Best NCERT Solutions for Class 10 Science Chapter 8 Heredity and Evolution

NCERT Solutions for Class 10 Science Chapter 8-Heredity and Evolution

Best NCERT Solutions for Class 10 Science Chapter 8 Heredity and Evolution .Two basic ideas in biology, heredity and evolution, describe how traits are passed down from one generation to the next and how species change over time. Gaining knowledge of these ideas aids in our comprehension of the mechanisms underlying the diversity of living forms and the mechanisms underlying adaptation.

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: Asexual reproduction does not entail the fusion of haploid gametes and necessitates the presence of a single parent. This results in kids that are nearly exact replicas of their parents’ DNA, making them identical to the parents.

But occasionally, DNA copies differ slightly from the original, resulting in altered variations. As a result, some mutations in the newly created DNA give rise to a new characteristic.

As a result, this feature is passed on to next generations, who then continue to add variations. Thus, it can be assumed that characteristic B has arisen earlier since the trait has continued to replicate and exist in a bigger percentage of the population, if 10% of the population possesses trait A and 60% of the same population possesses trait B.

2. How does the creation of variations in a species promote survival?

Answer: Under all conditions, organisms evolve to live in a certain habitat. Extreme environmental changes can occasionally alter the habitat, which can be lethal for some species. For instance, freshwater ponds are home to a variety of microorganisms.

A sudden increase in temperature will destroy the microorganisms that are present in freshwater. Some species, nevertheless, will be able to withstand the heat better than others since they are heat-resistant.

These species will survive and reproduce within the changing environment. If there have been no heat-resistant variants, the whole species of bacteria would be extinct. Hence, the survival of species is promoted.

1. How do Mendel’s experiments show that traits may be dominant or recessive?

Answer: Mendel started his pea plant genetic experiment in 1856 using a monohybrid cross, which is a single character with two alternate features. True-breeding dwarf plants (TRD) and true-breeding tall plants (TT) were crossed. He only got tall plants in the first filial generation; there was no sign of a dwarf feature.

Now that the F1 progeny had been self-pollinated, both tall and dwarf plants were produced. Mendel came to the conclusion that a character’s two qualities are recessive and dominant, based on the results of the monohybrid cross.

When the recessive trait is present in homozygous or heterozygous situations, its expression is obscured by the existence of the dominant trait, which is an allele that always manifests itself externally.

Thus, the recessive trait is expressed only in homozygous conditions. Eventually, the tall plants present in F1 were not true-breeding. They were heterozygous (Tt) tall plants. Hence, the expression of the recessive allele (t) gets suppressed by the dominant allele.

2. How do Mendel’s experiments show that traits are inherited independently?

Answer: Mendel focused on two sets of personalities that were in stark contrast to each other. The cross which involves two pairs of alleles is known as a dihybrid cross. He did a hybrid cross on pea, taking two characters at a time. His dihybrid cross revealed a distinct gene assortment. Mendel selected the two variables for his experiment to be seed colour and seed shape.

Mendel hybridised wrinkled and green (rryy) seeds with round and yellow (RRYY) seeds (parental generation). Due to the preponderance of round over wrinkled seed shapes and yellow over green seed colours, all round and yellow seeds were present in the first filial generation (F1).

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 information provided is insufficient to determine whether trait A or trait O is dominant.

Our biological parents determine our blood type. Three alleles—A, B, and O—are present. Two examples can be used to explain this:

Case I:

When O is recessive and A is dominant

Combination of man can be IAIA Or IAIO
A mix of females will be IOIO.

When a father is pure IAIA and A is dominant, the child’s blood group is A. However, if the father is IAIO, the child’s blood group is:

	Io	Io
IA	IA Io	IA Io
Io	Io Io	Io Io

Here When the father is heterozygous IAIO, 50% of the offspring have blood group O and 50% have blood group A.

Case II:

When O is dominant and A is recessive, the father-child combination is IAIA.

Mothers can combine to form either IAIO or IOIO. When a mother has IAIO, the child’s blood group is:

	IA	Io
IA	IA IA	IA Io
IA	IA IA	IA Io

Here also Half of the offspring belong to blood group A, and the other half to blood group O. The blood group of the infant would have been O, mother was homozygous IOIO.

Based on the aforementioned situations, we may infer that if any of the characters are dominant, the child’s blood group will be O. As a result, identifying the dominating character is challenging.

4. How is the sex of the child determined in human beings?

Answer:

In humans, the chromosomal makeup of the parents determines the child’s sex. Women have an excellent pair of sex chromosomes, or XX, whereas men have a mismatched pair, or XY. In females, the X chromosome is carried by the eggs, while in men, half the sperm carry the Y chromosome and the other half the X chromosome. Two scenarios can now be examined when they fertilise one another:

Case 1: when the egg combines with a sperm having the Y chromosome, the child will be a boy.

