GSEB Class 10 Science Solutions Chapter 9 Heredity and Evolution

 

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 probably emerged earlier because it appears in a much larger number of individuals within the population.
In simple words: The trait that more people have probably appeared first.

Exam Tip: In populations, traits that are more common often suggest they have been around for a longer time, allowing them to spread widely.

 

Question 2. How does the creation of variations in a species promote survival?
Answer: Variations enhance an organism's ability to adjust to its changing environmental conditions. This increased adaptability helps the species survive and thrive when surroundings change.
In simple words: Differences within a species help them survive better when their environment changes.

Exam Tip: Always link variations to environmental changes and adaptability, which are key concepts in natural selection and survival.

 

Question 3. How do Mendel's experiments show that traits may be dominant or recessive?
Answer: Mendel used pea plants with two distinct characteristics, for example, tall plants and short plants. The first generation of progeny, called F1, was entirely tall. This finding demonstrates that traits can be either dominant or recessive, and there is no intermediate mix of traits that occurs.
In simple words: Mendel crossed tall and short pea plants. All the offspring were tall, showing that 'tall' was the stronger (dominant) trait and 'short' was the weaker (recessive) one.

Exam Tip: When discussing Mendel's experiments, clearly define F1 and F2 generations and use examples like tall/short or green/yellow to illustrate dominance and recessiveness.

 

Question 4. How do Mendel's experiments show that traits are inherited independently?
Answer: When Mendel cross-bred pure tall pea plants with pure short pea plants, he observed that only tall plants were produced in the F1 generation. After that, Mendel further crossed the tall pea plants from the F1 generation with dwarf plants and obtained a ratio of 3:1 for tall to short plants in the F2 generation. This experiment proved that traits are inherited independently, meaning no other intermediate or new traits were formed.
In simple words: Mendel found that specific traits like height passed down without affecting other traits, acting on their own. This showed that different characteristics are inherited separately.

Exam Tip: For independent inheritance, focus on how different traits (like height and seed color) do not influence each other's segregation during gamete formation.

 

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?
Answer: The provided information is not sufficient to determine which blood group trait, A or O, is dominant. In blood group inheritance, type A is consistently dominant, and type O is consistently recessive. Here, the father's blood group could be \( I^A I^A \) (homozygous) or \( I^A i \) (heterozygous) genetically, while the mother's is \( ii \). For the daughter to be born with blood group O, she must get one \( i \) type gene from each parent. This means the father must have a heterozygous \( I^A i \) blood group, and the mother must have a homozygous \( ii \) blood group.
In simple words: No, it's not enough to tell which is dominant. For the daughter to have O blood, both parents must contribute an 'o' gene. Since the mother is O (oo), she gives 'o'. So, the father, with A blood, must also carry an 'o' gene hidden (Ao) for the daughter to get it. This means O is recessive.

Exam Tip: Remember that blood group O is recessive (ii) and blood groups A and B are dominant. For a child to express a recessive trait, both parents must contribute the recessive allele.

 

Question 6. How is the sex of the child determined in human beings?
Answer: In humans, females possess a pair of XX chromosomes (sex chromosomes), while males have a pair of XY sex chromosomes. When male and female gametes combine during fertilization, the child's sex is determined as follows:

This illustration demonstrates that the ratio of male to female children is equal (1:1), showing a 50% chance for each.
In simple words: The father's sperm carries either an X or a Y chromosome. The mother's egg always carries an X. If an X sperm fertilizes the egg, it's a girl (XX). If a Y sperm fertilizes the egg, it's a boy (XY). So, the father determines the baby's sex.

Exam Tip: Clearly state the chromosome types for males and females, and then explain how the father's contribution (sperm carrying X or Y) dictates the sex of the offspring.

 

Question 7. What are the different ways in which individuals with a particular trait may increase in a population?
Answer: The ways in which individuals with a specific trait can grow in a population are:
1. If the trait helps them survive in difficult conditions, leading to natural selection.
2. The trait can also increase through inheritance, as it passes from one generation to the next.
In simple words: A trait can become more common if it helps people survive bad conditions or if it is easily passed down to children.

Exam Tip: Remember that increased prevalence of a trait is primarily driven by natural selection (survival advantage) and successful reproduction (inheritance).

 

Question 8. Why are traits acquired during the life-time of an individual not inherited?
Answer: Traits gained during an individual's lifetime are only passed down from one generation to the next if there is a change or variation in the DNA. Traits acquired during a person's life may not cause alterations in the genes of their DNA.
In simple words: Traits learned or gained during life, like strong muscles from exercise, don't change your genes. Only changes in DNA can be passed to children.

Exam Tip: Emphasize the difference between somatic (body) cells and germ (reproductive) cells. Acquired traits affect somatic cells and are not passed on because they don't alter the DNA in gametes.

 

Question 9. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer: The low number of surviving tigers is a concern for geneticists because if they become extinct, the genes of this species will be lost forever. Without their genes, there will be no way to bring this species back to life.
In simple words: Few tigers mean less genetic variety. If they die out, their unique genes are gone forever, making it impossible to bring the species back.

Exam Tip: Connect the small population size to reduced genetic diversity, which makes a species vulnerable to diseases and environmental changes, and prevents future recovery.

 

Question 10. What factors could lead to the rise of a new species?
Answer: The elements that can contribute to the development of a new species include gene flow, genetic drift, reproductive isolation, and natural selection.
In simple words: New species can appear because of gene changes, random genetic shifts, groups not being able to reproduce together, and nature picking the strongest survivors.

Exam Tip: List the four main factors clearly: gene flow, genetic drift, reproductive isolation, and natural selection, and briefly explain how each contributes to speciation.

 

Question 11. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species. Why or why not?
Answer: No, geographical isolation cannot be a significant factor in the speciation of self-pollinating plant species. This is because such plants do not rely on other plants for their reproduction to take place.
In simple words: No, separating them by location won't make a new species of self-pollinating plants. They don't need other plants to reproduce, so being alone won't change their genes.

