10th chp 9 slusn

 

         Class 10 Science Solutions      

       Chapter 9 Heredity and Evolution      

Intext Question and Answer      

Page Number: 53        

1. 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?

Ans:

Trait B, because it is present in more members of the population. It is likely to have arisen earlier and has now spread to 60% of the population. Trait A is new and has spread to only 10% of the population.

2. How does the creation of variations in a species promote survival?
Ans:
★The variations provide stability to the population of various species by preventing them from getting wiped out during adverse conditions.
★ The natural environment also changes, and variations in species which become suited to the environment help it to survive.

Page Number: 57          

1. How do Mendel’s experiments show that traits may be dominant or recessive?

Ans: the characteristics appeared in first generation were called dominant (i.e. tall plants) and the characteristics that did not appear were called recessive (dwarf i.e. plants).

2. How do Mendel’s experiments show that traits are inherited independently ? 

Ans:

Mendel took two pairs of alternate expression of two traits and carried out dihybrid crosses by crossing them. The traits appeared in first generation were termed as dominant. When he used these F1 progeny to generate F2 progeny by self-pollination plants of different types were produced. In some plants both the traits were dominant, while in some plants both were recessive and some plants exhibited mixed traits. This indicates that traits are inherited independently.

3. 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 ?

Ans:

No this information is not sufficient to determine which of the traits: blood group A or O is dominant. Blood group A can be genotypically AA or AO. Hence, the information is incomplete.

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

Ans:

A child who inherits X chromosome from her father will be a girl and a child who inherits Y chromosome from his father will be a boy. Both the girl and the boy inherit only X chromosome from the mother. Therefore sex of a child is determined by the father.

Page Number: 60              

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

Ans: Natural selection, Genetic drift.

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

Ans:

The traits acquired during the life-time are changes in the non-reproductive cells of the organisms and are not capable of being passed on to the next generation.

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

Ans:

★Because in tigers there are negligible genetic variations. Due to this they are not well adapted.

★The rapid environmental changes cannot be favouable for them. If these changes are not controlled, tigers would be wiped out.

Page Number: 61           

1. What factors would lead to the rise of a new species?

Ans: 

Factors responsible for the rise of new species :

★ Geographical isolation

★ Natural selection

★ Inheritance of traits

★ Genetic drift / gene flow

★ Variation / mutuation / changes in DNA.

2. Will geographical isolation be a major factor in the speciation of a self- pollinating plant species ? Why or why not ?
Ans:
The geographical isolation cannot be major factor in the speciation of a self-pollinating plant species because it does not have to look the plants for its process of reproduction to be carried out.

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

Page No. 66             

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

Ans:

Birds and reptiles are great example of two close species. Feathers in some ancient reptiles, as fossils indicate, they were evolved to provide insulation in cold weather. However, they cannot fly with these feathers, later on birds adapted the feathers to flight. This means that birds are very closely related to reptiles, since dinosaurs were reptile.

2. Can the wing of a butterfly and the wing of a bat be considered homologous organs ? Why or why not ?
Ans:
The wings of a butterfly and the wings of a bat cannot be considered to be homologous organs because they have different basic designs though they are used for the same purpose of flying. They are analogous organs.

3. What are fossils ? What do they tell us about the process of evolution ?
Ans:
Fossils are the remains or traces of a dead organism.

★ They help to study evidence and missing link between different species.

★ They help to understand the sequence of evolution and help in classification of organisms.

Page No. 68            

1. 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 ?

Ans: Humans may be slightly different in different races of people, but there is no reproductive isolation. Reproductive isolation differentiates one species from the other. Human beings may be different in size, colour and looks , they can marry among themselves and produce fertile offspring.

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

Ans:

Bacteria is a primitive organism as they came into being very early in evolution. But these organisms are still surviving in the present conditions after millions of years. This is because they have adapted well to the changing environment over these years. Same is the case for all other organisms like spiders, fishes and chimpanzees which have adapted to their environment and have survived. Therefore, all the organisms which exist have a body design which is better as it is suited to their environment.

