HBSE 10th Class Science Solutions Chapter 9 Heredity and Evolution

Haryana State Board HBSE 10th Class Science Solutions Chapter 9 Heredity and Evolution Textbook Exercise Questions and Answers.

Haryana Board 10th Class Science Solutions Chapter 9 Heredity and Evolution

HBSE 10th Class Science Heredity and Evolution Textbook Questions and Answers

Question 1.
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
Answer:
(c) TtWW

Question 2.
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
Answer:
(d) all of the above

Question 3.
In evolutionary terms, we have more in common with ………………
(a) a Chinese school-boy
(b) a chimpanzee
(c) a spider
(d) a bacterium!
Answer:
(a) a Chinese school-boy.

Question 4.
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:

Reason:
1. No, the given information is not enough to consider the dominance or recessiveness of eye colour.

2. However, we can observe that generally in a population, the proportion of the people having light coloured eyes is much less than the people having dark coloured eyes. Based on this observation, we may consider that the light coloured eyes are a recessive trait and dark coloured eyes may be dominant.

Question 5.
How are the areas of study – evolution and classification – interlinked?
Answer:
1. In classification, the groups of organisms are based on the similarities and differences of characteristics of the organisms.

2. The organisms that have more similarities belong to nearer groups while the organisms having lesser similarities i.e. having more differences belong to distant groups.

3. In evolution, a study of identifying hierarchies of characteristics between the species is done. So, in such studies small groups of species with recent common ancestors are formed. Thus, the areas of study – evolution and classification are interlinked.

Question 6.
Explain the terms analogous and homologous organs with examples.
Answer:

Homologous organs	Analogous organs
1. These organs have similar internal structure. 2. These organs perform different functions. 3. These organs have evolved from a common ancestor. 4. For example, forelimbs of a frog, lizard, a bird, bat and a man are homologous	1. These organs have different basic design. 2. These organs perform similar functions. 3. These organs have not evolved from a common ancestor. 4. Wings of insects and birds are examples of analogous organs.

Question 7.
Outline a project which aims to find the dominant coat colour in dogs.
Answer:
1. In dogs, the coat colour is either black or white. The character of black coloured coat is indicated by ‘B’ and white coloured coat is indicated by ‘b’.

2. First of all the homozygous/pure parents with opposite characters are fertilized. Thus, applying Mendelian’s law, in the above case, the black coloured coat is a dominant character. So, black coat is dominant trait in dog.

Question 8.
Explain the importance of fossils in deciding evolutionary relationships.
Answer:
1. The remains of dead organisms buried under the earth for millions of years are known as fossils.
2. Fossils are impressions of dead plants or animals that lived in the past.
3. When plants or animals die, the micro-organisms get decomposed in the presence of moisture and oxygen.
4. However, sometimes due to environmental conditions, their bodies do not decompose completely.
5. Such body parts of the plants and animals become fossil and can be available on digging the earth.
6. Fossils can be in the form of imprints, burrow of a worm, or even an actual bone.

Example:

• If the dead leaf gets caught in the mud, leaf will not decompose completely.
• The mud around the leaf will set around it as a mould which will then slowly become hard to form a rock and retain the impression of the leaf. Thus fossil of a leaf is formed.
• By studying these fossils, scientists learn how organisms evolved over time.

Question 9.
What evidence do we have for the origin of life from inanimate matter?
Answer:
1. It is believed that life must have developed from simple inorganic molecules which were present on earth soon after it was formed.
2. It was also speculated that the conditions on earth at that time could have given rise to more complex organic molecules that were necessary for life.
3. It is believed that the first primitive organisms would have arisen from further chemical synthesis.

Question 10.
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:
(1) First, in sexual reproduction, there occurs a combination of genetic material of two different parents i.e. a male and a female. Hence, each new generation is a combination of two different parental DNAs.

(2) Second, during the formation of gametes i.e. formation of sperms and ovum, the cell undergoes cell division phase called meiosis.

• During meiosis, the genetic material gets distributed randomly. Moreover, all the gametes are not always similar and so there are more chances of variation during fertilization, in other words, there are so many sperm cells but only one fertilizes with the ovum. Naturally, this will create variation.
• Owing to these two reasons, there occur more variations in sexual reproduction as compared to asexual.
• The combination of different types of gametes which takes place is the root of variations. This also gives rise to new type of characters too. This also favours evolution.

Question 11.
How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer:
1. During gametogenesis (production of male and female sex cells), the meiosis type of cells division occurs.
2. During, meiosis the number of chromosomes becomes half. The DNA gets distributed to half in each gamete.
3. During fertilization, both the types of sex cells get fused and the quantity of DNA remains maintained. Thus, equal genetic contribution of male and female parents is ensured in the progeny.

