Students can download Class 8 Science Chapter 22 Evolution of Life Important Questions, KSEEB Class 8 Science Important Questions and Answers helps you to revise the complete Karnataka State Board Syllabus and to clear all their doubts, score well in final exams.
Karnataka State Syllabus Class 8 Science Important Questions Chapter 22 Evolution of Life
Question 1.
What is the approximate age of the earth?
Answer:
According to an estimate, the earth was formed around 4.6 billion years ago.
Question 2.
When did the first living beings emerge on earth?
Answer:
It is said that the first life emerged on earth around 3.8 billion years ago.
Question 3.
Name the scientist who advocated that only life begets life on the basis of experimental evidence.
Answer:
Louis Pasteur advocated that life begets life on the basis of his most famous ‘swan necked flask’. This means that living organisms emerge from pre-existing organisms.
Question 4.
Who proposed ‘chemical evolution theory’ to explain the origin of life forms on earth?
Answer:
Two scientists Alexander Oparin and J.B.S. Haldane independently developed the ‘chemical theory of evolution’ to explain the origin of life on earth.
Question 5.
Give the main points of Opar in-Haldane theory on the origin of life.
Answer:
According to Oparin-Haldane theory
- The earth’s atmosphere during the first billion years of its existence was radically different from today’s conditions.
- The atmosphere of the primitive earth did not contain oxygen.
- The first life emerged from a series of chemical reactions which formed organic molecules from inorganic molecules.
- Solar radiation, ultraviolet rays and lightning provided the required energy for these chemical reactions.
The first life forms emerged from the complex organic molecules formed from the chemical reactions.
Question 6.
What was the composition of the earth during its initial days after its formation?
Answer:
The early earth contained heavy elements such as iron and nickel in its core. Lighter elements such as aluminium and silicon occupied the crust. The lightest elements such as hydrogen and carbon were present in the outermost layer.
Question 7.
Describe the composition of the early atmosphere of the earth.
Answer:
When the Earth first started to form 4.6 billion years ago, the first atmosphere was probably made mainly of hydrogen and helium. During the first billion years, these light gases quickly escaped the Earth’s gravitational attraction and were replaced with carbon dioxide, water vapour and nitrogen from the large number of volcanoes that existed as the earth started to cool. This pre-life atmosphere contained carbon dioxide, nitrogen, methane, and ammonia. However, there was no oxygen.
Question 8.
Why did the early atmosphere of the earth not contain oxygen?
Answer:
The oxygen formed in the early earth quickly combined with the various metals and non-metals present in the earth to form their respective oxides. This is why the primitive atmosphere did not contain oxygen.
Question 9.
How did the oceans form on the earth?
Answer:
The oceans formed on Earth 3.8 billion years ago. At this time the age of the earth was about 1 billion years. The water that was present in the earth was in vapour state. As the earth cooled, water condensed to form the first clouds which brought in huge rain storms. The torrential rains filled the shallow regions of the earth to form primitive oceans.
Question 10.
How did the water in the primitive oceans turn into a hot dilute soup?
Answer:
As the early earth cooled, a number of simple organic molecules came into existence. As the process continued, simple organic compounds underwent chemical changes to form complex organic compounds inside the ocean. The accumulation of these compounds gradually turned water in the primitive ocean into a hot dilute soup.
Question 11.
What are coacervates?
Answer:
Coacervates are complex molecules formed during the chemical evolution of life. They were the first to exhibit the properties of life, growth and reproduction.
Question 12.
What are protobionts?
Answer:
Aggregates of abiotically-produced organic molecules, in the primitive oceans, surrounded by a membrane or a membrane-like structure are called protobionts. Such units which exhibited some of the properties associated with life, including simple reproduction., metabolism and excitability were known as protobionts. Sometimes they are simply called probiotics.
Question 13.
Which were the first autotrophic organisms to emerge on earth?
Answer:
Blue-green algae were probably the first autotrophs to emerge on earth. These organisms carried out photosynthesis and released oxygen into the atmosphere.
Question 14.
