NCERT Solutions Class 12 Biology Chapter 7
NCERT Solutions Class 12 Biology Chapter 7
The study of all living things, whether plants, animals, or microorganisms, is called Biology. The words “biology” and “logos” come from the Greek words “bios” (life) and “logos” (word) (meaning “study”). Biologists examine the structure, function, growth, origin, evolution, and distribution of living creatures. The process of gradual modification of simpler forms of life into the current complex forms over millions of years is called evolution.
Evolution also includes substantial changes in flora and fauna, as well as human beings. These characteristics result from random mutations in the organism’s DNA that are “chosen” by natural selection. Students study several theories of evolution in the Class 12th Evolution Chapter. In addition, the Charles Darwin theory of evolution is also being studied.
Biology may be both enjoyable and comprehensive due to its vast syllabus. The technique and platform that the student utilises to learn Biology could be the deciding factor. Therefore, Extramarks has come up with Chapter 7 Biology Class 12 NCERT Solutions. These solutions are intended to assist students in comprehending the central concept, course material, and chapter questions.
Not just NCERT Solutions Class 12 Biology Chapter 7, Extramarks provides comprehensive quality study material such as NCERT books, CBSE revision notes, CBSE sample papers, CBSE previous year question papers, and many more on the Extramarks website for all classes.
Key Topics Covered in NCERT Solutions Class 12 Biology Chapter 7
Mentioning below all the key topics that are covered in NCERT Solutions Class 12 Biology Chapter 7- Evolution:
|Origin of Life|
|Evolution of Life Forms- A Theory|
|What are the evidences for Evolution?|
|What is Adaptive Radiation?|
|Mechanisms of Evolution|
|Hardy – Weinberg Principle|
|A brief account of Evolution|
|Origin and Evolution of Man|
Let us look at Extramarks’ in-depth information on each subtopic in NCERT Solutions Class 12 Biology Chapter 7- Evolution.
Origin of Life
NCERT Solutions Class 12 Biology Chapter 7 explains that in the history of the cosmos, the origin of life is regarded as a singular occurrence. The universe is composed of a massive cluster of galaxies. Galaxies are made up of stars, dust, and smoke clouds.
The Big Bang Theory makes an effort to explain the universe’s creation. According to this hypothesis, a massive explosion creates several galaxies.
Earth is thought to have formed some 4.5 billion years ago when the solar system settled in its current layout. The early Earth had no atmosphere. The earth’s surface was coated in water vapour, methane, carbon dioxide, and ammonia that were emitted from molten matter.
The UV radiation from the sun decomposed the particles of water into hydrogen and oxygen. 500 million years after the Earth’s origin, life first emerged.
There are several hypotheses about how life came to be on earth:
- Some scientists think life originated on distant worlds. Early Greek philosophers believed that spores sent from other planets were the basic building blocks of life.
- Another idea claims that life emerges from dead and decomposing materials like dirt and straw. This hypothesis is known as the spontaneous origin theory.
- Louis Pasteur conducted experiments to demonstrate that only existing life can give rise to new life. After that, the spontaneous account of life’s genesis is rejected.
- Oparin and Haldane suggested that the initial form of life may have developed from pre-existing organic molecules that were not alive, such as RNA and protein. Chemical evolution came before the creation of life. The state of earth during that period was characterised with high temperature and frequent volcanic eruptions which were reducing the amount of CH4 and NH3 in our atmosphere.
Miller’s experiment on the origin of life was carried out in 1953 to demonstrate how life came to be on earth in a physical environment that was comparable to that of the time.
Miller established comparable pressure and temperature conditions on a small scale. At 8000C, he produced an electric discharge in a flask with water vapour, CH4, H2, and NH3.
After a period of 15 days of electric discharge, he saw the production of amino acids in the flask. Other scientists who conducted similar experiments discovered the creation of sugars, nitrogen bases, pigments, and lipids.
Similar molecules that indicate that similar processes are occurring elsewhere in space are also revealed by analysis of meteorite composition. Chemical evolution of life is the name given to this experimental proof of the genesis of life.
Evolution of Life Forms- A Theory
Various scientists and intellectuals have offered their theories on the origin of life.
- According to the theory of special creation, God created life as part of his divine act of creation.
