CBSE CLASS 11 CHAPTER 1 NOTES

CHAPTER 1

CBSE BIOLOGY
CLASS 11

THE LIVING WORLD

INTRODUCTION

·     Biology – science of life forms & living processes

·     Living world – consists of diversity of living organisms

WHAT IS LIVING?

·     When we define ‘Living’ – we look for characteristics exhibited by living organisms – Growth, reproduction, ability to sense environment & mount a suitable response

·     We can add few more features – metabolism, ability to self-replicate, self-organise, interact & emergence

GROWTH

·     Increase in mass & number of individuals – twin characters of growth

·     Multicellular organism – grow by – cell division

·     Plants – growth by cell division – occurs throughout life span

·     Animals – growth – only upto certain age

·     However cell division – occurs in some tissue – to replace lost cells

·     Unicellular organisms – grow by – cell division – can be observed in invitro cultures – by counting number of cells – under microscope

·     Higher animals & plants – growth & reproduction – mutually exclusive events

·     Remember – increase in body mass – also considered as growth

·     Non-living objects – mountains, boulders & sand mounds – also grow – by accumulation of material on the surface

·     In living organisms – growth is from inside

·     Growth – cannot be taken as defining property of living organisms

·     Conditions under which growth occurs have to be explained – then we understand it – as a characteristic of living systems

·     Dead Organisms – does not grow

 

REPRODUCTION

·     A characteristic of living organism

·     Multicellular organisms – reproduction – production of progeny – having features more or less similar to parents (sexual reproduction)

ASEXUAL REPRODUCTION

REPRODUCTION

·     Unicellular organisms – bacteria, unicellular algae or Amoeba – reproduction synonymous with growth – i.e., increase in number of cells

·     Growth – already defined as – increase in cell number or mass – hence in single-celled organisms – not clear about usage of the 2 terms – growth & reproduction

·     Many organisms – do not reproduce – mules, sterile worker bees, infertile human couples, etc

·     Hence reproduction – cannot be a defining characteristic of living organisms

·     Of course – non-living objects – not capable of reproducing or replicating itself

METABOLISM

·     All living organisms – made of chemicals

·     Chemicals – small & big – belongs to various classes, sizes, functions, etc.,

·     Chemicals – constantly made & changed into some other biomolecules

·     Conversions – called Chemical reactions or metabolic reactions

·     Thousands of metabolic reactions – occurring inside all living organisms – be it unicellular or multicellular

·     All plants, animals, fungi & microbes – exhibit metabolism

·     Sum total of all the chemical reaction occurring in our body – Metabolism

·     Non-living object – donot exhibit metabolism

·     Metabolism – defining property of living organisms

·     Isolated metabolic reaction – performed in a test tube (outside body) – Invitro – neither living nor non-living

·     These isolated reactions – not living thing – but they are living reactions – as they are similar to the reactions performing in our body

CELLULAR ORGANISATION

·     Cell – basic unit of life – all organisms – made of cells

·     Some organisms – made of single cell – Unicellular organism

·     Others – made of many cells – Multicellular organism

·     Unicellular organisms – exist independently – perform their essential functions of life

·     Cell – fundamental structural & functional unit of all living organisms

·     Non-living objects – donot have cells

·     Cellular organisation – is a defining property of life

CONSCIOUSNESS

·     Consciousness – the ability to sense the surrounding environment & respond to these environment stimuli – physical, chemical or biological

·     Most obvious & technically complicated feature – seen in all living beings

·     We sense our environment – through sense organs

·     Plants – respond to external factors – light, water, temperature, other organisms, pollutants, etc.,

·     All organisms (prokaryotes to complex eukaryotes) – show consciousness to the environmental cues

Examples of Consciousness:

·      In both plants & animals – Photoperiod (duration of light) – affects the reproduction in seasonal breeders

·      Plants – they perform flowering in a particular season

·      Some animals – perform breeding in a particular season 

·      All organisms – handle the chemicals entering their body

·     Therefore, all organisms – aware of their surroundings 

 

·     Human beings – only organisms – aware of themselves – i.e., Self Consciousness

·     Human being – difficult to define their living state

·     Coma patients – supported by machines – replace heart & lungs – has consciousness – so considered as living – but no self consciousness – because co-ordination of organs – lost

·     If there is no consciousness – patient is brain dead

 

·     Means – all the living phenomenon – due  to underlying interactions between different components of an individual – organs, tissues or cell

·     Living organisms – self replicating evolving and self-regulating – capable of responding to external stimuli

·     All living organisms – present, past & future – linked to one another – share common genetic material – but to varying degrees

DIVERSITY IN THE LIVING WORLD

·     The number of species – known & described – range between 1.7 to 1.8 million

