Title Med-RM_Bot_SP-1_Ch-3_The Living World.pdf ✅

Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter Contents The world of living beings is a world of interdependence and relatedness. It includes a large number of diverse and fascinating organisms. All of these organisms are, or should be important to us. Millions of plants and animals have been identified and described but a large number still remains unknown. The wide range of organisms in terms of size, colour, habitat, physiological and morphological features make us seek the defining characteristics of living organisms. So, in this chapter, in order to easily understand the kinds and diversity of organisms we shall study about certain rules and principles of identification, nomenclature and classification of organisms; taxonomic hierarchy, species concept, conservation and preservation of organisms for taxonomic study etc. WHAT IS LIVING? Life is a unique, complex organisation of molecules expressing itself through chemical reactions (metabolism) which lead to growth, development, responsiveness, adaptation and reproduction. Hence, “the object by itself exhibiting the growth, development, death, consciousness, reproduction etc. is designated as living being.” Characteristics of Living Beings 1. All the living organisms whether unicellular or multicellular grow by cell division. The pattern and duration of growth is distinct in different organisms like in plants growth can occur throughout their lifespan whereas in animals this can be seen only upto a certain age. In majority of higher animals and plants, growth and reproduction are mutually exclusive events, but in unicelled organisms like Amoeba, reproduction is synonymous with growth. Non-living objects also grow if we take increase in body mass as a criterion of growth. But in these objects growth is reversible and extrinsic i.e. increase in the mass of body from outside e.g., snow What is Living? Diversity in the Living World Taxonomic Categories Taxonomical Aids Chapter 3 The Living World
72 The Living World NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 mountains grow by addition of snow on them, and sand dunes increase by deposition of more sand on them. Growth, therefore, cannot be taken as a defining property of living organisms. 2. Reproduction : Reproduction is the formation of new individuals of similar kind. It is, however, required for survival of the population as it compensates for the loss of life due to death. Reproduction is of two types, asexual and sexual. Asexual reproduction is uniparental, that can occur through binary fission, multiple fission, spore formation, fragmentation and vegetative multiplication. Fungi multiply by asexual spores, yeast and Hydra show budding, Planaria exhibits true regeneration. Filamentous algae and fungi and protonema of mosses easily multiply by fragmentation. In such processes, parent body undergoes division to form two or more individuals i.e., number of cells increases. Reproduction is shown by all living organisms except a few which are sterile or infertile like mule, worker bees, infertile couples etc. Hence, reproduction can be regarded as characteristic of living organisms but it is not their exclusive defining characteristic. 3. Metabolism : It is the sum total of all chemical reactions occurring in an organism due to specific interactions amongst different types of molecules within the interior of cells. All living organisms from unicellular to multicellular possess metabolism of their own kind. Metabolism includes both anabolism and catabolism. Metabolic reactions can be demonstrated outside the body in cell free systems. An isolated metabolic reaction(s) in a test-tube is neither living nor non-living. But surely a living reaction. Hence, metabolism is a defining feature of all living organisms without exception. 4. Cellular organisation : Body of all living organisms consists of cells and their products. Hence, cellular organisation of the body is the defining feature of life forms. 5. Consciousness : Most obvious and technically complicated feature of all living organisms. All living beings, plants and animals, are aware of their environment. They sense their surroundings and can respond to them. Any change that can be detected by an organism is called stimulus. Organisms can respond by showing movements or behavioural changes in respect to stimuli. For instance, some plants like soyabean, radish etc. or animals like sheep, goat, horse etc. breed or reproduce in specific seasons only like in winters, summers, autumn. Hence, they are known as seasonal breeders as their reproductive behaviour changes with length of the day i.e, photoperiod. Humans have self consciousness along with awareness of the surroundings. Sensitivity or awareness is regarded as defining property of living organisms as non-living do not have power of sensing their surroundings and give response according to it. However, patients lying in coma in hospitals virtually supported by machines which replace heart and lungs are neither living nor dead otherwise brain-dead. All living phenomena are due to underlying interactions. Properties of tissues are not present in the constituents cells but arise as a result of interactions among the constituent cells. Similarly properties of cellular organelles are not present in the molecular constituents of the organelle but arise as a result of interactions among the molecular components comprising the organelle. These interactions result in emergent properties at a higher level of organisation. This phenomenon is true in the hierarchy of organisational complexity at all levels. Therefore, the living organisms can be said to be self-replicating, evolving and interactive systems capable of responding to external stimuli. All living organisms-present, past and future are linked to one another by the sharing of the common genetic material, but to varying degrees.
