The Living World

What is ‘Living’?

• Growth, reproduction, ability to sense environment and mount a suitable response come to our mind immediately as unique features of living organisms. One can add a few more features like metabolism, ability to self-replicate, self-organise, interact and emergence to this list.
• All living organisms grow. Increase in mass and increase in number of individuals are twin characteristics of growth. In plants, this growth by cell division occurs continuously throughout their life span. In animals, this growth is seen only up to a certain age.
• Unicellular organisms grow by cell division.
• In majority of higher animals and plants, growth and reproduction are mutually exclusive events.
• In living organisms, growth is from inside. Growth, therefore, cannot be taken as a defining property of living organisms. 
• Reproduction, likewise, is a characteristic of living organisms. Reproduction refers to the production of progeny possessing features more or less similar to those of parents.
• Invariably and implicitly we refer to sexual reproduction.
• Organisms reproduce by asexual means also.
• Fungi multiply and spread easily due to the millions of asexual spores they produce.
• In lower organisms like yeast and hydra, we observe budding. In Planaria (flat worms), we observe true regeneration, i.e., a fragmented organism regenerates the lost part of its body and becomes, a new organism.
• The fungi, the filamentous algae, the protonema of mosses, all easily multiply by fragmentation.
• Reproduction also cannot be an all-inclusive defining characteristic of living organisms.
• Of course, no non-living object is capable of reproducing or replicating by itself.
• Another characteristic of life is metabolism. All living organisms are made of chemicals. These chemicals, small and big, belonging to various classes, sizes, functions, etc., are constantly being made and changed into some other biomolecules.
• The sum total of all the chemical reactions occurring in our body is metabolism. No non-living object exhibits metabolism.
• Hence, while metabolism is a defining feature of all living organisms without exception, isolated metabolic reactions in vitro are not living things but surely living reactions. Hence, cellular organisation of the body is the defining feature of life forms.
• Plants respond to external factors like light, water, temperature, other organisms, pollutants, etc.
• Consciousness therefore, becomes the defining property of living organisms. 
• Living organisms are self-replicating, evolving and self- regulating interactive systems capable of responding to external stimuli.

Diversity in the Living World

• The number of species that are known and described range between 1.7-1.8 million. This refers to biodiversity or the number and types of organisms present on earth. Types of organisms present on earth.
• There is a need to standardise the naming of living organisms such that a particular organism is known by the same name all over the world. This process is called nomenclature.
• Nomenclature or naming is only possible when the organism is described correctly and we know to what organism the name is attached to. This is identification.
• In order to facilitate the study, number of scientists have established procedures to assign a scientific name to each known organism. This is acceptable to biologists all over the world.
• For plants, scientific names are based on agreed principles and criteria, which are provided in International Code for Botanical Nomenclature (ICBN).
• Animal taxonomists have evolved International Code of Zoological Nomenclature (ICZN).
• The scientific names ensure that each organism has only one name.
• Each name has two components - the Generic name and the specific epithet. This system of providing a name with two components is called Binomial nomenclature. 
• Carolus Linnaeus is being practised by biologists all over the world.
• This naming system using a two word format was found convenient.
• Example of mango to understand the way of providing scientific names better. The scientific name of mango is written as Mangifera indica.
• In this name Mangifera represents the genus while indica, is a particular species, or a specific epithet.
• Other universal rules of nomenclature are as follows:
• Biological names are generally in Latin and written in italics. They are Latinised or derived from Latin irrespective of their origin.
• The first word in a biological name represents the genus while the second component denotes the specific epithet. 
• Both the words in a biological name, when handwritten, are separately underlined, or printed in italics to indicate their Latin origin.
• The first word denoting the genus starts with a capital letter while the specific epithet starts with a small letter. It can be illustrated with the example of Mangifera indica.
• Name of the author appears after the specific epithet, i.e., at the end of the biological name and is written in an abbreviated form, e.g., Mangifera indica Linn. 
• It indicates that this species was first described by Linnaeus.
• Classification is the process by which anything is grouped into convenient categories based on some easily observable characters.
• The scientific term for these categories is taxa.
• Wheat is also a taxa. Similarly, ‘animals’, ‘mammals’, ‘dogs’ are all taxa - but you know that a dog is a mammal and mammals are animals. Therefore, ‘animals’, ‘mammals’ and ‘dogs’ represent taxa at different levels.
• Based on characteristics, all living organisms can be classified into different taxa. This process of classification is taxonomy.
• Characterisation, identification, classification and nomenclature are the processes that are basic to taxonomy.
• Human beings were, since long, not only interested in knowing more about different kinds of organisms and their diversities, but also the relationships among them. This branch of study was referred to as systematics. The word systematics is derived from the Latin word ‘systema’ which means systematic arrangement of organisms.
• Linnaeus used Systema Naturae as the title of his publication.
• The scope of systematics was later enlarged to include identification, nomenclature and classification. Systematics takes into account evolutionary relationships between organisms.

Taxonomic Categories

• Classification is not a single step process but involves hierarchy of steps in which each step represents a rank or category. Since the category is a part of overall taxonomic arrangement, it is called the taxonomic category and all categories together constitute the taxonomic hierarchy.
• Each category, referred to as a unit of classification, in fact, represents a rank and is commonly termed as taxon (pI.: taxa).
• Category further denotes rank. Each rank or taxon, in fact, represents a unit of classification. These taxonomic groups I categories are distinct biological entities and not merely morphological aggregates.
• Taxonomical studies of all known organisms have led to the development of common categories such as kingdom, phylum or division (for plants), class, order, family, genus and species.
• All organisms, including those in the plant and animal kingdoms have species as the lowest category.