How did blue-green algae change the composition and nature of the earth’s atmosphere?
Answer:
The atmosphere of the early earth did not contain oxygen. It was a reducing type of atmosphere which had large amount of carbon dioxide. Blue-green algae were capable of photosynthesis. During the process, they released oxygen to the atmosphere.
This changed the atmosphere from reducing type to oxidizing type. Further blue-green algae helped to reduce the proportion of carbon dioxide and increased the proportion of oxygen in the atmosphere.
Question 15.
Write the changes from the primitive earth till the formation of first cells. Follow the example and fill in the blanks.
Answer:
Question 16.
Which organisms changed earth’s atmosphere from reducing to oxidising type?
Answer:
Blue-green algae gradually transformed the atmosphere from reducing type to oxidizing type.
Question 17.
What is organic evolution?
Answer:
The process through which the present-day complex forms of life have descended from simple forms of the past is known as original evolution.
Question 18.
Who proposed the ‘theory of inheritance of acquired characteristics’? What are the other names by which this theory is known?
Answer:
Jean-Baptiste Lamarck proposed the ‘theory of inheritance of acquired characteristics’ in 1809 to explain the evolution of life forms. Lamarck’s theory is also known as Lamarckism. It is also known as theory of use and disuse.
Question 19.
State the main ideas of Lamarck’s theory of organic evolution.
Answer:
Lamarck’s evolutionary theory included the following main ideas
- Environmental changes generate new needs
- These needs determine the use or disuse of some organs
- Such organs develop or are diminished (use and disuse of organs)
- The acquired characters are passed on to the next generation (inheritance of acquired characters).
Question 20.
Explain Lamarck’s theory of use and disuse of organs with suitable examples.
Answer:
According to Lamarck, changes in the environment creates new needs in an organism. If the organism fails to make necessary changes favourably, it cannot survive. It may put a particular part of its body to more and more frequent use. Similarly, it may also be necessary for the organism to put a part of its body to less use or may not use it at all.
This idea came to be known as use and disuse of organs. Any part of the body that is used more and more, is likely to grow larger and become better and stronger. In the same way, any part of the body which is less frequently used, has a tendency to become less prominent and may even ultimately disappear.
Thus, by a differential overuse and disuse of various body parts, an organism would change to some extent and acquire new characters. Lamarck’s ideas on evolution may be explained by citing a few examples from his own writings. According to Lamarckism, giraffes started stretching their neck and limbs in order to reach the leaves of taller plants.
The practice of stretching the neck and limbs continued for several generations resulting in the gradual increase in the length of the neck and limbs. This example is often cited to support Lamarck’s idea that any organ put into continuous use has a tendency to develop better.
According to Lamarck, the absence of limbs in the snakes is an evolutionary change driven by disuse of organs. The ancestors of snakes, which had well-developed limbs, faced the problem of increased threat from their predators such as birds and mammals.
To protect themselves from their natural enemies, snakes started living in crevices and holes. The use of limbs gradually reduced and hence they became increasingly shorter over generations and finally disappeared.
Question 21.
State the two laws that summarize Lamarckism.
Answer:
Lamarck’s theory of evolution has been summarized in two laws
1. Law of Use and Disuse of organs:
The parts of an organism that are used more become more developed; parts that are not used become smaller and may-even disappear.
2. Law of Inheritance of Acquired Characteristics:
Changes acquired in the body of an organism in its lifetime are passed on to its offspring.
Question 22.
What were the limitations of Lamarckism?
Answer:
Lamarck’s theory could not explain how body cells pass on the acquired characteristics to reproductive cells. Experiments have shown that acquired characters are not inherited.
Question 23.
How did Weismann disprove Lamarck’s theory of inheritance of acquired characters?
Answer:
August Weismann conducted a simple experiment called mutilation experiment on rats. He cut off the tails of a male rat and a female rat. According to Lamarck, the taillessness is an acquired character and is heritable. To verify this, Weismann allowed these tailless rats to breed. Surprisingly, the offsprings were normal tailed.
