PSEB 10th Class Science Solutions Chapter 9 Heredity and Evolution

Punjab State Board PSEB 10th Class Science Book Solutions Chapter 9 Heredity and Evolution Textbook Exercise Questions and Answers.

PSEB Solutions for Class 10 Science Chapter 9 Heredity and Evolution

PSEB 10th Class Science Guide Heredity and Evolution Textbook Questions and Answers

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.
Answer:
(c) TtWW.

Question 2.
An example of homologous organs is :
(а) our arm and a dog’s fore-leg
(б) our teeth and an elephant’s tusks
(c) potato and runners of grass
(d) All of the above.
Answer:
(d) All of the above.

Question 3.
In evolutionary terms, we have more in common with :
(а) a Chinese school-boy
(b) a chimpanzee
(c) a spider
(d) a bacterium.
Answer:
(a) a Chinese school-boy.

Question 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:
On this basis we cannot say that light eye colour is dominant or recessive until a cross is made between parent having light eye colour and another with dark eye colour. Only then it will be possible to predict the dominant or recessive nature of the gene.

Question 5.
How are the areas of study of evolution and classification interlinked?
Answer:
Evolution and classification are interlinked as evident from following points :

• Characteristics are shared by most of the organisms. The characteristic in the next level of classification will be shared by most and not by all.
• Cell designs also indicate this relationship.
• Groups formed during classification are related to their similarities.

Question 6.
Explain the terms homologous and analogous organs with example.
Answer:
Homologous organs: The organs of different classes have different forms because they have to perform different functions but their structures basically remain similar. Such organs are called homologous organs.

Example:

• Fore limbs of amphibians, birds and mammals have same fundamental structural plans but perform different functions.
• In plants, the homologous organs may be a thorn of Bougainvillea or a tendril of cucurbita both arising in axillary position.

Analogous organs: The organs are quite different in their structure and origin but similar in function. Such organs are known as analogous organs. The presence of analogous organs proves that different structures can be modified to perform a similar function. Analogy indicates convergent evolution.
Examples. The wings of insects and vertebrates perform the same function.

Question 7.
Outline a project which aims to find the dominant coat colour in dogs.
Answer:
Make a chart or thermocol sheet showing the following monohybrid cross

Dominance of black coat colour in dogs

Question 8.
Explain the importance of fossils in deciding evolutionary relationship.
Answer:

Question 9.
What evidence do we have for the origin of life from inanimate matter?
Answer:
Urey and Miller provided experimental evidence regarding origin of life from inanimate matter. They assembled an atmosphere similar to that, thought to exist on early earth.

In a spark flask they collected ammonia, methane and hydrogen sulphide, but no free oxygen over water at a temperature just below 100°C and sparks were passed through the mixture of gases to stimulate lightning. At the end they obtained organic molecules such as amino acid, urea, sugars. Amino acids which make up protein molecules. Thus they showed life originated from inanimate matter.

Question 10.
Explain how sexual reproduction gives rise to more viable Variation than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
Answer:
Genetic variations arise in nature as a result of following mechanism during sexual reproduction are more viable and raw materials of evolution.

• Crossing over during gamete formation.
• Random segregation of chromosome during meiosis at the time of gamete formation has decreased.
• Random rejoining of gametes having different genetic set up in the chromosomes during fertilisation.

Question 11.
How is equal genetic contribution of male and female parents ensured in the progeny?
Answer:
During sexual reproduction fusion of gametes having haploid set of chromosomes belonging to male and female parents ensure equal contribution.

Question 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:
Yes. The organism with useful variations will adapt and survive. Moreover they leave behind more offsprings and populations with such genetic variations will survive.

Science Guide for Class 10 PSEB Heredity and Evolution InText Questions and Answers

Question 1.
If a trait A exists in 10% of 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 asexually reproducing organism trait B originated earlier. The variations in a population are only due to inaccuracies of DNA copying.

Question 2.
How does the creation of variations in a species promote survival?
Answer:
The useful variation in individuals of a species will enable them to adapt according to the changes and new needs. Thus they will enable the survival of species.

Question 3.
How do Mendel’s experiments show that gene may be dominant or recessive?
Answer:
Mendel conducted experiments on garden pea plant selecting seven visible contrasting characters. He selected and crossed homozygous tall pea plant having the genotype TT with a homozygous dwarf pea plant having the genotype tt. Fx generation consists only of tall plants, having genotype Tt. Since they have an allele for dwarfness also, they are all hybrids. The expressed allele T for tallness is dominant over the unexpressed allele t for dwarfness. The fact that the allele for dwarfness is present in the F1 plants can be verified by interbreeding them when F2 progeny will consist of both tall and dwarf plants in the ratio of 3 : 1. On this basis he proposed “Law of Dominance.”

Question 4.
How do Mendel’s experiments proved that traits are inherited indepen dently?
Answer:
Mendel proposed a law on the basis of a dihybrid cross between two homozygous parents. He selected a dominant plant with round and yellow seeds and a recessive plant with wrinkled and green seeds, yields Fx offspring showing the dominant form of both traits, viz. round and yellow. Fx plants, on selling, produce F2 progeny with two parental and two new recombinant phenotypes, that is round yellow: round green: wrinkled yellow: wrinkled green in the ratio of 9 : 3 : 3: 1. This ratio is called Mendel’s dihybrid phenotypic ratio. The factors (genes) of different traits are independent of each other in their distribution into the gametes and in the progeny. This is Mendel’s law of independent assortment.