Exercises Question            

1. 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

Ans:

(c) TtWW.

2. 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.

Ans:

(d) all of the above.

3. In evolutionary terms, we have more in common with

(a) a Chinese school-boy.

(b) a chimpanzee.

(c) a spider.

(d) a bacterium.

Ans:

(a) a Chinese school-boy.

4. 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 ?

Ans:

This information is not complete. On the basis of this, it cannot be decided light colour trait is dominant or recessive. So it cannot be said until one does not know the nature of this trait in the parents.

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

Ans:

Classification of organisms is based on relative similarities and differences among organisms. Resemblances in organisms are because they have arisen from a common ancestor and differences in them are due to adaptations to different types of environment. Since the organisms can be graded in order of increasing complexity it indicates at the concept of evolution.

6. Explain the terms analogous and homologous organs with examples. 

Ans:

Analogous organs : Those organs which have different basic structure (or different basic design) but have similar appearance and perform similar functions are called analogous organs.

For example, The wings of an insect and a bird are analogous organs.

Homologous organs :  Those organs which have the same basic structure (or same basic design) but different functions are called homologous organs.

For example, The wing of a bat, flipper of a seal, front leg of a horse and arm of a man are homologous organs.

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

Ans:

Suppose a black homozygous male is mated with a white homozygous female. If the progeny has all black dogs then the dominant coat colour is black.

8. Explain the importance of fossils in deciding evolutionary relationships.

Ans:

Fossils play important role in providing evolutionary evidences because by knowning the age of fossils we can know about the evolution process of an organism.

For example, a fossil bird called archaeopteryx that looked like a bird had many other features of reptiles. It had feathered wings like those of birds, but teeth and tail like those of reptiles. Archaeopteryx is, therefore, a connecting link between the reptiles and birds, and hence suggests that the birds have evolved from the reptiles.

9. What evidence do we have for the origin of life from inanimate matter? 
Ans:
A British scientist J.B.S. Haldane at first in 1929 suggested that life is originated from inanimate matter. According to him life must have developed from the simple inorganic molecules which were present at that time. Later, Miller and Urey in 1953 presented its evidences. They assembled an apparatus to create an early earth atmosphere which was supposed to consist of gases like methane, ammonia and hydrogen sulphide, etc. over water. This was maintained at a temperature just below 100°C and electric sparks were then passed through the mixture of gases to stimulate lightning for about one week. At the end of one week, it was found that about 15 per cent of carbon (from methane) had been converted into simple compounds and amino acids which make up protein molecules formed in living organisms. This experiment provides the evidence that the life originated from inanimate matter (or lifeless matter) like inorganic molecules.

10. 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 ? 

Ans:

During sexual reproduction there is ‘crossing over’ of chromosomes, that gives rise to variations. These variations are inherited and increase the chances of survival of an organism.

1. In sexual reproduction variations may occur due to errors in DNA copying.
2. There may be variations due to interchange of homologous chromosomes during crossing over of male and female.
3. In sexual reproduction, it is not predetermined that which gamete would fuse with another gamete. It depends only on chance. It is also a reason of variation.
   These variations enable the organisms to adapt themselves to the changing conditions and also help to give rise to new species.

11. How is the equal genetic contribution of male and female parents ensured in the progeny ?
Ans:
Genetic material in most organisms is present in pairs of chromosomes. Gametes in the sexually reproducing organisms are formed by the process of meiosis during which half of the genetic material goes into each gamete. When the gametes from male and female parents fuse with each other during sexual reproduction, the normal complement is restored. Half of the genetic material comes from the female and half from the male.

12. 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?

Ans:

Yes, variations that confer an advantage to an individual organism are inherited. The organism can survive longer in an environment and maintain its existence in the population.