Biology-The living world NCERT solution for class 11

The living world NCERT Solution for class 11 chapter Explanation and summary

Unit 1
Unit 1

Diversity in the living world

Biology is the science of life forms and living processes the living world comprises an amazing diversity of living Organism Early man could easily perceive the different between Inanimate matter and living Organism early man defied some of the inanimate matter (win , sea fire etc ) and some among the animals and plants A common feature of all such forms of inanimate and animate objective was the sense of awe or fear that they evoked the description of living Organism including human beings began much later in human history Societies which indulged in anthropocentric view of biology could register limited progress in biological knowledge systematic and monumental description of life forms brought in out of necessity detailed

systems of identification nomenclature and classification the biggest spin off of such studies was the recognition of the sharing of similarities among living Organism both horizontally and vertically that all present day living Organism are related to each other and also to all Organisms that ever lived on this earth was a revelation which humbled man and led to cultural movements for conservation of biodiversity in the following chapters of this Unit you will get a description Including classification of animals and plants from a taxonomist’s perspective

Ernst Mayr (1904-2004)

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 mayr joined harvard ‘s faculty of arts and sciences in 1953 and retired in 1975 assuming the title Alexander Agassiz Professor of Zoology Emeritus throughout his nearly 80-years career his research spanned Ornithology taxonomy Zoogeography evolution systematics and the history and philosophy of biology he almost single handedly made the Origin of

species diversity the central question of evolution biology that it is today he also pioneered the currently accepted definition of a biological species mayr was awarded the three prizes widely regarded as the triple crown for biology the Balzan Prize in 1983 the International Prize for biology in 1994 and the Crafoord Prize in 1999 Mayr died at the age of 100 in the years 2004

Chapter 1 The Living world

How wonderful is the living world ! the wide range of living types is amazing the Extraordinary habitats in which we find living Organisms be it cold Mountains deciduous forests Oceans fresh water lakes deserts or hot springs leave us speechless the beauty of a galloping horse of the migrating birds the valley of flowers or the attacking shark evokes awe and a deep sense of wonder the ecological conflict and Cooperation among members of a population and among populations of a community or even the molecular traffic inside a cell make us deeply reflect-on what Indeed is life” this question has two Implicit questions within it the first is a technical one and seeks answer to what living is as opposed to the non-living and the second is a as scientists we shall not attempt answering the second question we will try to reflect on -what is living ?”

Topics-The living world

  1. what is Living?
  2. Diversity in the living world
  3. Taxonomic Categories
  4. Taxonomical Aids
  5. Summary
  6. Question and answer
1.what is living”

when we try to define living” we conventionally look for distinctive characteristics exhibited by living Organism Growth reproduction ability to sense environment and mount a suitable response come to our mind Immediately as unique features of living Organism one can add a few more features like metabolism ability to self-replicate self Organism interact and emergence to this list let us try to understand each of these All Living Organisms grow ” Increase in mass and increase in number of individuals are twin characteristics of growth A Multicellular Organism

Grows by cell division In plants this growth by cell division Occurs continuously throughout their life span In animals this growth is seen only up to certain age however cell division Occurs In certain tissues to replace lost cells Unicellular Organism grow by cell division One can easily observe this in vitro Cultures by simply counting the number of cells under the microscope In majority of higher animals and plants growth and reproduction are mutually exclusive events one must remember that increase in body mass is

considered as growth Non-living Objects also grow if we take increase in body mass as a certain for growth Mountains boulders and sand mounds do grow however this kind of growth exhibited by Non-living objects in by accumulation of material on the surface In living Organism growth is from inside growth therefore Cannot be taken as a defining property of living Organism condition Under which it can be observed in all it is a characteristics of living systems A dead Organism does not Grow “

Reproduction, likewise” is a characteristics of living Organisms” In multicellular Organism reproduction refer to the Production of progeny Possessing features more or loss similar to those of parents Invariably and Implicitly we refer to sexual reproduction Organism reproduce by asexual Means also Fungi Multiply and spread easily due to the millions of sexual spores they produce In lower Organisms like yeast and hydra we observe budding In planaria (flat worms) we observe true regeneration i”e fragmented Organism regenerates the lost part of its body and become a new Organism the fungi the filamentous algae the protonema of Mosses all

easily multiply by fragmentation when it comes to Unicellular Organisms like bacteria Unicellular algae or Amoeba reproduction is synonymous with growth i”e Increase In number of cells we have already defined growth as equivalent to increase In cell number or mass hence we notice that in single celled Organism we are not very clear about the usage of these two terms growth and reproduce (mules, sterile worker bees Infertile human Couples etc, ) hence reproduction also cannot be an all Inclusive defining characteristics of living Organisms of course no Non-living Object is capable of reproducing or replacing by itself

