Here you get the CBSE Class 10 Science chapter 9, Heredity and Evolution: NCERT Exemplar Problems and Solutions (Part-II). This part of the chapter includes solutions for Question No. 26 to 36 from the NCERT Exemplar Problems for Class 10 Science Chapter: Heredity and Evolution. These questions include only the Short Answer Type Questions framed from various important topics in the chapter. Each question is provided with a detailed explanation.
NCERT Exemplar Solution for CBSE Class 10 Science Chapter 9: Heredity and Evolution (Part-I)
NCERT Exemplar problems are a very good resource for preparing the critical questions like Higher Order Thinking Skill (HOTS) questions. All these questions are very important to prepare for CBSE Class 10 Science Board Examination 2017-2018 as well as other competitive exams.
Find below the NCERT Exemplar problems and their solutions for Class 10 Science Chapter, Heredity and Evolution:
Short Answer Questions
Question. 26 How is the sex of a new born determined in humans?
Answer.
Humans follow XX- XY mechanism of sex determination. Human females have forty-six chromosomes arranged in twenty two homologous and homomorphic autosomes and two copies of X chromosomes as sex chromosomes (44+XX). Males have twenty-two homomorphic pairs and one heteromorphic pair, the XY pair (44+XY). During meiosis, all the gametes produced by females contain only the X chromosome (22 A + X), whereas males produce two kinds of gametes, 1/2 gametes with X- and 1/2 with Y-chromosome (22 A + X and 22 A + Y). Fertilization of egg (22 + X) with sperm carrying 22+X chromosomes results in female child (44A + XX). Fertilization of egg (22 + X) with sperm carrying 22+Y chromosomes results in male child (44A + XY).
Question. 27 Do genetic combination of mothers play a significant role in determining the sex of a new born?
Answer.
Humans follow XX- XY mechanism of sex determination. Human females have forty-six chromosomes arranged in twenty two homologous and homomorphic autosomes and two copies of X chromosomes as sex chromosomes (44+XX). They do not play significant role in sex determination of child.
Males have twenty-two homomorphic pairs and one heteromorphic pair, the XY pair (44+XY). Fertilization of egg (22 + X) with sperm carrying 22+X chromosomes results in female child (44A + XX). Fertilization of egg (22 + X) with sperm carrying 22+Y chromosomes results in male child (44A + XY). Therefore, presence or absence of Y chromosome male gamete determines the sex of human child.
CBSE Class 10 Science Syllabus 2017-2018
Question. 28 Mention three important features of fossils which help in the study of evolution.
Answer.
Fossils help in the study of evolution in following ways:
(i) Fossils exhibit mode of preservation of ancient species.
(ii) Fossils establish evolutionary relationship between organisms and their ancestors.
(iii) Fossils establish the geological time period in which organisms existed.
Question. 29 Why do all the gametes formed in human females have an X-chromosome?
Answer.
Human females have forty-six chromosomes arranged in twenty two homologous and homomorphic autosomes and two copies of X chromosomes as sex chromosomes (44+XX). Therefore, during meiosis, all the gametes produced by females contain only the X chromosome (22 A + X).
Question. 30 In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.
Answer.
Humans follow XX- XY mechanism of sex determination. Human females have forty-six chromosomes arranged in twenty two homologous and homomorphic autosomes and two copies of X chromosomes as sex chromosomes (44+XX). Males have twenty-two homomorphic pairs and one heteromorphic pair, the XY pair (44+XY). During meiosis, all the gametes produced by females contain only the X chromosome (22 A + X), whereas males produce two kinds of gametes, 1/2 gametes with X- and 1/2 with Y-chromosome (22 A + X and 22 A + Y). Therefore, possibility of fertilization of egg (22 + X) with sperm carrying 22+X chromosomes and hence chances of having a female child (44A + XX) is 50%. Likewise, there is 50% possibility that egg (22 + X) is fertilized with sperm carrying 22+Y chromosomes to have male child (44A + XY).
Question. 31 A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Answer.
Smaller populations are at greater threat of extinction as compared to large species. This is because less number of individual in smaller population imparts lesser changes in production of genetic variations. Lack of genetic diversity makes the smaller species more prone to extinction under any dramatic changes in prevailing environmental conditions.
On the other hand, large populations exhibit more genetic diversity on which evolutionary forces act upon to make it withstand any changes in surrounding.
Question. 32 What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?
Answer.
Homologous organs perform different functions and have different appearance but share common basic structural plan and origin. Divergent evolution refers to evolution of organisms in different directions from a common ancestry and leads to development of homologous organs. For example, forelimbs of reptiles, amphibians, birds and mammals.
Yes, homologous structures are inherited from a common ancestor. In the given example, the basic structure of forelimb of mammals, birds, reptiles and amphibians is similar but they are modified to perform different functions in various vertebrates. Thus, showing they have evolved from a common ancestor.
NCERT Solutions for CBSE Class 10 Science
Question. 33 Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Answer.
Animals on earth exhibit vast diversity in structure and function which in turn suggest their origin from diverse ancestors. For example, Reptiles, birds and mammals exhibit vast diversity and seem to have evolved from different ancestors.
However, detailed analysis of characters of these three groups reveals their common ancestry as all of them exhibit amniotic eggs. Presence of fluid filled sac (amnion) around the embryo during its development is key feature of amniotes. Amniotes includes three groups namely Reptilia, Aves and Mammalia. An approach to divide and sub divide each group of animals and try to find out their common characters, all diverse group seem to have evolved from a common ancestor. Diverse habitat of these groups caused them to developed different characters and to look diverse from each other as we see them today.
It can be concluded that all animals groups originated on earth from common ancestors and exhibited divergent evolution that in turn evolve them into diverse groups.
Question. 34 Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive
(i) Yellow seed
(ii) Round seed
Answer.
(i) Seed color: yellow (Dominant); green (Recessive)
(ii) Seed shape: rounds (Dominant); wrinkled (Recessive).
Question. 35 Why did Mendel choose pea plant for his experiments?
Answer.
Mendel studied the common garden pea plant, (Pisum sativum) because
- It was easy to cultivate and had a relatively short life cycle of 3 months.
- The plant exhibited discontinuous characteristics such as flower color and pea texture.
- It was easy to control the self pollination of the plant and cross-fertilization between desired parents could be accomplished artificially.
- Presence of pure breeding varieties and easily visible contrasting characters
Question. 36 A woman has only daughters. Analyze the situation genetically and provide a suitable explanation.
Answer.
Humans follow XX- XY mechanism of sex determination. Human females have forty-six chromosomes arranged in twenty two homologous and homomorphic autosomes and two copies of X chromosomes as sex chromosomes (44+XX). They do not play significant role in sex determination of child.
Males have twenty-two homomorphic pairs and one heteromorphic pair, the XY pair (44+XY). Fertilization of egg (22 + X) with sperm carrying 22+X chromosomes gives female child (44A + XX). Fertilization of egg (22 + X) with sperm carrying 22+Y chromosomes gives male child (44A + XY). Only daughters indicate fusion of egg with sperms carrying 22+X chromosomes every time.
CBSE Class 10 NCERT Textbooks & NCERT Solutions