THE LIVING WORLD

The Living World

Characteristics of Living Beings:

1. Growth: All living organisms grow in size and number. Some non-living things also grow. For example mountains develop over a period of time. But growth of non-living things is a result of accumulation of substances from outside. On the other hand growth of living beings comes from inside. A continuous process of cell division makes this growth possible. Most of the plants show growth in size throughout their life. But animals grow to a certain limit. After this the cell division facilitates repair in the organism.

2. Reproduction: All living beings reproduce their progeny. Progeny are more or less similar to their parents. Reproduction can be sexual or asexual. Most of the unicellular and less complex organisms reproduce by asexual methods. Multicellular and complex organisms reproduce by sexual methods. Reproduction by sexual method involves formation of male and female gametes and fusion of those gametes results in formation of zygotes, which ultimately give birth to the new progeny.

3. Metabolism: All living organisms are made of chemicals. These chemicals are constantly undergoing some change inside the body of a living organism. The process of this constant change is called metabolism. Metabolism can be classified in two types:

(a) Anabolism: The process which results in synthesis of something is called anabolism. Photosynthesis is a good example of anabolism as it involves synthesis of carbohydrates.

(b) Catabolism: The process which results in breaking down of a compound is called catabolism. Respiration is a good example of catabolism as it involves breaking down of carbohydrates into carbon-dioxide and water.

4. Response to Outside Stimuli: All living organisms show a response to outside stimulus. These stimuli can be light, heat, other organisms or chemicals. For example all green plants grow in the direction from which sunlight comes. All animals are sensitive to heat.

Diversity in the Living World

Biodiversity: The planet earth is full of variety of animals and plants. Every distinct geographical location has its own set of flora and fauna. This variety of living beings found in a given geographical area is called biodiversity of that area.

Nomenclature and Identification: Because of the huge diversity present in the living world it became necessary to develop a system to classify and name all plants and animals. International Code for Botanical Nomenclature has developed a system for identification and classification of plants. International Code of Zoological Nomenclature has developed a system for identifying and classifying the animals.

This system gives a unique name to each species. The name is called biological name and usually represented by two words. The first word always starts with a capital letter and the second word always starts with a small letter. Example; Mangifera indica is the biological name of mango. The word Mangifera indicates the genus and indica indicates the species.

Following are the general rules for nomenclature:

1. Biological names are generally in Latin and written in italics. They are Latinised or derived from Latin irrespective of their origin.

2. The first word in a biological name represents the genus while the second component denotes the specific epithet.

3. Both the words in a biological name, when handwritten, are separately underlined, or printed in italics to indicate their Latin origin.

4. The first word denoting the genus starts with a capital letter while the specific epithet starts with a small letter.

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 (pl.: taxa).

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. One should be able to distinguish one species from the other closely related species based on the distinct morphological differences. Let us consider Mangifera indica, Solanum tuberosum (potato) and Panthera leo (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. For example, 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 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. We can say that genera are aggregates of closely related species. For example, potato, tomato and brinjal are three different species but all 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

The next category, 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. Among plants for example, 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. Similarly, if you observe the features of a cat and a dog, you will find some similarities and some differences as well. They are separated into two different families – Felidae and Cancidae, respectively.

Order

Generally, order and other higher taxonomic categories are identified based on the aggregates of characters. 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. Plant families like Convolvulaceae, Solanaceae are included in the order Polymoniales mainly based on the floral characters. The animal order, Carnivora, includes families like Felidae and Cancidae.

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. All these, based on the common features like presence of notochord and dorsal hollow neural system, are included in phylum Chordata. In case of plants, classes with a few similar characters are assigned to a higher category called Division.

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.