Not satisfied with this, Weismann went on repeating the procedure for 21 generations and each time, he got normal tailed rats. Based on these results, he disproved Lamarck’s theory of inheritance of acquired characters.
Question 24.
What is the theory proposed by Charles Darwin to explain organic evolution?
Answer:
The theory developed by Charles Darwin is called ‘theory of organic evolution by natural selection’. It is also known as Darwinism.
Question 25.
What are the main ideas of Darwin’s theory of evolution by natural selection?
Answer:
The following are the key points of Darwin’s theory of evolution
- Existence of variation: There is variation in characteristics in every population.
- Overproduction: All organisms tend to produce more offspring than can survive.
- Struggle for existence: Organisms compete for limited resources.
- Survival of the fittest: Only those individuals who have most favourable variations will survive and reproduce. Darwin called this ‘natural selection’.
- Inheritance: Organisms with favourable adaptive characteristics will pass on their traits to their offspring.
- Origin of species: The accumulated changes over a long period of time lead to the emergence of new species.
Question 26.
What is overproduction? Why do organisms overproduce?
Answer:
The ability of a species to produce far more offspring than can possibly survive is known as overproduction. Overproduction in organisms gives a wider choice for natural selection. If there were only fewer offspring in a given species, there would be fewer variations.
This restricts the choice of selecting the most adaptive individuals. In order to increase the choices for natural selection, organisms overproduce offspring.
Question 27.
What is the consequence of overproduction in species?
Answer:
Overproduction creates competition for crucial resources like living space, food, water, mating opportunities, etc., which are limited in supply. This creates a competition among the individuals of the species. The struggle for existence is the primary force behind natural selection.
Question 28.
What is the role of variations in evolution?
Answer:
Generally young ones of an organism show differences compared to the parent. Darwin calls these differences as variations. Variations help an organism to adjust better to the environment.
Question 29.
What is ‘survival of the fittest in Darwin’s theory?
Answer:
The competition amongst the individuals for resources enables nature to select the best fits. Those which have most favourable adaptations will survive in the struggle for existence and those which have less favourable variations will perish. The most adaptable are the fittest among the species. They survive and reproduce. This is known as survival of the fittest. Darwin called this ‘natural selection’.
Question 30.
What is natural selection? What is its consequence?
Answer:
The process by which nature selects individuals with most favourable traits to survive and reproduce is known as natural selection. As a consequence of natural selection, individuals in a given species with most favourable adaptations will survive.
Those with less favourable adaptations perish. As a result, the individuals with favourable characteristics become more common in successive generations of a population and those with unfavourable characteristics become less common.
Question 31.
According to Darwin’s theory, how do new species originate?
Answer:
Darwin proposed in his theory that new species originate by natural selection. In the struggle for existence only the fittest will survive and reproduce. This will result in young ones which are better adapted for the next phase of struggle for existence. Darwin called it descent with modification. As the environment is ever changing, it demands new variations in the organisms.
Gradually new characters are accumulated in the offspring across generations. These accumulated changes over a long period of time will produce offspring which vary in a major way from their original ancestors and hence will form new species.
Question 32.
What were the limitations found in Darwinism?
Answer:
Darwinism suggested that small variations present in species form the basis for evolution. This means that the organs appear as small structures and gradually become perfect after several generations. In certain animals, some organs have developed beyond the stage of usefulness. These organs are more of a hindrance to the animals concerned.
According to the theory of natural selection, only the useful organs are selected in the struggle for existence. However, some organs which have no function continue to be present generation after generation. Darwin was not clear about the sources of variations and mechanisms of natural selection.
Question 33.
What are mutations?
Answer:
Variations brought about by sudden changes in the genetic make up of an organism are called mutations.
Question 34.
What is Neo-Darwinism?
Answer:
The modem version of Darwin’s theory of evolution which incorporates the principles of genetics to explain how inheritable variations can arise by mutation is known as Neo-Darwinism. It also explains the emergence of new species due to mutations.
Question 35.
What was the modification made by Victor Hugo to Darwin’s theory?