NEET The Living World 73 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 DIVERSITY IN THE LIVING WORLD According to IUCN, approximately 1.7 to 1.8 million species have been scientifically named and classified. Biodiversity is the number and various kinds of organisms found on earth. As we recognize the plants or animals in one area by their local names, which vary from place to place. Hence, these is a need to standardise the names of all living organisms after proper identification. The scientific need for simple, stable and internationally accepted systems for naming the living organisms of the world has generated, a process called ‘‘Nomenclature’’. And, before assigning a specific name to an organism, one should determine or know its kind or features correctly, so that one can identify it in each and every part of the world. This is known as ‘‘Identification’’. Nomenclature There is a need to standardize the naming of living organisms, such that a particular organism is known by same name all over the world. Binomial system of nomenclature : Swedish naturalist Carolus Linnaeus established binomial nomenclature though, it was first proposed by Casper Bauhin in his book PINAX. In binomial nomenclature, the first word is a generic name and second word is a specific epithet like Mangifera indica Linn. After end of biological name, the name of author is written in abbreviated form who first described that organism. International Code of Nomenclature Scientific names have been standardised through some international agencies, viz., International Code of Botanical Nomenclature (ICBN, 1961) and International Code of Zoological Nomenclature (ICZN, 1964), International Code for Nomenclature of Bacteria (ICNB), International Code of Nomenclature for Cultivated Plants (ICNCP) and International Code of Virus Classification and Nomenclature (ICVCN). Rules for Binomial Nomenclature ICBN and ICZN formulated certain rules and regulations for giving scientific names to all organisms. These rules are as follows : (i) Biological names are generally taken from Latin language irrespective of their origin. New names are now derived either from Latin language or Latinised. (ii) The valid name of an organism has two components, i.e., a generic name and a specific epithet. The generic name should begin with a capital letter and species name should begin with a small letter. (iii) Both the words in a biological name when handwritten are separately underlined or printed in italics to indicate their Latin origin. (iv) The name of the author should be written after the scientific name in Roman type with capital letter without any comma in between and is written in an abbreviated form, e.g., Homo sapiens Linn. is the complete scientific name for modern man. This shows that Linnaeus was the first scientist who described Homo sapiens. (v) Principle of priority : It is the most important of all the rules of ICBN. If first name given to the organism is valid (in terms of rules), that will be considered at the first preference. Any other valid name given after that will be considered as synonym. No names are recognised prior to those used by Linnaeus in 1758 in the 10th edition of Systema Naturae for animals and 1753 for plants in Species Plantarum. (vi) All the three words (generic name, species epithet and author citation) collectively form binomial epithet. (vii) If a species name has two or more words in its name, a hyphen is put between these. Such names are compound specific names (e.g., Hibiscus rosa – sinensis).
74 The Living World NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 Classification It is not possible to find out an organism of known characters from the vast number of organisms. A clearer understanding of this huge variety of organisms can be studied by dividing these into smaller groups or sub-groups (categories) and each group or sub-group comprising of organisms with more or less similar characters. This method of placing organisms into groups or sub-groups depending upon extent of similarities and differences is called classification. The division of organisms into different groups follows certain rules, that is why the term called taxonomy is used for classification of organisms following certain rules or principles. The classical taxonomy is based on observable morphological characters whereas modern taxonomic studies are based on some essential features like study of both external and internal structure of organisms along with their cell structure, development process and ecological information of organisms. Hence, characterisation, identification, classification and nomenclature are the processes that are basic to taxonomy. Human beings had not only studied different kinds of organisms but also tried to find out relationships among them. This led to the development of a new branch of study in science field, known as “Systematics”. The word systematics is derived from Latin word “Systema” which means systematic arrangement of organisms. It was first used by Carolus Linnaeus in the title of his book published as “Systema Naturae”. Systematics is more wider field of science as with identification, nomenclature and classification, it also takes into account evolutionary relationships between various organisms. “Systematics” is the science which deals with diversity of organisms and all their comparative and evolutionary relationships amongst them. Derived from two Greek words ‘taxis’ and ‘nomos’. Includes characterisation, identification, nomenclature and classification of organisms. Derived from Latin word ‘systema’. Includes characterisation, identification, nomenclature, classification of organisms alongwith their evolutionary study. 1. 2. 1. 2. Taxonomy Systematics Note : 1. The reasons for large scale biodiversity amongst living beings are : (a) Adaptations in organisms to diverse habitat in order to reduce competition. (b) Change in genetic constitution. (c) Isolation 2. Ontogeny is the life history of organisms. Phylogeny is the evolutionary history of organisms. 3. Systematics is taxonomy alongwith phylogeny. 4. Classical or old or descriptive systematics is based upon morphological characters. According to it basic unit of classification is species. Pioneer workers are Aristotle and Linnaeus. 5. New systematics / Biosystematics / Neosystematics is based upon all characters, i.e., morphological, cytological, ecological, biochemical, genetical etc. The term was coined by Julian Huxley. Basic unit of classification is population or sub-species for the new systematics.