·     This refers to biodiversity – number & types of organisms present on Earth

 

NOMENCLATURE

·     Plants & animals in our area – known by local names

·     There is a need to standardise the naming of living organisms – such that – a particular organism – known by same name all over the world – this process is called Nomenclature

·     Need for Nomenclature – to avoid confusion – when we talk to people from other place – referring to an organism we are talking about

·     Nomenclature / Naming – possible only when the organism is described correctly - & we know what organism the name is attached to – this is identification

·     Rules for Nomenclature are provided by

·      ICBN – International Code for Botanical Nomenclature (Plants)

·      ICZN – International Code for Zoological Nomenclature

·     Scientific names – ensures – each organism has only one name

·     Description of the organism – should enable people – to arrive at the same name

·     Also ensures – such name – not used for any other known organism

BINOMIAL NOMENCLATURE

·     Carolous Linnaeus – Father of Taxonomy – introduced the two word naming system – Binomial Nomenclature

·     Name with two components

·      Generic Name

·      Specific epithet

·     This system – used by biologists – all over the world – found convenient

·     Eg: Mango – Scientific Name – Mangifera indica

·     Mangifera – Genus ; indica – Species / Species Epithet

RULES FOR NOMENCLATURE

·     It should be Latin / derived from Latin

·     Written in italics – when typed; Underlined separately – when hand written

·     It has 2 parts – first word is Genus; second word is Species epithet

·     Genus name – starts with capital letter; Species name – starts with small letter

·     Example:

·      Mangifera indica (when typed)

·      Mangifera  indica (when hand written)

·     Name of the author – written in an abbreviated form – after species name

·      Example: Mangifera indica Linn. – indicates this species – first described by Linnaeus

CLASSIFICATION

·     Since it is impossible to study all the living organisms – classification is necessary

·     Classification – grouping of organisms into categories – based on observable characters

·     Scientific term for these categories – Taxa

·     Example: Animals, mammals, dogs – Taxa at different levels

·     Based on characteristics – all living organisms – classified into different taxa

·     Process of classification – Taxonomy

·     External & internal structure, cell structure, development process, ecological information of organisms – essential & forms basis of modern taxonomic studies

·     Characterisation, Identification, Classification & Nomenclature – processes – basic to Taxonomy

·     Taxonomy is not new – olden days – Humans categorised organisms based on their uses

·     Human beings – not only interested in knowing about different organisms – but also eager to know the relationship among them – This branch of study – Systematics

SYSTEMATICS

·     Systematics – derived from Latin word – ‘Systema’ – means systematic arrangement of organisms

·     ‘Systema Naturae’ – Linnaeus Publication

·     Systematics includes – identification, Nomenclature, classification & evolutionary relationships between organisms

TAXONOMIC CATEGORIES

·     Taxonomy – not a single step process – involves hierarchy of steps – each step represents – a rank or category

·     Since category – part of overall taxonomic arrangement – called taxonomic category – all category together forms – Taxonomic Hierarchy

·     Each category – referred as unit of classification – represents a rank - & commonly termed – Taxon (Pl. Taxa)

·     Taxonomical studies of all known organisms – led to development of common categories – such as – Kingdom, Phylum/Division (Plants), Class, Order, Family, Genus & Species

TRICK TO REMEMBER TAXONOMICAL HIERARCHY

 

TAXONOMIC CATEGORIES

·     All organisms (including plants & animals) – Species – lowest category

·     By knowing the character of an individual or group of organisms – we can identify similarities & dissimilarities – thereby classify the organisms in various categories

SPECIES

·     Taxonomic studies consider – a group of individual organisms – with fundamental similarities as –  Species

·     One should be able to distinguish – one species from another closely related species – based on – distinct morphological differences

·     Example: Mangifera indica, Solanum tuberosum & Panthera leo

·     indica, tuberosum & leo – Specific epithet

·     Mangifera, Solanum & panthera – Genera (higher level of Taxon)

·     Each genus – have one or more species – representing different organisms – with morphological similarities

·     Humans – species – sapiens ; Genus – Homo; Scientific name – Homo sapiens

GENUS

·     Genus – a group of related species – has more characters in common compared to species of other genera

·     Genera – aggregates of closely related species

·     Example: Solanum

·      Solanum tuberosum (Potato)

·      Solanum nigrum (Black berry nightshade)

·      Solanum melongena (Brinjal)

·     Panthera

·      Panthera leo (Lion)

·      Panthera tigris (Tiger)

·      Panthera pardus (leopard)

·     Panthera genus differs from another genus Felis includes Cats

FAMILY

·     Family – a group of related genera – with less similarities  – compared to genus & species

