Living World

1.1 Introduction:

• The world which contains life is known as the living world. It is also called earth or biosphere.

• Ernst Mayr called it “the Darwin of the 20th century”.

• The interplay of ecological conflicts and cooperation within a population, as well as the between populations within a community, or even the intricate molecular traffic within a cell, prompts profound reflection (deep and thoughtful consideration).

1.2 What is living?

• Living means having the characteristics of life. The word living is used especially to distinguish from non-living matter.

• The matter or things which have life is known as living things or living matter or living organisms.

• Definition: The living organisms are self-replicating, evolving and self-regulating 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.

1.2.1 General characteristics or unique features of living organisms:

1. Growth

2. Reproduction

3. Metabolism

4. Ability to sense environment and response

5. Self-replication

6. Self-organization

7. Interact and emergence (Appearance / arises).

8. Life span.

1.2.1.1 Growth:

• Growth is a process of irreversible increase in the size of an organism, or body mass, or number of individuals or formation of new cells.

• Twin characteristics of growth are increase in mass and increase in number.

• Multicellular organisms increase in size by cell division (Mitosis).

• Unicellular organisms increase in number by binary fission etc.,

• Growth in plants occurs continuously throughout their life span.

• Growth in animals only up to a certain age. But in animals few tissues or lost cells are replaced.

• Growth cannot be considered as a defining property of living organisms because non-living things also exhibit growth from outside. It occurs by the accumulation of material on the surface called accretion. Ex: Mountains, boulders and sand mounds do grow.

• Growth in living organisms occurs from inside. This proves that dead organisms do not grow.

• Growth is equivalent to increase in cell number or mass.

1.2.1.2 Reproduction:

• Reproduction is a biological process, the new individual or offspring or progeny give rise to their parents.

• Reproduction is synonymous to growth in unicellular organisms like bacteria, algae and amoeba because cell division itself is a mode of reproduction and increases in cell number (it is one twin character of growth).

• Reproduction is not considered as the defining property of living organisms because in nature so many creatures are unable to reproduce. Ex: Mules, worker bees, infertile couples etc.

• Reproduction is further divided into two types based on involvement of sex as follows;

1. Asexual reproduction and

2. Sexual Reproduction

1.2.1.2.1 Asexual Reproduction:

• Asexual reproduction is a mode of reproduction by which offspring arise from a single parent without involvement of sex.

• Asexual reproduction is divided into following types;

1. Binary fission

2. Fragmentation

3. Budding

4. Spores

i) Binary fission:

An one mother cell gives raises to two daughter cells by the process of mitosis is known as binary fission.

Ex: Bacteria’s, Amoeba etc.

ii) Fragmentation:

• In a few organisms, a single parent went fragmentation due to some external factors. Each fragment develops into new individuals.

• Ex: Plants, Star fish, Lichens, Oscillatoria, Planaria etc.

• In animals, fragmentation is called true regeneration.

• In plants, fragmentation is called vegetative propagation.

iii) Budding:

• A new individual develops from an outgrowth due to cell division at one particular site on the parental body is known as budding.

• The new individual separates from the parental body after maturity.

• Ex: Hydra, Yeast, Sycon, Sponges etc.

iv) Asexual Spores:

So many fungi’s and few algae’s multiply and spread easily by producing spores asexually 

Ex: Zoospores (Rhizopus) and Condia (penicillium).

1.2.1.2.2 Sexual Reproduction:

Sexual reproduction is another mode of reproduction by which offspring arise from a two parent with involvement of sex.

Ex: Humans, Birds, Cockroaches, Mosquitoes etc.

Note:

• In asexual reproduction, the progenies look the same as their parents (clones).

• In sexual reproduction, the progenies look similar to their parents.

1.2.1.3 Metabolism:

• Metabolism is the set of chemical reactions that occur within the cells of living organisms.

• The constant transformation of biomolecules from one form to another through chemical reactions constitutes metabolism.

• No non-living object exhibits metabolism due to this, metabolism considered as the defining property of all living organisms.

• There are thousands of metabolic reactions occurring simultaneously inside all living organisms.

• Metabolic reactions in-vitro (outside the body) are not living things but surely living reactions.

• Metabolism is usually divided into two categories based on utilizing or producing of energy;

1. Catabolism

2. Anabolism.

i) Catabolism:

Breakdown of complex organic matter into simple organic matter to produce energy is known as catabolism.

Ex: Digestion process of proteins, lipids, carbohydrates and nucleic acids.

ii) Anabolism:

The construction of complex organic matter from simple organic matters by using energy is known as anabolism.