- Early Greek thinkers proposed the panspermia/cosmosoic theory, which holds that spores or panspermia originated in space and transformed into living organisms.
- According to the theory of spontaneous generation, life first appeared in rotting and decaying substances like straw, muck, etc.
Louis Pasteur established that life originated from pre-existing life and rejected the hypothesis of spontaneous genesis.
He stored dead yeast cells in a pre-sterilised flask for his experiment and left another flask exposed to the air. In the first flask, life did not evolve, but new living things did in the second.
According to the Oparin-Haldane theory, which proposes that chemical evolution predated the genesis of life, life first evolved from previously existing non-living organic components.
The earth’s extremely high temperatures, volcanic storms, and reducing atmosphere with elements like CH4, NH3, water vapour, etc., were favourable for chemical development.
What are the evidences for Evolution?
NCERT Solutions Class 12 Biology Chapter 7 explains that there are several signs that life has evolved on earth, including those listed below:
- Paleontological evidence: Different types of fossilised living forms that likely perished during the creation of a given sediment can be found in various types of old rock deposits. Fossils are the brittle remnants of extinct living forms that are discovered in rocks. According to the study, different living forms have changed over time, and some have a limited geological time range. As a result, new life forms have emerged throughout Earth’s history.
- Homologous organs: Organs with a different function but a similar origin and structure are referred to as homologous organs. For instance, the forelimb bone patterns of humans, cheetahs, bats, and whales are similar, despite the fact that these forelimbs serve different purposes in each of the aforementioned creatures. These animals’ comparable structures evolved in various directions to meet their adaptability to various demands. Divergent evolution describes this.
- Analogous structures: Similar structures—although they are not physically identical organs, they serve the same purpose. For instance, the eyes of animals, the octopus, or the penguin and dolphin flippers. This is because diverse groups of creatures with comparable habitats have similar adaptive traits. Convergent evolution is the name given to this type of evolution.
- Evolution by Natural Selection: Before industrialisation, in the 1850s, in England, a peppered moth was found to have undergone natural selection (Biston betularia). This moth came in two colours: grey and black (Carbonaria). Only the grey-colored moths were present in the early nineteenth century, before industrialisation; the dark kinds were uncommon. The lichen-covered tree trunks were where the grey-colored moths were observed, which allowed them to flee from their assailants. The lichens died off and the tree trunks appeared black owing to the accumulation of industrial soot later in 1920 as a result of the expansion of industries and post-industralisation. Now that they could be seen, these moths may be eaten by birds. As a result, the dark-colored moths fled from the birds while the grey-colored moths were consumed by them. Then, enterprises began using electricity and oil in place of coal. As a result, there is less soot accumulating on tree trunks since there is less soot generation. Now, the colour of these tree trunks is grey once more. As a result, the population of gray-colored moths has once more grown. This example effectively illustrates how natural selection operates.
- Evolution by anthropogenic action: DDT was a huge success when it was used to control mosquitoes. The majority of the mosquitoes were killed because they were susceptible to DDT. Few mosquitoes in that population developed DDT resistance and lived. They grew in number, and today practically all mosquito populations are DDT-resistant.
The same pattern has been seen in bacteria that are multidrug resistant as a result of the overuse of pharmaceuticals.
What is Adaptive Radiation?
Adaptive radiation is the process by which several species evolve in a certain geographic region, starting at a point and spreading to other parts of geography (habitat). One of the greatest instances of adaptive radiation is Darwin’s finches. Australian marsupials developed differently from one another yet all lived on Australian island continents.
We might refer to this as convergent evolution when more than one adaptive radiation (representing various environments) appears to have happened in a remote geographic location. Examples include placental mammals and Australian marsupials.
In nature, the fittest survive, and fitness is dependent on hereditary traits. Some species can more successfully adapt to unfavourable environments. The ability to adapt and be chosen by nature leads to fitness.
Lamarck claimed that the use and abuse of organs was what caused the evolution of living forms. He used the example of how giraffes have to adapt by lengthening their necks in order to forage for leaves on towering trees. Natural selection and branching descent are the two main ideas of the Darwinian Theory of Evolution.
Darwin’s theory of natural selection was founded on a number of findings, including:
- A struggle for resources
- Limited natural resources.
- Struggle for existence.
