NCERT Solutions for Class 12 Biology Chapter 7: Evolution
1. Explain antibiotic, resistance observed in bacteria in light of Darwinian selection theory.
Ans. According to Darwin, environment selects organisms with favourable variations and these organisms are allowed to survive. When a bacterial population encounters a particular antibiotic, those sensitive to it die. But some bacteria having mutations become resistant to the antibiotic. Such resistant bacteria survive and multiply quickly as the competing bacteria have died. Some the resistance providing genes become widespread and entire bacterial population becomes resistant.
2. Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
Ans. Fossils of dinosaurs were found that have revealed to evolution of reptiles in jurassic period.
Two unusual fossils recently found in China which brings the controversy over the evolution of the birds. Confuciusornis lived during the cretaceous period in China is the genus of primitive bird.
3. Attempt giving a clear definition of the term species.
Ans. Species is population or group of individuals that have potential of interbreeding and are able to produce viable, fertile young ones but are reproductively isolated from members of other species.
4. Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
Ans. The various components of human evolution are as follows:
| S.No. | Name | Brain capacity (cm3) | Skeleton structure | Dietary preference |
| | Dryopethicus africans | – | Posture similar to chimpanzees and gorillas | Herbivore |
| | Rama-pithecus | – | Fully erect | Herbivore |
| | Australop- ithicus africans | 450 | Fully erect | Herbivore |
| | Homo habilis | 735 | Fully erect | Carnivore |
| | Homo erectus | 800-1100 | Fully erect | Omnivore |
| | Homo neander-thalensis | 1300-1600 | Fully erect | Omnivore |
| | Homo sapiens fossils | 1650 | Fully erect | Omnivore |
| | Homo sapiens sapiens | 1200-1600 | Fully erect | Omnivore |
5. Find out through internet and popular science articles whether animals other than man has self-consciousness.
Ans. They are many animals other than humans, which have self consciousness. These includes dolphins, elephants, chimpanzees, apes and monkeys.
6. List 10 modern-day animals and using the” internet resources link it to a corresponding ancient fossil. Name both.
Ans.
| Animal | Ancient fossils | |
| | Human | Ramapithecus |
| | Horse | Eohippus |
| | Camel | Protylopus |
| | Whale | Protocetus |
| | Bat | Archaeonycteris |
| | Giraffe | Palaeotragus |
| | Gorilla | Dryopithecus |
| | Octopus | Belemnite |
| | Tetrapods | Icthyostega |
| | Dog | Leptocyon |
7. Practise drawing various animals and plants.
Ans. (i) Elephant
(ii) Camel
(iii) Dog
(iv) Rose
(v) Dahlia
(vi) Hibiscus
8. Describe one example of adaptive radiation.
Ans. Darwin’s finches of the Galapagos islands had common ancestors but now have different types of modified beaks according to their food habits.
9. Can we call human evolution as adaptive radiation?
Ans. Adaptive radiation is not a term that can be used for human evolution. This is because adaptive radiation is an evolutionary mechanism that produces new species from a single, rapidly diversifying lineage, but human evolution does not.
10. 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.
Ans.Evolutionary stages of horse:
Eohippus
– Mesohippus – Merychippus – Pliohippus – Equus.
Evolutionary trend:
(i) Increase in body size.
(ii) Elongation of neck.
(iii) Lengthening of limbs.
(iv) Enlargement of third digit.
(v) Increase in structural complexity of teeth for feeding on grass.
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