Question 12.
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:
Yes, this is true.

Reason:

• If the variation achieved by an organism is helpful to adapt to the surrounding environment then it increases the probability of the survival of that organism.
• The survived organisms then produces more offspring with such genetic variations and thus the species survives.

HBSE 10th Class Science Heredity and Evolution InText Activity Questions and Answers

Textbook Page no – 143

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?
Answer:
Trait B which exists in 60% of population of an asexually reproducing species must have arisen earlier than trait A.

Reason:

• In asexually reproducing species, DNA copy error takes place, in very small amount and so new traits do not occur very fast.
• Since, the percentage of trait B is very large as compared to trait A. This suggests that trait B must have arisen quite before to trait A.

Question 2.
How does the creation of variations in a species promote survival?
Answer:
1. Variations in a species are created through two reasons,

• Due to inaccuracies in DNA copying or
• During sexual reproduction.

2. Different individuals gain different types of advantages with these variations. Several variations enable the individual to adapt to the environmental conditions. This increases the chances of their survival.

3. The individuals that survive then reproduce offspring and the existence of species remains continued.

Textbook Page no – 147

Question 1.
How do Mendel’s experiments show that traits may be dominant or recessive?
Answer:
1. Mendel conducted cross fertilization between pure tall plants (TT) and pure short (tt) plant. This resulted in all (Tt) plants in F₁ generation.

2. This shows that single copy of T is enough to make the plant tall. The trait that gets expressed over the other is called the dominant trait and the other recessive.

3. In Mendel’s trial, the trait which gets expressed in 75% individuals in F₂ generation after self-fertilization is dominant whereas the trait which appears in 25% individual is recessive.

Question 2.
How do Mendel’s experiments show that traits are inherited independently?
Answer:
1. Mendel performed the experiments of heredity on pea plant. He studied the heredity of two characters simultaneously and performed the dihybrid experiment.

2. On the basis of this experiment we can say that even though the F₁ progeny plants were dominant in both the characters, the F₂ progeny showed the new combinations. In F₂ progeny plants some were tall and wrinkled, while some were short and round.

3. The experiment clearly shows that the factors that control the shape, size and height of the seeds are inherited independently and that is the main reason why new combinations could be seen in F₂ generation.

Question 3.
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, the given information is not enough to determine which trait is dominant.

Reason:

• The daughter (or any child) receives two copies of genes, one from each parent.
• The trait of blood group depends on the genotype i.e. the types of genes which get combined. Hence, the provided information is insufficient and so we cannot tell which one is a dominant blood group.

Question 4.
How is the sex of the child determined in human beings?
Answer:
1. In human beings, sex of the child to be born is determined by the sex chromosome of the father.

2. The father or say male contains XY chromosomes and so during spermatogenesis, the male produces two types of sperms. 50% of these sperms have ‘X’ sex chromosome and 50% sperms have ‘Y’ sex chromosome.

3. If the sperm having ‘X’ chromosome fertilizes the ovum, a female child (= a girl) is born and if the sperm having ‘Y’ chromosome fertilizes the ovum, the male child (= a boy) is born.

Textbook Page no – 150

Question 1.
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 through two main ways. They are –

• Natural selection – It directs evolution with a survival advantage.
• Genetic drift – It leads to accumulation of different changes.

Question 2.
Why are traits acquired during the life-time of an individual not inherited?
Answer:
Change in non-reproductive tissues cannot be passed on to the DNA of the germ cells. Hence the experiences of an individual during its lifetime can neither be passed on to its progeny nor can such experiences result in evolution.

Example:

• If we breed a group of mice, all their progeny will have tails.
• Suppose we remove the tails of each generation of these mice by surgery then it does not mean that the progeny is tailless.
• Artificially removing the tail does not bring any change in the genes of the germ cells of the mice.
• So, the cut-tail that a generation of mice experienced cannot become a trait to be passed on to the next generation.

Question 3.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer:
1. A small population generally does not show much variation from generation to generation.
2. A very small population of surviving tigers indicates that very less amount of variation will occur in the genetic characteristics. This means they will not be able to adapt to the major environmental changes if any, in the future.
3. The tigers will not survive and the species will become extinct.

Textbook Page no – 151

Question 1.
What factors could lead to the rise of a new species?
Answer:
Factors that can lead to the rise of a new species are:

• Accumulated variations favourable to natural environment,
• Geographic isolation of a population,
• Gene flow,
• Genetic drift and
• Natural selection

Question 2.
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.