Ex: Synthesis of proteins, lipids, carbohydrates and nucleic acids.

1.2.1.4 Ability to sense environment and response:

• All organisms from prokaryotes to the most complex eukaryotes can sense and respond to environmental changes.

• All living organism’s response to external factors like light, water, temperature etc.

• Living organism’s response to internal factors like infections, hunger etc.

• All organisms handle chemicals entering their bodies. So all organisms are aware of their surroundings (consciousness).

• Human beings are the only organism that is aware of themselves, i.e., has self-consciousness.

• Self-consciousness in humans is disproved in the case of coma patients because their brain is dead and life is supported with machines.

• Photoperiod affects reproduction in seasonal breeders, both plants and animals (Photoperiodism).

1.2.1.5 Self-replication (Gr: Replica = copy):

• Self replication is any behavior of a dynamical system (cell) that yields construction of an identical copy of itself (cell-division), with the help of nucleic acid (DNA/RNA).

• All living organisms show this phenomenon.

• It comes under anabolism.

1.2.1.6 Cellular Organization:

• Organisms are typically made up of cells.
• The cells contain cytoplasm and cell organelles inside it. These also perform cellular level processes in an organized manner.
• Some are composed of single cells and are called unicellular organisms while others are composed of many cells called Multicellular organisms.
• They also follow an organization of cells followed by tissues which form organs and in turn again combine to form the organ system.
• Organ systems together form an organism. This kind of cellular organization is absent in non living beings.
• Ex: nerve cells, muscles, tissue, etc.

1.2.1.7 Interact and emergence:

• All living phenomena arise or emerge by involvement of interaction from molecular level to high level of Multicellular organisms.

• Properties of tissues are not present in the constituent cells but arise or emerge due to interactions among the constituent cells.

• Similarly cell organelles emerge due to interaction among molecular components.

1.2.1.8 Life Span:

• It is a period from birth to natural death of a living organism.

• Except single cell organisms are immortal because these organisms undergo binary fission.

1.3 Diversity in the living world:

• It means, on the earth, so many different varieties of organisms observed like plants, animals, insects, birds, fishes etc.

• Several organisms that cannot see with our naked eyes. This kind of organism is known as micro-organism. Ex: Bacterias, Viruses, Amoeba etc.

• At present the scientists or biologist identified approximately 1.7 to 1.8 million species on the earth.

• The different types of organisms found on earth are known as biodiversity.

• There are millions of plants and animals in the world. Each organism has different names in different localities. This kind of naming is called a vernacular name.

• Vernacular naming creates confusion and cannot be acceptable, all over the world.

1.3.1 Biological Nomenclature:(L: Nome = name and cloture = rules)

• Scientists developed some techniques to overcome vernacular names.

• Characterization, Identification, classification, systematic and nomenclature are the techniques used to standardize the naming of living organisms.

• The biologist or taxonomist developed scientific naming of living organisms, such that a particular organism is known by the same name all over the world by a set of rules called biological nomenclature or nomenclature.

1.3.1.1 Types of Nomenclature codes:

• ICBN: International code for Botanical Nomenclature; in this committee members provide scientific names for plants.

• ICZN: International code for Zoological Nomenclature; in this committee members provide scientific names for animals.

• ICMN: International code for Microorganism Nomenclature; in this committee members provide scientific names for microorganisms.

1.3.1.2 Binomial Nomenclature:

• Carolus Linnaeus proposed binomial nomenclature. He is called the “father of taxonomy”.

• Binomial means according to Latin language Bi = two; nome = name.

• Definition: Scientific naming of organisms contains two components or two names. First name is genus and the second name is species. This kind of nomenclature is called binomial nomenclature.

• Ex: The scientific name of mango is Mangifera indica.

• Where,

• Mangifera represents genus names.

• indica represents species name.

1.3.1.3 Universal Rules of Binomial Nomenclature:

1. Biological names are generally in Latin or in Greek language. They are Latinized at the time of translation.

2. The first word in a biological name represents the genus while the second name represents species.

3. The biological names must be in italic and bold if printed (Mangifera indica) and in handwritten underlined separately (Mangifera indica).

4. The genus name always starts with a capital letter (Mangifera) while the species name starts with a small letter (indica).

5. Name of the author appears after the species or at the end of the biological name. It is written in abbreviated form.

Ex: Mangifera indica Linn (Linn described by Linnaeus).

1.3.2 Taxonomy: (Gr: Taxo = arrangement; nomy = method)

• Taxonomy is defined as the branch of biology which deals with classification of living organisms.

• Taxa means a group of categories in classification (more than one group or categories). It is a plural form of taxon.

