Heredity and Evolution Important Questions Class 10 Science with Solutions

Heredity and evolution are central themes in biology that explain how traits are passed from generation to generation and how species adapt over time. Class 10 Science Chapter 8 Important Questions, Heredity and Evolution, not only covers the fundamental principles of genetics but also takes us into the mechanisms of evolution, the evidence supporting it, and its impact on biodiversity. Understanding these concepts is very important for exams and appreciating life's continuity and diversity.

Here is a detailed blog post on mastering this chapter and important questions to aid in your preparation.

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Chapter 8 Heredity And Evolution: Important Questions

1. Evolution in living organisms can be understood by studying the characteristics of different species. These characteristics can be different or similar based on their ancestors.

Given below are pictures of two sets P and Q, of organs of different species. Each set is grouped based on the evolution of these organs in different species.

(a) Name the scientific terms that describe the evolutionary relationship of the organs in sets P and Q.

(b) What are the differences between the two sets of organs?

Answer:

(a) Set P (Frog, Lizard, Human limbs): The organs in this set are homologous organs.

Set Q (Butterfly wing, Bat wing): The organs in this set are analogous organs.

(b)

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2. As part of a theatrical presentation on tracing evolutionary evidences, two teams of class 10 dressed up as the following:

Team P: One person each dressed as a cat and a dolphin to show the cat's leg and a dolphin's flippers as homologous organs.

Team R: One person each dressed as an insect and a bird to show the insect's wings and the bird's wings as homologous organs.

(a) Define homologous organs.

(b) Which of the two teams should win the presentation for correct depiction?

(c) What is incorrect about the losing team's presentation?

(d) Apart from such anatomical connections, name TWO other sources of evidence of evolution used by us.

Answer:

1. Homologous organs are structures in different species that have a similar underlying anatomy due to a common evolutionary ancestor but perform different functions. For example, a cat's leg and a dolphin's flipper are homologous because they have a similar bone structure but serve different purposes (walking vs. swimming).
2. Team P should win the presentation.

The cat's leg and the dolphin's flippers are homologous organs because they have a similar structure (e.g., bones like humerus, radius, and ulna) inherited from a common ancestor, even though they perform different functions.

3. Team R incorrectly presented the insect's wings and the bird's wings as homologous organs.

These are not homologous but analogous organs, meaning they perform a similar function (flying) but have different structural origins:

• Bird wings are modified forelimbs with bones.
• Insect wings are extensions of the exoskeleton and lack bones.

They evolved independently due to convergent evolution, not a common ancestor.

4. Fossil Evidence: Fossils show the gradual changes in species over time and transitional forms, such as Archaeopteryx (a link between reptiles and birds).

Molecular Evidence: Similarities in DNA sequences, proteins, and genetic material across different species indicate shared ancestry. For example, humans and chimpanzees share approximately 98–99% of their DNA.

3. Sex determination in humans happens through sex chromosomes. Along with other parameters, such processes often help in forensic studies in crime investigation and/ or identification of accidents and natural calamities,

In order to determine whether an accident victim is male or female, which cells can be used and why?

Answer:

To determine whether an accident victim is male or female, any nucleated cell from the victim's body can be used because these cells contain the sex chromosomes in their nuclei.

Commonly Used Cells:

Blood cells (White Blood Cells):

Red blood cells lack nuclei, but white blood cells (WBCs) are nucleated and contain DNA.

Skin cells:

Found on the body surface or in tissue samples.

Bone cells:

Bone tissue often survives accidents and natural calamities, making it a reliable source of DNA.

Hair follicle cells:

The base of hair strands contains nucleated cells.

Soft tissue cells:

If available, muscle or organ tissues can also be used.

Why These Cells?

The sex chromosomes in the cells (XX for females, XY for males) determine the sex:

• Females have two X chromosomes in their cells.
• Males have one X and one Y chromosome in their cells.

By analyzing the chromosomes through techniques like karyotyping, polymerase chain reaction (PCR), or fluorescence in situ hybridization (FISH), forensic experts can determine the victim's sex accurately.

4. Before the Industrial Revolution, the black peppered moth was rare. During the early decades of the Industrial Revolution in England, the countryside between London and Manchester became blanketed with soot from the new coal-burning factories. Many of the light-bodied lichens died from sulphur dioxide emissions, and the trees became darkened.

