Biology Chapter One.pdf

Chapter 1 – Classification of living c organisms Classification Several million types of living organisms are known to exist today. new species discovered each year increase this number. As millions of organisms may belong to a single species, it is not possible to investi...

Chapter 1 – Classification of living c organisms Classification Several million types of living organisms are known to exist today. new species discovered each year increase this number. As millions of organisms may belong to a single species, it is not possible to investigate and recognize the billions of individual organisms. To acquire sufficient information about organisms, classifying into smaller groups is necessary. Biologists have used observation methods since ancient times. many classifications are made by observation, some new techniques are used as well. The Science of classifying organisms is known as taxonomy. >TAXONOMY : The Science of classifying organisms. History of classification Aristotle : The Greek philosopher Aristotle (350 BC) listed only a few hundred plants and animals. Aristotle and his pupils grouped plants as grasses, bushes, or trees, and animals as aquatic or terrestrial. Another philosophers classified animals as useful, harmful or useless. Classification by appearance and similarities in function is called empiric (artificial) classification. This classification is based on observations. organisms were classified as plants (motionless organisms) or animals initially.  With the discovery of microorganisms in the 16th century, classification. problems became more complex. Organisms like bacteria, blue-green algae and euglena became problematic for botanists and zoologists. Use of analogous organs in classification was replaced with use of homologous organs. >EMPIRIC CLASSIFICATION : Classification by appearance and similarities in function. This classification is based on observations. Analogous organs These are organs generally similar in shape and function. For instance, wings in butterflies or birds provide flight, whereas legs in flies and cats function in walking. But these organs are embryologically different. Therefore we say that butterflies and birds aren't related. Homologous organs These are organs sharing the same origin and similar embryological stages are called homologous organs. Functions of homologous organs may be the same or different. Some similarities may be seen in structures seemingly unrelated in appearance. For instance, a human's arm seems quite different from a bat's wing. But these are seen to be similar both anatomically and embryologically. Homologous organs are the basis of modern classification. Before modern classification was developed in the 18th century, several methods had been used: John Ray (1626-1705) : tried to unify classification systems and was the first to use the term "species". Carolus Linnaeus : The founder of modern systematics. He applied his binominal nomenclature method to plants (in 1753) and to animals (in 1758) in his book Systema Naturac. 2 Q/ Compare between Analogous and Homologous organs ? Ans./ defines + example. System of classification Phylogenetic systematics used today depends on Linnaeus systematics and homology. Homology is used in determining the level of relatedness; eg. bats and humans are in the group Mammalia. The basis of modern systematics is the grouping of organisms according to similarities. In the classification of organisms, the following criteria are used: origins, relatedness, developmental stages. In the binomial system created by Linnaeus, species is the basic unit of nomenclature. A species is a group of organisms from the same population sharing the same embryological, morphological, and physiological features, and are capable of giving birth to fertile offspring when mated under natural conditions. -There are two points in Linnaeus’ hypothesis: There is an ideal type for each species. This ideal type: represents the standard features of every single individual of the species. The number of species and their types is constant and unchangeable. According to Linnaeus systematics, a species is named with two names. First is the genus name with the first letter capitalized. Second is the specific epithet (species name) and the first letter is not capitalized. Both are written in italics and in Latin. ◇The reason for this is to have a single name in the scientific world, thus simplifying the study of species. For example. Canis familiaris is the name for dogs, whereas Canis lupus is the wolf. The first name (Canis) shows that these two species are in the same genus. 3  A group of species similar in some characteristics forms a genus. similar genera form a family. similar families form an order. similar orders form a class. similar classes form a phylum. Similar phyla form a kingdom. In this system, species level has the largest number of common features and the least number of individuals compared to the higher levels. As you go up, common features decrease while the number of individuals increases. So the fewest common characteristics and the highest number of individuals are found in the kingdoms. >SPECIES : it is the basic unit of nomenclature. A species is a group of organisms from the same population sharing the same embryological, morphological, and physiological features, and are capable of giving birth to fertile offspring when mated under natural conditions. Canis familiaris → Dog Canis lupus → Wolf 4  How to memorize classification in order ! King Phillips Came Over For Good Soup. 5 QUIZ/ Chapter 1- Classification Define each of the following terms : Taxonomy – Empiric classification – Species – Analogous organs – Homologous organs – Carolus Linnaeus Answer : 1. Explain the classification of Aristotle ? 2. Explain the analogous organ with an example. 3. Explain the homologous organ with an example. 4. What are the two points in Linnaeus’ hypothesis ? 5. Explain how Linnaeus named organisms with an example. Fill in the blanks : 1. Aristotle Listed only a few hundred _______ and _______. 2. Plants classify as ________, __________, or _________. 3. Animals classify as __________ or ___________. 4. _________, _________ and __________ are called microorganisms 5. In the classification of organisms, the following criteria are used: ________, ____________, _____________. True or false, then correct wrong ones: 1. Aristotle was the first scientist to name organisms with binomial nomenclature. 2. Animals are non-motile eukaryotic organisms. 3. Similar genera form family. 4. Plants are photosynthetic, multicellular organisms. 6