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Science [2 Mark Questions]

heredity and evolution · Gujarat Board (GSEB) STD 10 (GSEB - English Medium). 27 questions.

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[2 Mark Questions]

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27 questions · timed · auto-graded

Question 12 Marks
Give the scientific reason : It is not true that human beings have evolved from chimpanzees.
Answer
  • Both human beings and chimpanzees had a common ancestor a long time ago.
  • This common ancestor is likely to have been neither human or chimpanzee.
  • The first step of separation from that ancestor is unlikely to have resulted in modern chimpanzees and human beings. Instead, the two resultant species have probably evolved in their own separate ways to give rise to the current forms.
  • That is why, it is not true that human beings have evolved from chimpanzees.
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Question 22 Marks
Give the scientific reason : The chances of birth of a male child (son) or a female child (daughter) are equal.
Answer
  • In human beings, the sex of the child is determined by the father.
  • The father produces two types of sperms.
  • Both the types of sperms are produced equally in number.
  • $50\%$ of the total sperms produced contain X-sex chromosome.
  • While the remaining $50\%$ of sperms produced contain Y-Sex chromosome along with autosomes.
  • The chances of each type of sperm to fertilise the ovum are therefore equal.
  • Hence, the chances of birth of a son or a daughter are equal.
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Question 32 Marks
Give the scientific reason : The characters are under the control of genes.
Answer
  • A gene is the unit of heredity.
  • It is a segment of $DNA$ of specific length, arranged Sequentially along the length of the chromosome.
  • Each gene is functionally specific and synthesizes a specific type of protein.
  • The enzymes are all proteins and these proteins (as enzymes) induce specific biochemical process.
  • The substances or proteins, formed during these processes, are responsible for the expression of characters.
  • Hence, the characters are under the control of genes.
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Question 42 Marks
Give the scientific reason : The pea plants (Pisum sativum) were selected for Mendel’s experiments.
Answer
  • $(1)$ They are small plants and can be easily grown.
  • $(2)$ They are annual plants. So there are more chances of studying more number of generations every year.
  • $(3)$ It produces a large number of offsprings.
  • $(4)$ Its flowers are bisexual and generally show self-fertilisation.
  • $(5)$ Artificially cross pollination can be done as and when required.
  • $(6)$ There are varieties of characters. Each character shows atleast two contrasting expressions.
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Question 52 Marks
Give the scientific reason : Sexual reproduction gives rise to variations.
Answer
  • Two parents are involved in sexual reproduction.
  • The offspring inherits the genetic material $(DNA)$ from both the parents through the gametes.
  • Gametes are produced by meiosis.
  • New combinations and new arrangement of genes are formed as a result of meiosis.
  • These new combinations of genes on the chromosomes generate one or more variations in the zygote that inherits into an offspring.
  • Hence sexual reproduction creates more variations.
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Question 62 Marks
Distinguish between: Artificial selection and Natural selection
Answer
Artificial selection Natural selection
$1$. It is an artificial process used by man for breeding. $1$. It is a natural process of evolution.
$2$. It is a controlled process for a limited period by the human beings. $2$. It is an on-going process for a continuous period by nature that affects all the global organisms.
$૩$. The selection of offsprings for improvement in their quality is beneficial for mankind. $3$. The characters selected for evolution are beneficial for the species because adaptation causes survival of species.
$4$. The results of artificial selection are obtained in a short period. $4$. The results of natural selection are obtained after a very long period of time.
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Question 72 Marks
Distinguish between: Homologous organs and Analogous organs
Answer
Homologous organs Analogous organs
$1$. The internal structure and fundamental origin of these organs are mostly similar. $1$. The fundamental structure and origin of these organs are totally dissimilar.
$2$. Functionally these organs may be similar or dissimilar. $2$. Functionally these organs are always similar.
$૩$. The presence of these organs indicates common ancestors. $3$. The presence of these organs does not indicate common ancestors.
$4$. The forelimbs of frog, lizard, bird and man are homologous organs. $4$. The wings of butterfly, wings of birds and those of bat are analogous organs.
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Question 82 Marks
Distinguish between: Dominant trait and Recessive trait
Answer
Dominant trait Recessive trait
$1$. The trait which is expressed in the $F_1$ generation is called the dominant trait. $1$. The trait which is not expressed in the $F_1$ generation is called the recessive trait.
$2$. The dominant trait is expressed through its identical or different (contrasting) genes. $2$. The recessive trait is expressed in the absence of the dominant gene.
$૩$. The number of individuals having dominant trait is larger in $F_1$ and $F_2$ generations. $3$. The number of individuals having recessive trait are very few in $F_2$ generation.
$4$. The dominant gene can be expressed in presence of recessive gene. $4$. The recessive gene cannot be expressed in presence of dominant gene.
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Question 92 Marks
Distinguish between: Acquired characteristics and Hereditary characteristics
Answer
Acquired characteristics Hereditary characteristics
$1$. These develop as a reaction to the environment. $1$. These develop as a reaction to the changes in $DNA$.
$2$. These changes occur in non-gametic somatic cells. $2$. These changes occur in the genes of gametes.
$૩$. These characteristics are not inherited in subsequent generations. $3$. These characteristics are inherited in subsequent generations.
$4$. Scar of injury on face, the cutoff tail of a rat, expertise in certain games, etc. are the examples of acquired characteristics. $4$. Skin colour, form of hair on the scalp, appearance of jaws, eye colour, etc. are the examples of hereditary characteristics.
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Question 102 Marks
Explain the terms analogous and homologous organs with examples.
Answer
  • Analogous organs: Organs with different structure and components but have common function.
  • Examples:
  • The wing of a bat and the wing of a bird.
  • Homologous organs:
  • Organs with similar basic structure but modified to perform different functions.
  • Examples Fore limbs of frog, lizard, bird and human.
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Question 112 Marks
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, we cannot say anything about whether the light eye colour trait is dominant or recessive on the basis of given information because information regarding cross between two traits, i.e., light colour with black eye colour is essential to determine it.
  • In general population light coloured eyes are in much less proportion as compared to dark eyes.