Exam Tip: For self-pollinating species, emphasize that genetic exchange with other individuals is minimal, so geographical barriers have little impact on creating new gene pools.

 

Question 12. 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 significant factor in the speciation of an organism that reproduces asexually. This is because asexually reproducing organisms do not rely on other organisms for their reproduction.
In simple words: No, separating asexual organisms won't really make a new species. They reproduce by themselves, so being alone doesn't stop them from sharing genes or changing.

Exam Tip: Similar to self-pollinating plants, asexual organisms do not depend on partners for reproduction, making geographical isolation less relevant for their speciation compared to sexually reproducing organisms.

 

Question 13. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer: Organisms with similar characteristics typically possess similar DNA codes. On the other hand, organisms with different characteristics will have different genes and different DNA structures. Therefore, comparing DNA sequences is a key method.
In simple words: Comparing the DNA of two species helps us see how closely they are related in evolution. If their DNA is very similar, they are close relatives.

Exam Tip: The most modern and reliable method for determining evolutionary closeness is molecular analysis, particularly comparing DNA or protein sequences.

 

Question 14. Can the wing of a butterfly and the wing of a bat be considered homologous organ? Why or why not?
Answer: The wing of a butterfly and the wing of a bat cannot be considered homologous organs because both have different structures but perform the same function. They lack a similar basic structural design and developmental origin. These are analogous organs.
In simple words: No, butterfly and bat wings aren't homologous. They both help to fly, but their basic structures and how they grew are completely different. They are analogous organs.

Exam Tip: Differentiate between homologous (same basic structure, different function, common ancestor) and analogous (different basic structure, same function, different ancestors) organs with clear examples.

 

Question 15. What are fossils? What do they tell us about the process of evolution?
Answer: Fossils are the preserved traces of living or dead organisms found on solid, hard surfaces. Fossils help us to understand the process of evolution. If a fossil is discovered closer to the Earth's surface, it is more recent in origin than fossils found in deeper layers. Fossils, such as Archaeopteryx, help us to discover evolutionary relationships between organisms.
In simple words: Fossils are old remains of plants and animals found in rocks. They show us how life on Earth has changed over a long time, helping us to understand how different species are connected.

Exam Tip: Define fossils precisely. Then, explain their significance in dating (relative and absolute), tracing evolutionary pathways, and identifying transitional forms.

 

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?
Answer: Despite differences in characteristics, human beings are considered to belong to the same species because they have the capacity to interbreed. Interbreeding is a crucial criterion for categorizing them as one species.
In simple words: Even though humans look different in size, color, and features, we are all one species because we can have babies together.

Exam Tip: The ability to interbreed and produce fertile offspring is the defining characteristic of a species. Emphasize this point clearly.

 

Question 17. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a better body design? Why or why not?
Answer: Evolution demonstrates that body designs have progressed from simple to complex. Consequently, bacteria possess the simplest body design, while chimpanzees have the most complex and therefore "better" body design in terms of complexity and organization.
In simple words: In evolution, body designs get more complex over time. So, chimpanzees have a more complex and generally considered "better" design than simple bacteria, spiders, or fish.

Exam Tip: When evaluating "better" in evolutionary terms, it often refers to complexity and adaptability to diverse environments, reflecting a longer evolutionary pathway.

 

Activity 9.1
Answer: The activity involves studying the earlobes of students in the class.
Observation: It is noticed that the lowest part of the ear, called the earlobe, is closely attached to the side of the head in some individuals and not in others. Thus, free and attached earlobes are two variations observed in human populations.
In simple words: We look at students' ears. Some have earlobes stuck to their head, others have them hanging free. These are two different traits in people.

Exam Tip: When describing observations, be specific about what is being noted and how it represents variation within a population.

 

Activity 9.2
Answer: This activity refers to Mendel's experiment.
In simple words: This is about Mendel's plant experiments.

Exam Tip: When referring to classical experiments, ensure you know the key aspects and findings associated with them.

 

Gujarat Board Class 10 Science Heredity and Evolution Textbook Questions and Answers

Dominant - WW (white colour) Recessive - ww (black colour)

F1 Progeny- all white dogs

F2 Progeny- on crossing of traits we get 1:2:1 ratio as follows:

T - is dominant hence
. TT - Tall
Tt - Tall
tt - Short

 

Question 1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny 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: (d) TtWw
In simple words: The tall parent had genes that made it tall (T) and genes that made its flowers violet (W). Since some offspring were short, the parent must have carried a recessive short gene (t), and since all had violet flowers, it must have been dominant for violet (W).

Exam Tip: For dihybrid crosses, analyze each trait (e.g., height and flower color) separately. If half the progeny are short, the tall parent must be heterozygous (Tt). If all progeny have violet flowers, the violet parent must have at least one dominant violet allele (W).

 

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.
In simple words: All the given options show homologous organs because they share a similar basic structure and origin, even if their functions are now different.

Exam Tip: Homologous organs demonstrate divergent evolution from a common ancestor, even if their current functions vary. Consider both animal and plant examples.

 

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
In simple words: Humans share more evolutionary similarities with other humans from any part of the world than with other animals like chimpanzees, spiders, or bacteria.

Exam Tip: Evolutionary closeness is determined by shared ancestry. Humans share the most recent common ancestor with other humans, followed by other primates like chimpanzees, then other mammals, and so on.

 

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: No, we cannot determine if the light eye color trait is recessive or dominant solely based on this information. To make such a determination, we need to understand the nature of the two variations of a specific trait.
In simple words: No, just knowing light-eyed kids have light-eyed parents isn't enough. We need more info about how light and dark eye color genes work together to say if one is stronger (dominant) or weaker (recessive).

Exam Tip: To identify dominance or recessiveness, one typically needs to observe crosses between individuals with different traits and track their offspring through multiple generations (like F1 and F2).

 

Question 5. How are the areas of study - evolution and classification - interlinked?
Answer: For classifying organisms, we generally group those with similar characteristics together, and those with different characteristics are grouped or categorized separately. A particular set of characteristics reveals the evolutionary level of an organism.
In simple words: Evolution and classification are linked because how we group living things (classification) depends on their shared traits, which show how they evolved.