Answer:
Victor Hugo De Vries suggested some modification in Darwin’s theory to account for some sudden variations in a population leading to the emergence of new species. De Vries suggested that large-scale variations occurring in a population are due to sudden changes in the genetic make up of organisms. He called these changes mutations.
Multiple Choice Questions
Question 1.
The earth is about
(a) 4.6 billion years old
(b) 3.5 billion years old
(c) 2.5 billion years old
(d) 10 billion years old
Answer:
(a) 4.6 billion years old
Question 2.
The phrase ‘hot dilute soup for primitive chemical-rich ocean was used by
(a) DeVries
(b) Darwin
(c) Haldane-Oparin
(d) Pasteur
Answer:
(c) Haldane-Oparin
Question 3.
Which one of the gases was absent in the atmosphere at the time of origin of life?
(a) ammonia
(b) oxygen
(c) hydrogen
(d) methane
Answer:
(b) oxygen
Question 4.
The earliest cellular life forms appear to have been
(a) viruses
(b) one-celled plants
(c) one-celled animals
(d) bacteria
Answer:
(d) bacteria
Question 5.
The life on earth is most likely to have started
(a) in the oceans
(b) deep inside the earth
(c) under frozen oceans
(d) on land near the equator
Answer:
(a) in the oceans
Question 6.
A construction worker has well developed muscles and he argues that it is due to the type of work inherited from his father would find support in
(a) Darwin’s theory
(b) Oparin-Haldane theory
(c) Mutation theory of De Vries
(d) Lamarck’s theory
Answer:
(d) Lamarck’s theory
Question 7.
The first organisms on primitive earth were
(a) autotrophic
(b) heterotrophic and anaerobic
(c) parasitic
(d) prokaryotic and autotrophic
Answer:
(b) heterotrophic and anaerobic
Question 8.
Which one of the statements correctly reflects what biologists refer to as ‘fittest’?
(a) Fitness is the ability of an organism to adapt to various habitats.
(b) Fitness is the physical strength of an organism.
(c) Fitness is the relative health of each individual in the population.
(d) Fitness is the ability of an organism to transfer powerful characteristics to its offspring.
Answer:
(a) Fitness is the ability of an organism to adapt to various habitats.
Question 9.
Which scientist most strongly supported the idea that evolutionary changes occurred because there was a need for them?
(a) Charles Darwin
(b) Lamarck
(c) Oparin
(d) Victor De Vries
Answer:
(b) Lamarck
Question 10.
The greatest weakness in Darwin’s theory was his failure to explain
(a) overproduction
(b) survival of the fittest
(c) struggle for existence
(d) variations
Answer:
(d) variations
Question 11.
Which one of the following ideas is not basic to Darwin’s theory of evolution?
(a) There is competition for survival
(b) There is variation in population
(c) Mutations cause changes in organisms
(d) Nature selects the best of organisms to survive
Answer:
(c) Mutations cause changes in organisms
Question 12.
According to Darwin’s theory, differences between species is the result of
(a) the disuse of body structures
(b) the transmission of acquired characteristics
(c) natural selection
(d) variations induced by mutation
Answer:
(c) natural selection
Fill In The Blanks
- About 4.6 billion years ago, the earth was a hot revolving ball of gases
- The gas present in largest amount in the early atmosphere of the primitive earth is hydrogen
- Variations caused by sudden changes in genetic make up is called mutation
- Darwin explained the survival of the fittest but not their origin/arrival
- The theory of ‘use and disuse’ is also known as Lamarckism
- The ‘swan neck experiment’ which proved that ‘life begets life’ was performed by Louis Pasteuri
- The aggregate of large organic molecules which are surrounded by an envelop is known as coacervate
- The type of respiration in the first group of organisms on earth was anaerobic
Match The Following
| A | B |
| 1. Lamarck | a. Neo Darwinism |
| 2. Darwin | b. Mutation theory |
| 3. Hugo De Vries | c. Theory of natural selection |
| 4. Oparin | d. Theory of inheritance of acquired characteristics |
| e. Theory of chemical evolution |
Answer:
1 – d, 2 – c, 3 – b, 4 – e.