Page No. 208
What name is given to the sequence of gradual changes over millions of years in which new species are produced ?
Name the scientist who gave the theory of evolution.
Charles Robert Darwin.
State whether the following statement is true or false :
Human beings have evolved from chimpanzees.
State one characteristic which shows that the birds are very closely related to dinosaurs.
The presence of feathers on birds and dinosaurs shows that they are closely related to each other.
Name an animal having rudimentary eyes.
Name the ancestor of the following :
Broccoli, Kohlrabi, Kale
Where did life originate on the earth ?
Write the names of at least three inorganic molecules which helped in the origin of life on the earth.
Methane, Ammonia and Hydrogen Sulphide.
Name the famous book written by Charles Robert Darwin.
The Origin of Species.
The forelimbs of a frog, a bird and a man show the same basic design (or basic structure) of bones. What name is given to such organs ?
Name two organisms which are now extinct and studied from their fossils.
Dinosaurs and Archaeopteryx.
Out of the wing of a bird, wing of an insect and the wing of a bat :
(a) which two are homologous organs ?
(b) which two are analogous organs ?
(a) Wings of bird and wings of bat.
(b) Wings of birds and wings of insects.
Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species ?
The human beings who look so different from each other in terms of size, color and looks are set to belong to the same species because they can inter breed to produce fertile offsprings.
Name five varieties of vegetables which have been produced from ‘wild cabbage’ by the process of artificial
Cabbage, Broccoli, Cauliflower, Kohlrabi and Kale.
Choose the one term from the following which includes the other three :
broccoli, wild cabbage, cauliflower, cabbage
Fill in the following blanks with suitable words :Fill in the following blanks with suitable words :
(a) The human forelimb and bat’s forelimb are an example of……………………organs whereas an insect’s wing and a bat’s wing are an example of…………………organs.
(b) The evolution of eye is an example of evolution by…………………
(c) The scientific name of all human beings is……………………..
(d) Broccoli has evolved from……………..by the process of artificial selection.
(e) The theory of natural selection for evolution was proposed by………………………
(a) Homologous: Analogous.
(c) Homo sapiens.
(d) Wild Cabbage.
Match the terms given in column I with those given in column II :
(ii) A theory of Evolution
(iii) Probable ancestor of birds
(iv) Gregor Mendel
(a) A famous evolutionist
(b) Survival of the fittest
(c) Petrified remains of prehistoric life
(d) Father of genetics
(i) – c.
(ii) – b.
(iii) – e.
(iv) – a.
(v) – d.
What is meant by acquired and inherited traits ? Explain with one example each.
A trait of an organism which is ‘not inherited’ but develops in response to the environment is called an acquired trait. Example – If a beetle does not get sufficient food for a considerable time, its weight will be reduced due to starvation. The low weight of the beetle is an example of acquired trait. A trait of an organism which is caused by a change in its genes (DNA) is called an inherited trait. Example – The change of colour from red beetle to green beetle is an example of inherited trait.
Why are the traits acquired during the lifetime of an individual not inherited ?
For a trait of an organism to be inherited, it should bring about a change in the genes present in the reproductive cells or gametes of that organism. The traits acquired during the life time of a person do not bring about a change in the genes present in its reproductive cells or gametes and hence they are not inherited by the offsprings.
Can the wing of a butterfly and the wing of a bat be considered homologous organs ? Why or why not ?
The wings of a butterfly and the wings of a bat cannot be considered homologous because though the function of wings in both the cases is same but they have different basic design. The butterfly has a fold of membranes as wings which are associated with few muscles but has no bones whereas the wings of bat are supported by bones.
Name two animals having homologous organs and two having analogous organs. Name these organs.
Forelimb of humans and forelimb of lizard are the homologous organs and the wing of insect and the wing of bird are analogous organs.
What are fossils ? Giving one example, explain how fossils provide evidence for evolution.
The remains of dead animals or plants that lived in the remote past are known as fossils. The fossils provide evidence of evolution. For example, a fossil bird called Archaeopteryx looks like a bird but it has many features which are found in reptiles. This is because Archaeopteryx has feathered wings like those of birds but teeth and tail like those of reptiles. Therefore, Archaeopteryx is a connecting link between the reptiles and birds and suggests that birds have evolved from reptiles. Thus, fossils provide evidence that the present plants and animals have originated from the previously existing ones through the process of continuous evolution.
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
The changes in DNA during reproduction are mainly responsible for evolution. The changes which take place in the DNA of species go on accumulating from one generation to the next. So, if the changes in the DNA of any two species are less, then the two species are quite close to one another in evolutionary terms. But if the changes in the DNA of two species are much more, then the two species will be far apart from one another in evolutionary terms. Thus, it is the characteristic of the extent of change in the DNA which is being used to determine how close two species are in evolutionary terms.
In what way are homologous organs evidence for evolution ?
The presence of homologous organs in different animals provides evidence for evolution by telling us that they are derived from the same ancestor who had the ‘basic design’ of the organ on which all the homologous organs are based.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics ?
Sometimes a species may completely die out. It may become extinct. Once a species is extinct, its genes are lost forever, it cannot reemerge at all. The small numbers of surviving tigers are a cause of worry because if they all die out and become extinct, their genes will be lost forever. Our coming generations will not be able to see Tigers at all.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Give reason for your answer.
Geographical isolation cannot be a major factor in the speciation of an asexually reproducing organism because it does not require any other organism to carry out reproduction.
Name the various tools of tracing evolutionary relationships which have been used for studying human evolution.
Human evolution has been studied by using the various tools of tracing evolutionary relationships like excavating (digging earth), carbon-dating, studying fossils and determining DNA sequences.
Out of bacteria, spider, fish and chimpanzee, which organism has a better body design in evolutionary terms ? Give reason for your answer.
