Chapter – 1 – Living world

Criteria that Determines What Is Living The following criteria determine whether a thing is living or not:

• A living thing is able to maintain the internal environment of the body. This is known as homeostasis. • The structure of a living thing is highly organized. • It should be able to breakdown or build-up nutrients to carry out the metabolic activities. • It should have the ability to adapt to changing environmental conditions. • It should have the ability to respond to external stimuli. • It should be able to increase in size and mass.

What is Binomial Nomenclature? The system of binomial nomenclature was introduced by Carl Linnaeus. Multiple local names make it extremely difficult to identify an organism globally and keep a track of the number of species. Thus, it creates a lot of confusion. To get rid of this confusion, a standard protocol came up. According to it, each and every organism would have one scientific name which would be used by everyone to identify an organism. This process of standardized naming is called as Binomial Nomenclature. All living species including plants, animals, birds and also some microbes have their own scientific names. For eg.,

• The scientific name of the tiger is presented as Panthera tigris. ‘Panthera’ represents the genus and ‘Tigris’ represents a particular species or specific epithet. • The scientific name of humans is presented as Homo sapiens. ‘Homo’ represents the genus and ‘sapiens’ represents a particular species. • The Indian bullfrog is scientifically written as Rana tigrina. ‘Rana’ is the name of the genus and ‘tigrina’ is the name of the specific species.

Rules of Binomial Nomenclature A Biologist from all over the world follows a uniform set of principles for naming the organisms. There are two international codes which are agreed upon by all the biologists over the entire world for the naming protocol. They are:

• International Code of Botanical Nomenclature (ICBN) – Deals with the biological nomenclature for plants. • International Code of Zoological Nomenclature (ICZN) – Deals with the biological nomenclature of animals.

These codes make sure that each organism gets a specific name and that name is globally identified. The naming follows certain conventions. Each scientific name has two parts:

• Generic name • Specific epithet The rest of the binomial nomenclature rules for writing the scientific names of organisms include the following:

1. All the scientific names of organisms are usually Latin. Hence, they are written in italics. 2. There exist two parts of a name. The first word identifies the genus and the second word identifies the species. 3. When the names are handwritten, they are underlined or italicized if typed. This is done to specify its Latin origin. 4. The name of the genus starts with a capital letter and the name of the species starts with a small letter.

Drawbacks of Binomial Nomenclature Some of the basic drawbacks of binomial nomenclature are:

• If two or more names are currently in use, according to the law of priority, the correct name will be the one used first and the others end up being synonyms as validity is the senior synonym. Providing stability in the naming and classification of organisms must be emphasized. • Also, the names used prior to those included in the “Systema Naturae”, by Linnaeus are not recognized.

What is Taxonomic Hierarchy? The word “Taxonomy” is derived from a Greek word – “taxis”, meaning arrangement or division, and “nomos”, meaning method. Taxonomy is a branch of Biology that refers to the process of classifying different living species. A taxon is referred to as a group of organisms classified as a unit. “Taxonomic hierarchy is the process of arranging various organisms into successive levels of the biological classification either in a decreasing or an increasing order from kingdom to species and vice versa.” Each of this level of the hierarchy is called the taxonomic category or rank. In this system of classification, kingdom is always ranked the highest followed by division, class, order, family, genus, and species.

Taxonomic Hierarchy

Taxonomic Hierarchy Categories Following are the important taxonomic hierarchies in which different organisms are classified:

Kingdom The kingdom is the highest level of classification, which is divided into subgroups at various levels. There are 5 kingdoms in which the living organisms are classified, namely, Animalia, Plantae, Fungi, Protista, and Monera.

Phylum This is the next level of classification and is more specific than the kingdom. There are 35 phyla in kingdom Animalia. For Example – Porifera, Chordata, Arthropoda, etc.

Class Class was the most general rank in the taxonomic hierarchy until phyla were not introduced. Kingdom Animalia includes 108 classes including class mammalia, reptilia, aves, etc. However, the classes used today are different from those proposed by Linnaeus and are not used frequently.

Order Order is a more specific rank than class. The order constitutes one or more than one similar families. There are around 26 orders in class mammalia such as primates, carnivora, etc.

Family This category of taxonomic hierarchy includes various genera that share a few similarities. For eg., the families in the order Carnivora include Canidae, Felidae, Ursidae, etc.

Genus A group of similar species forms a genus. Some genera have only one species and is known as monotypic, whereas, some have more than one species and is known as polytypic. For eg., lion and tiger are placed under the genus Panthera.

Species It is the lowest level of taxonomic hierarchy. There are about 8.7 million different species on earth. It refers to a group of organisms that are similar in shape, form, reproductive features. Species can be further divided into sub-species.

Examples of Taxonomic Hierarchy Following are some of the examples of taxonomic hierarchy:

Taxonomic Hierarchy Examples

Kingdom Animalia

Phylum Chordata

Class Mammalia

Order Primates

Family Hominidae

Genus Homo

Species sapiens

TAXONOMICAL AIDS

The taxonomical Aids are the main source which helps us in studying the relative level of a group of organisms, their taxonomic hierarchy and the taxonomic rank. Taxonomical Aids are required for:

1. Taxonomic studies of various species of plants, animals, and other organisms, which require correct classifications and identification. 2. Identification of organisms require laboratory and field studies. 3. Museum. 4. Herbarium. 5. Zoological Parks. 6. Botanical Gardens.

Let us study some of the taxonomical aids which provide specimens for such intensive studies.

Types of Taxonomical Aids

Herbarium It is a store that houses a collection of preserved plant species. Plant specimens are preserved in forms of herbarium sheets which are prepared by drying, pressing and preserving the samples on sheets. These sheets are then arranged in their order of classification in the taxonomic hierarchy. These herbarium sheets carry all the information about the respective specimen.

Botanical garden These are gardens in which specific plants are grown and are labeled according to their taxonomy. Thus, the labels carry their scientific names and family. The main purpose of botanical gardens is to identify the plant species under consideration.

Museum Biological museums are found in schools and colleges; like the biology laboratory that we find in our schools. In these museums, plants and animal species are preserved in jars and containers with the help of appropriate preservatives. They may also be dried and preserved. Birds and larger animals are usually stuffed before preserving and insects are killed and pinned in boxes. We sometimes find skeletons of various animals too.

Zoological park These are places where animals and birds are kept in protected boundaries. An attempt is made to provide them with a habitat closest to their natural habitats. Thus, we get a chance to learn about their natural habits and behaviour. Zoological parks are open for human visits.

Key This is a taxonomical aid where plants and animals are recognized based on contrasting characteristics known as keys. Two contrasting keys are generally kept as a pair, thus leading to acceptance of once and rejection of another. Stay tuned with BYJU’S to learn more about Taxonomy, Taxonomic Hierarchy and Taxonomical Aids.