Outline and Chapter notes to accompany chapter 6 CLASSIFYING NATURE Dec., 2003 A. WHY CLASSIFICATION IS IMPORTANT "ALL THOSE NAMES" All societies give names to groups of similar species such as birds, insects, oaks, ferns, and orchids. Scientists need formal names for these groups in order to be able to discuss them and form hypotheses about them. Related species are grouped into GENERA (singular: genus), related genera into FAMILIES, related families into ORDERS, related orders into CLASSES, related classes into PHYLA, and related phyla into KINGDOMS. Any one of these groups is called a TAXON (plural, TAXA). Taxa above the species level are called HIGHER TAXA. Formal scientific names of taxa are usually based on Latin and Greek. TAXONOMIC THEORY A grouping of taxa within larger taxa is called a CLASSIFICATION. The study of classifcations and the principles of their construction is called TAXONOMY. Levels among higher taxa are based on interpretations of data and are thus somewhat arbitrary: what one expert calls a class may be only a subclass to another expert. Traditional classifications were based on grouping species together on the basis of shared resemblances. Unfortunately, groupings based on different traits (e.g., mouthpart characters instead of wing characters) may give different classifications. A modern theory of classification, called CLADISTICS, is based on drawing up a treelike diagram (cladogram) based on a large number of consistent characters. The classification is then based on the cladogram. B. MODERN CLASSIFICATIONS RECOGNIZE A GREAT DIFFERENCE BETWEEN PROCARYOTIC AND EUCARYOTIC CELLS PROCARYOTIC CELLS The earliest cells were PROCARYOTIC, resembling those of present- day simple bacteria. Bacterial and other procaryotic cells have only a single unpaired chromosome (containing DNA but no protein) and no internal membrane-limited ORGANELLES. The DNA of procaryotic cells is not enclosed in a well-defined nucleus. EUCARYOTIC CELLS contain protein in their chromosomes, which are usually multiple in number and diploid during at least some portion of the life cycle. They also contain large numbers of membrane-limited ORGANELLES: mitochondria, endoplasmic reticulum, golgi apparatus, vacuoles, lysosomes, and (in plants) chloroplasts. The chromosomes of eucaryotic cells are contained in a well-defined nucleus which is enclosed in a nuclear envelope. ENDOSYMBIOSIS AND THE ORIGIN OF EUCARYOTES In 1970, Lynn Margulis proposed a theory of the origin of eucaryotic cells by ENDOSYMBIOSIS: large procaryotic cells became eucaryotic by engulfing smaller procaryotic cells and maintaining them inside without digesting them. The smaller procaryotes became organelles, and their plasma membranes became the membranes around the organelles. Evidence for this theory includes the fact that both chloroplasts and mitochondria contain their own DNA that resembles procaryotic DNA and differs from the DNA in the nuclei of eucaryotic cells. C. SIX KINGDOMS OF ORGANISMS ARE INCLUDED IN THREE DOMAINS KINGDOMS OF ORGANISMS (See also Classification on the Web site) Since 1970, most biologists have recognized five kingdoms of organisms: EUBACTERIA: Bacteria and blue-green Cyanobacteria (procaryotic) PROTISTA: Simple eucaryotic organisms such as Protozoa (eucaryotic) MYCOTA: Fungi, characterized by absorptive nutrition (eucaryotic) PLANTAE: Plants, containing plastids (eucaryotic) ANIMALIA: Animals, usually containing motile, multicellular life stages (eucaryotic). The discovery of ARCHAEBACTERIA, a very primitive group of procaryotic organisms, has added a sixth kingdom. Boundaries between these kingdoms, especially between plants and protists, are drawn differently by different experts, depending on their different interpretations of the available data. Nucleic acid sequences have revealed that these kingdoms are arranged in three domains: one for the Archaea, one for the Eubacteria, and a third domain for all eucaryotic organisms. DOMAIN AND KINGDOM ARCHAEA Includes certain simple procaryotes with unusual metabolic abilities. DOMAIN AND KINGDOM EUBACTERIA Includes the true bacteria and the blue-green bacteria. KINGDOM PROTISTA Includes single-celled eucaryotic organisms that lack the specializations of other eucaryotic kingdoms. Different Protista are distinguished by their means of locomotion and in some cases by their means of reproduction. Some experts include algae among the Protista. KINGDOM PLANTAE Includes photosynthetic organisms possessing chloroplasts. Subkingdom Thallophyta includes simple plants (algae) lacking differentiated organs and having eggs not protected by nonreproductive cells. Most algae are aquatic. Subkingdom Embryophyta includes plants whose eggs are surrounded by nonreproductive cells, forming an embryo. Most live on land. Bryophyta includes mosses and liverworts, which lack vascular tissues capable of efficiently transporting materials. Tracheophyta or vascular plants are those possessing vascular tissues capable of efficiently transporting materials from one part of the plant to another, thus allowing different parts of the plant to specialize into different organs. The simplest