CHAPTER 1 Classification: Taxonomy PDF

CHAPTER I CLASSIFICATION: TAXONOMY On a fundamental level, there are only two classes’ objects on our planet. One class consists of objects whose structure and behavior are essentially inert – they obey physical forces in a purely mechanical way. These objects are the H2O of the oc...

CHAPTER I CLASSIFICATION: TAXONOMY On a fundamental level, there are only two classes’ objects on our planet. One class consists of objects whose structure and behavior are essentially inert – they obey physical forces in a purely mechanical way. These objects are the H2O of the oceans, the rocks of the mountain ranges, the sands of the deserts, briefly NON-LIVING OBJECTS. In contrast, the objects in the second class come in a rich and practically infinite variety. This class consists of LIVING OBJECTS, which we call ORGANISMS. One of the most striking characteristics of organisms – and one that clearly separates them from inert objects – is that they REPRODUCE; that is they produce new organisms. In fact, they produce organisms more or less like themselves, which means that organisms must have HEREDITY, a set of instructions that specifies the properties of their descendants. According to the fossil records, the most primitive organisms known, - the bacteria and cyanobacteria- dates back to over 3 Billion Years Before Present (BP), first land plants and insects over 400 Million Years BP, and the first birds and the mammals over 180 Million Years BP. Since the simplest forms of life arose, innumerable different kinds of organisms, increasingly complex, adapted to widely varying environments through a process called EVOLUTION. As the time passed, a system is required to establish an order to classify these organisms. Although many such systems were established, the one which uses the evolutionary relationships betweens organisms – the commonality of ancestry- find increasingly more support from the scientific circles. The TAXONOMIC system that we will be following recognizes 5 broad categories, or KINGDOMS (see CHAPTERI.PPT file: Slide 2) which are: 1) MONERA 2) PROTISTA 3) FUNGI 4) PLANTAE 5) ANIMALIA 1) MONERA KINGDOM Members of the Monera differ from those of the 4 other kingdoms in that their cells lack a membrane-enclosed nucleus, as well as other intracellular membranous structures present in the cells of other types of organisms. Therefore they are PROKARYOTIC organisms (Slide 3). This kingdom has two broad subgroups:  a) Bacteria b) Cyanobacteria a) Bacteria The most abundant organisms in the world, bacteria, are single-celled (unicellular) and can be seen only under magnification. Most bacteria can not manufacture their own food from simple inorganic substances and must instead obtain their nutrients, already synthesized from other organisms. Some obtain these nutrients from dead organisms (decomposer bacteria); other from living organisms (pathogenic bacteria). Most bacteria have strong cell walls (Slide 3) which protect them from damage as well as other structures present (e.g. flagellum and pillus for locomotion (Slides 4-5) make them to survive in many diverse habitats ranging from hot springs to glaciers in Antarctica. Though some bacteria are disease-producing agents (pathogenic) that attack human beings, other animals and/or plants, most are beneficial. Many act as decomposers, destroying the dead bodies and bodily wastes of other organisms and in the process, recycling important compounds from these organisms to environmental reservoirs where they become available to other living things. Some bacteria are used in industrial and manufacturing processes such as yoghurt and cheese making bacteria. Finally, study of bacteria enabled biologists to learn many important principles about life that have proved applicable to other organisms including ourselves. b) Cyanobacteria All cyanobacteria (Slide 6), formerly called blue-green algae, contain chlorophyll, which enables them to carry out Photosynthesis, a process by which they manufacture sugars from CO2 and H2O with the help of energy from the sun. Because they can synthesis their own food, they can survive in an amazing variety of habitats, in moist places on land as well as in fresh and salt water (marine). However, the most obvious contribution of cyanobacteria to the life on land is their ability to produce O2 as a byproduct of photosynthesis which help the ozone layer to form and enable the land to be able to be colonized by living things in the early times. Still today, they contribute heavily to the replenishment of O2 in the world. 