This led to an increase in bird predation for light-coloured moths, as they no longer blended in a well in their polluted ecosystem.(Source: Wikipedia:- https://en.wikipedia.org/wiki/Peppered_moth_evolution)

4.1 What would have happened to the population of light-coloured moth over time and why?

4.2 What could be an external factor that determines the return of the light-coloured moths?

Answer:

4.1 The population of light-coloured moths would have decreased over time.

• This is because the soot-darkened environment made light-coloured moths more visible to predators, such as birds.
• As a result, more light-coloured moths were preyed upon, reducing their survival and reproductive success.
• The process of natural selection favored the darker (melanistic) moths, as they were better camouflaged and less likely to be eaten, leading to an increase in their population.

4.2 An external factor that could determine the return of light-coloured moths is a reduction in pollution.

• With cleaner air and the removal of soot from trees (due to stricter pollution control measures, like those in the late 20th century), the trees could regain their lighter, lichen-covered appearance.
• This would once again provide camouflage for light-coloured moths, increasing their survival and allowing their population to recover.

5. The farmer crosses two heterozygous green seeded plants and obtains 100 plants in the F1 generation.

What would be the number of green and yellow seeds respectively in the F1 generation?

Answer:

To solve this, we use a Punnett square and Mendel's principles of inheritance:

Green seed color (G) is dominant.

Yellow seed color (g) is recessive.

Both parent plants are heterozygous (Gg).

Punnett Square:

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Genotype Ratios:

• GG: 1
• Gg: 2
• gg: 1

Phenotype Ratios:

• Green seeds (GG + Gg): 3
• Yellow seeds (gg): 1

Total Offspring: 100

• Green seeds: 3/4×100=75
• Yellow seeds: 1/4×100=25

Green seeds: 75

Yellow seeds: 25

6. Coelacanth is a deep sea dwelling fish that was believed to be extinct 66 million years ago, around the same time the dinosaurs went extinct. However, in 1938 a specimen of the fish was discovered near the shores of South Africa. Scientists also believe that this fish may be the member of species of fish that crawled onto land to evolve into animals with legs. Upon investigation of the specimen by marine biologists certain features of the fish was discovered.

Some of them are listed below:

(i) It has paired lobe-shaped fins that move in an alternating pattern similar to the limbs of a four-legged animal. 

(ii) It has a lung in its body but carries out exchange of gases through gills.

6.1 The lobed fin of the fish and limbs of a terrestrial animal have similar structure but different function. What are such organs called?

6.2 A vestigial organ is an organ that is carried forward to progeny by evolution but serves no specific purpose in the body of the individual. What organ in the fish can be called a vestigial organ?

6.3 How can scientists so accurately determine the apparent time of extinction of the fish?

Answer:

6.1 These are called homologous organs.

Homologous organs have a similar structure due to a common evolutionary ancestor but may perform different functions in different species.

6.2 The lung in the coelacanth can be considered a vestigial organ.

• While the lung exists in the fish's body, it does not perform gas exchange, as the coelacanth relies on its gills for respiration.
• This lung may be a remnant from its evolutionary ancestors, which possibly used it for breathing air.

6.3  Scientists use fossil records to determine the apparent time of extinction.

• Fossils provide evidence of when the species last existed and can be dated using methods like radiometric dating, which calculates the age of rock layers containing the fossils.
• The coelacanth's fossils were last found in rock layers dated to about 66 million years ago, coinciding with the mass extinction event that wiped out the dinosaurs.

7. Plants that reproduce through asexual reproduction give rise to similar and not identical offsprings.

What could be the most likely reason for the above statement to be true?

Answer:

The most likely reason for the statement to be true is:

"Mutations in the genetic material during DNA replication."

In asexual reproduction, offspring are produced from a single parent without the involvement of gametes. The process usually involves mitotic cell division, resulting in offspring that are genetically identical to the parent.

However, errors during DNA replication (mutations) can introduce slight genetic differences, leading to offspring that are similar but not identical to the parent.

These mutations are rare but are the primary source of genetic variation in organisms that reproduce asexually.

8. Consider a pea plant that is recessive for plant height. Its 'genotype' is tt and 'phenotype' is dwarf.

(a) Assuming that the gene for plant height obeys the Mendel's laws of inheritance, indicate the genotypes and phenotypes of ALL the possible parent pairs that could have dwarf offspring.

(b) Using any of the parent pairs mentioned by you in (a), perform a cross to show the genotypes of the offspring that might arise in the next generation.