Exam Tip: Classification systems are built upon evolutionary relationships (phylogeny). Shared characteristics are evidence of common ancestry, and the degree of similarity reflects evolutionary closeness.

 

Explain the terms analogous and homologous organs with examples.
Answer:
1. Analogous organs - These are organs with different structures but the same function. An example is the wings of birds and insects, which both help to fly but have very different underlying structures.
2. Homologous organs - These are organs that have the same basic structure but perform different functions. An example is the forearm of a lizard, bird, and human, all sharing a similar bone arrangement but used for different activities like running, flying, or grasping.
In simple words: Analogous organs have different structures but do the same job (like a butterfly wing and a bird wing). Homologous organs have a similar basic structure but do different jobs (like a human arm and a bat wing).

Exam Tip: Remember that analogous organs indicate convergent evolution (similar function, different origin), while homologous organs indicate divergent evolution (different function, similar origin).

 

Question 7. Outline a project which aims to find the dominant coat colour in dogs.
Answer: A project to find the dominant coat color in dogs would involve the following steps:
1. **Selection of Parents:** Choose two purebred dogs with distinct, contrasting coat colors (e.g., one pure white dog and one pure black dog), ensuring that these dogs are homozygous for their respective coat colors.
2. **First Generation Cross (F1):** Breed these two parent dogs and observe the coat colors of all their offspring (the F1 generation). If one color appears in all F1 offspring, that color is likely dominant.
3. **Second Generation Cross (F2):** Allow two F1 offspring (which are heterozygous for the trait) to mate with each other. Observe the coat colors of the F2 generation.
4. **Data Analysis:** Count the number of offspring with each coat color in the F2 generation. A dominant trait would typically appear in approximately a 3:1 ratio (dominant to recessive) in the F2 generation, assuming a monohybrid cross.
5. **Conclusion:** Based on the observed ratios and the appearance of traits in F1 and F2 generations, determine which coat color is dominant and which is recessive.
In simple words: To find the dominant dog coat color, you'd breed a purebred dog of one color with a purebred dog of another. See what colors their puppies (F1) have. Then, breed two F1 puppies together and count the colors of their puppies (F2). The color that shows up more in F1 and F2 is the dominant one.

Exam Tip: When designing genetic crosses, always start with purebred (homozygous) parents to clearly observe dominance and recessiveness in F1, and then look for characteristic ratios in F2.

 

Dominant - WW (white colour) Recessive - ww (black colour)

F1 generation-all white dogs

F2 generation
WW : Ww : Ww : ww
White : White : Black
3 : 1

 

Question 8. Explain the importance of fossils in deciding evolutionary relationships.
Answer: Fossils give us valuable information about the following:
1. Fossils help to trace the racial history of various organisms, showing their lineage.
2. They help to determine geological time periods by providing dating clues.
3. Older fossils are typically found at greater depths, while newer fossils are closer to the Earth's surface.
4. More complex organisms usually appear in upper layers, while simpler forms are in lower, older layers.
5. Fossils like Archaeopteryx demonstrate the connection between two different types of species, such as birds and reptiles.
In simple words: Fossils show us how life has changed over time. They help us understand when different animals lived, how they are related to each other, and how they developed from simple to complex forms.

Exam Tip: When discussing fossil importance, cover dating methods (relative dating by strata depth), evidence for evolutionary change, and identification of transitional forms.

 

Question 9. What evidence do we have for the origin of life from inanimate matter?
Answer: Miller and Urey, in 1953, created an atmosphere similar to what was believed to exist during an early period on Earth (containing gases like ammonia, methane, and hydrogen sulfide). This setup was kept at a temperature just below 100°C, and sparks were passed through the gas mixture to mimic lightning. At the end of a week, 15% of the carbon (from methane) had transformed into simple carbon compounds, including amino acids, which are building blocks of protein molecules. The presence of protein cell membranes aligns with this experiment, suggesting that life originated from non-living matter.
In simple words: The Miller-Urey experiment showed that basic chemicals on early Earth, with energy from lightning, could form amino acids, which are vital for life. This suggests life might have started from non-living things.

Exam Tip: Clearly describe the Miller-Urey experiment, including the gases used, energy source, and the key outcome (formation of amino acids), linking it to the concept of abiogenesis.

 

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: More variations are observed in sexual reproduction compared to asexual reproduction. This happens because variations occur due to changes in DNA coding and, in sexual reproduction, two genes from different sexes (male and female) cross over, leading to greater variation. This increased variation provides more raw material for natural selection, allowing sexually reproducing organisms to adapt more quickly and effectively to changing environments, thus accelerating their evolution.
In simple words: Sexual reproduction creates more differences because two parents mix their genes. This means more variety, which helps species change and adapt better over time.

Exam Tip: Highlight genetic recombination and the fusion of gametes from two parents as the primary sources of variation in sexual reproduction, contrasting it with the clonal nature of asexual reproduction.

 

Question 11. How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer: The equal genetic contribution of male and female parents is ensured in the offspring through the process of fertilization, where each parent contributes one set of chromosomes. For humans, this can be observed by examining the crossing over of male and female sex genes as follows:

This will result in a female child if the sperm carrying X fertilizes the egg, forming a XX zygote. If the sperm carrying Y fertilizes the egg, it will form an XY zygote, resulting in a male child. So, essentially, the male gametes determine the sex of the unborn child. Both parents equally contribute genetic material (23 chromosomes each), with one determining sex.
In simple words: Each parent gives half of their genes (one set of chromosomes) to their child. This means both the male and female parent contribute an equal amount of genetic information to the offspring.

Exam Tip: Explain meiosis, gamete formation (each containing a haploid set of chromosomes), and subsequent fertilization as the mechanism ensuring equal genetic contribution from both parents.

