CBSE Class 10 Biology Heredity Worksheet Set K

Very Short Answer Type Questions :

Question. What indication do we get by reappearance of dwarf plant in F2 generation?
Answer : After obtaining progeny in F2 generation in a dihybrid cross, Mendel concluded that when two pairs of traits are combined in a hybrid, one pair of character segregates independently of the other pair of character.

Question. Tails of some mice were amputated and they were allowed to breed. The mice that were produced also had their tails amputated and it was repeated for many generations. What is the reason of tail appearing again and again?
Answer : Such traits are acquired traits. Traits acquired during the life-time of an individual are not inherited as these changes are not in the genes of reproductive tissues.
The changes in the non-reproductive tissues cannot be passed on to the DNA of the germ cells, hence such acquired changes are not inherited by the progeny.
Example: tailless mice (if tail is removed by surgery) cannot produce tailless progeny.

Question. a. “Recent fossils are found closer to the earth’s surface”. Comment on the statement stating reason.
b. List two factors which could lead to the rise of new species.
Answer :
a. This statement is correct as the fossils found closer to the surface of earth are more recent and those found in deeper layers are older ones.
b. Natural selection and genetic drift.

Question. What are sex chromosomes? Which sex chromosomes are found in male and female human beings? State the chromosome responsible for the development of male child in human beings?
Answer : Sex chromosomes are set of chromosomes present in human beings which help in sex determination.
XX and XY.
Y chromosome.

Short Answer Type Questions : 

Question. How do we know how old fossils are?
Answer : We can find the relative of the fossil by the depth at which the fossil is found. The ones that are found near the surface are more recent than the fossils found in the deeper layer. The second way of dating fossils in detecting the ratios of different isotopes of the same element in the fossils material.

Question. Variation is useful for the useful over long time. But the variants have unequal chances of survival. Explain this statement.
or
Define variation in a species. How does it increases the survival chances of a species?
a. Identify the organism shown in the above figure.
b. Name one incipient feature selected by the nature.
c. Mention any other primitive feature of birds.
Answer : Variation are minor differences among members of a population. They are useful for the process of evolution which take place over long time. But some of the variants find it more advantageous in the present environmental conditions to survive than others variants by virtue of the variation possessed by them hence they have unequal chances of survival. Thus some get selected and others get eliminated. Those which survive pass their genes to next generation therefore frequency of genes possessed by them increase in frequency in the population. Example - in a population of beetles, a new variation (green colour) get survival benefit/advantage to green beetles whereas other (red) perishes.

Question. What are fossils? What do they tell us about the process of evolution?
Answer : The remains of dead plants and animals which were buried under the rocks millions of years ago are called fossils.
Fossils tell us about the process of evolution. The fossils of different organisms have some features similar to one species while some features are similar to the other species. In this way, they show the link between two species. They tell us that one species evolves from the other.

Question. What evidence do we have for the origin of life from inanimate matter? 
Answer : Stanley L. Miller and Harold C. Urey provided evidence regarding origin of life from inanimate matter. They assembled an atmosphere similar to that existed on early earth. The atmosphere had molecules like ammonia, methane and hydrogen sulphide, but no oxygen and kept over water at temperature just below 100°C. Sparks were passed through the mixture of gases. At the end of a week, 15% carbon from methane had been converted to simple compounds of carbon like amino acids which make-up protein molecules. So, life arose afresh on earth.

Question.”The sex of the children is determined by what they inherit from their father and not their mother.” Justify. 
Answer : It is because a child who inherits an X chromosome from her father will be a girl and one who inherits a Y chromosome from his father will be a boy. But all children inherit a X chromosome from their mother regardless of whether they are boys or girls.

Question. Distinguish between acquired and inherited traits by giving one example of each. Why are traits acquired during the lifetime of an individual not inherited?
Answer : Acquired trait is a particular characteristic that is developed during the lifetime of an individual. Such characteristics are not genetically controlled and cannot be passed on to the next generation. Example: Loss of weight due to starvation.
Inherited trait is the transmission of particular characteristics from parents to their off springs, generation to generation. Such traits are genetically determined characteristic that distinguishes a person.
Example: Colour of skin.
The acquired traits cannot change the DNA of the germ cells. Therefore, the acquired traits cannot be inherited over generations during the lifetime of an individual.

Question. How does the creation of variations in a species promote survival?
Answer : Variations increases the adaptability of an organism to its changing environmental conditions.

Question. How do Mendel’s experiments show that traits may be dominant or recessive?
Answer : Mendel took pea plants of two different characters i.e., tall plants and short plants. The first generation of F1 progeny formed were all tall. This shows that traits may be either dominant or recessive, there is no way in between traits obtained.

