Question 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 ?
Trait B, because it is present in more members of the population. It is likely to have arisen earlier and has now spread to 60% of the population. Trait A is new and has spread to only 10% of the population.
Question 2.
How does the creation of variations in a species promote survival ?
The variations provide stability to the population of various species by preventing them from getting wiped out during adverse conditions.
The natural environment also changes, and variations in species which become suited to the environment help it to survive.
Question 3.
How do Mendel’s experiments show that traits may be dominant or recessive ?
Mendel took pea plants with contrasting characteristics tall plant and dwarf (or short) plant. On cross pollination, he got all tall plants in first generation (F1). But by the self¬pollination of F1 tall plants, the plants of second generation consisted of tall and short pants in the ratio of 3 : 1. On the basis of these experiments, the characteristics appeared in first generation were called dominant (i.e. tall plants) and the characteristics that did not appear were called recessive (dwarf i.e. plants).
Question 4.
How do Mendel’s experiments show that traits are inherited independently ?
Mendel took two pairs of alternate expression of two traits and carried out dihybrid crosses by crossing them. The traits appeared in first generation were termed as dominant. When he used these F1 progeny to generate F2 progeny by self-pollination plants of different types were produced. In some plants both the traits were dominant, while in some plants both were recessive and some plants exhibited mixed traits. This indicates that traits are inherited independently.
Question 5.
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 ?
This information is not enough. This is because each individual is carrying two alleles. The recessive trait can occur only when who alleles are similar. It blood group A is dominant and O is recessive, then daughter can have blood group O only when both recessive alleles occur together in mother, and father has one allele of O and other of A.
Question 6.
How is the sex of the child determined in human beings ?
OR
“The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it.” Justify this statement with the help of a flow chart showing determination of sex of a newborn.
Half of the male gametes (sperms) carry X chromosome and other half carry Y chromosomes. All the female gametes carry only X chromosomes. When a sperm fertilizes an egg, the following situations become possible.
- (i) When a sperm carrying X chromosome fertilises an egg that contains only X chromosome), the resulting zygote develops into a female (XX condition).
- (ii) When a sperm carrying Y chromosome fertilises an egg (that contains only X chromosome), the resulting zygote develops into a male (XY condition).
Thus there are 50 – 50 chances of a male or female child and none of the parents may Sex determination in humans be considered responsible for it.
The sex-determination mechanism is shown alongside.
Question 7.
What are the different ways in which individuals with a particular trait may increase in a population ?
Different ways in which individuals with a particular trait may increase in a population are as follow :
- If it gives the benefit of survival through natural selection.
- Due to a sudden increase in a particular trait in a population, i.e., by genetic drift.
Question 8.
Why are traits acquired during the life-time of an individual not inherited ?
The traits acquired during the life-time are changes in the non-reproductive cells of the organisms and are not capable of being passed on to the next generation.
Question 9.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics ?
The small numbers of surviving tigers are a cause of worry from the point of view of genetics because in tigers there are negligible genetic variations. Due to this they are not well adapted. The rapid environmental changes cannot be favouable for them. If these changes are not controlled, tigers would be wiped out.
Question 10.
What factors would lead to the rise of a new species ?
The factors that would lead to the rise of a new species are the following :
- Geographical isolation of a population caused by various types of barriers (such as mountain ranges, rivers and sea). The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of pupulation.
- Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
- Variations caused in individuals due to a natural selection.
Question 11.
Will geographical isolation be a major factor in the speciation of a self- pollinating plant species ? Why or why not ?
The geographical isolation cannot be major factor in the speciation of a self-pollinating plant species because it does not have to look the plants for its process of reproduction to be carried out.
Question 12.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Why or why not ?
Geographical isolation cannot be a major factor in the speciation of an asexually reproducing organism because it does not require any other organism to carry out reproduction.
Question 13.
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
If similar characteristics are shown in different organisms, then these are considered to be inherited from the common ancestry. It also shows the closeness of the species.
For example, bats and birds have some similarity in their wings, so they are closely related, while lizard and squirrel do not have wings so these are not closely related to the birds and bats.
Question 14.
Can the wing of a butterfly and the wing of a bat be considered homologous organs ? Why or why not ?
The wings of a butterfly and the wings of a bat cannot be considered to be homologous organs because they have different basic designs though they are used for the same purpose of flying. They are analogous organs.
