NCERT Solutions for Class 10 Science Unit 9

Heredity and Evolution Class 10

Unit 9 Heredity and Evolution Exercise Solutions

Heredity : The passing of traits from the parents to offspring is called heredity. This is heredity which is responsible for many commonly observable facts; like siblings looking similar in overall appearance.

Evolution : The change in inherited traits in biological population over subsequent generations is called evolution. Scientists have proven that life evolved in the form of simple unicellular organisms on this earth; and all the organisms which are present today have evolved from a common ancestor. The idea of evolution is based on the premise of a common ancestry.
<< Previous Chapter 8 : How do Organisms Reproduce? Next Chapter 10 : Light - Reflection and Refraction >>

Question : Solutions of Questions on Page Number : 143

Q1 :  

If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?


Answer :

In asexual reproduction, the reproducing cells produce a copy of their DNA through some chemical reactions. However, this copying of DNA is not accurate and therefore, the newly formed DNA has some variations.

Itcan be easily observed in the above figure that in asexual reproduction, very few variations are allowed. Therefore, if a trait is present in only 10% of the population, it is more likely that the trait has arisen recently. Hence, it can be concluded that trait B that exists in 60% of the same population has arisen earlier than trait A.

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Q2 :  

How does the creation of variations in a species promote survival?


Answer :

Sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. For example, if the temperature of water increases suddenly, most of the bacteria living in that water would die. Only few variants resistant to heat would be able to survive. If these variants were not there, then the entire species of bacteria would have been destroyed. Thus, these variants help in the survival of the species.

However, not all variations are useful. Therefore, these are not necessarily beneficial for the individual organisms.

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Q3 :  

How do Mendel's experiments show that traits may be dominant or recessive?


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Q4 :  

How do Mendel's experiments show that traits are inheritedindependently?


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Q5 :  

A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits - blood group A or O - is dominant? Why or why not?


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Q6 :  

How is the sex of the child determined in human beings?


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Q7 :  

What are the different ways in which individuals with a particular trait may increase in a population?


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Q8 :  

Why are traits acquired during the life-time of an individual not inherited?


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Q9 :  

Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?


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Q10 :  

What factors could lead to the rise of a new species?


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Q11 :  

Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?


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Q12 :  

Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?


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Q13 :  

Give an example of characteristics being used to determine how close two species are in evolutionary terms.


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Q14 :  

Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?


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Q15 :  

What are fossils? What do they tell us about the process of evolution?


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Q16 :  

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?


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Q17 :  

In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a 'better' body design? Why or why not?


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<< Previous Chapter 8 : How do Organisms Reproduce? Next Chapter 10 : Light - Reflection and Refraction >>

Exercise : Solutions of Questions on Page Number : 159

Q1 :  

A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as

(a) TTWW

(b) TTww

(c) TtWW

(d) TtWw


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Q2 :  

An example of homologous organs is

(a) our arm and a dog's fore-leg.

(b) our teeth and an elephant's tusks.

(c) potato and runners of grass.

(d) all of the above.


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Q3 :  

In evolutionary terms, we have more in common with

(a) a Chinese school-boy.

(b) a chimpanzee.

(c) a spider.

(d) a bacterium.


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Q4 :  

A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?


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Q5 :  

How are the areas of study - evolution and classification - interlinked?


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Q6 :  

Explain the terms analogous and homologous organs with examples.


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Q7 :  

Outline a project which aims to find the dominant coat colour in dogs.


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Q8 :  

Explain the importance of fossils in deciding evolutionary relationships.


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Q9 :  

What evidence do we have for the origin of life from inanimate matter?


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Q10 :  

Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?


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Q11 :  

How is the equal genetic contribution of male and female parents ensured in the progeny?


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Q12 :  

Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?


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<< Previous Chapter 8 : How do Organisms Reproduce? Next Chapter 10 : Light - Reflection and Refraction >>

Science : CBSE NCERT Exercise Solutions for Class 10th for Heredity and Evolution will be available online in PDF book form soon. The solutions are absolutely Free. Soon you will be able to download the solutions.

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