Another characteristics of life is metabolism ” all living Organisms are made of chemical these Chemical small and big belonging to various classes size function etc, are constantly being made and changed into some other biomolecules these conversion are chemical reaction or metabolic reaction there are thousands of metabolic reaction Occurring simultaneously inside all living Organism be they

Unicellular Multicellular all plants animals fungi and microbes exhibits Metabolism the sum total of all the chemical reaction Occurring in our body is metabolism No Non-living object exhibits Metabolism Metabolic reactions can be demonstrated outside the body in cell free systems an Isolated Metabolism reaction (s) outside the body of an Organism Performed in a test tube is nether living nor Non-living hence while Metabolism is a defining feature of all living Organism without exception Isolated Metabolism reaction in vitro are not living things but surely living reactions hence cellular Organisation of the body is the defining feature of life forms

Perhaps the most obvious and technically complicated feature of all living Organism is this ability to sense their surrounding or enironment and respond to these Environment stimuli which could be physical chemical or biological we sense our environmrnt through our sense Organs plants respond to external factor like light water temperature other Organisms pollutants etc all Organism from the Prokaryotes to the most complex eukaryotes can sense and respond to environment cues Photoperiod affects reproduction in seasonal breeders both plants and animals all Organism handle chemical entering their bodies all Organisms therefore are aware , of their surroundings human being is the only Organism who is aware of himself , I”e has self Consciousness , Consciousness therefore becomes the defining property of living Organisms

When it comes to Human beings it is all the more difficult to define the living state we observed patients Lying in in coma in hospitals virtually supported by machines which replace heart and lungs the patient is otherwise Brain dead the patient has no self Consciousness are such patients who never come back to normal life living or Non-living ?” In higher classes you will come to know that all living phenomena are due to underlying interactions Properties of tissues are not present in the constituent cells similarly properties of cellular Organelles are not present in the Molecular constituents of the Organelle but arise as a result of interaction among the molecular components comprising the Organelle these Interaction result

in emergent Properties at a higher level of Organisation this phenomenon is true in the hierarchy of Organisms are self-replicating envolving and self-regulatting interactive systems capable of responding to external stimuli biology is the story of life on earth biology is the story of evolution of living Organisms on earth all living Organisms present past and future are linked to one another by the sharing of the common genetic material but to varying degree

2.Diversity In the Living world

if you look around you will see a large variety of living Organisms be it potted plants Insert birds your pets or other animals and plants there are also several Organisms that you cannot see with your naked eye but they are all around you if you were to Increase the area that you make Observations In the range and variety of Organisms that you see would Increase Obviously if you were to visit a dense forest you would probably see a much greater number and kinds of living Organisms In it each different kind of plant animal or Organism that

you see represents a species 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 we should Remember here that as we explore new areas and even old ones new Organisms are Continuously being identified

As stated earlier there are millions of plants and animals in the world we know the plants and animals in our won area by their local names these local names would vary from place to place to place even within a country Probably you would recognise the confusion that would be created if we did not find ways and Means to talk to each other to refer to Organisms we are taking about

Hence there is a need to standardise the Naming of living Organisms such that a particular Organisms is known by the same name all over the world this process is called nomenclature Obviously 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) you may ask how are animals named?

Animal taxonomists have evolved International code of Zoological Nomenclature (ICZN) the scientific names ensure that each Organism has only one name Description of any Organism should enable the people that such a name has not been used for any other known Organism

Biologists follow Universally accepted Principles to provide scientific names to known Organisms each name has two components a name with two components is called Binomial nomenclature this naming system given by Carolus Linnaeus is being Practised by Biologists all over the world this naming system using a two word format was found convenient Let us take the Example of Mango to Understand the way of

Providing Scientific names better the scientific name of Mango is written as Mangifera Indica let us see how it is a binomial name In this same Mangifera represents the genus while Indica is a particular species, or a specific Epithet others Universal Rules of nomenclature are as follows”

  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 word 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 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, since it is nearly impossible to study all the living Organisms it is Necessary to devise some Means to make this possible this Process is Classification , Classification is the Process by which anything is grouped into Convenient categories based on some easily Observable Characters for Example” , we easily recognise groups such as plants or animals or dogs cats or insects the moment we use any of these terms we associate certain character with the Organism in that group what Image do you,

