NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution

NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution: topic 9.1 Page Number 143

Q. 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?

Answer:

Trait B is more likely to have arisen earlier because it has a higher percentage of the population and in asexual reproduction, traits are carried over to the next generation with minimal changes in the traits.

For example, all the sugarcanes in the field which reproduce asexually, have almost similar characteristics, however, the animals and human which reproduce sexually, have more chances of traits in the next generation.

Q. 2. How does the creation of variations in a species promote survival?

Answer:

Variation in our characteristics occurs due to sexual reproduction and inaccurate copying of DNA. The varied characteristics which fit for surviving passes on to the next generation more easily and the characteristics which are not favourable for surviving will get vanish after some generation.

Favourable variations help a species to adapt to changes in their environment and they promote survival of a species.

Heredity and Evolution Class 10: Topic 9.2 Solutions, Page Number 147

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

Answer:

Mendal Conducted many experiments by crossing the Tall plants and Short plants. he found that the trait Tall which appears in the first generation also appeared in the second generation with 75 % in number. and the trait short appeared in the second generation by 25% in number. Hence he concluded that trait Tall is Dominant and the trait short is recessive.

in other words:

Tall + Tall = Tall

Tall + Short = Tall

Short + Tall = Tall

Short + Short = Short

As we can see there are 3 out of 4 Tall in the Next Generation. Hence it is a dominant trait.

Hence by this experiment, he showed that traits can be Dominant or Recessive.

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

Answer:

In Mandel's one of the experiments he crossed the Pure breeding Tall plants having round seed with Short plants having wrinkled seed. here he found some of the new traits like Tall plant having wrinkled seed and Short plants having round seed.

Tall and Round + Short and Wrinkled = Tall and Round + Tall and Wrinkled +Short and Wrinkled + Short and Round

( Previous Trait) (New Trait) (Previous Trait ) (New Trait)

Those new traits would not have been there if traits are inherently dependent.

And hence he concluded that traits are inherited independently

Q. 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?

Answer:

No, This information is not sufficient to conclude any trait dominant or recessive. this is because we don't know the blood group of all offsprings.

The given blood group A can be AA or AO, so we can't really draw any conclusion from it.

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

Answer:

Half the male gametes have X-chromosomes and the other half have Y-chromosomesThe human male has one X-chromosome and one Y-chromosome. In other words, The human male has one X-chromosome and one Y-chromosome On the other hand, all-female gametes have only X-chromosomes. If a sperm carrying Y-chromosome fertilizes an ovum then the child born will be a boy.

On the other hand, if a sperm carrying X-chromosomes fertilizes an ovum then the child born will be a girl.

X + X = Girl

X + Y = Boy.

Heredity and Evolution: topic 9.3, Page Number 150

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

Answer:

The different ways in which individuals with a particular trait may increase in a population are

1) Natural Selection: if a trait is useful to the population, it will increase naturally.

2) Genetic Drift: if a population faces any accidents such that the majority of the population get killed, then the remaining ones can pass their genes to the next generation and increase the population of their traits.

3) Sexual Selection: some traits also increases in choosing a suitable partner for mating. if there is mating between male and female, their offspring will contain their traits and the population with that trait increases. So, sexual selection of partner plays a much more important role than we realize. for example, most of the creativity traits like music and art skills are the result of sexual selection.

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

Answer:

The traits acquired during the lifetime of an individual are not inherited because acquired traits involve a change in non-reproductive tissues and do not affect the genetic makeup like DNA.

Hence they can not be transferred sexually to the next generation.

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

Answer:

1) The small number member in a population does not produce a large variation in the genes which are essential for the survival of the species.it means Small numbers of tigers mean that fewer possible variations of genes are available.

2) If any natural calamity occurs or any disease spreads and kills these small numbers of surviving tigers, they will become extinct resulting in the loss of these genes forever.

3) Less number of species means less number of diversity and a lesser number of traits which reduces the chances of adaptability with respect to change in the environment.

