Class 10 Science Chapter 9 Solution – Heredity and Evolution | SEBA Assam

Class 10 Science Chapter 9 – Heredity and Evolution – All Textual Solutions | ASSEB Assam (English Medium)

Class 10 Science Chapter 9 – Heredity and Evolution Complete Textual Solutions (ASSEB / SEBA Assam – English Medium)

The ninth chapter of the Class 10 Science curriculum, ‘Heredity and Evolution’, is a fascinating biological topic that connects the transmission of traits to the diversity of life on Earth. These complete textual solutions (Class 10 Science Chapter 9 Textual Question Answer) have been prepared based on the latest ASSEB (Assam State School Education Board) syllabus and the newest guidelines of the National Education Policy (NEP) for the upcoming board exams. This comprehensive collection includes Very Short Answers (VSA), Short Questions, Long Answers, and detailed explanations of genetic principles. At Ospin Academy, these solutions are provided in a simple, accurate, and completely exam-oriented format.

This chapter explores the foundational concepts of genetics, detailing Mendel’s experiments with pea plants, the rules for the inheritance of traits, and how sex is determined in human beings. It also delves into the mechanisms of evolution, speciation, and the evidence provided by fossils and homologous/analogous organs. It is highly essential for matric candidates to clearly grasp these concepts. Our textual solutions cover all textbook exercise questions, in-text questions, and additional exam-focused questions to ensure students are fully equipped for their examinations.

What you will learn and get from these textual solutions:

• Clear, step-by-step explanations of Mendel’s monohybrid and dihybrid crosses.
• Flawless answers for 1-mark VSA (objective type) and 2-3 mark short questions regarding the difference between acquired and inherited traits.
• Standard and easy-to-memorize solutions detailing the process of sex determination in human beings.
• Detailed information on the evidence of evolution, differentiating clearly between homologous and analogous organs.
• Solutions to all important questions along with the latest pattern MCQ questions as per the new syllabus.

Special features of these textual solutions by Ospin Academy:

• Complete textual solutions prepared strictly according to the latest ASSEB new syllabus.
• 100% accurate, high-quality notes written in simple English, making it easy for students to understand and memorize complex biological concepts (Class 10 Science Notes).
• Simplified answers specially designed for Quick Revision right before the examinations.
• A special compilation of extra important questions that are highly likely to appear in the board exams from this biology chapter.

Keeping in mind the academic upliftment of students, Ospin Academy has brought forward these special textual solutions. Start your matric exam preparation now and step forward towards scoring the highest marks in Science.

Class 10 Science

Chapter: 9                                                      Ospin Academy

Heredity and Evolution

Textual Questions and Answers

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: In asexual reproduction, the reproducing cells create copies of their DNA through chemical processes. However, this copying process is not always perfect, leading to small variations in the newly formed DNA.

Since asexual reproduction allows only a limited number of variations over generations, a trait that appears in a smaller percentage of the population is likely to have emerged more recently.

Thus, trait B, which is found in 60% of the population, is more likely to have arisen earlier than trait A, which exists in only 10% of the population.

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

Answer: Genetic variations enable the species to better adapt to changes in its environment. Moreover, it is an important force in evolution as it allows the frequency of alleles to increase or decrease through natural selection. These variations will determine the difference between extinction or continuation of the species.

3. How do Mendel’s experiments show that traits may be dominant or receive?

Answer: Mendel demonstrated that traits can be dominant or recessive by performing a monohybrid cross. When he crossed two pure-breeding varieties, the F1 generation always displayed one parental trait, while the other trait was not expressed. This showed that:

(a) The expressed trait is dominant.

(b) The unexpressed trait is recessive.

(c) The presence of the dominant allele in the F1 generation masked the expression of the recessive allele.

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

Answer: Mendel carried out dihybrid crosses by crossing two pea plants differing in contrasting traits of two characters. For example, he crossed a pea plant having yellow colour and round seed characters with another pea plant bearing green colour and wrinkled seed characters. In the F2 generation, he obtained pea plants with two parental and two recombinant phenotypes as yellow round and green wrinkled (parental) and yellow wrinkled and green round (recombinant). This indicated that traits separated from their original parental combinations and got inherited independently.

5. A man with blood group A marries a woman with the 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 determine which of the traits – blood group A or O – is dominant. This is because we do not know about the blood group of all the progeny. Blood group A can be genotypically AA of AO. Hence, the information is incomplete to draw any such conclusion.

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

Answer: Sex of a child depends on the chromosome in the gamete of the father. The unfertilized egg has one X chromosome. The sperm either has X chromosome or Y chromosome. If sperm carrying the Y chromosome fertilizes with the egg, male child will be born with the genetic constitution XY. But if sperm carrying the X chromosome fertilized with the egg, the female child will be born with the genetic constitution XX.

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

Answer: An individual trait may increase in a population in the following ways:

(i) Natural Selection: If a trait is useful to the population, it will increase naturally. It may directly lead to the evolution of species populations by adaptations to fit their environment better. That particular trait may thus increase in the population.