Ex: Animals, Plants, Kingdoms, Phylum, Micro-organisms.

• Taxon means a unit of classification or any rank in the taxonomic category. It is a singular form of taxa.

Ex: species,genes, family (only one group), cats, dogs, humans etc.

1.3.2.1 Features of Modern Taxonomic Studies:

• Study external and internal structure, along with the structure of cells in an organism.

• Development process and ecological information of organisms.

1.3.2.2 Basic Processes of Taxonomy:

1. Characterization

2. Identification

3. Classification

4. Systematic and 

5. Nomenclature.

Note: 

• The organism is described according to its all morphological, anatomical, physiological and behavioural properties. This process is called characterization.

• Identification is a psychological process of an individual to recognize and name living organisms based on correct description.

• Classification is the process by which anything is grouped into convenient categories based on some easily observable characters.

1.3.2.3 Systematics: (La: Systema = systematic arrangement of organisms).

• Systematics deals with study of relationships among different kinds of organisms and their diversities.

• Carolus Linnaeus used “Systema Naturae” as the title of his publication.

• Scope of systematic: helps in identification, nomenclature, classification and evolutionary relationships between organisms.

1.4 Taxonomic Categories:

• Classification is not a single stem process but involves hierarchy of steps in which each step represents a rank or category.
• A part of overall taxonomic arrangement is called Taxonomic categories. It is also called a taxonomic group.
• All taxonomic categories together constitute the taxonomic hierarchy. It is also called the Linnaeus hierarchy
• 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.

1.4.1 Taxonomic groups / categories showing hierarchical arrangement:

Species:

• A group of fundamental similar organisms which can interbreed truly and produce viable offspring are called species.

•  A species is one of the basic and lowest level units of biological classification and taxonomic rank.

Common Name	Scientific Name	Species Name
Mango	Mangifera indica	indica
Man	Homo sapien	sapien
Potato	Solanum tuberosum	tuberosum
Brinjal	Solanum melongena	melongena
Blackberry Nightshade	Solanum nigrum	nigrum
Lion	Panthera leo	leo
Tiger	Panthera tigris	tigris
Leopard	Panthera pardus	pardus
House fly	Musca domestica	domestica
Wheat	Triticum aestivum	aestivum

Musca = a fly (Lt); Triticum = harvesting machine; aestivum = summer, nigrum = dark or black

Genus:

• Genus comprises a group of related species. In the hierarchy of biological classification genus comes above species and below family.

• Ex 1: Mangoes (Mangifera indica, Mangifera austro).

• Ex 2:Big cats (Panthera leo, Panthera pardus, Panthera tigris).

• Ex 3: Small cat’s genus is Felis.

Family:

• It is a group of related genera. In this hierarchy of biological classification family comes above genus and below order.

• Animal families end with the suffix - idae.

• Plants families end with the suffix - aceae.

• A family is a group of related genera with less number of similarities as compared to genus and species.

• Both vegetative and reproduction features are taken as the basis of plant classification.

Family	Ex: Genus
Anacardiaceae (Fruits are drupes)	Mangifera, Anacardium
Felidae (all cats)	Panthera and Felis
Hominidae (Humans)	Homo
Canidae (all dogs)	Canis, Urocyon (tailed fox)
Solanaceae (sun shape flowers and alkaloids)	Solanum, Petunia and Datura

Diptera: Di = 2; ptera = Wings

Order:

It is a group of related families. In this hierarchy of biological classification order comes above family and below class.

Order	Ex: families
Polymoniales (floral characters) and Sapindales (stamens inserted in disk or stamens inside the flower)	Convolvulaceae(funnel shape flower) and Solanaceae
Primata (living on trees)	Monkeys, Apes and Hominidae
Carnivora (meet eating)	Canidae and felidae

Class:

It is a group of related orders. In the hierarchy of biological classification, class comes above order and below phylum or division.

Ex: Dicotyledonae, Mammalia.

Phylum or Division:

• In the hierarchy of biological classification, phylum or division comes above class and below kingdom.

• A group of related classes of animals is known as phylum.

Ex: Chordata and Non-chordata

• A group of related classes of plants is known as division.

Ex: Angiosperms, Gymnosperms Pteridophytes

Kingdom:

• Kingdom is the highest level of category or rank or taxon observed in the hierarchy of biological classification.

• It is a group of related phyla or related divisions.

• Ex: Animalia (group of animal phylum’s), Plantae (group of plant divisions).

1.4 2 Taxonomic Categories features:

• As we go higher from species to kingdom, the number of common characteristics decreases but general characters increases.

• 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 the other taxa at the same level.