Introduction to Living Organisms:
The world of Living things is extremely huge in numbers, old in history, and complicated in diversity. Science of biology has several disciplines, all trying to give true picture of nature of living things. The informal examination of living organisms will expose a wide variety of plants and animals varying in sizes, shapes, colour, speed of locomotion, etc. Also, they exhibit some similarities of features or behaviours. Therefore in this unit, we shall be looking at the various methods of classification of living organisms, and the characteristics of each group by which it can be identified.
Classifications of Living Organisms:
More than 1.8 million kinds of living organisms have been examined and described. There are still many more to be discovered and described, therefore, we must have a meaningful way of classifying, identifying and naming them. Aristotle (384-322 BC) a Greek philosopher, was the first to make an attempt to classify living organisms. The present method of classifying and naming living organisms is based on the work of Linnaeus (1707-1778), a Swedish naturalist. The study of the general principle of classification is known as taxonomy or systematic.
Hierarchy of Living Organisms:
Kingdom has the largest group of organisms. Each kingdom is split into smaller groups, and these groups into even smaller groups and so on. The arrangement of living organisms in this hierarchy from the highest to the lowest is as follows:
Kingdomà Phylum or Division (Plants)à ClassàOrder àClassà Genus àSpecies
As we go down variety of organisms reduces. The kingdom has largest diversity of organisms. They have certain significant characteristics in common but illustrate several differences. The species is smallest unit of categorization. They are indistinguishable in general form.
This is the use of the standard system to name living organisms however we are familiar with common names of living organisms like Goat, Mango, Lion, Pawpaw, etc. In Binomial Nomenclature, every kind of organisms is provided two names: first name is genus to which organism belongs and second been species to which it belongs. On genius name starts with the initial capital letter, therefore scientific name of Pawpaw is Carica Papaya, Lizard - Agama agama. Names are written in italics or underlined separately.
Kingdoms of Living organisms:
Every living organism were placed into 2 kingdoms by Linnaeus. Kingdom was plants and animals. This is called as 2 - kingdom classification. In this categorization, several one-celled organisms couldn't fit in properly; it failed to set up clear-cut difference between plants and animals. It also couldn't point to right relations among organisms. Whittaker suggested five- kingdom categorization that is commonly utilized at present. Categorizations are:
Kingdom Monera has prokaryotes - That are very simple -celled organisms whihc has no true nuclei. Eukaryotes- that cells are extremely prepared with definite or true nuclei are categorized into 4 remaining kingdom: fungi, protist, animalia and plantae.
The features of Five - Kingdom Organisms
i) Kingdom Monera (Prokaryotes):
Single- Celled organisms, motile or non-motile, microscopic
Simple - Celled Structure with no definite nucleus. Examples comprises Bacteria, Blue-green algae, actinomycetes
ii) Kingdom Protista (Eukaryotes):
Single -Celled, motile or non-motile. Organisms are much larger than monerans. Complicated Cell Structure with the definite nucleus. Examples comprises: Chlamydomonas, Amoeba
iii) Kingdom Fungi (Eukaryotes):
Non-motile organisms generally of thread-like structure or hyphae. Plant- like but can't perform photosynthesis because of absence of chlorophyll, get food through surface from living or non living organism source by absorption, reproduction could be by asexual or sexual or sexual spores. Examples comprises: Mushrooms, yeasts, moulds, shine moulds.
iv) Kingdom Plantae:
Many-celled, non-motile, get Chlorophyll which allows them make their own food by Photosynthesis. Plants include undefined growth. Examples comprises: Ferns, Pines, Mosses, Seed Plants (yam, bean, and plants).
Plants can readily be defined in context of the autotrophic mode of nutrition. They just transform light energy in chemical energy by fastening tightly in one place with maximum surface area to capture sunlight. Plants use cheapest material around, water and carbohydrate to make size. As plants are immobile, they are very receptive to ecological cues and have their life cycle in ideal synchrony with seasons.
Plants have the exclusive form of development. This engages providing by meristems at their tips. They have extraordinary power of regeneration. Any single plant cell can renew the complete plant with the cell kinds. The cells contain cellulose cell wall. Plant kingdom is chiefly categorised into:
Algaes, also called as Thallophytes are simple green plants. They are aquatic plants (lives in water) which are thread like or flat (thallus) bodies with no roots or stems. They live in damp places on land surface. They show the different alternation of generation. Sporophyte is always joined and dependant on gametophyte.
Although bryophytes colonized terrestrial habitats but they are still dependant on water for completion of the life cycle. They make motile gametes that need the thin film of water for the motility. Only in presence of the film of water male gamete can attain nonmotile female gamete to achieve fertilization. Because this reason, bryophytes are considered as amphibians.
Algae shows biological diversity and have skill to make the extensive variety of metabolic products, therefore they are widely exploital in biotechnology. Algae other utility comprises: the significant source of food for fresh water and marine organisms and supplies oxygen to them. Utilized as biofertilizer, for instance nitrogen fixing algae that Farmers can grow in the fields are utilized to develop soil Controlling pollution in water bodies and also in cleansing of sewage.
Tracheophytes (Pteridophytes, Gymnosperm and Angiosperm):
The tracheophytes are called as vascular plants. This is due to they possess vessels or vascular tissues for performing water and food. They are largest group of plants that comprises seed plants (flowering plants) and some spore-bearing, non flowering plants such as ferns.
Every animals belong to Animalia kingdom. They are multicellular, eukaryote heterotrophy (organism). They are short of photosynthetic pigments and get nutrients by ingesting other organisms. The Cells do not have cell wall. Many members show complex tissue separation and complicated organ systems and move about generously, they are distinguished by quick reply to stimuli, with specialized nervous tissue for synchronization. Development is determinate, generally with definite size and shape.
Animals are categorized into 2 Main Groups:
i) Invertebrata (invertebrate): animals with no backbone
ii) Vertebrata (vertebrate): animals with backbone
The division and subdivision of animals are based on numerous significant features comprising body symmetry, body design and body lavity.
Vertebrates comprise huge bulk of living chordates, and they have developed huge variety of forms. Backbone of vertebrates protects nerve cord and serves as axis of internal skeleton. Skeleton gives strength and rigidity to body and is the attachment site for muscles. Vertebrae in middle region of trunk give rise to pairs of ribs that surround and protect internal organs. The cartilaginous or bony case surrounds brain. Bone is the substance unique to vertebrates. It was previously supposed that vertebrates with cartilage skeletons (cyclostomes and shark like fishes) were descended from early vertebrates which had not yet evolved bone. Though, very primitive fishes with bone skeletons are recognized from fossil record, so lack of bone is now thought to be degenerate rather than primitive feature. All but most ancient vertebrates, called as jawless fishes, contain jaws and paired appendages. Fishes and, to the lesser extent, amphibians and reptiles illustrate the segmental arrangement of muscles of body wall and of nerves leading to them.
The 2 subphyla of invertebrate chordates, subphylum Urochordata (1250 species) and subphylum Cephalochordata (45 species), are short of vertebral column. Though unimportant and little known, the marine animals are of great scientific concern as it is usually accepted that the ancestors were close relatives of ancestral vertebrate. Studies of living invertebrate chordates have been very significant in helping to solve mystery of 'origin of vertebrates'.
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