Case 2: A female will be born when the egg and sperm combine to form an offspring with an X chromosome.

ParentsXX (Female)XY(Male)

$↓$

Gametes X XY

Female →

Male↓

XX (female)

XX(female)

XY (male)

1. What are the different ways in which individuals with a particular trait may increase in a population?

Answer:

The several methods that have been mentioned are:

I. Natural selection: Some differences allow members of a population to survive in a changing environment, which leads to an increase in population. Better adaptable individuals fit the bill for natural selection.

II. Genetic drift: In small groups, there may be an increase in some individuals even though they do not provide a survival advantage in the event of an accident.

III. In certain instances, an individual may learn certain qualities during their lifetime rather than having them inherited. The character that is gained aids in the individual’s improved survival and population growth.

2. Why are traits acquired during the lifetime of an individual not inherited?

Answer: When procreation occurs, parent germ cells are passed on to the progeny. Therefore, any modifications to the germ cells that result in variety or novel features are passed on to the offspring. An individual picks up certain traits during their lives as a result of external circumstances or environmental effects.

Modifications in non-reproductive tissues (somatic cells) are indicative of an acquired characteristic. Since acquired qualities do not require modifications to the germ cells, they cannot be inherited.

3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Answer: Small population species will accrue fewer variations. Reproduction in such a species results in fewer offspring with certain beneficial changes (that will give a higher survival advantage). As a result, they won’t be able to withstand an illness. There will be an extinction event, and the genes will vanish forever.

1. What factors could lead to the rise of a new species?

Answer: Speciation is the process by which one or more new species diverge from an existing species through evolutionary processes. Among the elements influencing the emergence of new species are:

(i) Genetic drift

(ii) Natural selection

(iii) Severe DNA change.

(iv) Reproductive isolation.

2. Will geographical isolation be a major factor in the speciation of self-pollinating plant species? Why or why not?

Answer: Geographic isolation aids in preventing the genetic exchange of two species. Pollen is moved from the anther of one bloom to the stigma of that flower or another flower on the same plant in a self-pollinating plant.

It does not need another plant to pollinate it, nor does it require an outside agent. Therefore, in self-pollinating plants, geographic isolation cannot harm the species and cannot affect the species itself.

3. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

Answer: Geographic isolation aids in halting the flow of genes (gene transfer) between populations within a species. Asexual reproduction allows for the creation of new people from a single organism. Variation happens in these reproductive organisms when there is a mistake in the DNA copying process.

Thus, in an asexually reproducing creature, geographic isolation cannot influence the emergence of new species.

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

Answer: Similar traits of species can be used to determine their evolutionary relationships. Few attributes Few traits are shared by many organisms because they were passed down from a common ancestor. Additionally, a connection is made between several phases of a species’ evolutionary process. The dinosaurs that gave rise to modern birds also had feathers. However, feathers were not employed by dinosaurs to fly but as insulation.

The feathers appeared to be modified for flying by later birds. Given that dinosaurs were reptiles, this suggests that birds and reptiles are very closely connected. This demonstrates the strong kinship between reptiles and birds as well as the fact that reptiles are where wings originated in evolution.

2. Can the wing of a butterfly and the wing of a bat be considered homologous organs?

Answer: The organs having the same underlying structure but differing functions are called homologous organs. For instance, the wings of a bat and a butterfly are not homologous organs since they differ in their fundamental structure and place of origin.

Despite having different origins and structures, the wings of a butterfly and a bat serve the same purpose of flight, making them comparable anatomical structures.

3. What are fossils? What do they tell us about the process of evolution?

Answer: Fossils are the remnants or impressions of an animal’s hard parts, such as its skeleton. There was a time when people lived in these buildings. Since fossils allow us to understand the evolutionary history of creatures, they rank among the most credible pieces of evidence supporting evolution.

It is possible to determine the modifications that these species underwent to become their current forms by examining the fossils. As a result, a relationship is seen between the organisms of the past and the present.

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:

A species is a collection of individuals that breed together. are all of the observable characteristics of humans, such as size, appearance, and skin colour, typically regulated by their environment.

As a result, these characteristics are used to create different human races. All humans, however, are able to procreate and have children, regardless of factors like ethnicity, language, height, or skin colour. As a result, Homo sapiens is the single species to which all humans belong.

2. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?

Answer:

Since evolution entails the creation of the most effective and suitable elements in a body design for survival and adaptation, it is challenging to determine which species—bacteria, spiders, fish, and chimpanzees—has a “better” body design. As an illustration, consider the fact that while creatures with simpler body designs, like bacteria,

can live in harsh environments, those with more complicated body designs have multiple challenges when trying to thrive in specific circumstances. Therefore, evolution cannot be linked with progress; it only results in the growth of complicated bodily designs.