 

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: No, I do not entirely agree with this statement. Depending on the type of variations, different individuals might have different advantages. However, when a significant change occurs in the environment, only those organisms in the population that possess an advantageous variation will survive in the altered environment.
In simple words: No, not always. Sometimes, variations might not offer a big advantage but still survive. But if the environment changes a lot, only the variations that help an organism live through the change will definitely continue.

Exam Tip: While advantageous variations are favored by natural selection, not all surviving variations are necessarily "advantageous" in every context. Neutral variations can also persist, and genetic drift can cause non-adaptive changes in gene frequency.

 

Gujarat Board Class 10 Science Heredity and Evolution Additional Important Questions and Answers

Very Short Answer Type Questions

 

Question 1. Define heredity.
Answer: Heredity refers to the passing of characteristics from one generation to the next.
In simple words: Heredity is when traits are passed from parents to children.

Exam Tip: Keep the definition concise and focused on the transmission of traits between generations.

 

Question 2. Define variations.
Answer: Variations are the differences that exist among organisms of the same species, despite sharing the same basic features.
In simple words: Variations are the small differences you see between individuals of the same type of animal or plant.

Exam Tip: Emphasize that variations are within a species and involve differences in traits.

 

Question 3. How does the creation of variations in a species promote survival?
Answer: Variations enhance an organism's ability to adjust to its changing environmental conditions. This increased adaptability helps the species survive and thrive when surroundings change.
In simple words: Differences within a species help them survive better when their environment changes.

Exam Tip: Always link variations to environmental changes and adaptability, which are key concepts in natural selection and survival.

 

Question 4. What is a trait?
Answer: A characteristic feature of an organism is called a trait.
In simple words: A trait is a special feature or quality of a living thing.

Exam Tip: Provide simple examples like height, eye color, or flower color to illustrate what a trait is.

 

Question 5. Name two human traits that show variations.
Answer: Two human traits that show variations are the colors of eyes and the shape of external ears.
In simple words: Eye color and ear shape are two human traits that can be different between people.

Exam Tip: Choose easily observable traits that are known to vary significantly among individuals.

 

Question 6. What is adaptation?
Answer: An adaptation is a characteristic feature that helps an organism survive in its habitat more effectively.
In simple words: Adaptation is a special feature that helps a living thing survive better in its home environment.

Exam Tip: Stress that adaptations are features evolved over time that provide a survival or reproductive advantage in a specific environment.

 

Question 7. Which of the two sperm or egg-decides the sex of the child?
Answer: The sperm determines the sex of the child.
In simple words: The father's sperm decides if a baby will be a boy or a girl.

Exam Tip: Recall that the egg always carries an X chromosome, while sperm can carry either an X or a Y chromosome.

 

Question 8. The forelimbs of frog, reptiles, birds and arms of man show the same basic design. What kind of organs are these?
Answer: These are homologous organs.
In simple words: These are called homologous organs.

Exam Tip: Homologous organs point to a common evolutionary ancestry, even if their functions have diverged.

 

Question 9. What is microevolutions?
Answer: Microevolution is the process of evolution that happens on a relatively small scale at the population level and can alter the common characteristics of specific species.
In simple words: Microevolution is small changes in a species over time, like shifts in gene frequency within a group, not leading to a new species.

Exam Tip: Distinguish microevolution (small-scale changes within a species) from macroevolution (large-scale changes leading to new species or groups).

 

Question 10. What is speciation?
Answer: Speciation is the process of forming a new species from an already existing one through the buildup of variations, natural selection, gene flow, genetic drift, and other factors.
In simple words: Speciation is when a new type of animal or plant develops from an old one because of changes like new genes, natural selection, or being separated.

Exam Tip: Define speciation as the formation of new species and list the contributing factors (genetic variation, isolation, natural selection).

 

Question 11. What is a gene?
Answer: A gene is the unit of inheritance. It is a segment of the chromosome that controls the appearance of a particular set of hereditary characteristics.
In simple words: A gene is a tiny part of DNA that holds instructions for a specific trait, like eye color.

Exam Tip: Emphasize that genes are located on chromosomes and carry the code for specific traits.

 

Question 12. Who is known as the "father of Genetics"?
Answer: G.J. Mendel is known as the "father of Genetics".
In simple words: G.J. Mendel is called the "father of Genetics".

Exam Tip: Remember Gregor Mendel's name as the pioneer in the study of heredity.

 

Question 13. What is evolution?
Answer: Evolution is the sequence of gradual changes that take place in living organisms over millions of years, leading to the emergence of new species.
In simple words: Evolution is how living things slowly change over many, many years, leading to new kinds of animals and plants.

Exam Tip: Define evolution as descent with modification, focusing on gradual changes in populations over generations.

 

Question 14. What type of reproduction gives rise to more number of successful variations?
Answer: Sexual reproduction gives rise to a greater number of successful variations.
In simple words: Sexual reproduction creates more useful variations.

Exam Tip: Connect sexual reproduction with genetic recombination and meiosis, which are key drivers of variation.

 

Question 15. What are fossils?
Answer: Fossils are preserved traces or remains of living organisms from the geological past.
In simple words: Fossils are very old remains or signs of plants and animals found in rocks.

Exam Tip: Ensure your definition highlights preservation and ancient origin.

 

Question 16. What are the uses of fossils?
Answer: Fossils are useful for:

• Helping to trace the racial history of organisms, showing their lineage.
• Helping to analyze past climatic conditions by providing environmental clues.
• Helping to determine geological time periods by serving as markers.

In simple words: Fossils help us learn about old life, past climates, and how long ago events happened.

Exam Tip: List key uses such as evolutionary history, paleoclimate reconstruction, and geological dating.

 

Question 17. Name the scientist who put forth the theory of natural selection.
Answer: Charles Darwin.
In simple words: Charles Darwin.

Exam Tip: Charles Darwin is the central figure associated with the theory of natural selection.

 

Question 18. What is artificial selection?
Answer: Artificial selection is the process of modifying a species through selective breeding. Animals and plants with desired characteristics are chosen and bred to pass on those traits. For example, artificial selection by farmers has resulted in the creation of cauliflowers, cabbage, broccoli, and kohlrabi from wild cabbage.
In simple words: Artificial selection is when humans choose specific animals or plants with desired traits to breed, making new types over time.