Heredity and Evolution Topic 9.4 Questions, Page Number 151

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

Answer:

The factors could lead to the rise of a new species are :

1) Natural Selection

2) Method of Genetic Drift

3) Gene Variation on Mutation

4)Geographical and environmental factors

Q. 2. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?

Answer:

No. Geographical isolation prevents the transfer of pollen among different plants. whereas, if the plant is self-pollinating which means they pollen are transferred from the same plant, The Geographical isolation cannot prevent speciation in this case.

However, there is some possibility of some environmental change which could result in some variation.

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

Answer:

No. Geographical isolation prevents gene flow between populations of a species that reproduces sexually. whereas asexual reproduction generally involves only one individual. In an asexually reproducing organism, variations can occur only when the copying of DNA is not accurate.

Therefore, geographical isolation cannot prevent the formation of new species in an asexually reproducing organism.

Heredity and Evolution Topic 9.5 Solutions, Page Number 156

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

Answer:

The similar kind of organs is one such evidence that is used to determine how close two species are related. The presence of feathers in dinosaurs and birds indicates that they are evolutionarily related. Dinosaurs had feathers, not for flying but instead, these feathers provided insulation to these warm-blooded animals. However, the feathers in birds are used for flight.

This proves that reptiles and birds are closely related and that the evolution of wings started in reptiles,

Also if we consider the example of Human and Ape, the body style of both is similar and hence they are closely related in evolutionary terms.

Q. 2. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?

Answer:

Homologous organs have different look and perform a completely different function, however, shares a common basic structure. wing of a butterfly and the wing of a bat performs a similar function but have a different basic structure. wings of a butterfly are membrane supported by muscles and wings of a bat is the body skeleton.

Hence they are not the homologous organ rather analogous organ because they perform the same function.

Q. 3. What are fossils? What do they tell us about the process of evolution?

Answer:

Fossils are dead remains (may be a part of the organism or the whole organism) of plants, animals or any other organisms that existed on earth in the past

Fossils help us in many ways like,

(i) They give great insight into the evaluation. for example, the pattern of fossil distribution gives us an idea of the time in history when various species were formed and extinct.

(ii) They help us in establishing evolutionary relations between present organisms. Example: Archaeopteryx (connecting link between reptiles and birds).

Heredity and Evolution Class 10 Topic 9.6 Solutions, Page Number: 158

Q. 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?

Answer:

Human beings who look so different from each other in terms of size, color and looks said to belong to the same species because their genetic makeup is similar and have the same organization at the genetic level. We all have the same number of chromosome and we breed among ourselves to produce fertile offspring.

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

Answer:

Evaluation should not be equated with progress or any kind of better quality like better body design. Evaluation simply creates a more complex body design. And this does not mean that simple body design is inefficient. for example, a bacteria has a very simple body but still is the most cosmopolitan organism found on the earth. They can survive deep sea, hot spring, and even icy-cold freezing environment.

So, we can't really say there's a better body design as these organisms evolved in the different-different environment and made changes in their body structure according to "Their " need.

Heredity and Evolution Class 10 NCERT Exercise Solutions

Q. 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

Answer:

As half the progenies are short, this implies that the parent plant also will have a collection of short genes. Also since all progenies bore violet flowers, the violet color is dominant over white.

Hence TtWW might be the correct answer.

Q. 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.

Answer:

Homologous organs have the same origin but different function. all the given option have the same origin and hence correct option is d.

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

(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.

Answer:

We are human beings like a Chinese boy. Thus, option (a) is correct.

Both human and Chinese boy are of the same ancestry and belongs to Homo Sapiens .

Q. 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?

Answer:

For considering a trait as dominant or recessive, we need the information of a minimum of 3 generations.

If the grandparent, parent and the children. all have the light colored eye, then we can conclude that light eye color is a dominent trait.

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

Answer:

Classification involves grouping of organisms into a formal system based on similarities and differences. Two species are more closely related if they have more characteristics in common and if two species are closely related then it means they have a more recent common ancestor.

