Doubtnut Now

Class 12 BiologyEvolutionNcert Video Solutions - Only On DoubtnutDownload Doubtnut NowExercise 7.1Explain antibiotic resistance observed in bacteria in light ofDarwinian selection theory.SOLUTION:Darwinian selection theory states that individuals withfavourable variations are better adapted than individualswith less favourable variation. It means that natureselects the individuals with useful variation as theseindividuals are better evolved to survive in the existingenvironment. An example of such selection is antibioticresistance in bacteria. When bacterial population was

grown on an agar plate containing antibiotic penicillin,the colonies that were sensitive to penicillin died,whereas one or few bacterial colonies that were resistantto penicillin survived. This is because these bacteria hadundergone chance mutation, which resulted in theevolution of a gene that made them resistant to penicillindrug. Hence, the resistant bacteria multiplied quickly ascompared to non-resistant (sensitive) bacteria, therebyincreasing their number. Hence, the advantage of anindividual over other helps in the struggle for existence.View Text Solution On Doubtnut AppExercise 7.2Find out from newspapers and popular science articles any newfossil discoveries or controversies about evolution.

SOLUTION:Fossils of dinosaurs have revealed the evolution ofreptiles in Jurassic period.As a result of this, evolution of other animals such asbirds and mammals has also been discovered. However,two unusual fossils recently unearthed in China haveignited a controversy over the evolution of birds.Confuciusornis is one such genus of primitive birds thatwere crow sized and lived during the Creataceous periodin China.View Text Solution On Doubtnut AppExercise 7.3Attempt giving a clear definition of the term speciesSOLUTION:

Species can be defined as a group of organisms, whichhave the capability to interbreed in order to producefertile offspring.View Text Solution On Doubtnut AppExercise 7.4Try to trace the various components of human evolution (hint: brainsize and function, skeletal structure, dietary preference, etc.)SOLUTION:The various components of human evolution are asfollows.(i) Brain capacity(ii) Posture iii. Food / dietary preference and otherimportant features

View Text Solution On Doubtnut AppExercise 7.5Find out through internet and popular science articles whetheranimals other than man have self-consciousness.SOLUTION:There are many animals other than humans, which haveself-consciousness. An example of an animal being selfconscious is dolphins. They are highly intelligent. Theyhave a sense of self and they also recognize othersamong themselves and others. They communicate witheach other by whistles, tail-slapping, and other bodymovements. Not only dolphins, there are certain otheranimals such as crow, parrot, chimpanzee, gorilla,orangutan, etc., which exhibit self-consciousness.

View Text Solution On Doubtnut AppExercise 7.6List 10 modern-day animals and using the internet resources link itto a corresponding ancient fossil. Name both.SOLUTION:The modern day animals and their ancient fossils arelisted in the following table.View Text Solution On Doubtnut AppExercise 7.7

Practise drawing various animals and plants.SOLUTION:Ask your teachers and parents to suggest the names ofplants and animals and practice drawing them. You canalso take help from your book to find the names of plantsand animals.View Text Solution On Doubtnut AppExercise 7.8Describe one example of adaptive radiation.SOLUTION:Adaptive radiation is an evolutionary process thatproduces new species from a single, rapidly diversifyinglineage. This process occurs due to natural selection. An

example of adaptive radiation is Darwin finches, found inGalapagos Island. A large variety of finches is present inGalapagos Island that arose from a single species,which reached this land accidentally. As a result, manynew species have evolved, diverged, and adapted tooccupy new habitats. These finches have developeddifferent eating habits and different types of beaks to suittheir feeding habits. The insectivorous, blood sucking,and other species of finches with varied dietary habitshave evolved from a single seed eating finch ancestor.View Text Solution On Doubtnut AppExercise 7.9Can we call human evolution as adaptive radiation?SOLUTION:

No, human evolution cannot be called adaptive radiation.This is because adaptive radiation is an evolutionaryprocess that produces new species from a single, rapidlydiversifying lineage, which is not the case with humanevolution. Human evolution is a gradual process thattook place slowly in time. It represents an example ofanagenesis.View Text Solution On Doubtnut AppExercise 7.10Using various resources such as your school library or the internetand discussions with your teacher, trace the evolutionary stages ofany one animal say horse.SOLUTION:The evolution of horse started with Eohippus during

Eocene period. It involved the following evolutionarystages.Gradual increase in body sizeElongation of head and neck regionIncrease in the length of limbs and feetGradual reduction of lateral digitsEnlargement of third functional toeStrengthening of the backDevelopment of brain and sensory organsIncrease in the complexity of teeth for feeding on grassThe evolution of horse is represented as

(i) EohippusIt had a short head and neck. It had four functional toesand a splint of 1 and 5 on each hind limb and a splint of1 and 3 in each forelimb. The molars were shortcrowned that were adapted for grinding the plant diet.(ii) MesohippusIt was slightly taller than Eohippus. It had three toes ineach foot.(iii) MerychippusIt had the size of approximately 100 cm. Although it still

had three toes in each foot, but it could run on one toe.The side toe did not touch the ground. The molars wereadapted for chewing the grass.(iv) PliohippusIt resembled the modern horse and was around 108 cmtall. It had a single functional toe with splint of 2nd andth4 in each limb.(v) EquusPliohippus gave rise to Equus or the modern horse withone toe in each foot.They have incisors for cutting grass and molars forgrinding food.View Text Solution On Doubtnut App

Class 12 Biology Evolution Ncert Video Solutions - Only On Doubtnut Download Doubtnut Now Exercise 7.1 Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory. SOLUTION: Darwinian selection theory states that individuals with favourable variations are better adapted than individuals with less favourable variation.