devise test of predictions Carry out test and analyze results

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

Role of Experiments Procedures 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 –Non-representative sample skews results –Minimize by using large samples

CONTROL GROUP Gets regular potato chips EXPERIMENTAL GROUP Gets Olestra potato chips Make Prediction Eat potato chips Analyze Results Draw Conclusion Eating Olestra potato chips does not cause intestinal distress If Olestra ® potato chips cause intestinal distress then people who eat them will get cramps Perform Experiment 93 of 529 people (17.6%) suffer from cramps later 89 of 563 people (15.8%) suffer from cramps later About the same number of people in each group get cramps

Field Experiment Control Group 34 H. cydno individuals with yellow markings Experimental Group 46 H. cydno individuals with white markings Experiment Both yellow and white forms of H. cydno butterflies are introduced into isolated rain forest habitat of yellow H. eleuchia butterflies. Numbers of individuals resighted recorded on a daily basis for two weeks. Results Experimental group (H. cydno individuals without yellow wing markings) is selected against. 37 of the original group of 46 white butterflies disappear (80%), compared with 20 of the 34 yellow controls (58%). Study of Heliconius butterflies

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

Science and the Supernatural Science has run up against religious belief systems –Copernicus suggested that sun, not the Earth, was center of universe –Darwin suggested that life was shaped by evolution, not a single creation event

Asking Questions Scientists still ask questions that challenge widely held beliefs The external world, not internal conviction, is the testing ground for scientific beliefs