(ii) Genetic drift: If a population faces an accident such that the majority of its members get killed, the remaining members will pass on their traits to the subsequent generations. This leads to an increase of the trait in the population. This is the notion of genetic drift, which provides diversity without any adaptation.

(iii) Geographic isolation: Where a population of species gets separated by their respective group due to physical/natural barriers.

(iv) Mutation: Slight changes in the genetic information of the offspring during fertilization.

(v) The trait is beneficial to the population: If a trait is beneficial to a population, it will increase naturally. Such green color in beetles is favorable as it helps them in camouflage against predators.

8. Why are traits acquired during the life – time of an individual not inherited?

Answer: For a trait of an organism to be inherited, it should bring about a change in the genes present in the reproductive cells or gametes of that organism. The traits acquired during the lifetime of a person do not bring about a change in the genes present in its reproductive cells or gametes and hence they are not inherited by the offspring.

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

Answer: A small number of surviving tigers are a cause of worry from the point of genetics because these tigers carry the genes which have made them adapt to the particular environment during the long process of evolution. If these tigers become extinct by some diseases or by hunting then the genes responsible for survival would also become extinct and would not be able to contribute to the survival of future generations.

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

Answer: The main factors which lead to the rise of new species are natural selection, genetic drift, geographical isolation, and mutation. In speciation, a single evolutionary lineage gets split into two or more genetically independent lineages due to the actions of several environmental factors.

 

Exercise Questions and Answers

1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing with 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 for can be depicted as –

(a) TTWW

(b) TTww

(c) TtWW

(d) TtWw

Answer: (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 tasks.

(c) Potatoes and runners of grass.

(d) All of the above.

Answer: (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.

Answer: (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?

Answer: No because we cannot say with certainty whether light eye colour is dominant or recessive. However, since both children and their parents have light eye colour, the possibility that light eye colour is recessive trait.

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

Answer: Classification and evolution are highly interlinked fields of study. Classification is influenced by evolution. The modern system of classification is also called

phylogenetic classification; which means it is based on evolutionary relationships. Hence, evolution and classification are closely related.

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

Answer: Homologous organs are those organs which have the same basic structural design and origin but have different functions.

For example: the forelimbs of humans and the wings of birds look different externally (morphologically dissimilar) but their skeletal structure is similar.

Analogous organs are those organs which have the different basic structural design and origin but have similar functions.

For example: the wings of birds and insects.

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

Answer: Cross the homozygous male BB and homozygous female bb, and then observe the coat colour in dog progeny (offspring). If all progeny have black colour, this means that black colour will be the dominant coat colour in dogs and if progeny will have brown colour then the brown colour will be dominant coat colour.

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

Answer: Fossil provide us evidence about:

(i) The organisms that lived long ago such as the time period during which they lived, their structure etc.

(ii) Evolutionary development of species i.e., line of their development.

(iii) Connecting links between two groups. For example, feathers present in some dinosaurs means that birds are very closely related to reptiles.

(iv) Which organisms evolved earlier and which later.

(v) Development of complex body designs from the simple body designs.

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

Answer: Miller-Urey experiment provided evidence for the origin of life from inanimate matter. In the experiment, they created an atmosphere containing molecules like

ammonia, methane and hydrogen sulphide, but no oxygen. This atmosphere was similar to the atmosphere present during the primitive Earth. Temperature was maintained constant at 100°C and sparks were passed through the mixture to stimulate lightning. After a particular time, a certain amount of the carbon from methane had been converted to simple compounds of carbon like amino acids.

Amino acids are the precursors of the proteins and proteins are the molecules that support the life in basic form.

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

Answer: 

(i)  In asexual reproduction, there is no fusion of gametes, and only 1 parent is involved. So the only reason for variation is errors during DNA copying.

(ii) These variations are very minute and can only be seen over a long period of time since too much deviation can lead to unsurvivable alterations in the genetic makeup for the progeny.

(iii) Sexual reproduction gives rise to more viable variations than asexual reproduction because 2 gametes from different individuals combine to produce an organism.

(iv) It involves 2 parents so the offspring (child) shows variation due to the presence of characteristics of both parents.

(v) These variations help adapt to the environment in a better, more efficient manner , and result in evolution and formation of new species over time .

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

Answer: There are 23 pairs of chromosomes. Most human chromosomes have material and a paternal copy. We have 22 such pairs. These pairs contain half chromosomes from mother and half from father. One pair is called sex chromosomes. At the time of sex determination, the egg cell fuses with the sperm cell which are haploid to form zygote. Zygote is diploid which contains 23 chromosomes from mother and 23 from father. In this way, an equal genetic contribution of male and female parents is ensured in the progeny.

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

Answer:  Yes, it is true that only variations that provide an advantage to an organism increase its chances of survival in a population. However, not all variations are beneficial or contribute equally to survival.

The survival of an organism depends on how useful a variation is in a given environment. For example, if a bacterial population is exposed to high temperatures, bacteria with heat-resistant traits will have a higher chance of survival, while others may perish. This demonstrates how favorable variations help organisms adapt and persist in changing environments.