Science of Biology 1 Exploring Life on Its Many Levels Properties of Life Form high degree of ordered structures Regulate internal conditions Harvest and use energy Reproduce and evolve Grow and develop Respond to environmental stimuli Each level of biological organization has emergent properties Biological organization is based on a hierarchy of structural levels each building on the levels below At the lowest level are atoms that are ordered into complex biological molecules Molecular S P O N C H carbohydrates proteins fats and nucleic acids Biological molecules are organized into structures called organelles the components of cells Molecules Organelles Cells Tissues Organs Systems Organisms Cells are the fundamental unit of structure and function of living things Some organisms consist of a single cell others are multicellular aggregates of specialized cells Whether multicellular or unicellular all organisms must accomplish the same functions uptake and processing of nutrients excretion of wastes response to environmental stimuli and reproduction 2 Biological systems are much more than the sum of their parts The whole is greater than the sum of its parts The combination of components can form a more complex organization called a system Examples of biological systems are cells organisms and ecosystems Consider the levels of life With each step upward in the hierarchy of biological order novel properties emerge that are not present at lower levels These emergent properties result from the arrangements and interactions between components as complexity increases A cell is much more than a bag of molecules Our thoughts and memories are emergent properties of a complex network of neurons This theme of emergent properties accents the importance of structural arrangement The emergent properties of life are not supernatural or unique to life but simply reflect a hierarchy of structural organization The emergent properties of life are particularly challenging because of the unparalleled complexity of living systems The complex organization of life presents a dilemma to scientists seeking to understand biological processes We cannot fully explain a higher level of organization by breaking it down into its component parts At the same time it is futile to try to analyze something as complex as an organism or cell without taking it apart IG Lecture Outlines 1 1 Reductionism reducing complex systems to simpler components is a powerful strategy in biology The Human Genome Project the sequencing of the genome of humans and many other species is heralded as one of the greatest scientific achievements ever Research is now moving on to investigate the function of genes and the coordination of the activity of gene products Biologists are beginning to complement reductionism with new strategies for understanding the emergent properties of life how all of the parts of biological systems are functionally integrated 3 The unity and diversity of life Biology can be viewed as having two dimensions a vertical dimension covering the size scale from atoms to the biosphere and a horizontal dimension that stretches across the diversity of life The latter includes not only present day organisms but also those that have existed throughout life s history Life is enormously diverse Biologists have identified and named about 1 8 million species This diversity includes 5 200 known species of prokaryotes 100 000 fungi 290 000 plants 50 000 vertebrates and 1 000 000 insects Thousands of newly identified species are added each year Estimates of the total species count range from 10 million to more than 200 million Underlying the diversity of life is a striking unity especially at the lower levels of organization The universal genetic language of DNA unites prokaryotes and eukaryotes Among eukaryotes unity is evident in many details of cell structure Above the cellular level organisms are variously adapted to their ways of life How do we account for life s dual nature of unity and diversity The process of evolution explains both the similarities and differences among living things 4 Evolution is the core theme of biology The history of life is a saga of a changing Earth billions of years old inhabited by a changing cast of living forms Charles Darwin brought evolution into focus in 1859 when he presented two main concepts in one of the most important and controversial books ever written On the Origin of Species by Natural Selection Darwin s first point was that contemporary species arose from a succession of ancestors through descent with modification This term captured the duality of life s unity and diversity unity in the kinship among species that descended from common ancestors and diversity in the modifications that evolved as species branched from their common ancestors Darwin s second point was his mechanism for descent with modification natural selection Darwin inferred natural selection by connecting two observations Observation 1 Individual variation Individuals in a population of any species vary in many heritable traits Observation 2 Overpopulation and competition Any population can potentially produce far more offspring than the environment can support This creates a struggle for existence among variant members of a population Inference Unequal reproductive success Darwin inferred that those individuals with traits best suited to the local environment would leave more healthy fertile offspring IG Lecture Outlines 1 2 Inference Evolutionary adaptation Unequal reproductive success can lead to adaptation of a population to its environment Over generations heritable traits that enhance survival and reproductive success will tend to increase in frequency among a population s individuals The population evolves Natural selection by its cumulative effects over vast spans of time can produce new species from ancestral species For example a population fragmented into several isolated populations in different environments may gradually diversify into many species as each population adapts over many generations to different environmental problems Fourteen species of finches found on the Gal pagos Islands diversified after an ancestral finch species reached the archipelago from the South American mainland Each species is adapted to exploit different food sources on different islands Biologists diagrams of evolutionary relationships generally take a treelike form Just as individuals have a family tree each species is