Exam Tip: Contrast artificial selection (human-driven) with natural selection (environment-driven) and provide clear examples like dog breeds or crop varieties.

 

Short Answer Type Questions

 

Question 1. How can we trace evolutionary relationships?
Answer: Evolutionary relationships can be traced by studying fossils, by examining homologous and analogous organs, by comparing the embryos of different animals, and by comparing the DNA of different species.
In simple words: We can find out how species are related by looking at old fossils, comparing body parts, studying how babies grow inside, and checking their DNA.

Exam Tip: List the various lines of evidence for evolution: fossils, comparative anatomy (homologous/analogous structures), comparative embryology, and molecular biology (DNA/protein).

 

Question 2. What is phylogeny and molecular phylogeny?
Answer: Phylogeny is the evolutionary history of an organism. Molecular phylogeny traces the evolutionary relationships by comparing the differences in the DNA of different organisms.
In simple words: Phylogeny is a species' family tree through time. Molecular phylogeny uses DNA differences to map these relationships.

Exam Tip: Define both terms clearly, highlighting that molecular phylogeny uses genetic data to reconstruct evolutionary histories.

 

Question 3. What is environmental selection?
Answer: Environmental selection is the process of selection within a population resulting from the influence exerted by the environment. It leads to a change in the composition of genes within a population, as individuals best suited to the environment are more likely to survive and reproduce.
In simple words: Environmental selection is when nature picks which living things survive and have babies based on how well they fit into their surroundings, changing the traits in the group over time.

Exam Tip: Environmental selection is synonymous with natural selection, where the environment acts as the selective agent, favoring individuals with advantageous traits.

 

Question 4. What term did Mendel use for genes? Where are the genes located?
Answer: Mendel used the term 'factors' for genes. Genes are segments of DNA that code for a single protein. Genes are located on chromosomes within the nucleus of a cell.
In simple words: Mendel called genes "factors." Genes are found on chromosomes inside the cell's nucleus.

Exam Tip: Recall that Mendel's "factors" were later identified as genes. Mentioning their location on chromosomes is important.

 

Question 5. How many pairs of chromosomes do human beings have, specify the types of chromosomes also?
Answer: Human beings have 23 pairs of chromosomes. The first 22 pairs are called autosomes, which are similar in males and females. The 23rd pair is known as the sex chromosome. In males, the sex chromosomes are XY, and in females, they are XX.
In simple words: Humans have 23 pairs of chromosomes. 22 pairs are autosomes (same for everyone), and one pair is sex chromosomes (XX for females, XY for males).

Exam Tip: Clearly distinguish between autosomes and sex chromosomes, specifying their numbers and types for males and females.

 

Question 6. What are homologous organs? Explain with an example.
Answer: Homologous organs are those organs in different plants or animals that possess the same basic structural design and origin but may have different functions. For example, the hand of a human and the forelimb of a frog are homologous organs.
In simple words: Homologous organs are body parts in different animals that look alike inside and come from the same basic plan, even if they do different jobs now. A human hand and a frog's front leg are examples.

Exam Tip: Emphasize that homologous structures indicate shared ancestry (divergent evolution), even with different functions.

 

Question 7. What are analogous organs? Explain with an example.
Answer: Analogous organs have the same function but possess different structural designs and origins. For example, the wings of birds and insects serve the same function (flight) but have completely different basic structural designs and developmental origins.
In simple words: Analogous organs do the same job but have different structures and come from different origins. Bird wings and insect wings both fly, but they are built very differently.

Exam Tip: Emphasize that analogous structures result from convergent evolution, where different species evolve similar solutions to similar environmental challenges.

 

Question 8. What is the significance of studying homologous and analogous organs?
Answer: Organisms that possess homologous organs demonstrate relatedness and share a common ancestry, providing evidence for divergent evolution. In contrast, analogous organs show how different species can evolve similar functions independently, providing evidence for convergent evolution.
In simple words: Studying these organs helps us understand how living things are related. Homologous organs show shared ancestors, while analogous organs show different animals finding similar ways to do things.

Exam Tip: The significance lies in understanding evolutionary pathways: homologous structures indicate shared ancestry, while analogous structures highlight adaptation to similar environments.

 

Question 9. Which of the following combinations of sex chromosomes produces a male or a female child-XX or XY?
Answer: The XX combination produces a female child, while the XY combination produces a male child.
In simple words: XX makes a female child, and XY makes a male child.

Exam Tip: This is a direct recall question; ensure you know the standard human sex chromosome combinations.

 

Question 10. Which of the following are homologous and analogous organs?
(a) Wings of birds and insects.
(b) Flippers of whale and fins of fish
(c) Flippers of whale and wings of bat.
(d) Our teeth and elephants tusks.
(e) Potato and runners of grass.
Answer: (a) - Analogous organs
(b) - Analogous organs
(c) - Homologous organs
(d) - Homologous organs
(e) - Homologous organs
In simple words: Birds' and insects' wings are analogous (different structure, same function). Whale flippers and fish fins are also analogous. Whale flippers and bat wings are homologous (similar structure, different function). Human teeth and elephant tusks are homologous. Potatoes and grass runners are homologous.

Exam Tip: Carefully analyze each pair: if they have a common basic structure but different functions, they are homologous. If they have different basic structures but the same function, they are analogous.

 

Question 13. A true breeding tall plant is crossed with a true breeding short plant. All the offsprings of the F₁ generation are tall. Of these two characters which one is dominant and which is recessive.
Answer:

In the F₁ generation, only tall plants were produced. This shows that the tall trait is dominant, and the short trait is recessive. The dominant trait always shows up when both types of genes are present.
In simple words: When a tall plant and a short plant breed, all their first generation babies are tall. This means "tall" is the strong trait (dominant), and "short" is the hidden trait (recessive).

Exam Tip: Remember that dominant traits mask recessive traits in the first generation of a monohybrid cross.

