Solution of Heredity and Evolution (Page No - 210 - Biology by Lakhmir Singh, Class 10 | Extra Documents, Videos & Tests for Class 10 PDF Download

Question 33:
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.
Solution :
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.

Question 34:
(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 ?
Solution :
(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.

Question 35:
What do you understand by the term ‘evolution’ ? State Darwin’s theory of evolution.
Solution :
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:

1. Within any population there is natural variation. Some individuals have more favourable variations than others.
2. Even though all species produce a large number of offspring’s, populations remain fairly constant naturally.
3. This is due to the struggle between members of the same species and different species for food, space and mate.
4. The struggle for survival within populations eliminates the unfit individuals. The fit individuals possessing favourable variations survive and reproduce. This is called natural selection.
5. The individuals having favourable variations pass on these variations to their progeny from generation to generation.
6. These variations when accumulated over a long period of time, lead to the origin of a new species.

Question 36:
(a) Explain the terms ‘analogous organs’ and ‘homologous organs’ with examples.
(b) In what way are analogous organs evidence for evolution ?
Solution :
(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.

Question 37:
(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.
Solution :
(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.

Question 38:
(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.
Solution :
(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.