Question 5.
A man with blood group A married a person with blood group O. Their daughter has blood group O. Is this information enough to tell you which of the blood group trait A or O is dominant. Why or why not?
Answer:
As blood groups is hereditary character, the knowledge of blood groups of parents can give information about the possible blood groups of children and vice-versa.

In this case illustration is as follow :

In the above cross, 50 per cent of progeny will have A blood group and 50 per cent O blood group.
At the same time this data is insufficient. It is not mentioned father has homozygous or heterozygous A blood group. If it is homozygous A then 100 per cent of progeny will have A blood group as Gene IA is dominant over Gene I°.

Question 6.
How is the sex of child determined in human beings?
Answer:
Determination of the sex of child. Sex chromosomes determine sex in human beings. In males, there are 44 +
XY chromosomes, whereas, in female there are 44 + XX chromosomes. Here,
X and Y chromosomes determine sex in the human beings.

Sex determination in man (Note that all the eggs carry X-chromosome but one-half of the sperm carry an X-chromosome and one half carry a Y-chromosome)

Two types of gametes are formed in male, one type is having 50%
X-chromosome, whereas the other type is having Y-chromosome. In female, gametes are of one type and contain X-chromosome.

The females are homogametic. If male gamete having Y-chromosome (androsperm) undergoes fusion with female gamete having X-chromosome the zygote will have XY chromosomes and this gives rise to male child.

If the male gamete having Fig. 9.1. Sex determination in man (Note X-chromosome undergoes fusion with that all the eggs carry X-chromosome but female gamete having X-chromosome, one-half of the sperm carry an the zygote will be having XX-chromosome X-chromosome and one half carry a and this gives rise to female child. Y-chromosome)

Question 7.
What are different ways in which individuals with a particular trait may increase in a population?
Answer:
A particular population with specific traits will increase due to following reasons :

• Sexual reproduction which results into variations.
• Inheritance of variations.
• Natural Selection. The individuals with special traits survive the attack of their predators and multiply while the others will perish.
• Genetic drift provides diversity without any adaptation.

Question 8.
Why are traits acquired during life-time of an individual not inherited?
Answer:
Change in non-reproductive tissue (somatic cells) cannot be passed on to the DNA of germ cells. Thus the acquired trait will die with the death of individual. It is non- heritable and cannot be passed on to its progeny. Changes that occur in DNA of germ cells are inherited.

Question 9.
Why are the small number of surviving tigers is a cause of worry from the point of view of genetics?
Answer:
As the population of tigers is decreasing, there is loss of genes from the gene pool. There cannot be recombinations and variations. Hence no evolution. If number falls suddenly they may become extinct.

Question 10.
What factors could lead to the rise of new species?
Answer:
Factors leading to rise of new species

• Genetic variations
• Mutations
• Natural selection
• Reproductive isolation
• Origin of new species.

Question 11.
Will geographical isolation be a major factor in the speciation by a self- pollinating plant species? Why or why not?
Answer:
No, m self-pollinating species, geographical isolation will not play any role for speciation because the self-pollination is occurring on the same plant.

Question 12.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer:
No, as there is neither genetic drift nor gene flow play any role during speciation. Moreover asexual reproduction involves single parent and natural geographical barrier can occur between different organisms.

Question 13.
Give an example of characteristic being used to determine how close two species are in evolutionary terms.
Answer:
Homologous organs helps to identify the relationship between organisms. These characteristics in different organisms would be similar because they are inherited from a common ancestor. Example. Fore limbs of mammals having same basic structural plans in birds, reptiles and mammals however the functions get modified in different species.

Question 14.
Can the wing of butterfly and wing of a bat be considered homologous organs? Why or why not?
Answer:
Wings of insects and wings of birds have different basic structural plan and origin. They perform the same function. Thus they are analogous organs and not homologous organs.

Question 15.
What are fossils? What do they tell us about the process of evolution?
Answer:
Fossils are preserved remains, tracks or traces of organisms that lived in the past. Fossils have been found linking all major groups of vertebrates.

Significance of fossils

• Fossils are direct evidence in support of evolution.
• Living forms with simple organization appeared earlier than the complex forms. We can conclude this because fossils of lower layers of the earth are simple as compared to fossils of the upper layers.
• Several forms bearing intermediate characters indicate the transition from an earlier simple to a later complex.
• Fossils of Archaeopteryx serve as a missing link between reptiles and birds. This bird has wings and unlike birds, it had teeth and a long tail.
• On the basis of the fossil records, the complete evolutionary history of present-day horse has been studied.

Question 16.
Why are human beings which look so different from each other in terms of size, colour, and looks are said to be belonging to the same species?
Answer:

• DNA studies have shown that human beings belong to the same species.
• The number of chromosomes is the same.
• All have originated from a common ancestor.
• They interbreed among themselves to produce fertile young ones of their own kind.

Question 17.
In evolutionary terms can we say that which among bacteria, spiders, fish, and chimpanzees have a ‘better’ body design? Why or why not?
Answer:
Chimpanzees have a better body design as compared to the other three mentioned. They are better adapted for locomotion, communication, and thinking.