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) Violet flower colour (V) is the dominant trait that conceals the recessive trait (v) (white flower colour). There are two flower colours: violet and white. However, F1 exclusively displayed violet flowers. Plants from the F1 progeny were half tall and half short. Thus, the F1 progeny expresses both recessive and dominant characteristics. So, it may be claimed that the tall plants were not true-breeding and must be genetically heterozygous for the character height (Tt). Thus, TtVV can be used to reflect the tall parent’s genetic composition. As a result, the cross in the provided question is:

TtVV × ttvv

$↓$

TtVv − ttVv

Therefore, half the progeny is tall, but all of them have violet flowers

2. An example of homologous organs is

our arm and dog’s fore-leg
our teeth and an elephant’s tusks
potato and runners of grass
all the above

Answer: (d) All of the Above.

The organs’ basic internal makeup and place of origin are the same in all of the aforementioned cases, but their purposes vary. It is known as a homologous organ as a result. An elephant’s tusk, for instance, is thought to be a modified incisor; as such, it has the same genesis but a distinct purpose.

Both grass runners’ and potatoes’ tubers are stem modifications, but they serve different purposes, making them homologous organs.

3. In evolutionary terms, we have more in common with

(a) a Chinese schoolboy.

(b) a chimpanzee.

(c) a spider.

(d) a bacterium

Answer. (a)

When it comes to evolution, we are more alike with a Chinese schoolboy. Given that they are both members of the Homo sapiens species. Humans and chimpanzees are two distinct species that shared an ancestor.

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: Youngsters with light-colored eyes may be genotyped LL, Ll, or ll. It is reasonable to assume that the kids have the genotype LL (both dominant alleles). Only in the event that both parents carry the LL genotype is this possible.

LL $\times$ LL

$↓$

If ll genotype is present in children with light-coloured eyes, then their parents will also have ll genotype.

ll $\times$ ll

$↓$

Therefore, it would be difficult to conclude whether light eye colour is dominant or recessive.

5. How are the areas of study − evolution and classification − interlinked?

Answer: The process of classifying involves scientists putting two living species together based on their shared characteristics. More similar traits indicate a tight relationship between the species. Additionally, a closer relationship between two species indicates a more recent common ancestor.

In a family, for instance, brothers and sisters have a closer relationship than cousins. Thus, we can claim that the brother and sister share parents as recent ancestors. Their grandparents are the common ancestors of the brother, sister, and cousin.

As we progress down a family (evolution) tree, distinct phenotypes and genotypes are created as a result of the accumulation of variety brought about by sexual reproduction over successive generations.

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

Homologous organs are similar in origin (or are embryologically similar) but perform different functions. Forelimbs of frogs, lizards, pigeons, bats, whales, horses and humans have the same basic structural plan but different functions.

For example, the wings help in flight whereas the human forearm helps in various activities.

Answer: Anatomically similar organs differ in their origin, function, and structural characteristics. For instance, although the functions of a bat’s and bird’s wings are similar, this does not imply that the two species are more closely related.

Although their general structures are different, insects’ wings resemble those of birds and bats. Furthermore, upon further inspection, we discover that, in contrast to the wings of birds, which extend the entire length of the arm, the wings of a bat are merely skin folds that are stretched between its fingers.

Similarly, similar organs are the flippers on whales and the fins on fish. These organs are hence comparable.

7. Outline a project which aims to find the dominant coat colour in dogs.

Answer: There are a variety of genes present in dogs that govern coat colour. At least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) are present that influence coat colour in dogs.

The dog receives one gene from each of its parents. The phenotype is the result of dominant gene expression. For instance, a dog that inherits the “B” gene may be genetically black or brown. Suppose for the moment that:

(i) homozygous black (BB) in one parent

(ii) The homozygous brown parent (bb) is the other parent.

bb		B	B
	b	Bb	Bb
	b	Bb	Bb

Since.

Because black (B) is dominant, all of the progeny have a black phenotype; yet, they are heterozygous for the B allele (Bb). All of the progeny are heterozygous black.

Crossing the F1 heterozygous pups will result in 25% homozygous black (BB), 50%

25% of the progeny were homozygous brown (bb) and heterozygous black (Bb).

	B	b
B	BB	Bb
b	Bb	Bb

8. Explain the importance of fossils in deciding evolutionary relationships.

Answer: Remains of the organism that once existed on earth are called fossils. Fossils serve as a representation of the ancestors of the living things that exist now. For millions of years, they are preserved beneath the layers of mud, silt, and dirt. Fossils are created by buried animals after they die.