 

Question 14. In Question 14. on previous page the tall plant of the F₁ generation is selfed. What is the outcome or ratio of the F2 progeny?
Answer: When the F₁ generation tall plant (Tt) is selfed, the F₂ progeny will have a phenotypic ratio of 3 Tall : 1 Short, and a genotypic ratio of 1 TT : 2 Tt : 1 tt. This outcome explains how recessive traits can reappear in later generations.
In simple words: When the tall plants from the first generation breed with themselves, the next generation will have 3 tall plants for every 1 short plant.

Exam Tip: Always remember Mendel's F2 generation phenotypic ratio for a monohybrid cross is 3:1.

 

Question 15. How is the sex of the child determined in human beings?
Answer: Human beings possess 23 pairs of chromosomes. Out of these, 22 pairs are called autosomes, and the 23rd pair is the sex chromosome. Males have XY sex chromosomes, while females have XX. All gametes formed by females contain an X chromosome. Males produce two types of sperm: those carrying an X chromosome and those carrying a Y chromosome. The specific sperm that fertilizes the egg determines the child's sex. If an X-carrying sperm fertilizes the egg, the zygote becomes XX, resulting in a female child. If a Y-carrying sperm fertilizes the egg, the zygote becomes XY, resulting in a male child. Thus, the male gametes ultimately decide the sex of the unborn child.

In simple words: Humans have sex chromosomes (XX for girls, XY for boys). Females always give an X. Males can give either an X or a Y. So, it's the father's sperm (X or Y) that decides if the baby will be a boy or a girl.

Exam Tip: Focus on explaining the role of the male gamete (sperm) in determining the sex of the offspring, as it carries either an X or a Y chromosome.

 

Question 16. What is genetic drift?
Answer: Genetic drift refers to random changes in the frequency of certain genes within a small population over successive generations. These changes can occur by chance, even if they do not provide any survival advantage to the organisms. It is a source of genetic diversity but is not driven by adaptations. The frequency of alleles can shift randomly in a population because of this process.
In simple words: Genetic drift is when gene numbers in a small group change by chance, not because they are better. It's a random change that happens over time.

Exam Tip: Highlight that genetic drift is a random process, especially impactful in small populations, and does not involve natural selection for advantageous traits.

 

Question 17. Which is gene flow?
Answer: Gene flow is the movement of genetic material between different populations of the same species through interbreeding. When individuals from one population mate with individuals from another, they exchange genes, which increases the variety of traits in the recipient population. This process helps to mix up the gene pool and prevent populations from becoming too different from each other.
In simple words: Gene flow is when genes move between different groups of the same animal or plant species, usually by mating. This makes the groups more similar genetically.

Exam Tip: Define gene flow as the transfer of genetic material between populations, emphasizing its role in increasing genetic variation and reducing differences between populations.

 

Question 18. How do we know how old fossils are?
Answer: We can determine the age of fossils in two main ways. First, by examining their relative depth: fossils found closer to the Earth's surface are generally more recent than those found in deeper layers. This method gives a comparative age. Second, we can use radiometric dating, which involves detecting the ratios of different isotopes of the same element present in the fossil material. This technique provides a more precise absolute age.
In simple words: We find out how old fossils are by looking at how deep they are in the ground (deeper means older) or by checking special atoms inside them (radioactive dating).

Exam Tip: Mention both relative dating (depth) and absolute dating (isotope ratios/radiometric dating) methods to get full marks.

 

Question 19. What is speciation? How does it occur?
Answer: Speciation is the process by which new and distinct species evolve from existing ones over a long period. This occurs through several key factors. These include gene flow (where genetic exchange between populations stops), genetic drift (random changes in gene frequencies), reproductive isolation (when populations can no longer interbreed), and natural selection (where environmental pressures favor certain traits). Eventually, these processes combine to create genetically distinct groups that can no longer reproduce with the parent species.
In simple words: Speciation means new species form from old ones over time. This happens because groups get separated, genes change randomly, they stop breeding together, or nature picks certain traits.

Exam Tip: Provide a clear definition of speciation and list at least three key mechanisms like genetic drift, reproductive isolation, and natural selection.

 

Question 20. What is natural selection?
Answer: According to Darwin's theory, natural selection is the fundamental process that drives the evolution of new species of plants and animals. It involves the following steps:

• Populations tend to produce more offspring than needed, yet the population size generally stays stable.
• Individual organisms within a population show variations in their traits.
• Some of these variations provide adaptations that help individuals survive and reproduce better in a changing environment (this is known as "survival of the fittest").
• Nature then "selects" the organisms with the most favorable adaptations, allowing them to pass on their genes.
• Over many generations, these selected traits become more common, leading to the formation of new species with improved adaptations.

In simple words: Natural selection is how nature picks the strongest living things to survive and pass on their good traits. It means that the ones best suited to their environment will live, breed, and make more babies with those helpful traits, slowly creating new species.

Exam Tip: Explain natural selection using Darwin's four main points: overproduction, variation, struggle for existence, and survival of the fittest leading to adaptation.

 

Question 21. Define Genetics. What did Mendel's contribution to genetics?
Answer: Genetics is the branch of science that studies heredity and variation. It explores how traits are passed from parents to offspring and the differences among individuals. Mendel's major contribution to genetics involved conducting breeding experiments on garden pea plants (Pisum sativum). He used contrasting pairs of characters and observed that only one character from each pair appeared in the first generation, but both characters reappeared in the subsequent generation. Based on these findings, Mendel proposed fundamental principles of inheritance and suggested that each character is controlled by a pair of "factors," which we now call genes.
In simple words: Genetics is the study of how traits are passed down and why we're all a bit different. Mendel figured out these rules by breeding pea plants, showing how traits go from parents to children and introducing the idea of "factors" (now called genes).

Exam Tip: Start with a clear definition of genetics, then elaborate on Mendel's pea plant experiments and his discovery of 'factors' (genes) and principles of inheritance.