- Survival of the fittest.
Mechanisms of Evolution
Hugo deVries developed the concept of mutation based on his research on evening primrose. A population’s abrupt emergence of a significant variation is called a mutation.
Darwin variations are modest and directed while mutations are random and directionless. Hugo de Vries used the term “saltation” because he thought that mutation leads to speciation (single step large mutation).
Hardy – Weinberg Principle
- The principle argues that allele frequencies in a population are steady and consistent from generation to generation, implying that the gene pool is stable. When the sum of all allelic frequencies equals one, this is called genetic equilibrium.
- Let p and q denote the frequency of alleles A and an in a diploid. Then, the product of the probabilities is the likelihood that an allele A with a frequency of p exists on both chromosomes of a diploid person.
- Gene flow, genetic drift, genetic recombination, mutation, and natural selection are five processes that influence the Hardy-Weinberg principle.
- The founder effect occurs when the initial drifting population becomes founders.
A brief account of Evolution
The earliest cellular forms of life originally arose on Earth some 2000 million years ago.
- Single-celled creatures gradually gave way to multicellular forms until, by 500 mya, invertebrates had developed and were functioning.
- Fish without jaws first appeared about 350 mya.
- From the sea to the land, organisms began to invade. Fish with robust fins had the ability to walk on land and return to the water. The first amphibians descended from these creatures, known as lobefins.
- These amphibians later transformed into reptiles. They lay eggs with shells. Then, reptiles of all sizes and forms ruled the planet, including terrestrial reptiles like dinosaurs and fish-like reptiles like ichthyosaurs. The Tyrannosaurus Rex was the largest of them all.
- A few of the reptiles transformed into birds, and some into mammals. Mammals were viviparous and better at recognising and avoiding danger.
Origin and Evolution of Man
Primates like Dryopithecus existed around 15 million years ago. In terms of appearance and locomotion, these creatures resembled chimps and gorillas.
- Ramapithecus was more humanoid, but Dryopithecus was more like gorillas.
- In Ethiopia and Tanzania, fossilised bones resembling human bones have been discovered.
- Australopithecines lived two million years ago. Most often encountered in the grasslands of East Africa.
- They used weapons that were created specifically for hunting.
- Initially, they followed a vegetarian diet.
The hominid, also known as Homo habilis, was the earliest human-like entity.
- The hominid’s brain capacity ranged from 650 to 800 cubic centimetres.
- Hominids continued to eat only plants.
Fossils discovered in Java in 1891 looked to belong to the next evolutionary step, Homo erectus. Homo erectus appeared 1.5 million years ago. Homo erectus had a big brain with a volume of 900 cubic centimetres. They were most likely non-vegetarians who ate meat.
- They evolved in Africa and then spread to other continents, producing numerous races.
- Modern Homo sapiens arose 75,000-10,000 years ago during the cold period.
- Around 18,000 years ago, prehistoric cave art was created.
- Agriculture emerged roughly 10,000 years ago, followed by human habitation.
NCERT Solutions Class 12 Biology Chapter 7 Exercise and Solutions
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NCERT Solutions Class 12 Biology Chapter 7, students can easily understand all the concepts of Evolutions This encourages the students to master the topic and increases their confidence to achieve a high grade.
Key Features of NCERT Solutions Class 12 Biology Chapter 7
NCERT Solutions by Extramarks include all of the essential concepts and topics as per the latest CBSE board examinations. It is necessary for students to go through NCERT Solutions upcoming board examinations. But why go for Extramarks? Here’s why:
- These Solutions are prepared in a stepwise and detailed manner by the experienced faculty with years of experience.
- The subject experts curate these Solutions in a simple and straightforward language. It gives you an in-depth understanding of the subject, so that students can strengthen their fundamental concepts.
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Q.1 Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
According to Darwinian selection theory that the members of a population who have inheritable variations, each generation produces many more offsprings than can possibly survive and some individuals have adaptive characteristics that enable them to survive and reproduce better than other individuals. This resulted in an increasing proportion of individuals to have adaptive characteristics in succeeding generations which in turn results in a population adapted to that particular environment. The phenomenon of antibiotic resistance observed in bacteria can be very well explained in terms of Darwinian selection theory. In a population of bacteria, some bacteria already have inheritable variations in the gene responsible for resistance towards a specific antibiotic. When such a mixed population of bacteria is exposed to that specific antibiotic, those who are sensitive to it die but those with the genetic variation for antibiotic resistance, survive in the presence of that antibiotic. This antibiotic resistance trait is passed on to the next generation. When the next generation bacteria are also exposed to the antibiotic the bacteria which have inherited the trait are able to survive and those who may have and Slowly, the population of such bacteria increases and the entire population, over the time, becomes resistant to that particular antibiotic.