Question 15.
What are fossils ? What do they tell us about the process of evolution ?
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Question 16.
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 ?
This is because although genetic make up of humans may be slightly different in different races of people, there is no reproductive isolation. Reproductive isolation differentiates one species from the other. Human beings different in size, colour and looks can marry among themselves and produce fertile offspring.
Question 17.
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design ? Why or why not ?
Bacteria is a primitive organism as they came into being very early in evolution. But these organisms are still surviving in the present conditions after millions of years. This is because they have adapted well to the changing environment over these years. Same is the case for all other organisms like spiders, fishes and chimpanzees which have adapted to their environment and have survived. Therefore, all the organisms which exist have a body design which is better as it is suited to their environment.
Question 18.
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
(c) TtWW
Question 19.
An example of homologous organs is :
(a) our arm and a dog’s fore-leg
(b) our teeth and an elephant’s tusks
(c) potato and runners of grass
(d) all of the above
(d) All of the above
Question 20.
In evolutionary terms, we have more in common with :
(a) a Chinese school-boy
(b) a chimpanzee
(c) a spider
(d) a bacterium
(a) A Chinese school-boy
Question 21.
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 ?
This information is not complete. On the basis of this, it cannot be decided light colour trait is dominant or recessive. So it cannot be said until one does not know the nature of this trait in the parents.
Question 22.
How are the areas of study-evolution and classification interlinked ?
OR
‘Two areas of study namely ‘evolution’ and ‘classification’ are interlinked”. Justify this statement.
Classification of organisms is based on relative similarities and differences among organisms. Resemblances in organisms are because they have arisen from a common ancestor and differences in them are due to adaptations to different types of environment. Since the organisms can be graded in order of increasing complexity it indicates at the concept of evolution.
Question 23 .
Explain the terms analogous and homologous organs with examples.
Analogous organs : Those organs which have different basic structure (or different basic design) but have similar appearance and perform similar functions are called analogous organs.
For example, The wings of an insect and a bird are analogous organs.
Homologous organs : Those organs which have the same basic structure (or same basic design) but different functions are called homologous organs.
For example, The wing of a bat, flipper of a seal, front leg of a horse and arm of a man are homologous organs.
Question 24.
Outline a project which aims to find the dominant coat colour in dogs.
Suppose a black homozygous male is mated with a white homozygous female. If the progeny has all black dogs then the dominant coat colour is black.
Question 25.
Explain the importance of fossils in deciding evolutionary relationships.
Fossils play important role in providing evolutionary evidences because by knowning the age of fossils we can know about the evolution process of an organism.
For example, a fossil bird called archaeopteryx that looked like a bird had many other features of reptiles. It had feathered wings like those of birds, but teeth and tail like those of reptiles. Archaeopteryx is, therefore, a connecting link between the reptiles and birds, and hence suggests that the birds have evolved from the reptiles.
Question 26.
What evidence do we have for the origin of life from inanimate matter ?
A British scientist J.B.S. Haldane at first in 1929 suggested that life is originated from inanimate matter. According to him life must have developed from the simple inorganic molecules which were present at that time. Later, Miller and Urey in 1953 presented its evidences. They assembled an apparatus to create an early earth atmosphere which was supposed to consist of gases like methane, ammonia and hydrogen sulphide, etc. over water. This was maintained at a temperature just below 100°C and electric sparks were then passed through the mixture of gases to stimulate lightning for about one week. At the end of one week, it was found that about 15 per cent of carbon (from methane) had been converted into simple compounds and amino acids which make up protein molecules formed in living organisms. This experiment provides the evidence that the life originated from inanimate matter (or lifeless matter) like inorganic molecules.
Question 27.
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 ?
During sexual reproduction there is ‘crossing over’ of chromosomes, that gives rise to variations. These variations are inherited and increase the chances of survival of an organism.
- In sexual reproduction variations may occur due to errors in DNA copying.
- There may be variations due to interchange of homologous chromosomes during crossing over of male and female.
- In sexual reproduction, it is not predetermined that which gamete would fuse with another gamete. It depends only on chance. It is also a reason of variation.
These variations enable the organisms to adapt themselves to the changing conditions and also help to give rise to new species.
Question 28.
How is the equal genetic contribution of male and female parents ensured in the progeny ?
