NCERT Class 12 Biology Solutions: Chapter 7 - Evolution

May 7, 2019

Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.

Solution: Darwinian selection theory states that individuals with favorable variations are better adapted than individuals with a less favorable variation.

An example of such selection is antibiotic resistance in bacteria. When the bacterial population was grown on an agar plate containing antibiotic penicillin, most of the colonies died, whereas one or few bacterial colonies that were resistant to penicillin survived. This is because these bacteria had undergone chance mutation, which resulted in the evolution of a gene that made them resistant to penicillin drug. Hence, the resistant bacteria multiplied quickly as compared to non-resistant (sensitive) bacteria, thereby increasing their number.

Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.

Solution: Fossils of dinosaurs have revealed the evolution of reptiles in Jurassic period. As a result of this, evolution of other animals such as birds and mammals has also been discovered. However, two unusual fossils recently unearthed in China have ignited a controversy over the evolution of birds. Confuciusornis is one such genus of primitive birds that were crow-sized and lived during the Cretaceous period in China.

Attempt giving a clear definition of the term species

Solution: Species can be defined as a group of organisms, which have the capability to interbreed in order to produce fertile offspring.

Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)

Solution: The various components of human evolution are as follows.

S no:NameBrain capacityPostureFoodFeatures1.Dryopithec us Africans-Knuckle, walker, walked similar to gorillas and chimpanzees (was more ape-like)  Soft fruit and leaves Canines large, arms and legs are of equal size2.Ramapithe cus-Semi-erect (more man - like)Seeds, nuts Canines were small while molars were large.3.Australopit hecus Africans Full erect posture, height ()Herbivorous (ate fruits)  Hunted with stone weapons, lived at trees, canines and incisors were small 4.Homo habilis Fully erect posture, height  carnivorous Canines were small. They were the first tool makers. 5.Homo erectus Fully erect posture, height  OmnivoursThey used stone and bone tools for hunting games.6.Homo neandertha Insis Fully erect posture, height  OmnivoursCave dwellers used hides to protect their bodies and buried their dead7.Homo sapiens fossilis Fully erect posture with height  OmnivoursThey had a strong jaw with teeth close together.  They were cave dwellers, made paintings and carvings in the caves.  They developed a culture and were called the first modern men.8.Homo sapiens sapiens Fully erect posture, height  OmnivoursThey are living modern men, with high intelligence. They developed art, culture, language, speech, etc. They cultivated crops and domesticated animals

Find out through the internet and popular science articles whether animals other than man have self-consciousness.

Solution: Many animals other than humans have self-consciousness. An example of an animal being self-conscious is dolphins. They are highly intelligent. They have a sense of self and they also recognize others among themselves and others. They communicate with each other by whistles, tail slapping, and other body movements. Not only dolphins, but there are also certain other animals such as crow, parrot, chimpanzee, gorilla, orangutan, etc., which exhibit self-consciousness.

List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.

Solution: The modern day animals and their ancient fossils are listed in the following table.

Related: NCERT Class 12 Biology solutions - Chapter 6 -  Molecular Basis of Inheritance

Practise drawing various animals and plants.

Solution: Ask your teachers, parents, and friends to suggest the names of plants and animals and practice drawing them. You can also take help from your book or internet to find the names of plants and animals.

Describe one example of adaptive radiation.

Solution: Adaptive radiation is an evolutionary process that produces new species from a single, rapidly diversifying lineage.

An example of adaptive radiation is Darwin finches, found in Galapagos Island. A large variety of finches is present in Galapagos Island that arose from a single species, which reached this land accidentally. As a result, many new species have evolved, diverged, and adapted to occupy new habitats. These finches have developed different eating habits and different types of beaks to suit their feeding habits. The insectivorous, bloodsucking, and other species of finches with varied dietary habits have evolved from a single seed-eating finch ancestor.

Can we call human evolution as adaptive radiation?

Solution: No, human evolution cannot be called adaptive radiation. This is because adaptive radiation is an evolutionary process that produces new species from a single, rapidly diversifying lineage, which is not the case with human evolution. Human evolution is a gradual process that took place slowly in time. It represents an example of anagenesis.

Using various resources such as your school library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal say horse.

Solution: The evolution of the horse started with Eohippus during Eocene period. The stages in the evolution of horse with their short description are given below:

(i) Eohippus

It had a short head and neck. It had four functional toes and a splint of 1 and 5 on each hind limb and a splint of 1 and 3 in each forelimb. The molars were short crowned that were adapted for grinding the plant diet.

(ii) Mesohippus

It was slightly taller than Eohippus. It had three toes in each foot.

(iii) Merychippus

It 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 were adapted for chewing the grass.

(iv) Pliohippus

It resembled the modern horse and was around 108 cm tall. It had a single functional toe with splint of 2nd and 4th in each limb.

(v) Equus

Pliohippus gave rise to Equus or the modern horse with one toe in each foot. They have incisors for cutting grass and molars for grinding food.


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