Q.2 Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
Fossils are preserved remains or traces of animals, plants or other organisms that existed a long time ago in history. They give us very important clues about the life forms that existed millions of years ago. Also, a lot has been understood in terms of origin and evolution of various groups of animals based on a study of different fossils found at different locations across the world. Few examples :
Dinosaur fossils have been known about for millennia. The Chinese considered them to be dragon bones, while Europeans believed them to be the remains of giants and other creatures killed by the Great Flood. The first dinosaur species to be identified and named was Iguanodon, discovered in 1822 by the English geologist Gideon Mantell, who recognised similarities between the fossils and the bones of modern iguanas.
- The discovery of a rare human skull in October 2013, sparked an evolution controversy. Researchers have discovered the fossilised skull of an early human relative in Dmanisi, Georgia. It is said to be the most complete skull ever of the early Homo genus. They say it could represent a single evolving Homo erectus lineage that came out of Africa and spread into Europe and Asia — a conclusion that is still controversial.
- Archaeopteryx fossil has been a classic textbook example of a species in evolutionary transition, displaying features that are a part bird, part reptile. However, scientists have reclassified it based on a newly discovered fossil of a two-legged feathered creature in China as a feathered dinosaur, one of the many that were fluttering around in the Jurassic period more than 150 million years ago.
Q.3 Attempt giving a clear definition of the term species.
Species can be defined as a group of the reproductively isolated population that inter-breed to produce fertile offspring and share phenotypic similarities.
Q.4 Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
Human evolution has been a lengthy process of change by which human originated from ape-like ancestors. Scientific evidence shows that the physical and behavioral traits shared by all people originated from ape-like ancestors and evolved over a period of approximately six million years. The following chart depicts some components of human evolution:
|S.No.||Name||Brain Size||Posture||Skeletal Structure||Dietary Preference||Features|
|1||Dryopithecus africans||—||Walked similar to gorillas and chimpanzees in knuckles||Legs and arms were of same size.||Soft fruits and leaves||Had large canines.|
|2||Ramapithecus||—||Semi-erect (more man like)||semi-erect posture||Herbivorous, seed eaters||Small canines with well-developed and large molars.|
|3||Australopithecines||~440 cc brain||Walked upright with fully erect posture
|Pelvis resembled a modern human and a tibia/femur design supporting bipedal locomotion||Herbivorous (leaves, fruits, wood and bark)||Greater reasoning skills and more control of motor functions. Knew hunting with stones.|
|650-800 cc brain||Fully erect posture with 1.5 m height||They had a smaller snout and bigger nose, and an elevated forehead different from the earlier ancestors||Carnivorous||Had rational thought and problem solving capacity. Canines were small. They were the first to make tools.|
|5||Homo erectus||900 cc||Fully erect posture with 1.5-1.8 m height.||Fully erect posture||Omnivorous||They used stone and bone tools for hunting and gaming.|
|6||Neanderthal man||1400 cc||Fully erect posture with 1.5-1.66 m height||larger bones and more heavily muscled than most modern humans.||Omnivorous||Cave dwellers, used hides to protect their body and buried their dead.|
|7||Homo sapiens fossilis||1650 cc||Fully erect posture with 1.8 m height||Erect posture||Omnivorous||Strong jaws with close teeth. Cave dwellers; made painting and carvings in the caves. First modern man.|
|8||Home sapiens sapiens||1200-1600 cc||Fully erect posture with 1.5-1.8 m height||Erect posture||Omnivorous||Modern living humans with high levels of intelligence. Well developed art, culture, language and speech.|
Q.5 Find out through internet and popular science articles whether animals other than man have self-consciousness.