Genetic material in most organisms is present in pairs of chromosomes. Gametes in the sexually reproducing organisms are formed by the process of meiosis during which half of the genetic material goes into each gamete. When the gametes from male and female parents fuse with each other during sexual reproduction, the normal complement is restored. Half of the genetic material comes from the female and half from the male.
Question 29.
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?
Yes, variations that confer an advantage to an individual organism are inherited. The organism can survive longer in an environment and maintain its existence in the population.
Question 30.
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 ?
As species are asexually reproducing, there would be only very minor differences generated due to small inaccuracies in DNA copying, so trait B, which exists in 60% of the same population may get inherited earlier while trait A, which exists in 10% of the population may be originated late due to variations. Thus, trait B have arisen earlier since it is present in 60% of the same population.
Question 31.
How does the creation of variations in a species promote survival ?
Natural selection selects the individuals having useful variations which ensure their survival in the prevailing conditions of environment. Variant individuals that can withstand or cope with prevailing environment will survive better and will increase in number through differential reproduction.
Question 32.
How do Mendel’s experiments show that traits may be dominant or recessive ?
Mendel took pea plants with contrasting characteristics – tall plant and dwarf (short) plant. On cross pollination, he got all tall plants in F1 generation. Then by self pollination of F1 tall plants, he produced second generation (F2) consisting of tall and short plants in the ratio of 3 : 1. Then he concluded that, ‘T’ (tall) trait is dominant while ‘t’ trait for shortness is recessive.
Question 33.
How do Mendel’s experiments show that traits are inherited independently ?
In a dihybrid cross made by Mendel, it was observed that when two pairs of traits or characters were considered; each trait expressed independent of the other. Thus, Mendel was able to propose the Law of Independent Assortment which says about independent inheritance of traits.
Question 34.
A man with blood group A marries a woman with blood 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 ?
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 35.
What are the different ways in which individuals with a particular trait may increase in a population ?
Different ways are : variation, natural selection and genetic drift (isolation).
Question 36.
Why are traits acquired during the lifetime of an individual not inherited ?
Because acquired characters bring changes only in non-reproductive tissues and cannot change the genes of the germ cells. Thus, acquired traits cannot be passed to next generation.
Question 37.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics ?
(i) If any natural calamity occurs and kills these small number of surviving tigers, they can become extinct resulting in the loss of some genes forever.
(ii) Small number will lead to little recombination and, therefore, lesser variations. These both are very important for giving better survival chances to the species.
(iii) Less number of species means lesser extent of diversity and lesser number Of traits which reduces the chances of adaptability with respect to the change in the environment.
Question 38.
What factors could lead to the rise of a new species ?
Genetic variations, natural selection and reproductive isolation could lead to the rise of a new species.
Question 39.
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species ? Why or why not ?
No, because pollination occurs on the same plant in self-pollinating plant species.
Question 40.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Why or why not ?
No, because asexual reproduction involves single parent or organism.
Question 41.
Give an example of characteristics being used to determine how close two species am in evolutionary terms ?
Homologous organs, analogous organs and vestigial organs help to identify evolutionary relationships amongst the species.
Question 42.
Can the wing of butterfly and the wing of a bat be considered homologous organs ? Why or why not ?
No, wing of a bat and wing of a bird cannot be considered as homologous organs because they have different basic structure.
Question 43.
What are fossils ? What do they tell us about the process of evolution ?
Fossils are the impression or remains of ancient life found preserved in the sedimentary rocks. Fossils are direct evidences of evolution. Fossils also help to identify evolutionary relationship between apparently different species. They also tell about the extent of evolution that has taken place.
Question 44.
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 ?
They look different because of interaction of genes with environment which results in change in their appearance. But they belong to the same species as they have same number of chromosomes and can breed among themselves.
Question 45.
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better body design’ why or why not ?
No, because different designs are the product of evolution and different species have different body design to suit or adapt to their environment.
Question 46.
A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing whfte flowers. The progeny all bore violet flowers, but almost half of them are short. This suggests that the genetic make-up of the tall parent can be depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
(c) Genetic make-up of tall plant can be depicted by TtWW.
Question 47.
An example of homologous organs is
(a) our arm and a dogs fore-leg.
(b) our teeth and an elephants tusks.
(c) potato and runners of grass.
(d) All of the above.
(d) Both organs in all options have same basic structural design but have different functions and appearance.
Question 48.