In evolutionary terms, we can say that bacteria has a ‘better’ body design than spiders, fish, and, chimpanzees. This is because though bacteria is one of the simplest and primitive life forms but it still inhabits and survives in some of the most inhospitable (most unfavourable) habitats such as hot springs, deep-sea thermal vents and ice in Antarctica. Most other organisms (including spider, fish and chimpanzees) cannot survive in such harsh environments.
With the help of an example, explain how variation leads to evolution.
Some amount of variations are produced even during asexual reproduction but it is very small. The number of variations produced during sexual reproduction is, however, very large. It is due to these variations that no two human beings look alike. The number of successful variations is maximized by the process of sexual reproduction, so we can conclude that the variation is a necessity for organic evolution. Example: Animal reproduced by sexual reproduction show large number of variations.
(a) What is meant by a species ? Give two examples of plant species and two of animals.
(b) State the various factors which could lead to the formation of new species.
(a) A species is a population of organisms consisting of similar individuals which can breed together and produce fertile offspring’s. Plant species – Wheat, Paddy, Sunflower etc. Animal species – Cat, Dog, Tiger, etc.
(b) The important factors which could lead to the rise (or formation) of a new species are the following:
What evidence do we have for the origin of life from inanimate matter (lifeless matter) ?
The evidence was given by Stanley L. Miller and Harold C. Urey in 1953. They assembled an apparatus to create an early earth atmosphere which was supposed to consist of gases like ammonia, methane and hydrogen sulphide, but no oxygen) over water. This was maintained by them at a temperature just below 100o C and electric sparks were passed through the mixture of gases to stimulate lightning. At the end of a week, they found that 15% of the carbon (from methane) had been converted to simple compounds of carbon including amino acids which make up protein molecules.
Does geographical isolation of individuals of a species lead to the formation of a new species ? Provide a suitable explanation for your answer.
Geographical isolation is the major factor in the speciation of sexually reproducing animals because it interrupts the flow of genes between their isolated populations through the gametes.
Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria ? Explain your answer.
Bacteria have simpler body plan when compared with human beings. Both of them have evolved differently. Bacteria can inhabit most of the unfavourable habitats such as hot springs, deep- sea thermal vents and the ice in Antarctica.
(a) Name the scientist who gave the theory of origin of life on earth. What is this theory ?
(b) How are those species which are now ‘extinct’ studied ?
(a) The theory of origin of life on earth was given by J.B.S Haldane. He suggested in 1929 that life must have developed from the simple inorganic molecules (such as methane, ammonia, hydrogen sulphide, etc.) which were present on the earth soon after it was formed. He said that the conditions on earth at that time (including frequent lightning) could have converted simple inorganic molecules into complex organic molecules which were necessary for life. These complex organic molecules must have joined together to form first primitive living organisms. Haldane also suggested from theoretical considerations that life (or living organisms) originated in the sea water.
(b) Those species which are now extinct are studied by studying their fossils which are found during the digging of earth.
What do you understand by the term ‘evolution’ ? State Darwin’s theory of evolution.
Evolution is the sequence of gradual changes that takes place in the primitive organisms over millions of year in which new species are produced. Darwin’s theory of evolution is known as ‘The Theory of Natural Selection’. It can be described as follows:
(a) Explain the terms ‘analogous organs’ and ‘homologous organs’ with examples.
(b) In what way are analogous organs evidence for evolution ?
(a) Analogous Organs: Organs which performs similar function but are different in structure and origin. Example – wings of a bird and wings of an insect. Homologous Organ: Organs which have different functions but similar structure and origin. Example – fore arm of frog, lizard, bird and human.
(b) The presence of analogous organs indicates that even the organisms having organs with different structures can adapt to perform similar functions for their survival under hostile environmental conditions. Thus, the presence of analogous organs in different animals provide evidence for evolution by telling us that though they are not derived from common ancestors, they can still evolve to perform similar functions to survive, flourish and keep on evolving in the prevailing environment.
(a) Define ‘speciation’. Explain how speciation occurs.
(b) Will geographical isolation be a major factor in the speciation of a self-pollinating plant species ? Give reason for your answer.
(a) The process by which new species develop from the existing species is known as speciation. New species are formed when the population of same species splits into two separate groups which then get isolated from each other geographically by the barriers such as mountain ranges, rivers or the sea. The geographical isolation of the two groups of population leads to their reproductive isolation due to which no genes are exchanged between them. However, breeding continues within the isolated populations producing more and more generations. Over the generations, the processes of genetic drift (random change in gene frequency), and natural selection operate in different ways in the two isolated groups of population and make them more and more different from each other. After thousands of years, the individuals of these isolated groups of population become so different that they will be incapable of reproducing with each other even if they happen to meet again. We then say that two new species have been formed.
(b) Geographical isolation will not be a major factor in the speciation of a self pollinating plant because it does not depend on other plants for its process of reproduction to be carried out.
(a) Define ‘natural selection’.
(b) “Only variations that confer an advantage to an individual organism will survive in a population”. Do you agree with this statement ? Give reason for your answer.
(a) Natural selection is the process of evolution of a species whereby characteristics which help individual organisms to survive and reproduce are passed on to their offspring, and those characteristics which do not help are not passed on.
(b) Yes, only those variations that confer advantage to an individual organism will survive in a population. This will become clear from the following example. Suppose there is a population of red beetles in the green bushes and a colour variation arises during reproduction so that one beetle is now green in colour (instead of red). This variation offers advantage of survival because the green beetle can mix up with green bushes, it cannot be spotted and eaten up by a crow and hence its population will increase. If, however, the variation had produced a blue coloured beetle, then this colour could not offer any survival advantage because blue beetle in green bushes could be easily spotted by a crow and eaten by it.