Self-consciousness means having conscious knowledge of one’s own character, feelings, motives and desires – and imagining how others might perceive us. It extends right up to having self-conscious emotions like pride or shame. It is a measure of intelligence – and most living species on the planet do not possess it. Of the hundreds of animals tested (by mirror test) so far, only 10 animals have been proven to have any measurable degree of self-awareness. They are Humans, Orangutans, Chimpanzees, Gorillas, Bottlenose Dolphins, Elephants, Orcas, Bonobos, Rhesus Macaques and European Magpies.
Q.6 List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.
List of 10 modern-day animals along with corresponding ancient fossil:
|S. No.||Modern-day animal||Ancient fossil|
Q.7 Describe one example of adaptive radiation.
Adaptive radiation is the rapid development of many new species from a single ancestral species, which then spread out and become adapted to various ways of life. One of the best examples of adaptive radiation has been Galapagos finches. During his HMS Beagle voyage, Darwin had observed an amazing diversity of small black birds (Darwin’s finches) on the same island. According to him, all these evolved on the island itself from one single species. The original birds were seed-eating creatures and then evolved forms with altered beaks, enabling them to become insectivorous and vegetarian finches. A small number of mainland finches arrived at one of the Galapagos islands. Genetic drift and natural selection process began acting on this group. This group then migrated to two more islands where there was no more gene flow between these groups and each was again subjected to genetic drift and different kinds of selection pressures. As they migrated back to the original island, they did not interbreed and behaved as independent species. They became adapted to the new environment and thus, evolved as separate species.
Q.8 Can we call human evolution as adaptive radiation?
No, human evolution cannot be called as adaptive radiation. Adaptive radiation is the rapid development of many new species from a single ancestral species, which then spread out and become adapted to various conditions. Human evolution took place slowly over millions of years and is an example of anagenesis where change occurs very slowly.
Q.9 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.
In the evolutionary history of the horse, an overall evolutionary trend in the lineage is clearly visible. During the phylogenetic history of horse or Equus, the following points are distinctly noticeable:
- Increased overall size along with an increase in the length of feet and legs.
- Increased grinding surface of the molar teeth.
- Reduced number of toe.
- Strengthening of back.
- Development of brain and other sensory organs
Evolutionary History: The history of horse begins with Hyracotherium (also known as Eohippus). They were dog-sized mammals with a small head and small, low-crowned molars with cusps. The feet, with 4 toes on each front foot and 3 toes on each hind foot, were padded. They were present in the Eocene era and were adapted to the forest-like environment present at that time. The small size allowed them to hide easily among the trees for protection, and the low-crowned teeth were appropriate for browsing on leaves.
With the passage of time, grasslands replaced forests, thus putting selective pressure on the Eohippus. They were required to develop strength, intelligence, speed and durable grinding teeth. This resulted in their increased size to provide more strength, a larger skull for a larger brain, elongated legs ending in hooves for greater speed to escape enemies, and the durable grinding teeth to feed efficiently on grasses. These characters slowly evolved in Miohippus, Merychippus and Pliohippus with passage of time from Eocene to Pliocene era.
The modern-day Equus came into existence sometime in the Pleistocene era. They have one toe in each foot. The incisors for cutting and molars for grinding are also very well developed.
Q.10 Practise drawing various animals and plants.
Select a few plants and animals that you find comparatively easy to draw and label. Practice on these diagrams to make them neat, clear and precise. You can also use the internet to find the name of different parts of their body. The labelled diagrams of goat and banana tree are given below for your reference.
FAQs (Frequently Asked Questions)
1. Give suggestions for an effective study plan for Biology Chapter 7 in Class 12?
To achieve good grades, students must prepare their own study timetable and then prioritise them as per their difficulty level. Check the exam pattern and revise important topics and practise diagrams and labelling them. Second, before consulting the NCERT Solutions , the student must go through the NCERT books, especially for subjects like Biology, which require notes, revision, and sample papers. Finally, if the student needs any help, you can bank on Extramarks for doubt clearing sessions, past years’ question papers, mock tests to check their preparation level and be confident. The systemic and well-laid out balanced study plan boosts their performance naturally and effortlessly.
2. What is chapter 7 of Class 12 Biology all about?
Class 12, Chapter 7 of Biology discusses different forms of living creatures, their evolution, traits, and the changes across generations. This chapter is all about how living things evolve biologically through time.