 

Question 22. Explain the Monohybrid Cross.
Answer: A monohybrid cross is a genetic cross where only two contrasting characters are studied at one time. For his first experiment, Mendel performed a monohybrid cross, choosing a pair of contrasting traits, such as tall plants and short plants. In this cross, TT represents the genotype of a tall plant, and tt represents the genotype of a short plant. In the F₁ generation, all plants were tall, but their genotype was Tt, meaning they were not pure tall plants. This was confirmed by the reappearance of the short trait in the F₂ generation, where most plants were tall, but some were short. This experiment showed that the short character was recessive in the F₁ generation and therefore not visible. The ratio of tall plants to short plants in the F₂ generation was 3:1.
In simple words: A monohybrid cross looks at how one trait (like plant height) is passed on. Mendel crossed tall and short pea plants. All the first generation plants were tall (Tt), but when these bred, the next generation had 3 tall plants for every 1 short plant, showing that the short trait was hidden at first.

Exam Tip: Clearly define a monohybrid cross and use Mendel's tall vs. short pea plant example to explain the F1 and F2 generations and the resulting 3:1 phenotypic ratio.

 

Question 23. State Mendel's first law.
Answer: Mendel's first law is the Law of Segregation. This law states that every individual possesses a pair of alleles (different forms of a gene) for a particular trait. During the formation of gametes (sex cells), these alleles separate, so that each gamete receives only one allele for that trait. This means a particular trait can be dominant (expressed) or recessive (hidden) in a given generation, depending on which allele is inherited.
In simple words: Mendel's first law says that for any trait, each parent has two gene copies, but they only pass one copy to their child. These copies separate when sex cells are made.

Exam Tip: Remember to name the law (Law of Segregation) and explain that each gamete receives only one allele from the pair an individual possesses.

 

Question 24. What are alleles?
Answer: Alleles are two or more alternative forms of a gene. These alternative forms arise through mutation and are found at the same location (locus) on a chromosome. For example, a gene for eye color might have an allele for blue eyes and another allele for brown eyes.
In simple words: Alleles are different versions of the same gene, like different colors for eye color. They are found at the same spot on a chromosome.

Exam Tip: Define alleles as alternative forms of a gene and mention their origin through mutation and location on chromosomes.

 

Question 25. State the second law of Mendel.
Answer: Mendel's second law is the Law of Independent Assortment. This law states that the alleles for different characters separate independently from each other during gamete formation. In simpler terms, the inheritance of one trait does not affect the inheritance of another trait when they are located on different chromosomes or are far apart on the same chromosome. For example, the inheritance of pea shape (round or wrinkled) is independent of the inheritance of pea color (yellow or green).
In simple words: Mendel's second law says that genes for different traits sort themselves out independently when sex cells are made. One trait's inheritance doesn't depend on another's.

Exam Tip: State the law clearly and explain that alleles for different traits segregate independently during gamete formation, usually illustrated with a dihybrid cross.

 

Question 26. Define Genotype and Phenotype.
Answer:

• Genotype: The genotype refers to the complete set of genes present in an organism's genome. It represents the genetic makeup that determines a specific trait or characteristic.
• Phenotype: The phenotype refers to the observable characteristics of an organism, which are a result of its genotype interacting with the environment. For instance, while a plant's genotype might contain genes for tallness, its actual height (phenotype) could be influenced by soil quality or sunlight. Due to this interaction, many phenotypes are not directly inherited but are expressed based on environmental factors.

In simple words: Genotype is all the genes an organism has inside it. Phenotype is what you can actually see, like its color or height, which comes from genes and the environment.

Exam Tip: Clearly distinguish between genotype (genetic makeup) and phenotype (observable traits), emphasizing that phenotype is influenced by both genes and the environment.

 

Question 27. Discuss how the variation is seen/accumulated during different types of reproduction.
Answer: Variation occurs and accumulates differently depending on the type of reproduction:

• Asexual Reproduction: This involves a single parent, which means it is not ideal for generating significant variations. Minor differences do occur, primarily due to inaccuracies during DNA replication or spontaneous mutations. However, these variations would be very small and would require an extremely long time to show any noticeable or distinctive effect on the population.
• Sexual Reproduction: This process is ideal for creating and accumulating variations because it involves two parents. The offspring's genetic makeup receives contributions from both parents, leading to a unique combination of genes. This mixing of genetic material from two different sources greatly increases the chances of generating new variations in the progeny.

In simple words: In asexual reproduction (one parent), changes are small and take ages to show up, mostly from copying mistakes. In sexual reproduction (two parents), changes happen a lot because genes mix from both parents, making new combinations.

Exam Tip: Compare asexual and sexual reproduction, explaining that sexual reproduction generates more significant variation due to the combination of genetic material from two parents.

 

Question 28. List down the reasons for the choice of pea plant by Mendel for his experiment.
Answer: Mendel chose the pea plant (Pisum sativum) for his experiments for several key reasons:

• Pea plants can be considered biennial, meaning two generations can grow within a single year. This allowed Mendel to observe a larger number of generations in a shorter timeframe.
• The plants possess many easily identifiable and contrasting characters, such as tall/short height, round/wrinkled seeds, and yellow/green seeds. These distinct traits made it easy to track inheritance patterns.
• Cross-pollination can be easily induced in pea plants, allowing Mendel to control breeding experiments and observe specific crosses.
• Pea plants are generally self-pollinating, which helped maintain pure lines for his experiments before cross-pollination.

In simple words: Mendel picked pea plants because they grow fast (many generations in a year), have clear, different traits (like tall or short), are easy to cross-breed, and can also self-pollinate.

Exam Tip: List at least three distinct reasons for Mendel's choice of pea plants, focusing on their reproductive characteristics and easily observable traits.