Answer:

1. The recessive trait for plant height (dwarf) is expressed when both alleles are recessive (tt). For offspring to have the tt genotype, each parent must contribute a t allele. The possible parent combinations are:

tt × tt

Both parents are homozygous recessive.

All offspring will be dwarf (tt).

Tt × tt

One parent is heterozygous (Tt), and the other is homozygous recessive (tt).

50% of the offspring will be dwarf (tt), and 50% will be tall (Tt, but phenotypically tall).

Tt × Tt

Both parents are heterozygous (Tt).

25% of the offspring will be dwarf (tt), and 75% will be tall (25% TT and 50% Tt).

2. Let's use the Tt × tt parent pair for this demonstration.

Parent Genotypes:

• Parent 1: Tt (heterozygous, tall phenotype)
• Parent 2: tt (homozygous recessive, dwarf phenotype)

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Genotypes of Offspring:

• 50% Tt (heterozygous, tall phenotype)
• 50% tt (homozygous recessive, dwarf phenotype)

Phenotypes of Offspring:

• 50% Tall
• 50% Dwarf

This demonstrates Mendel's laws of segregation and dominance.

9. Select the option that correctly summarises the given observations in the passage.

a. Majority of the peppered moths changed their appearances to become melanistic moths so that they could survive.

b. The predator birds help in controlling the number of any given type of moth so that neither one gets an undue advantage of survival.

c. Different types of moths had to continuously make efforts to adapt themselves in order to survive in the changing environmental conditions.

d. It is by chance that different types of moths were present at any given point of time and the environmental factors determined which type got a survival benefit.

Answer:

(d) It is by chance that different types of moths were present at any given point of time and the environmental factors determined which type got a survival benefit.

Explanation: 

• The passage likely refers to the classic example of natural selection in peppered moths during the Industrial Revolution. The melanistic moths did not "choose" to change their appearance; rather, the environmental conditions (pollution darkening the environment) favored those with darker coloration, which provided better camouflage. This survival advantage increased their population.
• The presence of different moth types is due to genetic variation, and environmental factors (e.g., pollution, predation) determined which type had a better chance of survival.

This aligns with the principles of natural selection.

10. Attached earlobes in humans is an inherited condition. The allele for attached earlobes is recessive.

What are the chances of parents, both having attached earlobes, to have a child with attached earlobes?

a. 0%

b. 25%

c. 75%

d. 100%

Answer:

(d) 100%

Explanation: 

If both parents have attached earlobes, their genotype must be homozygous recessive (aa) since the allele for attached earlobes is recessive.

• Genotype of both parents: aa
• A child inherits one allele from each parent.
• Since both parents can only pass on the recessive allele (a), all offspring will inherit aa.

The chances of the child having attached earlobes are 100%.

Understanding the Basics of Heredity and Evolution

Before beginning to learn and solve the questions, we should first understand the basics of the chapter for a better grasp of better knowledge of it and retain the chapter in our memory for a long time:

Heredity

Heredity refers to the transmission of traits from parents to offspring through genes. The chapter explores:

Mendelian Principles of Inheritance: Gregor Mendel's experiments on pea plants laid the foundation of genetics.

Key Concepts:

• Dominant and recessive traits.
• Monohybrid and dihybrid crosses.
• The 3:1 and 9:3:3:1 ratios.

Examples: Inheritance of plant height and flower colour in pea plants.

Sex Determination in Humans:

• The XX and XY chromosome system determines the gender of offspring.
• Fathers contribute the determining chromosome (X or Y).

Evolution

Evolution explains the gradual changes in species over generations, leading to biodiversity.

Key Mechanisms:

• Natural Selection: Traits that offer survival advantages are passed on more frequently.
• Variation: Differences among individuals arising from mutations and genetic recombination.
• Speciation: Formation of new species due to geographic isolation or reproductive barriers.

Evidence for Evolution:

• Fossil records show transitional forms.
• Homologous and analogous organs indicate common ancestry and functional adaptation.
• Vestigial organs as remnants of evolution.

Applications of Heredity and Evolution

The concepts of heredity and evolution have numerous applications in science and society:

Medicine and Healthcare

Genetic Counselling - Helps identify risks for inherited diseases such as haemophilia, sickle-cell anaemia, and cystic fibrosis.

Advancements in Genetics - DNA analysis aids in diagnosing genetic disorders, and gene therapy offers potential cures by correcting defective genes.