Question. Define Genetics. What did Mendel’s contribution to genetics?
Answer : The science of heredity and variation is called Genetics. Mendel conducted breeding experiments in a plant called garden pea (pisum sativum) with contrasting pair of characters, found that only one character of the pairs appeared in the first generation but both the characters appeared in the subsequent generation. On the basis of these results of his experiments he put forth the various principals of inheritance. He also suggested that each character is controlled by a pair of factors which are now called as genes.

Question. With the help of suitable examples explain natural selection. 
Answer : Let us assume that there exist a group of red beetles in some green bushes. Due to variation during sexual reproduction one green beetle evolved among them. This green beetle can pass the colour to its progeny which are green beetles.
Crows cannot see green beetles in green bushes and therefore, cannot eat them. The progeny of green beetles are not eaten while the progeny of red beetles continued to be eaten. As a result there are more and more green beetles in the beetle population. The progeny of green beetles increase due to natural selection which gives survival advantage.

Question. Explain with examples how the following are evidences in favour of evolution in organisms. (i) Homologous organs (ii) Analogous organs (iii) Fossils 
Answer : (i) Forelimb of human and bird are homologous organs. They have same structural design and developmental origin but they have different functions and appearance. Homologous organs help us to understand that the organism has evolved from a common ancestor. The more common characteristics the two species have, the more closely they are related.
(ii) Analogous organs are those organs design and developmental origin but have similar appearance and perform similar functions.
Example: The wings of birds and bats look similar but have different design in their structure. They have a common function of flying but their origins are not common. So, birds and bats are not closely related.
(iii) Fossils and their study is useful in knowing about the species which are no longer alive. They provide evidence and missing links between two classes. They are helpful in forming a sequence of organisms in the pathway of evolution. Thus, fossils have an importance in deciding evolutionary relationship. Archaeopteryx is a fossil bird. It had feathers, fused bones and beak which are exclusively bird structures. It also had some features which are found in reptiles, e.g. teeth in jaw, claws on free fingers and a long tail. This fossil provides a clue that birds have evolved from reptiles.

Question. What are homologous organs? Can the wing of a butterfly and the wing of a bat be regarded as homologous? Why? 
Answer : Homologous organs are those organs which have the same basic structural design and developmental origin but have different functions and appearance.
Example: The forelimb of a frog, a lizard, a bird and a man seem to be built from the same basic design of bones, but they perform different functions.
No, the wing of a butterfly and the wing of a bat cannot be considered homologous organs because they have a common function for flying but their origin and structure are not common. So, they are analogous organs.

Question. What evidence do we have for the origin of life from inanimate matter?
Answer : Miller and Urey in 1953 assembled an atmosphere similar to that thought to exist at early period (Gases like ammonia, methane, hydrogen sulphide) over earth. This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lighting. 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. Presence of protein cell membrane correlates with above experiment. This shows that life originated from inanimate matter.

Question. Describe briefly four ways in which individuals with a particular trait may increase in a population. 
Answer : The four ways in which individuals with a particular trait may increase in a population are as follows:
1. Sexual reproduction results into variations.
2. The individuals with special traits survive the attack of their predators and multiply while the other will perish.
3. Genetic drift provides diversity without any adaptation.
4. Variations in the species may lead to increased survival of the individuals.

Question. Give an example of body characteristics used to determine how close two species are in terms of evolution and explain it. 
Answer : Homologous organs help to identify the relationship between organisms. These characteristics in different organisms would be similar because they have inherited from a common ancestor. For example, forelimbs of human and wings of birds show closeness between the two species because the organs have similar basic structural design of limbs though it has been modified to perform different functions.

Question. What is a sex chromosome? 
Answer : Sex chromosome is a chromosome that operates in the sex-determining mechanism of a species. Many animals have two different types of sex chromosomes. For example, in human there is a large X chromosome and a much smaller Y chromosome.

Question. Explain the terms: (i) Speciation (ii) Natural selection 
Answer : (i) Speciation is the evolution of reproductive isolation among once-interbreeding populations, i.e. the development of one or more species from an existing species.
(ii) Natural selection is the process, according to Darwin, which brings about the evolution of new species of animals and plants.

LONG ANSWER TYPE QUESTIONS 

Question. After the death of two insects, one of the insect was burried in hot mud and the other in usually found mud. Which of the two is more likely to be preserved better and why?
Answer : The insect burried in hot mud. The body will not get decomposed in hot mud and the impression of the body will remain.

Question. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer : Small numbers of tigers means that fewer variations in terms of genes are available. This means that when these tigers reproduce, there are less chances of roducing progeny with some useful variations . Hence, it is a cause of worry from the point of view of genetics.

Question. 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 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 or AO. Hence, the information is incomplete to draw any such conclusion.

Question. How are the areas of study − evolution and classification − interlinked?
Answer : Classification involves grouping of organism into a formal system based on similarities in internal and external structure or evolutionary history.
Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor.
For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation.
With subsequent generations, the variations make organisms more different than their ancestors.
This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.

Question. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer : Geographical isolation prevents gene flow between populations of a species 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.

