Adolescence

 Basic Science VIII208Addictive habitsDid you notice the illustration?Extreme rashness and misuse of mobile phones andcomputers are dangerous bad habits, aren’t they?Which are the other similar problems faced by adolescents?How can we overcome such problems?Discuss.Tobacco contains more thanseven thousand chemicals suchas nicotine, benzene etc. About70 of these chemicals arecarcinogens. Smoking reducesthe diameter of blood capillariesand prevents the diffusion ofoxygen into the tissues. Smokingand the use of tobacco productsare the main causes of cancer inthe mouth, lungs, throat,oesophagus etc. Collectinformation regarding the healthand social issues caused bysmoking, alcoholism, drugaddiction etc. Record them inyour science diary. 

Path to destruction

 Did you notice the illustration?Extreme rashness and misuse of mobile phones andcomputers are dangerous bad habits, aren’t they?Which are the other similar problems faced by adolescents?How can we overcome such problems?Discuss.

Need for assertiveness

What is your response towards this statement?Can you cite such instances?How will you respond if such instances occur in yourlife?Discuss.

  Personality developmentProgrammesWe have around us a lot of possibilities forpersonality development. Participate incollective efforts in and outside theschool that help us nurture our talentsand also develop and promote servicementality, leadership and discipline.Develop and grow as impressivepersonalities

 Such programmes can be conducted in your schooltoo.What all topics may be discussed in such aprogramme?List out your suggestions.$$Put your doubts in the question box and give it tothe resource person who leads the class. It will makethe class more effective.Write a report of the programme in your sciencediary

 Adolescence

 – A period of possibilitiesWe have around us many possibilities to developas good individuals by overcoming challenges. Wecan create a better tomorrow if we judiciously makeuse of today’s possibilities.Self esteemIdealismFriend

 Adolescence – A period of possibilitiesWe have around us many possibilities to developas good individuals by overcoming challenges. Wecan create a better tomorrow if we judiciously makeuse of today’s possibilities.Self esteemIdealismFriend

CLASSIFICATION

 Did you notice the opinion of the girl searching for a book?What are the advantages of arranging books in proper order?Haven’t you noticed the arrangement of books in a library?In what all ways books may be arranged? Discuss

Things need to be classified first in order to arrange themproperly. Aren’t the things in your study room and kitchenarranged according to their types?Human beings show a tendency to classify things around them.What are the bases for such classification?

Shape 

$Colour 

$Size 

$Use 

$Observe the figures 

What criteria can be used for classifying these organisms?

$size

 $beauty 

$speed 

$sharp incisors 

$claws that can be withdrawn into the feet  

Which among these criteria is the most suitable one forclassification? Why? Discuss.If more specific criteria are adopted, classification becomes moreaccurate.It will be easy to study organisms if they can be classifiedaccording to suitable criteria

Let’s classify and learn

Observe the illustration given below.Do you know all the peculiarities of the organisms shown in the illustration?Notice the classification of these organisms on the basis of certain observablecharacteristics. Analyse the criteria used for classification

Why is the classification of these organisms very easy?

$Less number of organisms

 $Specific indicators

 $Two clear options for each indicator   

Classification becomes easier with the use of such specific indicators.Analyse with the help of the indicators the note given below and writedown the inferences in the science diary

Taxonomic keys are the scientific indicators used for identifying and classifying plantsand animals. One of the most important taxonomic keys is the dichotomous key.Each indicator in this key has two possibilities of selection. By choosing thepeculiarities of the organism to be identified and by proceeding systematically onecan identify and classify the organism. Illustration 12.1 is a dichotomous key. Thetaxonomic keys are continuously revised by including peculiarities of newly identifiedorganisms

Indicators 

Taxonomic keys

 Peculiarity of dichotomous keysThus, the method of classification is the act of grouping of organismsbased on similarities or differences     

Taxonomy is the branch of biology that identifies organisms, classifiesthem on the basis of similarities and differences and names themscientifically. For the purpose of classification, the characteristic featuresof organisms, their external and internal features, genetic constitution,evolutionary relationships etc., are to be thoroughly studied. This studyreveals the relation between various groups of organisms. It also enablesus to acquire a general idea about the plants and animals of variousgeographical areas. Moreover, taxonomy provides evidences that arehelpful to explain the stages of evolution of organisms from the simpleto the complex

Based on similarities or differences, all organisms including humanbeings are placed in different levels of classification. It was a scientistnamed Carl Linnaeus who fixed taxonomic hierarchy and provided ascientific base for classification. Hence he is known as the Father ofTaxonomy

Let’s familiarise ourselves with some scientists who have made valuablecontributions in the history of taxonomy.