Agriculture and Animal Breeding

Selective Breeding - Enhances desirable traits in crops and livestock, such as disease resistance and higher yield.

Hybridisation produces hybrids with superior qualities, e.g., hybrid maize, wheat, and high-yielding dairy cattle.

Forensic Science

DNA Fingerprinting - Used for criminal investigations and paternity testing.

Conservation Biology

Understanding Biodiversity - Evolutionary studies help identify and conserve species at risk of extinction.

Preparation Tips for Ch 8 CBSE Class 10:

Preparing for heredity and evolution requires a focused, methodical approach. This chapter intertwines biological principles with real-world applications, making it both intriguing and challenging. Here are a few tips to help you excel in this topic:

Focus on Key Concepts

Understanding the fundamental concepts of heredity and evolution is the foundation for mastering this chapter. Key concepts like -

Genetics: Begin with Mendel's principles of inheritance. Understand terms like dominant and recessive traits, phenotype, genotype, and alleles. Learn how to draw and interpret Punnett squares to predict inheritance patterns. Understand monohybrid crosses (involving one trait) and dihybrid crosses (involving two traits), and memorise the ratios (3:1, 9:3:3:1).

Mechanisms of Evolution: Study Darwin's theory of natural selection and its importance in evolutionary biology. Grasp the role of variation, adaptation, and survival of the fittest in shaping species. Learn about genetic drift, speciation, and the importance of geographical and reproductive isolation in forming new species.

Examples of Organs:

• Homologous Organs: Organs with a similar structure but different functions, e.g., the forelimbs of humans and the wings of bats.
• Analogous Organs: Organs with a similar function but different structures, e.g., wings of birds and insects.
• Vestigial Organs: Reduced or functionless organs functional in ancestors, e.g., human appendix and tailbone.

Study Diagrams and Tables

• Practice drawing monohybrid and dihybrid crosses, ensuring you can label and explain each step clearly.
• Familiarise yourself with how traits are passed from parents to offspring using Punnett squares and family pedigree charts.
• Learn diagrams illustrating homologous and analogous structures, such as forelimbs of vertebrates or wings of birds and bats.
• Represent the fossil record, showcasing transitional forms like Archaeopteryx.
• Create tables summarising Mendel’s observations, evolutionary examples, and the differences between homologous and analogous organs.

Practice Questions Regularly

Consistent practice is the key to understanding complex concepts and knowing problem-solving techniques better than ever.

• To build a strong foundation, begin by solving the in-text and end-of-chapter questions from your NCERT textbook.
• Work on problems involving genetic disorders, sex determination, and real-life examples of natural selection (e.g., industrial melanism).
• Attempt CBSE sample papers and previous years’ questions to understand the exam pattern and improve time management.
• Pay attention to diagram-based and long-answer questions, common in board exams.

Understand Evolutionary Evidence

The evidence supporting the theory of evolution is crucial for both exams and a better understanding of biology.

Fossil Records:

• Learn how fossils provide a chronological record of species evolution.
• Understand transitional forms like the Archaeopteryx, which bridges reptiles and birds.

Homologous and Analogous Organs:

• Recognise how homologous structures indicate a common ancestry while analogous structures show adaptive similarities.

Industrial Melanism:

• Study how the peppered moth adapted to industrial pollution, a classic example of natural selection.

Darwin’s Finches:

• Explore how finches on the Galápagos Islands evolved different beak shapes to adapt to available food sources.

Clarify Doubts

The interconnected nature of heredity and evolution can lead to confusion, so make it a priority to clear all doubts.

• If you find concepts like genetic drift, natural selection, or Punnett squares challenging, don’t hesitate to ask for help.
• Refer to online videos, previous year question papers, and practice quizzes for additional explanations and examples.
• Create concise notes summarising key points, ratios, and examples.
• Use flashcards to quickly revise Mendel’s laws, definitions, and evolutionary evidence.

Preparing for heredity and evolution requires conceptual understanding, regular practice, and thorough revision. By focusing on key concepts, mastering diagrams, and practicing questions regularly, you can build confidence in tackling this chapter. Remember to approach the topic with curiosity, as it provides insights into the diversity and adaptability of life on Earth. Stay consistent, clarify doubts, and you’ll be well-prepared to ace this chapter in your exams.

By understanding the mechanisms of heredity and evolution and practicing with Heredity And Evolution Class 10 Important Questions, students can excel in exams. Start preparing today and stay ahead!