vascular plants do not possess seeds. Seeds are reproductive structures in which the plant embryo and some food reserves are enclosed in several protective layers. The most advanced vascular plants are he flowering plants or angiosperms (division Anthophyta). KINGDOM MYCOTA Includes fungi, characterized by absorptive nutrition. Most fungi have threadlike filaments called hyphae, and most reproduce using spores. KINGDOM ANIMALIA Includes multicellular organisms that develop from a hollow ball of cells called a blastula. Most animals are motile at some life stage. Sponges (phylum Porifera) are simple animals without tissues. Most animals are differentiated into tissues, consisting in the simplest cases of an outer layer (ectoderm) and an inner layer (endoderm). Many animals also have a middle layer (mesoderm). Phylum Cnidaria contains jellyfish and other animals with just two tissue layers (ectoderm and endoderm). Phylum Platyhelminthes (flatworms) contains animals with three tissue layers (ectoderm, mesoderm, and endoderm) but no body cavities. Animals more complex than the Platyhelminthes all possess body cavities. A body cavity surrounded entirely by mesoderm is called a coelom. A body cavity containing other tissue layers in its lining is called a pseudocoel. Most animals with body cavities also have a digestive system with an entrance (mouth) at one end and an exit (anus) at the other end. Annelid worms (phylum Annelida) and arthropods (phylum Arthropoda) have bodies divided into a series of segments. The Arthropoda, including the shrimp, lobsters, spiders, mites, and insects, are the largest phylum by far, including over three fourths of the whole animal kingdom. The phylum Chordata, to which we belong, is characterized by a stiff notochord, gill slits, and a dorsal, hollow nerve cord at some stage of development. Most Chordata also have a backbone and are called vertebrates. Vertebrates include fishes, amphibians, reptiles, birds, and mammals. D. HUMANS ARE PRODUCTS OF EVOLUTION OUR PRIMATE HERITAGE Humans all belong to the kingdom Animalia, the phylum Chordata, and the class Mammalia. Mammals maintain a steady internal body temperatures (usually above that of their surroundings) with the help of insulation (usually hair or fur). All mammals provide parental care and nurse their young with milk. Among the mammals, humans, apes, monkeys, and lemurs belong to the order Primates. Primates show many anatomical and behavioral adaptations to life in trees, such as grasping hands and feet, good depth perception, and a prolonged period of spatial learning associated with high intelligence and extensive parental care. Among primates, humans are distinguisted from apes by upright locomotion (bipedal walking). EARLY HOMINIDS The earliest known hominds lived about 6 million years ago and are placed in the genus Sahelanthropus. Other early hominids include Ororrin and Ardipithecus. The best known early hominids belong to the genus Australopithecus. Most fossils of Australopithecus come from South or East Africa. Both large and small Australopithecus are known. Small, early species include A. anamensis and A. afarensis. The best-known small species is the late-appearing A. africanus of South Africa. Larger ("robust") species include A. robustus in South Africa and A. boisei in East Africa. Anatomical study of the feet, pelvis, and lower vertebral column shows that Australopithecus walked erect and bipedally. Footprints at Laetoli, Kenya confirm this. Stone tools and tools made of bones and teeth were made by hand. Many tools were used as weapons. Hunting seems to have been cooperative, which implies some language or communication. THE GENUS HOMO Homo habilis was a contemporary of later Australopithecus. It was small, but it brain was proportionately larger than that of a comparably sized Australopithecus would have been. Homo erectus was widespread across Africa, Asia, and much of Europe. Its brain size was larger than that of Australopithecus. There is evidence of the use of fire. Homo sapiens came after (and evolved from) Homo erectus. Homo sapiens had larger brains than Homo erectus, especially in the vertical dimension. Stone tools were mounted on shafts to make spears, and larger animals were hunted. Cave paintings show artistic sophistication and religious rituals. Cultural changes took place throughout human evolution. Agriculture presented humans with new selection forces: new foods, new needs, new diseases (and an increase in many old ones). Many infectious diseases (like malaria and tuberculosis) were able to spread more rapidly in larger, settled populations than they did when populations were sparse. Industrial society presents new hazards and thus new forces of natural selection, including motor vehicle accidents, industrial accidents, more alcohol and drugs, pollution, etc. ---------------------------------- Dec., 2003 PERMISSION IS HEREBY GRANTED to instructors who have adopted the book BIOLOGY TODAY for classroom use to download, modify, and use these notes as needed to aid them in in their teaching. Students of such instructors may likewise use and modify these notes as study aids.