Species

• Taxonomic studies consider a group of individual organisms with fundamental similarities as a species. Species is the lowest or basic taxonomic category comprising of one or more natural population of individuals that interbreed freely.
• Mangifera indica, Solanum tuberosum (potato) and Panthera lea (lion). All the three names, indica, tuberosum and leo, represent the specific epithets, while the first words Mangifera, Solanum and Panthera are genera and represents another higher level of taxon or category.
• Each genus may have one or more than one specific epithets representing different organisms, but having morphological similarities. 
• Panthera has another specific epithet called tigris and Solanum includes species like nigrum and melongena.
• Human beings belong to the species sapiens which is grouped in the genus Homo. The scientific name thus, for human being, is written as Homo sapiens.

Genus

• Genus comprises a group of related species which has more characters in common in comparison to species of other genera.
• Potato and brinjal are two different species but both belong to the genus Solanum. Lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris) with several common features, are all species of the genus Panthera. This genus differs from another genus Felis which includes cats.

Family

• Family, has a group of related genera with still less number of similarities as compared to genus and species.
• Families are characterised on the basis of both vegetative and reproductive features of plant species.
• Three different genera Solanum, Petunia and Datura are placed in the family Solanaceae. Among animals for example, genus Panthera, comprising lion, tiger, leopard is put along with genus, Felis (cats) in the family Felidae.

Order

• Order being a higher category, is the assemblage of families which exhibit a few similar characters. The similar characters are less in number as compared to different genera included in a family.

Class

• This category includes related orders. For example, order Primata comprising monkey, gorilla and gibbon is placed in class Mammalia along with order Carnivora that includes animals like tiger, cat and dog. Class Mammalia has other orders also.

Phylum

• Classes comprising animals like fishes, amphibians, reptiles, birds along with mammals constitute the next higher category called Phylum.
• Based on the common features like presence of notochord and dorsal hollow neural system, are included in phylum Chordata.

Kingdom

• All animals belonging to various phyla are assigned to the highest category called Kingdom Animalia in the classification system of animals.
• The Kingdom Plantae, on the other hand, is distinct, and comprises all plants from various divisions.

Taxonomic categories showing hierarchical arrangement in ascending order

• The biological organization starts with the submicroscopic molecular level, where four types of molecules, i.e. carbohydrates, lipids, proteins, and nucleic acid are organized into organelles of the cell. Hence, biological organization begins at Submicroscopic molecular level.
• These are broad categories.
• Lower the taxa, more are the characteristics that the members within the taxon share.
• Higher the category, greater is the difficulty of determining the relationship to other taxa at the same level. Hence, the problem of classification becomes more complex.

Organisms with their Taxonomic Categories

• Muscidae are a family of flies such as house flies. Firefly belongs to the family lampyridae, grasshopper is present in the family of acrididae and cockroach is kept in Blattidae family.

Taxonomical AIDS

• Taxonomic studies of various species of plants, animals and other organisms are useful in agriculture, forestry, industry and in general in knowing our bio-resources and their diversity. The collection of actual specimens of plant and animal species is essential and is the prime source of taxonomic studies.
• It is used for classification of an organism, and the information gathered is also stored along with the specimens.

Herbarium

• Herbarium is a store house of collected plant specimens that are dried, pressed and preserved on sheets. 
• These sheets are arranged according to a universally accepted system of classification.
• These specimens, along with their descriptions on herbarium sheets, become a store house or repository for future use.

Botanical Gardens

• These specialized gardens have collections of living plants for reference.
• Plant species in these gardens are grown for identification purposes and each plant is labelled indicating its botanical/scientific name and its family.
• The famous botanical gardens are at Kew (England), Indian Botanical Garden, Howrah (India) and at National Botanical Research Institute, Lucknow (India).

Museum

• Biological museums are generally set up in educational institutes such as schools and colleges.
• Museums have collections of preserved plant and animal specimens for study and reference.
• Specimens are preserved in the containers or jars in preservative solutions.
• Plant and animal specimens may also be preserved as dry specimens.
• Insects are preserved in insect boxes after collecting, killing and pinning. Larger animals like birds and mammals are usually stuffed and preserved. Museums often have collections of skeletons of animals too.

Zoological Parks

• These are the places where wild animals are kept in protected environments under human care and which enable us to learn about their food habits and behaviour.
• Children love visiting these parks commonly called zoos Figure 1.3.

Key

• Key is another taxonomical aid used for identification of plants and animals based on the similarities and dissimilarities.
• The keys are based on the contrasting characters generally in a pair called couplet.
• It represents the choice made between two opposite options.
• Each statement in the key is called a lead.
• Separate taxonomic keys are required for each taxonomic category such as family, genus and species for identification purposes. Keys are generally analytical in nature.
• Flora, manuals, monographs and catalogues are some other means of recording descriptions. They also help in correct identification.
• Flora contains the actual account of habitat and distribution of plants of a given area. These provide the index to the plant species found in a particular area.
• Manuals are useful in providing information for identification of names of species found in an area. Monographs contain information on anyone taxon.

Tips/Tricks/Techniques ONE-Liners

(Exam special)

• Born on 5 July 1904, in Kempten, Germany, Ernst Mayr, the Harvard University evolutionary biologist who has been called ‘The Darwin of the 20th century’, was one of the 100 greatest scientists of all time.
• Carrolus Linnaeus, a Swedish naturalist is Father of taxonomy, He coined the terms ‘class’ and ‘systematics’.
• Tautonym- It defined as a binomial name in which the names of genus and species are the same. For example: Gorilla gorilla.
• Trinomial nomenclature- It includes genus, species and subspecies and is applicable to animal only.
• Monographs (information on anyone taxon), manuals (information for identifying species in an area), flora (account of habitat and distribution of plants of a given area) and catalogue are some other useful taxonomic aids.