  • This indicates that it may be recessive trait.
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Question 122 Marks
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
  • All human beings look so different from each other in size, colour and looks due to environmental factors, new combination of genes during reproduction.
  • All they belong to Homo sapiens and have descended from a common ancestor in Africa.
  • They have capacity of interbreeding which is an important criteria to categorize them as one species.
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Question 132 Marks
Explain the idea of evolution.
Answer
  • Evolution creates the diversity and then shapes it by environmental selection.
  • The only progressive trend in evolution seems to be that more and more complex body designs have emerged over time. However it does not mean that older designs are inefficient.
  • So many of the older and simpler designs still survive.
  • Example:
  • One of the simplest life forms – bacteria inhabit in most adverse habitats like hot springs, deep-sea thermal vents and the ice in Antarctica.
  • Human beings are not the peak (pinnacle) of evolution, but simply yet another species in the teeming spectrum of evolving life.
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Question 142 Marks
What are fossils? What do they tell us about the process of evolution ?
Answer
  • Fossils are the remains or impressions of the dead animals and plants that lived in the past.
  • Fossils are the direct evidence of evolution.
  • If the fossils are found closer to the surface then they are more recent than the fossils found in deeper layers.
  • One can find evolutionary relationships between ancient and present organisms by study of fossils.
  • We also come to know the time period of evolutionary process by studying fossils.
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Question 152 Marks
Can the wing of a butterfly and the wing of a bat be considered homologous organs ? Why or why not ?
Answer
  • No, they are not considered homologous organs because the wing of a butterfly and the wing of a bat are similar in function but the designs of two wings, their structure and components are very different.
  • So, they can be considered as analogous organs and not homologous.
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Question 162 Marks
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer
  • Homologous organs are the characteristics being used to determine two species are close in evolutionary terms.
  • Example:
  • The basic structure of the limbs of mammals, birds, reptiles and amphibians is similar though it has been modified to perform different functions.
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Question 172 Marks
Which method is extensively used to define evolutionary relationships?
Answer
  • The way of tracing evolutionary relationships depends on the changes in $DNA$ during reproduction.
  • The changes in $DNA$ are the basic events in evolution.
  • The comparison of the $DNA$ of different species should give the estimate of how much the $DNA$ has changed during the formation of these species.
  • So, this method is extensively used to define evolutionary relationships.
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Question 182 Marks
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Answer
  • No, geographical isolation will not be a major factor in the speciation of a self-pollinating plant species because single parent is involved in it.
  • There is no gene flow between two geographically isolated population.
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Question 192 Marks
What factors could lead to the rise of a new species?
Answer
  • Factors that can lead to the rise of a new species are
  • $(1)$ Gene flow,
  • $(2)$ Genetic drift,
  • $(3)$ Natural selection and
  • $(4)$ Reproductive isolation.
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Question 202 Marks
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer
  • The small numbers of surviving tigers is a cause of worry from the point of view of genetics because if they become extinct then the genes of this species will be lost forever.
  • There will be no chance of getting this species back again to life in future.
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Question 212 Marks
Why are traits acquired during the life-time of an individual not inherited?
Answer
  • Traits acquired during the life-time of an individual may not be inherited because they may be changes in non-reproductive tissues which cannot be passed on to the $DNA$ of the germ cells and hence cannot be passed on its progeny.
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Question 222 Marks
What are the different ways in which individuals with a particular trait may increase in a population?
Answer
  • A particular trait may increase in a population by following ways:
  • $(1)$ Natural selection-directing evolution with a survival advantage.
  • $(2)$ Genetic drift-provides diversity without any adaptations,
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Question 232 Marks
What is the meaning of similarities and differences?
Answer
  • A child or offspring bears all basic features of its parents.
  • These common basic features are referred to as similarities.
  • However, due to small inaccuracies in DNA copying, child/ offspring does not look exactly like its parents.
  • Population of any species show variations either in small scale or large scale which are called differences.
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Question 242 Marks
How does the creation of variations in a species promote survival?
Answer
  • The creation of variations in a species is either due to inaccuracies in $DNA$ copying or during sexual reproduction.
  • Depending on the nature of variations, different individuals have different kinds of advantages.
  • The individuals with useful variations can adapt to the prevailing environment and show better survival.
  • The individuals with useful variations then increase in numbers.
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Question 252 Marks
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
  • $A$ trait $B$ which exist in $60\%$ of population of an asexually reproducing species, must have arisen earlier than trait $A$.
  • Because in asexually reproducing species there are chances of appearance of very few new traits due to small inaccuracies during $DNA$ copying.
  • So, populations having trait $A$ have arisen later.
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Question 262 Marks
How does reproduction link to variation?
Answer
  • Every organism produces offsprings either through asexual or through sexual reproduction.
  • The offsprings produced through these reproductive processes are similar, but subtly different.
  • In asexual reproduction, although all the offsprings resemble each other and to their single parent, yet minor variation arise in them.
  • Very little differences among the individual plants can be seen in a field of sugar cane.
  • In most of sexually reproducing animals including human beings, quite distinct variations are visible among offsprings.
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Question 272 Marks
From the diagram, state the result in case $I, II$ and $III.$
Answer
  • $I.$ It is a case of natural selection of green beetle population.
  • $II.$ It is a case of genetic drift which provides diversity without any adaptations.
  • $III.$ It is a case of acquired trait of low weight beetles due to starvation.
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