See when you think of a dog? Obviously each one of us will see dogs and not cats Now if we were to think of Alsatians we know what we are taking about similarly suppose we were to say mammals you would of Course think of animals with external ears and body hair Likewise in Plants if we try to talk of wheat the picture in each of our minds will be of wheat plants not of rice or any other plant Animals, etc are Convenient Categories we use to study Organism the scientific term for these Categories is Taxa

here you must Recognise that taxa can indicate categories at very different level plants -also form a taxa wheat is” also a taxa similarly animals Mammals dogs” are all taxa -but you know that a dog is a mammal and mammal are animal therefore animals mammals and dogs” represent taxa at different levels hence based on characteristics all living Organisms can be classified into different taxa this Process of classification is taxonomy External and internal structure along with the structure of cell, development

Process and ecological information of Organism are essential and form the basis of modern taxonomic studies hence Characteristics identification classification and nomenclature are the Processes that are basis to taxonomy , taxonomy is not something new Human beings have always been interested in knowing more and more about the various kinds of Organisms particularly with reference to their own use In early days human beings needed to find sources for their basic needs of food clothing and shelter hence the earliest classifications were based on the uses, of Various Organisms

Human beings were since long not only interested in knowing more about different kinds of Organisms and their diversities but also the relationship 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 was later enlarged to include identification nomenclature and classification systematics take into account evolutionary relationships between Organisms

3.Taxonomic categories

Classification is not a single step Process but involves Hierarchy of steps in which each step represent 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 )

Taxonomic categories and hierarchy can be Illustrated by an example” insects represent a group of Organisms sharing common features like three pairs of jointed legs it Means Insects are recognisable Concrete Objects with can be classified and thus were given a rank or category can you name other such groups of Organisms ? Remember groups represents category further denotes ran Each rank of Taxon” / in fact represent a unit of classification these Taxonomic groups/ 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 Ordre family genus and species all Organisms including those in the plant and animal kingdoms have species as the lowest category now the question you may ask is how to place an

Organisms in various categories? the basic requirement is the knowledge of characters of an individual or group of Organisms this helps in identifying similarities and dissimilarities among the individuals of the same kind of Organisms as well as of other kinds of Organisms

  1. 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 India 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 the genus Homo the scientific name thus for human being is written as homo Sapiens”

2. Genus

Genus” Comprises a group of related species which is 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 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,

3. 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 Comparising 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 Canidae respectively ,


You have seen earlier that categories like species genus and families are based on a number of similar characters 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 Canidae

5. 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 ,

6. 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 Chordata In case of plants classes with a few similar characters are assigned to a higher category called Division

7. 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 henceforth we will refer to these two groups as animal and plant kingdoms the taxonomic categories from species to kingdom have been shown in ascending order starting with species in Figure, 1.1 these are broad categories however taxonomists have also developed sub-categories in this hierarchy to facilitate more Sound and scientific placement of various taxa

Figure 1.1 Taxonomic categories showing hierarchial arrangement in ascending order

Look at the hierarchy in figure 1.1 can you recall the basis of arrangement? say for example as we go higher from species to kingdom the number of common Characteristics goes on Decreasing lower the taxa more are the Characteristics that the members within 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 Table 1.1 indicates the taxonomic categories to which some common Organisms like housefly man mango and wheat belong

Table 1.1 Organisms with their Taxonomic Categories
Common Name Biological Name Genus Family Order Class Phylum/ Division
Man Homo Sapiens Homo Hominidae Primata Mammalia Chordata
Housefly Musca Domestica Musca Muscidae Diptera Insecta Arthropoda
Mango Mangifera Indica Mangifera AnacardiaceaeSapindales Diocotyledonae Angiospermae
wheat Triticum aestivum Triticum Poaceae Poales Monocotyledonae Angiospermae
Table 1.1
4.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 these studies would require correct classification and identification of organisms Identification of organisms requires Intensive Laboratory and field studies the collection of actual specimens of plant and animal species is essential and is the prime source of taxonomic studies these are also fundamental to studies and essential for training in systematics it is used for classification of an Organisms and the information gathered is also stored along with the specimens In some cases the specimen is preserved for future studies Biologists have established certain Procedures and techniques to store and preserve the information as well as the specimens some of these are explained to help you understand the usage of these aids