We classify organisms according to their characteristics which is similar to the things we analyze in evaluation. Hence both areas of study are interlinked.

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

Answer:

Analogous organs: Those organs which have different basic structure but have a similar appearance and perform similar functions are called analogous organs. Example - wings of bird and insect.

Homologous organs: Those organs which have the same basic structure but different functions are called homologous organs. Example: forelimb of humans and forelimb of lizard.

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

Answer:

(i) Select two varieties of dogs one with white coat color, the other with black coat color.

(ii) Crossbreed them taking a male dog from one variety and bitch (female dog) from the other variety.

(iii) Observe the color of offsprings of the F1 generation.

(iv) Now, bring about breeding among the organisms of the F1 generation.

(v) Observe the coat color of organisms (pups) of F2 generation and note the variations in coat color.

(vi) Draw conclusions on the basis of your study.

One of the probable inheritance patterns may be as given below.

Phenotypic ratio = 3 : 1,

Black coat colour (3) : White coat colour (1)

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

Answer:

Fossils provide us evidence about many things like:

1) The organisms that lived long ago in the past.

2) Connecting links between two groups. for example, the feather in some dinosaurs means that birds are very closely related to reptiles.

3)The development of any particular species by evaluation.

4) The time period of the organisms.

5) Simple to complex body design journey.

Q. 9. What evidence do we have for the origin of life from inanimate matter?

Answer:

The evidence for the origin of life from inanimate matter was provided through an experiment, conducted in 1953, by Stanley L. Miller and Harold C. Urey.

In the experiment, they assembled an atmosphere containing molecules like ammonia, methane and hydrogen sulfide, but no oxygen, over water. This was similar to the atmosphere that thought to exist on the early earth. This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning.

At the end of a week, 15% of the carbon from methane, had been converted to simple compounds of carbon including amino acids which make up protein molecules and support the life in the basic form.

Thus, this experiment suggests that life on earth arose fresh.

Q. 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?

Answer:

Sexual reproduction causes more viable variations due to the following reasons:

1)Error in the copying of DNA, which are not highly significant.

2) Random segregation of paternal and maternal chromosome at the time of gamete formation.

3)Exchange of genetic material between homologous chromosomes during the formation of gametes.

4) Accumulation of variations occurred due to sexual reproduction over generation after generation and selection by nature created wide diversity.

In the case of asexual reproduction, only the very small changes due to inaccuracies in DNA copying pass on the progeny. Thus, offsprings of asexual reproduction are more or less genetically similar to their parents. So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually reproducing organisms.

Q. 11. How is the equal genetic contribution of male and female parents ensured in the progeny?

Answer:

The inheritance of equal parent chromosomes ensures equal genetic contribution within the relative of male and female folk. There are 23 pairs of chromosomes. There is no pairing of all human chromosomes. The primary twenty-two trials are called autosomes out of those twenty-three pairs, and the remaining one pair is also thought to be sex chromosomes drawn as X and Y. Females have an ideal trial of 2 X sex chromosomes and males have an inappropriate trial of I X and I Y chromosome.
During the replication process, the male germ cell (haploid) fuses with the feminine gamete (haploid) resulting in the formation of the diploid fertilized ovum as the fertilization method takes place. Within the relative, the fertilized ovum receives the associated degree of equal contribution from the oldsters of genetic material. Of the comparatively twenty-three pairs of chromosomes, the parent contributes twenty-two autosomes and one X or sex chromosome, whereas the feminine parent contributes twenty-two autosomes and one chromosome.

Q. 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?

Answer:

It is not always true. The variations that confer an advantage to an individual organism are definitely of more survival value because natural selection prefers these variations. But there are several other variations which, though do not provide an advantage to the organism in if present condition, survive and are inherited to the next generations. Such non-advantageous variations may become advantageous in future when the environmental conditions change.

For example, at this stage of evolution, The art, and music skills that we acquire doesn't give us any survival benefit but still called a good quality trait or variation.