Taxonomic hierarchy proposed by Linnaeus

According to biological definition, species is a group of organisms that canproduce fertile offsprings through sexual reproduction. Species is the basiclevel of classification. Organisms of a species share maximum similarity offeatures. Organisms of similar species constitute the genus. Similar genusconstitute the family and families join to form the order. Various ordersconstitute the class. Related classes join to form phylum. All phyla constitutethe kingdom, which is the highest level.Observe the illustration given below and discuss it on the basis of theindicators. Write down your inferences in the science diary.

      Indicators 

•Which are the organisms included inkingdom Animalia?•Which organisms are excluded at eachconsecutive levels? Why?•At what levels of this illustration canhumans be included?Complete the worksheet identifying the levelsof classification of cat.

Kingdom ̨Phylum ̨Class ̨Order ̨Family ̨Genus ̨Species

Taxonomic hierarchy of plants

Linnaeus also classified plants by including them in various levels from species tokingdom. Though revised in course of time, these are still used as the basic levels ofclassification

Find out more examples of the classification of plants and write them down in thescience diary

Basic Science VIII174Diversity in names

If an organism has so many names in a single language, how much will bethe diversity when their names in other languages are also considered! Isthe presence of different names a hindrance to their study?Discuss

Binomial nomenclature

Binomial nomenclature was proposed to solve the difficulties arising out ofan organism being known by various names in different languages and regions.This is a commonly accepted scientific method of naming. Binomialnomenclature is the scientific method of naming by joining two words.It was Carl Linnaeus who proposed binomial nomenclature. The first word ofthe scientific name indicates the genus and the second word indicates thespecies. By this method the scientific name of an organism is the same allover the world. According to this, the scientific name of human beings isHomo sapiens

Towards more precision

According to the two kingdom classification that was prevalentearlier, organisms were classified under two large categoriesnamely, Kingdom Plantae (plants) and Kingdom Animalia(animals).In the light of the knowledge gained later on the diversity ofspecies, an American botanist Robert H.Whittaker classifiedorganisms into five kingdoms

Basic Science VIII176Modern trends in taxonomy

In the past, knowledge of the peculiarities of microorganisms likebacteria was limited. Later, it was found out that the archaebacteriabelonging to the Kingdom Monera are different from otherbacteria in cell structure and physiological functions. Thenkingdom Monera was further divided into two Kingdoms; namelyarchaea and bacteria. Besides this, one more level of classificationnamed domain was added above the kingdom. It was theAmerican scientist Carl Woese who proposed this six kingdomclassification.Analyse the illustration given below with the help of theindicators. Discuss it and write down your inferences in thescience diary

IndicatorsLimitations of two kingdom classification.Possibilities of five kingdom classification.Circumstances that led to the formulation of six kingdom classification

Find out the various levels of classification of human beings basedon the six kingdom classification and complete the table suitably

Ebola casting deathNew Delhi : The world under the threat of Ebola!According toWHO reports, a total of 9208 havedied of Ebola.The illness is caused by Ebola virus

ndicators

What are the peculiarities of virus?Can virus be included in any of the classification methodswe have discussed earlier? Why?No attempts at classification can be perfect and complete. Theattempts still continue. The fact is that the more acceptable onesgain general approval.     

How do we ensure that the organisms mentioned in such reportshave never been identified ?Based on the given indicators, discuss and write down theinferences in the science diary.Observation of peculiarities

Verification of details

Use of taxonomic keys

Scientific naming 

ClassificationThere are millions of unidentified organisms on Earth. Thescientific world accepts newly identified organisms by classifyingthem on the basis of their peculiarities and name themscientifically. Researchers all over the world continue their searchfor new organisms  

Significant learning outcomes

The learner can 

 

 identify and explain the significance and importance oftaxonomy.

 

prepare notes on scientists who have contributed to the fieldof taxonomy. 

 

 list the peculiarities of organisms by identifying the relevanceof classification

 

explain the relevance of naming organisms according tobinomial nomenclature.

 

identify, list and exhibit the scientific names of familiarorganisms. 

 

 compare and explain modern trends in taxonomy and variousmethods of classification

. 

list the peculiarities of virus.   

Let us assess 

1.Identify the word pair relation and fill in the blanks.a.Five kingdom classification: Robert H.WhittakerSix kingdom classification:b.Charaka:Charaka SamhitaJohn Ray: 

2.Hints about some organisms are given below. Name thekingdom to which these organisms belong:a.Multicellular heterotrophic organisms with a nucleusand capacity for locomotion

.b.Multicellular, heterotrophic, non-motile organisms witha nucleus.

 c.Unicellular organisms with a nucleus.d.Multicellular, autotrophic, non-motile organisms with anucleus