In evolutionary terms, we have more in common with
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.
(a) A Chinese school-bpy is also a human being.
Question 49.
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?
We can say that light eye colour trait is dominant because only dominant traits are expressed in the first generation.
Question 50.
How are the areas of study – evolution and classification— inteilinked?
Evolution and classification are interlinked with each other in many ways. Classification is the most important term to explain evolution. It is based on the similarities and differences between two species or among two organisms. More closer the characteristics, the moe doser is the evolution and chances to be in the same group of classification. Thus, the classification of species is a reflection of their evolutionary relationship.
Question 51.
Explain the terms analogous and homologous organs with examples.
Analogous organs are those organs which have different basic structural designs and developmental origins but have similar appearance and perform similar functions.
Examples:
Wings of an insect and wings of a bat.
Homologous organs are those organs which have the same basic structural design and developmenta’ origin but have different functions and appearance.
Examples: Forelimbs of frog and forelimbs of human.
Question 52.
Outline a project which alms to find the dominant coat colour in dogs.
A homozygous black (RB) male dog and a homozygous white (bb) female dog is taken and given to mate and produce offspring in F1 generation. If black colour is dominant out of every 4 dogs, 3 will be black and if white colour is dominant 3 out of 4 dogs will be white.
Question 53.
Explain the importance of fossils in deciding evolutionary relationships.
Fossils and their study is useful to know 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 importance in deciding evolutionary relationships.
Question 54.
What evidence do we have for the origin of life from inanimate matter?
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, hydrogen sulphide and water, but no oxygen. The mixture was maintained at a temperature just below 100◦C and 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 aminoacids which make up protein molecules. So, life arose afresh on earth.
Question 55.
Explain how sexual reproduction gives rise to more viable variations that asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually ?
Variations occurring during sexual reproduction may be due to:
- Separation of homologous chromosomes (by chance only) during gamete formation.
- Crossing over (recombination) of homologous chromosomes.
- Fertilisation of gametes to form zygote.
- Errors during DNA copying or mutations.
In asexually reproducing organisms only errors during DNA copying or mutations cause variations.
Since the extent of variations is much larger in sexually reproducing organisms, therefore, the chances of evolution is also much in sexually reproducing These variations enable the organisms to adapt themselves to the changing conditions and also help to face the struggle for Over the time, they and rise to new species.
Question 56.
How is the equal genetic contribution of male and female parents ensured in the progeny?
Genetically organisms are of types
(i) Haploid : They have single set of chromosomes, where each chromosome is represented singly. As the chromosomes are the bearer of genes so haploids have single set of genes. A single gene determines the expression of character.
(ii) Diploid : ‘They have two sets Of homologous chromosomes, where the chromosome occur in pair, one maternal contributed by the mother through her ovum and the second Of the pair is contributed by the male parent through his sperm. The resultant cell zygote produces by the fusion of male and female gametes have two sets of chromosomes – each set contributed’ by each parent. In diploids a character is controlled by two genes/factors. Both the father and mother contribute practically equal amount of genetic material to the child. It means that each trait can be influenced by both paternal and maternal DNA.
Question 57.
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 ?
No, many of the times the variations are not advantageous to an individual organism but still survive in a population, e.g., take the case of free ear lobe and attached ear lobe. Most of the other variations not only give survival advantage to an individual but also contribute to genetic drift. Thus, we can say that most of the variations lead to better adaptation of an organism to the changing environment. In this way, it gives survival advantage to that organism and will also survive in the coming population.
Question 58.
An example of homologous organs is
(a) our arm and a dog’s foreleg
(b) our teeth and an elephant’s tusks
(c) potato and runners of grass
(d) All of the above
(a) Our arm and a dog’s foreleg is the example of homologous organs.
Question 59.
The science, which deals with study of heredity and variations is called
(a) phylogeny
(b) embryology
(c) genetics
(d) palaeontology
(c) The genetics is the study of heredity and variations and includes their occurrence, causes, benefits, disadvantages, significance, etc.
Question 60.
Archaeopteryx is a connecting link between
(a) reptiles and aquatic animals
(b) birds and insects
(c) reptiles and birds
(d) birds and dinosaurs
(c) Archaeopteryx is a connecting link- between the reptiles and birds. It appears like a bird, but has other features which are present in reptiles, e.g. it has wings like bird, but teeth and tail like the reptilians.