NCERT Exemplar Solutions for Class 10 Science Chapter 9 Heredity and Evolution
These Solutions are part of NCERT Exemplar Solutions for Class 10 Science. Here we have given NCERT Exemplar Solutions for Class 10 Science Chapter 9 Heredity and Evolution
NCERT Exemplar Solutions for Class 10 Science Chapter 9 Short Answer Questions
How is a sex of new born determined in humans ?
Natural selection is preferential survival and differential reproduction of individuals of a population which possess variations that provide better adaptability to the existing environment. Peppered Moth of England has two forms, light grey and dark grey. Prior to industrial revolution, tree trunks in the forests around.
Manchester were light greyish green due to presence of lichens. Most of the Peppered Moth found in the area were light coloured with dark spots which could not be spotted easily by predator birds. During 1845 to 1890, air pollution killed the lichen flora. The deposition of soot changed the colour of the tree trunks to blackish one. Peppered Moth of the area also exhibited switch over to melanic or blackish form.
It provided better survival value against dark background. The light grey form largely disappeared as it could be easily spotted by predator birds and devoured.
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Does genetic combination of mothers play a significant role in determining the sex of a new born ?
No. Mothers have no role in determining the sex of the new born. Mothers are homogametic, that is, they produce only one type of ova (22 + X). Fathers are heterogametic, that is, they produce two types of sperms, gynosperms (22 + X ) and androsperms (22 + Y). If gynosperm (22 + X) fertilises the ovum (22 + X), the sex of new born will be female (44 + 2X). If androsperm (22 + Y) fuses with ovum (22 + X), the new born will be boy (44 + XY).
Mention three important features of fossils which help in the study of evolution.
Fossils are remains or impressions of past organisms that are found in the rocks. Fossils of lower strata belong to early periods while those of upper strata are of later periods. Arranging the fossils stratumwise will indicate the occurrence of different forms of life at different times. It is found that the early fossils generally belong to simple organisms. Complexity and elaboration increased gradually with evolution. Evolution has never been linear or straight. A number of variants or branches appeared, some of which were more complex while others were less complex.
- Fossils indicate the path of evolution of different groups.
- They can indicate the phylogeny of some organisms, e.g, Horse, Elephant.
- Some fossils have characteristics intermediate between two groups,
e.g., toothed bird Archaeopteryx. They indicate how one group has evolved from another.
Why do all the gametes formed in human females have an X-chromosome ?
Human females are homogametic. Their generic constitution is 44 + XX The two sex chromosomes are similar. Their ova which are produced after meiosis carry a gametic constitution of 22 + X No other combination is possible.
In human beings the satistical possibility of getting either a male or female child is 50 : 50. Give suitable explanation.
Human females (44 + XX) are homogametic, that is, they produce only one type of ova (22 + X). Human males are heterogametic. They produce two types of sperms (22 + X and 22 + Y) in equal proportion, that is, 50 : 50 ratio. The chance of male or female child is also 50 : 50, as there is equal chance of androsperm (22 + Y) or gynosperm (22 + X) fertilizing an ovum.
A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
A small population is always at a risk of degeneration and extinction due to
- Excessive inbreeding that brings about inbreeding depression or degeneration,
- Fewer recombinations and variations which are otherwise essential for maintaining vitality and vigour of the species.
- Lesser adaptability to changes in the environment,
- Increased threat to survival due to poaching, habitat destruction and environmental change.
What are homologous structures ? Give an example. Is it necessary that homologous structures always have a common ancestor ?
Homologous structures or organs are those structures which have similar origin, similar development, similar internal structure and similar basic plan but show different external form and function, e.g., forelimbs of amphibians, reptiles, mammals and birds. Homologous structures are always have a common ancestry because otherwise there cannot be any similarity in basic plan, internal structure, development or origin. Modifications have occurred in them due to varied adaptations.
Does the occurrence of diversity of animals on earth suggest their diverse ancestry also ? Discuss this point in the light of evolution.
Diversity of animals does not mean that they have diverse ancestry. Animals can be grouped into distinct lineages (e.g., mammals, birds, reptiles, annelids). Many of the lineages further show some similarities in basic traits indicating a common ancestry, e.g.,
vertebrates. Therefore, animals having a common ancestor in the remote past have successively developed newer and newer traits forming various groups of animals.
Give the pair of contrasting traits of the following characters in Pea plant and mention which is dominant and recessive
- Yellow seed
- Round seed.
- Seed Colour: Yellow (dominant), green (recessive).
- Seed Shape: Round (dominant), wrinkled (recessive).
Why did Mendel choose Pea plant for his experiments ?
Mendel chose Garden Pea or Edible Pea (Pisum sativum) as his experimental material because of
- Easy availability of detectable contrasting traits of several characters,
- Flower structure normally allows self fertilization but cross fertilization can also be carried out easily.
