Invitation to Biology

Organization Within An Organism  Atoms are organized into molecules  In multicelled species, cells are organized into tissues, organs, and organ systems  All organisms consist of one or more cells

Organization of Groups of Organisms  Population All individuals of one species in a specific area  Community All populations in a specific area  Ecosystem A community interacting with its environment

Organization of Life on Earth  Biosphere All regions of Earth that hold life Land, water, and atmosphere

Levels of Organization

Overview of Life’s Unity  Organisms require energy and materials to sustain their organization and activities Nutrients are required for growth and survival Producers make their own food Consumers eat other organisms

Ecosystem: Energy Flow and Material Cycling

Overview of Life’s Unity  Organisms sense change Receptors respond to stimulation Responses keep internal conditions within ranges that cells can tolerate (homeostasis)

Overview of Life’s Unity  Organisms grow and reproduce Based on information encoded in DNA Inheritance transmits DNA from parents to offspring through reproduction mechanisms Development transforms first cell into an adult

KEY CONCEPTS: LIFE’S UNDERLYING UNITY  All organisms are alike in key respects: Consist of one or more cells Live through inputs of energy and raw materials Sense and respond to changes in their external and internal environments Cells contain DNA (molecule that offspring inherit from parents; encodes information necessary for growth, survival, and reproduction)

So Much Unity, So Many Species  The world of life, past and present, shows great diversity  Classification systems organize species in ever more inclusive groups

Genus and Species  Species: One kind of organism  Each species has a two-part name First part: Genus name Combined with the second part, it designates one particular species

Domains  Current classification groups all species into three domains Bacteria (single-celled prokaryotes) Archaea (single-celled prokaryotes) Eukarya (protists, plants, fungi, and animals)

Bacteria and Archaea Bacteria Archaea

Eukarya

An Evolutionary View of Diversity  Life’s diversity arises from mutations Changes in molecules of DNA which offspring inherit from their parents  In natural populations, mutations introduce variation in heritable traits among individuals

Variation in Heritable Traits  Some trait forms are more adaptive than others Bearers are more likely to survive and reproduce  Over generations, adaptive forms of traits tend to become more common in a population Less adaptive forms of the same traits become less common or are lost

Evolution  Populations evolve Traits that help characterize a population (and a species) can change over generations  Evolution Change which occurs in a line of descent

Selection  Natural selection In natural populations Differential survival and reproduction among individuals that vary in one or more heritable traits  Artificial selection Breeding of captive populations Traits selected are not necessarily adaptive

Artificial and Natural Selection

Critical Thinking and Science  Critical thinking is a self-directed act of judging the quality of information as one learns  Science is a way of looking at the natural world Helps minimize bias in judgments Focuses on testable ideas about observable aspects of nature

How Science Works  Researchers generally Observe something in nature Form hypotheses (testable assumptions) about it Make predictions about what might occur if the hypothesis is not wrong Test their predictions by observations, experiments, or both

Experiments  Tests used to support or falsify a prediction Variable characteristic is measured and changed In the control group, variables do not change

A Scientific Approach

Hypothesis Olestra® causes intestinal cramps. Prediction People who eat potato chips made with Olestra will be more likely to get intestinal cramps than those who eat potato chips made without Olestra. ExperimentControl GroupExperimental Group Percentages are about equal. People who eat potato chips made with Olestra are just as likely to get intestinal cramps as those who eat potato chips made without Olestra. These results do not support the hypothesis. Conclusion Eats regular potato chips Eats Olestra potato chips 93 of 529 people get cramps later (17.6%) 89 of 563 people get cramps later (15.8%) Results