  1. Herbarium

Herbarium is a store house of collected plant specimens that are dried pressed and preserved on sheets further these sheets are arranged

Figure 1.2 Herbarium showing stored specimens

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 (Figure 1.2) the Herbarium sheets also carry a label Providing information about date and place of collection English local and botanical names family collector’s name etc herbaria also serve as quick referral system in taxonomical studies

2. Botanical Gardens

These specialised garden have collection of living plants for reference plant species in these garden are grow for identification Purpose and each plant is labelled indicating garden are at kew (England ) Indian Botanical Garden Howrah (India ) and at national Botanical Research Institute Lucknow (India )

3. Museum

Biological museums are generally set up n educational Institute such as schools and colleges Museums have collections of Preserved plant and animal specimens for study and reference specimen are preserved in the Containers or jars in Preservative as dry specimen Insects are preserved in insect may also be preserved as dry specimens Insects are preserved In insect boxes after collecting killing and planning Larger animals like birds and mammals are usually stuffed and Preserved Museums often have collection of skeletons of animals too

4. Zoological Parks

These are the places where wild animals are kept in Protected environment Under human care and which enable us to learn about their food habits and behaviour all animals in a Zoo are provided as far as possible the Conditions similar to their natural habitats Children love visiting these parks Commonly called Zoos (Figure 1.3 )

Figure 1.3 Pictures showing animals in different Zoological parks of India

5. 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 this results in acceptance of only one and rejection of the other 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 Purpose keys are generally analytics in nature

Flora manuals Monographs and catelogues 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 any one taxon ,

Summary of this chapter

The living world is the rich in variety millions of plants and animals have been identified and described but a large number still remains Unknown the very range of Organisms is term of size colour habits physiological and Morphological features make us seek the defining characteristics of living Organisms In order to facilitate the study of kinds and diversity of Organisms biologists evolved certain rules and principles for identification Nomenclature and classification of Organisms the branch of knowledge dealing with these aspects is referred to as taxonomy the taxonomic studies of various species of plant and animals are useful in agriculture forestry industry and In general for knowing our bio-resources and their diversity the basics of taxonomy like

identification naming and classification of Organisms are universally evolved under international codes based on the resemblances and distinct difference each Organism is identified and assigned a correct scientific / biological name comprising two words as per the binomial system of nomenclature an organism represents / occupies a place or position in the system of classification there are many categories / ranks and are generally referred to as taxonomic categories or taxa all the categories constitute a taxonomic hierarchy ,

Taxonomists have developed a variety of taxonomic aids to facilitate identification naming and classification of Organisms these studies are carried out from the actual specimens which are collected from the field and preserved as referrals in the form of herbaria museums and in botanical gardens and Zoological parks it require special techniques for collection and preservation of specimens in herbaria and museums live specimens on the other hand of plants and animals are found in botanical garden or in zoological parks taxonomists also prepare and disseminate information through manuals and monographs for further taxonomic studies taxonomic keys are tools that help in identification based on Characteristics

Question and answers

Question”1 why are living Organisms classified?

Answer” As there are millions of living Organisms on earth studying each of them is Impossible therefore scientists have mechanisms to classify all living Organisms these methods of classification are based on rules and Principles that allow identification Nomenclature and finally classification of an Organisms therefore the biological classification helps in revealing the relationship between Vanous Organisms it als helps in making study of Organisms easy and Organized

Question”2 why are the classification systems changing every Now and their?

Answer” Millions of plants animals and Microoganisms are found on earth many of these have been identified by the scientists while many new species are still being discovered around the world therefore to classify these newly discovered species new system of classification have to be devised every now and then this creates the requirement to change the existing systems of classification

Question”3 what different Criteria would you choose to classify people that you meet often?

Answer” (1)On the bases of sexes classification will result in the formation of two major groups -boys and grils

(2) Further classified on the basis of their name it is possible that more than one have someone

(3) So, Further classified on the basis of the surname since there is still chance that more than one have same surname”

(4) Final level of classification will be based on the roll number of each student

Question”4 what do we learn from identification of individuals and populations?

Answer” The knowledge of Characteristics of an Individual or its entire population helps in the identification of similarities and dissimilarities among the Individuals of some kind or between different types of Organisms It helps the scientists to classify Organisms in various categories

Question”5 Define a taxon give some Examples of taxa of different hierarchical levels

Answer” Each unit of category of classification is termed as taxon It represents a rank for example the basic level of classification is species followed by genus family order class Phylum or division in ascending order the highest level of classification is known as kingdow


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