- Annual nature of the plant,
- Formation of a large number of seeds by each plant,
- Requirement of little care except at the time of cross breeding.
A woman has only daughters. Analyse the situation genetically and provide a suitable, explanation.
A woman produces only one type of ova (22 + X) while her husband produces two types of sperms, gynosperms (22 + X) and androsperms (22 + Y) in equal proportion. It is a chance that each time the woman conceived, only the gynosperm fertilised the egg so that only daughters were born.
NCERT Exemplar Solutions for Class 10 Science Chapter 9 Long Answer Questions
Does geographical isolation of individuals of a species lead to formation of a new species ? Provide a suitable explanation.
Yes. Geographical isolation of a population will lead to genetic drift as there will be no gene flow between it and the parent species. Inbreeding in small population will result in fixation of certain alleles and elimination of others. There will be change in gene frequency. Mutations will produce new alleles and hence a new gene pool. Accumulation of new alleles and hence new variations over several generations will ultimately lead to the formation of new species.
Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria. Provide a suitable explanation.
Both bacteria and human beings perform all the activities of life and live comfortably in their environments. They, therefore, seem
to be equally evolved. However, human beings have a far more complex organisation and differentiation which are absent in bacteria. Since complex organisation and differentiation develop only through evolution, humans are far more evolved than bacteria.
All the human races like Africans, Asians, Europeans, Americans and others might have evolved from a common ancestor. Provide a few evidences in support of this view.
All the human races have evolved from a common ancestor because they possess
- Common body plan
- Common structure
- Similar physiology
- Similar metabolism
- Similar chromosome number
- Common genes or genetic blue print
- Free interbreeding.
Differentiate between inherited and acquired characters. Give one example of each type.
|1. Development. The traits develop during life time of an individual.
2. Nature. They are somatic variations.
3. Cause. Acquired traits develop due to direct effect of environment, use and disuse and conscious efforts.
4. Fate. They die with the death of the individual.
Ex. Muscular body of a wrestler.
|The traits are obtained from the parents.
They are genetic variations.
The traits develop due to mutations and reshuffling of genetic material.
They are passed on to the next generation.
Ex. Fused and free ear lobes.
Give reasons why acquired characters are not inherited.
Many of the variations have no immediate benefit to the species. They function as preadaptations which can be beneficial under certain environmental conditions like heat tolerance variation if the temperature of the area rises.
Evolution has exhibited greater stability of molecular structures when compared with morphological structures. Comment on the statement and justify your opinion.
Life is a highly organised system of biochemicals and their reactions. It is expressed inside the cells. They are the same right from bacteria to human beings. However, the method of procurement of the raw materials for forming bio-chemicals is not the same in various organisms. It has helped in avoiding cut throat competition amongst the living beings. They developed different morphological features and modes of obtaining nutrients. As a result a huge diversity has appeared in the living world.
In the following crosses, write the characteristics of the progency
(a) All Round Yellow
(b) Round Yellow, Round Green, Wrinkled Yellow and Wrinkled Green in the ratio of 9 : 3 : 3 : 1.
(c) All Wrinkled Green (et) All Round Yellow (Rr Yy).
Study the following cross showing self pollination in F1. Fill in the blank and answer the question that follows :
Rr Yy (Round Yellow ).
In the above question, what are combination of characters in F2 progeny ? What are their ratios ?
Round Yellow – 9,
Round Green – 3,
Wrinkled Yellow – 3,
Wrinkled Green -1
i.e., 9 : 3 : 3 : 1.
Give the basic features of the mechanism of inheritance.
Basic Features of Inheritance
- Unit Characters: An organism is made of a large number of characters, each of which behaves as a unit.
- Genes: Characters are controlled by genes.
- One Gene-One Character: A single gene generally controls one character.
- Location of Genes: Genes are located on chromosomes.
- Alleles: A gene may have two or more forms called alleles. They represent different traits of a character.
- Paired Alleles: An individual possesses two alleles of every gene. The two may be similar or dissimilar.
- Dominance: Where there are two different forms or alleles of the gene, generally one expresses its effect. It is called dominant allele. The other which does not express its effect in presence of dominant allele, is called recessive allele.
- Segregation: The two alleles separate at the time of gamete formation. A gamete has only one allele or form of the gene.
- Independent Assortment: The alleles of different genes located on separate chromosomes behave independent of one another.
- Pairing: Fusion of gametes during fertilization, brings together the two forms of a gene in the zygote.
Give reasons for the appearance of new combination of characters in the F2 progeny.
Independent Assortment: The two forms of a gene separate and pair independent of the two forms of other genes during gametogenesis and fertilisation. It causes new combination of characters, e.g.;
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