2) PROTISTA KINGDOM The kingdom protista includes a variety of groups whose members are predominantly unicellular and more importantly starting from this kingdom, all the rest of the members of the remaining kingdoms are EUKARYOTIC; meaning that they have organized cells with well defined intracellular membranous structures or COMPARTMENTS called ORGANELLS (Slide 7). Members of this kingdom are classified according to their feeding habits and two broad subgroups are readily recognized: a) The Plant-like Protists b) The animal-like Protists  a) The Plant-like Protists Members of this subgroup have chlorophyll and therefore photosynthetic. Although they are classified as primitive plants in older classifications, their unicellular nature classifies them as protists. Some examples in this subgroup are: Euglenoids, diatoms and volvox (Slide 8). b) The animal-like Protists Members of this subgroup lack chlorophyll and therefore non-photosynthetic. Some of them are fungus-like, but others, known as PROTOZOA, have traditionally been viewed as unicellular animals. Protozoa are often highly specialized, their single cell exhibiting a complexity and a separation of functions similar to those observable in multicellular animals. Protozoa are generally much larger than bacteria, most are very mobile, swimming rapidly in water in which they live in. Some (e.g. Giardia) propel themselves by the whip-like motion of long hair-like structures known as flagella (Slide 9) others like Paramecium bear many shorter hair-like structures called cilia (Slide 9), and still others like Amoeba have neither flagella nor cilia, but move by a complex flowing motion in which the cell constantly changing shape, sends out extensions called pseudopodia (Slide 9) or false feet into which the rest of the cell contents flow. 3) FUNGI KINGDOM Before 1969, older classification systems used to assign fungi in to the plant kingdom because like plants they are predominantly sedentary and because their cells have walls. But unlike plants, they lack chlorophyll and therefore can not manufacture their own food. However, fungi, like animals, must obtain their food in an already synthesized form from outside, but unlike animals, they can not ingest this food but only can absorb it. They either live on other organisms (parasitic) or on the dead remains of organisms (decomposer). Since fungi differ from both plants and animals in so many ways, the classification system that we use assigns them to a kingdom of their own. Some fungi (e.g. Yeast) are unicellular (Slide 10), but most are multicellular like Bread molds, Fruit molds and mushrooms (Slide 10). 4) PLANTAE KINGDOM Common to all plants are cells with rigid walls and chloroplasts (Slide 11) (organelles containing chlorophyll). Thus plants, unlike fungi and animals, can themselves synthesize the high energy compound, they need for maintenance and growth. This kingdom having more than 250,000 members is subdivided in to many groups. On a broad scale there exist two subgroups depending the presence or absence of the vascular tissue (made up of Xylem and Phloem cells which are responsible for the transport of water + minerals and photosynthetic products respectively, within the plant): a) Non-vascular plants b) Vascular plants a) Non-vascular plants Plants within this group lack major structures present in higher plants such as roots, flowers, fruits etc. and since they do not posses vascular tissues, they either live in water or only in very moist environments. This group in turn is further subdivided into 3 subgroups: i) Brown & Red Algae ii) Green Algae iii) Mosses, Liverworts and their allies i) Brown & Red Algae Brown and Red Algae are primarily marine (live only in sea water) and are commonly known as SEAWEEDS (Slide 12). They are especially prevalent in the inter-tidal zones along rocky coasts, where they can easily be observed at low tide. Their colors are due to the brown and red pigments, which often mask the chlorophyll these algae also contain. ii) Green Algae Green algae are relatively simple plants that live only in water or in very moist environments on land. Some are unicellular, others multicellular (Slide 13). In multicellular green algae, most of the cells are similar to one another and are not highly specialized; they form what might be considered as a single continuous tissue, which is the plant body. The plants are green because their chlorophyll is not masked by accessory pigments like the browns and reds. In this and many other biochemical characteristics, the green algae are similar to the higher land plants and most botanists agree that it was probably from ancestral green algae that the land plant groups arose. iii) Mosses, Liverworts and their allies (Slide 14) Although these plants live on land, their survival is strictly dependent on moisture and shade. One reason is that parts of their reproductive cycle is dependent on abundant moisture another is that, on land, because of the lack of vascular system, they could only obtain water through the moisture surrounding the plants. b) Vascular Plants Of all members of the plant kingdom, the vascular plants show the greatest internal specialization into tissues and organs- roots, stems, leaves and reproductive organs (cones, flowers). Because they posses vascular tissue, which provides conduits in which water and dissolved substances can move from one part of the plant body to another, they are less dependent than the other plant groups on water in the surrounding environment. They are the dominant plant group on land today. Vascular plants are divided into 3 subgroups: The FERNS, the conifers and their allies (GYMNOSPERMS), and the flowering plants (ANGIOSPERMS). Of these 3 groups, the ferns are the most primitive (Slide 15); they appeared on the ancient earth before the other 2 groups and dominated the land for a long time. Eventually, they gave way to the other groups, first to gymnosperms and then to angiosperms and are now largely overshadowed by them. The gymnosperms and the flowering plants are collectively called as the SEED PLANTS; they are more highly specialized for a terrestrial existence than the ferns. Some common gymnosperms are Pine, Cedar, Spruce (Slide 16) and fir; all of these bear cones and have needle-like leaves, though not all gymnosperms do (e.g. Ginkgo biloba Slide 16). The angiosperms; or the FLOWERING PLANTS, are the most advanced of the three groups. The majority of the land plants familiar to you belong to this group which includes plants of every shape and size from grasses to cacti and from tiny herbs and wild flowers to large oak and maple trees. This huge and very diverse group of Angiosperms is customarily divided into two subgroups: DICOTYLEDONS (Dicots for short), which include beans, peas, roses, maple trees, oak trees, potatoes and a great variety of other plants (Slide 17); and the MONOCOTYLEDONS (Monocots), which include the grasses and grass-like plants such as corn, lilies, wheat, barley, rice and the palm trees(Slide 18). The two subgroups differ in many characteristics including three that are easily observable (Slide 19): 1) The seeds of dicots are composed of two halves (actually the name of the group comes from this characteristic) whereas the monocots have a whole single seed structure. 2) The leaves of dicots usually show a network of veins, whereas monocots usually show parallel veins. 3) The petals (colored leaves of flowers) of dicots occur in fours or fives (or multiples) whereas in monocots petal number is three or multiples of three. 5) ANIMALIA KINGDOM Of many characteristics that distinguish the animals from the plants and fungi we shall here mentioned but two; First: Animal cells lack a rigid cell wall Second: The principle mode of nutrition in animals is digestion of food; most plants, by contrast depend on photosynthesis and most fungi on absorption. This kingdom also divided in to subgroups according to their degree of complexity. A) COELENTERATES The coelenterates constitute a large group of primitive aquatic (in the water: sea or fresh water) animals whose body plan is radially symmetrical rather than the bilateral symmetry most other animals display (Slide 20). These animals have a sac-like body with only one opening which serves both as the mouth and the anus. Tentacles often present around this opening and are used in capturing prey. The nerves and muscles of these animals are exceedingly primitive and no circulatory system is present. The group includes, jelly fish, sea anemones and corals (marine forms: Slide 21). A fresh water form of coelenterates is the hydra (Slide 22). B) FLATWORMS The flatworms are more complex than the coelenterates in some ways, but they too have a digestive tract with only one opening. Many flatworms, such as tapeworms (Slide 23), are parasites and show numerous interesting specializations for this mode of existence. Others such as planarians (Slide 24) are small free-living non-parasitic aquatic organisms. C) MOLLUSCS Members of this group are fairly complex animals, most of which have shells. Some examples that do have shells are snails and oysters (Slide 25), as well as octopuses and squids (Slide 25), which do not have obvious shells. These animals are particularly abundant in the oceans but they are also common in freshwaters. Over time, some snails have evolved lungs and have become fully terrestrial.  D) ANNELIDS The annelids are often called segmented worms and as this term implies, the bodies of these highly evolved organisms are divided into a series of units, or segments, which are often clearly visible externally (Slide 26). Though most annelids are aquatic, some such as earthworms, occur in land, but always in moist places. One parasitic example is the leeches (Slide 26). E) ARTHROPODS The arthropods constitute an immense group of very advanced animals that includes more different species than all other animal groups combined. All arthropods have jointed legs and a hard outer skeleton. Spiders, scorpions, crabs, lobsters, crayfish (Slide 27) and INSECTS (Slide 28) all belong to this major group. Of these, insects are by far the largest subgroup; they are the most successful of all land animals rivaled only by the mammal, particularly humans. F) ECHINODERMS All echinoderms are strictly marine; they have apparently never been able to invade either the freshwater or the terrestrial habitats. The group includes sea stars or starfish, sea urchins, sea cucumbers and a variety of other forms (Slide 29).  G) CHORDATES This very important group contains a major subgroup called the VERTEBRATES, which comprises all animals possessing an internal body skeleton, particularly a backbone. Fish (Slide 30), amphibians (e.g. frogs and salamanders (Slide 31)), reptiles (e.g. snakes, lizards, turtles and alligators (Slide 32)), birds (Slide 33) and mammals (including humans (Slide 34)) belong to this group. -END OF CHAPTER I-