Reason:

• Only a single parent is involved in self-pollination. So, there is no gene flow between two geographically isolated populations.
• If it would be a cross-pollination species, the geographical isolation would be a major factor as it would lead to faster accumulation of variation (genetic drift) in the two geographically separated populations.

Question 3.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer:
No, geographical isolation will not be a major factor to the speciation that reproduces asexually.

Reason:
Asexually reproducing organisms show very little variation over generations. These little variations are not sufficient enough to raise a new species having such variations.

Textbook Page no – 156

Question 1.
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer:
1. One of the ways to determine how close two species are with respect to evolution is to obtain evidence from their homologous organs.

2. For example, the basic design of internal structure of bones of forelimbs of a frog, lizard, bird, bat and man is same, even though these organs perform different functions.

3. This indicates that all these forelimbs have evolved from a common ancestral animal, which had a same basic internal structure.

Question 2.
Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Answer:
No, the wings of a butterfly and the wings of a bat cannot be considered homologous organs.

Reason:
Although the wings of a butterfly and the wings of a bat perform similar function, but the design, structure and components of their wings are very different. Hence, the wings of these two can be considered as analogous organs and not homologous.

Question 3.
What are fossils? What do they tell us about the process of evolution?
Answer:
1. The remains of dead organisms buried under the earth for millions of years are known as fossils.
2. Fossils are impressions of dead plants or animals that lived in the past.
3. When plants or animals die, the micro-organisms get decomposed in the presence of moisture and oxygen.
4. However, sometimes due to environmental conditions, their bodies do not decompose completely.
5. Such body parts of the plants and animals become fossil and can be available on digging the earth.
6. Fossils can be in the form of imprints, burrow of a worm, or even an actual bone.

Example:

• If the dead leaf gets caught in the mud, leaf will not decompose completely.
• The mud around the leaf will set around it as a mould which will then slowly become hard to form a rock and retain the impression of the leaf. Thus fossil of a leaf is formed.
• By studying these fossils, scientists learn how organisms evolved over time.

Textbook Page no – 156

Question 1.
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:
1. Across the earth, there is a great diversity in humans and so we look so different from each other in terms of size, colour and looks.

2. Initially, human race was identified on the basis of skin colour and the humans were known as yellow, black, white or brown. However, in the recent years, it has been proved that all the human beings have evolved from a single species called the Homo sapiens.

3. Hence, in spite of having different skin colour, looks and size, we all belong to the same species.

Question 2.
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Answer:
1. In evolutionary terms, we can say that chimpanzees have a better developed body design.
2. The reason for this is that chimpanzees are highly complex organisms compared to remaining three.

Activities:

Activity -1

Aim: To study inheritance in the type of earlobes.

Background:

• The lowest part of the ear pinna (external ear) is known as an earlobe.
• The earlobe may be either closely attached to the (lateral) side of the head, or not-attached i.e. might be free.

Procedure:

• Observe the ears of all the students in the class. Prepare a list of students having free or attached earlobes and
• Find out about the earlobes of the parents of each student in the class. Correlate the earlobe type of each student with that of their parents. Based on this evidence, suggest a possible rule for the inheritance of earlobe types.
• Students can observe the earlobes of other students. They can also ask about the type of earlobes of their parents.
• Make a chart as given below. Write 1F’ for the free earlobes and A’ for the attached earlobes.

Observation:
We can observe that more number of students have inherited the trait of ‘free earlobes’ i.e. trait F as compared to attached earlobes i.e. A.

Conclusion:
From studies it has been proved that free earlobe is a dominant trait whereas an attached earlobe is a recessive trait.

Activity 2.

In Fig. 9.3 of textbook, what experiment would we do to confirm that the F₂ generation did in fact have a 1:2:1 ratio of TT, it and tt trait combinations?

Observation:
Although the experiment phenotypically shows the ratio of 3 : 1 ratio between tall and dwarf, genetically the ratio is 1 : 2 : 1.
This can be proved by the following experiment. We can raise F₃ generation by allowing self-pollination of F₃ generation plants.

Then we may calculate ratio for —

• Tall plants which produced only tall plants. These plants will be pure dominant (TT).
• Tall plants which produced both tall and dwarf pea plants. These plants are hybrid (Tt).
• Dwarf plants produced only dwarf plants. This means they are pure recessive (tt).

Observing the data carefully, one can find the appearance of 1 : 2 : 1 ratio of TT Tt and tt trait combination in F₃ generation (also known as genotypic ratio).