·     Families – characterised on the basis of – both vegetative & reproductive features of plant species

·     Example: In plants – Genus Solanum, Petunia, Datura – Family Solanaceae

·     In animals – Genus Panthera (Lion, Tiger, Leopard), Felis (Cats) – Family Felidae

·     Cats & Dogs – have some similarities & dissimilarities – belong to 2 different families – Felidae & Canidae respectively

ORDER

·     Order – higher category – assemblage of families – have few similar characters

·     Similar characters – less in number – compared to different genera included in a family

·     Example: In plants – Families Convolvulaceae, Solanaceae – Order Polynomiales – based on Floral characters

·     In animals – Families Felidae & Canidae – Order Carnivora

CLASS

·     Class – includes related Orders

·     Example: Order Primata (Monkey, Gorilla, Gibbon) & Order Carnivora (Tiger, Cat, Dog) – placed in Class Mammalia

·     Class Mammalia – has other orders too

 

PHYLUM

·     Classes (animals) – Fishes, Amphibians, Reptiles, Birds & Mammals – Phylum – the next higher category

·     Based on common feature – presence of notochord & dorsal hollow neuro system – included in Phylum Chordata

·     In plants – Classes – assigned to higher category – Division

KINGDOM

·     All animals of various phyla – assigned to the highest category – Kingdom Animalia

·     All plants of various Divisions – assigned to Kingdom Plantae

·     Generally referred as Plant & Animal Kingdom

TAXONOMIC CATEGORIES

·     Taxonomic categories – from species to kingdom – broad categories

·     Taxonomists – also developed sub-categories – to facilitate placement of various taxa

·     As we go higher from species to kingdom – the number of common characteristics – decreases

·     Lower the taxa – more are the characteristics they share among the members

·     Higher the taxa – more difficult to determine relationship to other taxa at the same level

TAXONOMICAL AIDS

·     Taxonomic studies of various species (plants, animals, other organisms) – useful in agriculture, forestry, industry & in knowing the biodiversity

·     These studies require – correct classification & identification

·     Taxonomic studies – require collection of actual specimens as prime source – it is used for classification of an organism – & information stored along with specimen

·     In some cases – specimens preserved – for future studies

·     Biologists – established – procedures & techniques – to store & preserve the information & specimens – Taxonomical aids

·     Herbarium, Botanical garden, Museum, Zoological parks, Keys, etc.,

HERBARIUM

·     Store house – collected plant specimen – dried, pressed & preserved – on sheets – Herbarium sheets

·     These sheets – arranged according to universally accepted system of classification

·     Herbarium sheets – have specimen along with description – serves as store house

·     Herbarium sheets – have label with information about – date & place of collection, English, local & botanical names, family, Collector’s name, etc.,

·     Herbaria – quick referral system – in taxonomical studies

BOTANICAL GARDENS

·     Specialised gardens – have collections of living plants – for reference

·     Plants in the garden – grown for identification purposes

·     Each plant – labelled – indicating Botanical name & its family

·     Famous Botanical Gardens

·      Kew (England)

·      Indian Botanical Garden (Howrah)

·      National Botanical Research Institute (Lucknow)

 

MUSEUM

·     Biological museums – set up in educational institutes – like schools & colleges

·     Museums – have collections of preserved plant & animal specimens – for study & reference

·     Specimens – preserved in containers or jars – in preservative solutions

·     Plant & animal specimens – also preserved as dry specimens

·     Insects – collected, killed & pinned – in insect boxes

·     Larger animals – like birds & mammals – stuffed & preserved

·     Also have collections of animals’ skeletons too

 

ZOOLOGICAL PARKS

·     Commonly called Zoos

·     Places where wild animals – kept in protected environments – under human care

·     Enables us to learn about – their food habits & behaviour

·     All animals – provided with conditions – similar to their natural habitats

 

KEYS

·     Another taxonomical aid – used for identification of plants & animals – based on similarities & dissimilarities

·     Keys – based on contrasting characters – generally in pair – called Couplet

·     Represents – choice made between two opposite options – results in acceptance of only one & rejection of the other

·     Each statement in the key – called Lead

·     Separate taxonomic keys required – for each taxonomic category – Family, Genus & Species – for identification purposes

·     Keys – analytical in nature

OTHER TAXONOMICAL AIDS

·     Flora, Manuals, Monographs & Catalogues – other means of recording descriptions

·     They help in correct identification

·     Flora – contain actual account of habitat & distribution of plant – of a given area – also provide index of plant species in a particular area

·     Manuals – provide information – for identification of names of species – found in an area

·     Monograph – contains information of only any 1 taxon – 1 family / genera at a time – a detailed & well documented work on any particular taxon