The hard bones or shells of an individual are left behind when their soft tissue breaks down swiftly. Further, the sediment piles over and hardens into rock. As a result, upon further investigation, we can discover that the fossils found nearer the surface are more recent than those found in deeper strata.

Let’s travel back a billion years. Buried in the sand, dead seabed invertebrates are rare. Sand builds up and exerts pressure, forming sandstones. The local dinosaur population perishes after millions of years, and their remains are buried in mud as well. Above the rock housing the older invertebrate fossils, the mud is crushed and turns into rock.

In addition, a few equine-like species perished in the region millions of years later and became fossilised in the rocks above the dinosaur remains.

The remains of equine-like creatures that perished in the region during the following years are fossilised in the rocks that atop these earlier rocks. If the area is investigated further, fossils of invertebrates and dinosaurs may also be discovered.

Therefore, by excavating that region, scientists can confidently infer that equine evolution occurred after the evolution of dinosaurs and invertebrates. Therefore, it can be inferred from the example above that the fossils found nearer the earth’s surface are more recent than the fossils found in lower layers.

9. What evidence do we have for the origin of life from inanimate matter?

Answer: In order to learn more about the beginnings of life on Earth, Stanley L. Miller and Harold C. Urey carried out an experiment in 1953. J.B.S. Haldane proposed the theory that basic inorganic molecules were the ancestors of life.

He claimed that the planet was a heated, gaseous mass made up of components like nitrogen, oxygen, carbon, hydrogen, and so forth when it first began. Chemicals such as carbon dioxide (CO2), water (H2O), and methane (CH4)

), ammonia (NH3)

), etc., were created by these substances.

The earth’s surface cooled gradually throughout the formation of the water, allowing the inorganic molecules to mix and produce simple organic molecules like sugars, fatty acids, amino acids, etc. Energy was therefore supplied for these reactions. It was produced by lightning, volcanic eruptions, sun radiation, etc.

Miller and Urey created an atmosphere over water that resembled the early earth’s atmosphere and had molecules like ammonia, methane, and hydrogen sulphide but no oxygen. To mimic lightning, sparks were pushed through the gas mixture

while it was kept at a temperature slightly below 100°C. 15% of the carbon (from methane) was transformed into simple carbon compounds by the end of the week, including the amino acids that make up protein molecules.

Best NCERT Solutions for Class 10 Science Chapter 8 Heredity and Evolution

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: It takes two parents to reproduce sexually. The children receive genetic material from both parents. One receives half of the chromosomes from the mother and half from the father. This indicates that a gene is inherited in two copies, one from the mother and one from the father.

Thus, by combining their DNA, two individuals with distinct variances give birth to a new human. Variations are therefore a result of sexual reproduction.

Variation arises in asexual reproduction due to inaccurate DNA copying. But more variants are possible thanks to sexual reproduction, since the resulting DNA can also endure, making the variations viable.

The process of sexual reproduction is crucial for an organism’s ability to better adapt to its surroundings. Variations aid in the survival of the species. Variation aids in the survival of the species in each of these circumstances. A place’s environmental factors, such illness, pests, and food availability, can change quickly.

Only those varieties that are resistant to it will be able to survive in this situation. It will eventually cause a better-adapted species to evolve. As a result, variety aids in the evolution of species capable of sexual reproduction.

A abrupt shift in the environment, however, has the potential to wipe out asexually reproducing species.

11. How is the equal genetic contribution of male and female parents ensured in the progeny?

Answer: Every human body has 23 pairs of chromosomes in its somatic cells. Of the 23 pairs of chromosomes, 22 are referred to as autosomes, while the other pair—represented by the letters X and Y—is referred to as the sex chromosomes. Males have one X and one Y chromosome,

while females have two X chromosomes. Meiosis takes place during gametogenesis, or the production of gametes, and the gametes receive half as many chromosomes as before.

As a result, the X or Y chromosome and 22 autosomes are present in the male gametes. In contrast, the female gamete possesses X chromosomes and 22 autosomes.

Male and female gametes merge during the process of sexual reproduction, restoring the zygote’s chromosomal count. Consequently,

(i) From a male parent: the offspring inherits one X or Y chromosome and 22 autosomes.

(ii) From Female: The offspring inherits one X chromosome and 22 autosomes from the female parent.

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: A fundamental mechanism of evolution is known as “natural selection.” It provides advantages for survival that encourage diversity. The individuals with the benefit of survival procreate within the population and transfer the advantageous variation to their offspring.

Natural selection leads to the evolution that takes place within the organisms. Other modifications, on the other hand, might happen by chance and provide no benefit for survival.

Even though these variants are not crucial for survival, they may alter the frequency of the genes in some populations. We call this unintentional shift in small groups “genetic drift.” It follows that both kinds of variants are capable of surviving in a population.