Question. How does the creation of variations in a species promote survival?
Answer : Sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. For example, if the temperature of water increases suddenly, most of the bacteria living in that water would die. Only few variants resistant to heat would be able to survive. If these variants were not there, then the entire species of bacteria would have been destroyed. Thus, these variants help in the survival of the species. However, not all variations are useful. Therefore, these are not necessarily beneficial for the individual organisms.

Question. 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 : A species is a group of organisms that are capable of interbreeding to produce a fertile offspring. Skin colour, looks, and size are all variety of features present in human beings. These features are generally environmentally controlled. Various human races are formed based on these features. However, there is no biological basis to this concept of races. Therefore, all human beings are a single species as humans of different colour, size, and looks are capable of reproduction and can produce a fertile offspring.

Question. 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 : In species, variations that offer survival advantages are naturally selected. Individuals adjust to their environments with the help of these selected variations and consequently these variations are passed on to their progeny. Evolution of organisms occurs as a result of this natural selection.
However, there can be some other variations, which do not offer any survival advantage and arise only accidentally. Such variations in small populations can change the frequency of some genes even if they are not important for survival. 
This accidental change in the frequency of genes in small populations is referred to as genetic drift.
Thus, genetic drift provides diversity (variations) without any survival advantage. 

Question. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Answer : Evolution cannot always be equated with progress or better body designs. Evolution simply creates more complex body designs. However, this does not mean that the simple body designs are inefficient. In fact, bacteria having a simple body design are still the most cosmopolitan organisms found on earth. They can survive hot springs, deep sea, and even freezing environment.
Therefore, bacteria, spiders, fish, and chimpanzees are all different branches of evolution.

Question. 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 : In sexual reproduction, two individuals having different variations combine their DNA to give rise to a new individual. Therefore, sexual reproduction allows more variations ,whereas in asexual reproduction, chance variations can only occur when the copying of DNA is not accurate.
Additionally, asexual reproduction allows very less variations because if there are more variations, then the resultant DNA will not be able to survive inside the inherited cellular apparatus.
However, in sexual reproduction, more variations are allowed and the resultant DNA is also able to survive ,thus making the variations viable.
Variation and Evolution: Variants help the species to survive in all the conditions. Environmental conditions such as heat, light, pests, and food availability can change suddenly at only one place. At that time, only those variants resistant to these conditions would be able to survive. This will slowly lead to the evolution of a better adapted species. Thus, variation helps in the evolution of sexually reproducing organisms.

Question. A study found that children with light-coloured eyes are likely to have parents with lightcoloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Answer : Let us assume that children with light-coloured eyes can either have LL or Ll or ll genotype. If the children have LL genotype, then their parents will also be of LL genotype.
LL × LL
↓
LL
If the children with light-coloured eyes have ll genotype, then their parents will also have ll genotype.
ll × ll
↓
ll
Therefore, it cannot be concluded whether light eye colour is dominant or recessive.

Question. (i) What is genetics?
(ii) Give the common name of the plant on which Mendel performed its experiments.
(iii) What for did Mendel use the term factors and what are these factors called now?
(iv) What are genes? Where are the genes located?
Answer : (i) Science which deals with the study of heredity and variations is called genetic.
(ii) Pea plant.
(iii) Mendel used the term factors for ‘genes’.
(iv) Genes is the unit of inheritance. It is a part of the chromosome which controls the appearance of a set of hereditary character. Genes are located on the chromosome.

Question. What are the different ways in which individuals with a particular trait may increase in a population? 
Answer : Individuals with a particular trait may increase in a population as a result of the following:
(i) Natural selection: When that trait offers some survival advantage.
(ii) Genetic drift: When some genes governing that trait become common in a population.
(iii) When that trait gets acquired during the individual’s lifetime.

Question. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer : 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.

Question. What factors could lead to the rise of a new species?
Answer : Natural selection, genetic drift and acquisition of traits during the life time of an individual can give rise to new species.

Question. What are fossils? What do they tell us about the process of evolution?
Answer : Fossils are the remains of organisms that once existed on earth. They represent the ancestors of plants and animals that are alive today. They provide evidences of evolution by revealing the characteristics of the past organism and the changes that have occurred in these organisms to give rise to the present organisms.

Question. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species ? Why or why not?
Answer : Geographical isolation can prevent the transfer of pollens among different plants. However, since the plants are self-pollinating, which means that the pollens are transferred from the anther of one flower to the stigma of the same flower or of another flower of the same plant, geographical isolation cannot prevent speciation in this case.

Question. How do Mendel’s experiments show that traits are inherited independently?
Answer : When Mendel crossed pure bred tall pea plants with pure bred short pea plants, he found that only tall plants were produced in F1 generation. Mendel, further crossed the tall pea plants obtained in F1 generation with dwarf plants and obtained the ratio of Tall: Short plant as 3 : 1 in F2 generation. This experiment proved that traits are inherited independently so other intermediate traits or new traits were formed.