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:

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.

Biological Evolution

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.
• Overpopulation.

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.

Homo sapiens

• 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.
• These Solutions help students  deal with  the challenging topics and get accurate and concise answers. It actually saves their time and unnecessary stress and anxiety.