 

Question 29. State the result of Mendel's experiment.
Answer: Mendel conducted experiments on pea plants and, based on his observations, proposed fundamental rules of inheritance. He noticed that characters often appeared in pairs, and he called a pair of contrasting characters an allele. His experiments demonstrated that in the first (F₁) generation, typically only one character from a pair was expressed, while the other was hidden. However, in the subsequent (F₂) generation, both characters reappeared, showing a specific ratio. This led to his laws of inheritance, explaining dominance, segregation, and independent assortment of traits.
In simple words: Mendel found that traits come in pairs called alleles. In the first generation, only one trait would show up, but in the next, both would reappear in a set pattern.

Exam Tip: Focus on the observation that one trait is expressed in F1 while both reappear in F2, leading to the concept of alleles and principles of inheritance.

 

Question 30. What is classification?
Answer: Classification is the systematic arrangement of organisms into a series of groups or categories based on their similarities in various characteristics. These similarities can include aspects of their physiology (how their bodies function), anatomy (their physical structure), morphology (their external form), and other evolutionary relationships. This process helps scientists organize and understand the vast diversity of life on Earth.
In simple words: Classification is how we sort living things into groups based on how similar they are in body, function, and other ways.

Exam Tip: Define classification as the systematic grouping of organisms and mention at least two criteria used, such as physiology, anatomy, or morphology.

 

Question 31. State the importance of variations.
Answer: Variations are the differences in characteristics found among individuals of the same species. These variations are incredibly important because they allow organisms to adapt themselves to changing environmental conditions. By providing a range of different traits, variations act as the raw materials for evolution and are essential for the formation of new species. Without variations, a species would be unable to respond to changes in its environment, making it vulnerable to extinction.
In simple words: Variations are the differences between living things of the same kind. They are important because they help species adapt to new environments, which is key for evolution and creating new species.

Exam Tip: Emphasize that variations are the raw material for evolution and enable species to adapt to changing environments, ensuring survival.

 

Long Answer Type Questions

 

Question 1.
1. What is genetics?
2. Give the common name of the plant on which Mendel performed its experiments.
3. What for did Mendel use the term factors and what are these factors called now?
4. What are genes? Where are the genes located?
Answer:
1. Genetics is the science that deals with the study of heredity and variations.
2. The common name of the plant on which Mendel performed his experiments is the pea plant.
3. Mendel used the term 'factors' to describe the units of inheritance, and these factors are now called 'genes'.
4. Genes are the units of inheritance. They are specific parts of a chromosome that control the appearance of a set of hereditary characteristics. Genes are located on the chromosomes.
In simple words: 1. Genetics studies how traits are passed on. 2. Mendel used pea plants. 3. He called genes "factors" back then. 4. Genes are tiny parts of chromosomes that carry instructions for traits.

Exam Tip: For multi-part questions, ensure each sub-part is answered distinctly and accurately. Define key terms clearly and remember specific names and locations.

 

Question 2. Define 'evolution'. State Darwin's theory of evolution.
Answer: Evolution is a change in the genetic makeup of a population over successive generations. It describes the gradual process by which living organisms have developed and diversified from earlier forms.
Darwin's theory:

• The size of a population generally remains constant, even though more offspring are produced than are actually needed to maintain it.
• Variations among individuals provide adaptations that give some organisms an advantage in survival.
• The best adapted organisms are more likely to survive in a changing environment (this is known as the "survival of the fittest").
• Nature then selects the organisms with better adaptations, and after many generations, new species are formed through this natural selection process.

In simple words: Evolution is how a population's genes change over time, making new life forms. Darwin's theory says more babies are born than can survive, so the ones with the best changes (adaptations) live longer, have more babies, and pass on those good traits, slowly making new species.

Exam Tip: Provide a concise definition of evolution and then clearly articulate Darwin's theory, including the concepts of overproduction, variation, and natural selection (survival of the fittest).

 

Question 3. What are various evidences in factors of evolution?
Answer: There are various types of evidence that support the concept of evolution:

• Homologous organs: These are organs that share the same basic structure and developmental origin but have different functions. For example, the wings of a bat, the hands of a man, and the limbs of a monkey all have a similar bone structure, indicating a common ancestor.
• Analogous organs: These are organs that perform a similar function but have different structural designs and developmental origins. For instance, the wings of a bat, insects, and birds all allow for flight, but their internal structures are entirely different.
• Vestigial organs: These are organs that appear in an organism but are now functionless, or have a reduced function, compared to their functional counterparts in ancestral species. Examples include the vermiform appendix and the nictitating membrane in the human eye.
• Embryological evidence: The study of embryos of vertebrates shows striking similarities in their early stages of development. For example, the embryos of a frog, fish, and human all look alike at the initial stages, suggesting a common origin.
• Fossils as evidence: Fossils, which are preserved remains or traces of ancient organisms, provide direct evidence of past life forms. For instance, the Archaeopteryx fossil shows characteristics of both birds and reptiles, indicating an evolutionary link between these two different types of species.

In simple words: We know evolution happens because of several clues: some body parts look the same but do different jobs (homologous), others do the same job but look different (analogous), some parts are useless leftovers (vestigial), baby animals look alike in early stages, and old preserved remains (fossils) show links between different creatures.

Exam Tip: List and briefly explain at least four types of evolutionary evidence (e.g., homologous organs, analogous organs, vestigial organs, embryological evidence, fossils), providing a clear example for each.

 

Question 4.
1. What are traits?
2. Explain the inherited trait and acquired traits.
3. Define speciation. What are the factors which could lead to the rise of a new species?
Answer:
1. Traits: A characteristic feature of an organism is called a trait.
2. Inherited traits: These are characteristics that are passed down from parents to their offspring through genes. For example, eye color, hair type, and blood group are inherited traits.
Acquired traits: These are characteristics that an individual develops during their lifetime due to environmental influences, learning, or lifestyle choices. They are not encoded in the genes and cannot be passed on to the next generation. For example, a learned skill like playing a musical instrument or a larger muscle mass gained from exercise are acquired traits.
3. Speciation is the process by which new species evolve from existing ones. The factors that could lead to the rise of a new species include gene flow (disruption of genetic exchange), genetic drift (random changes in gene frequencies), reproductive isolation (inability of populations to interbreed), and natural selection (environmental pressures favoring certain traits).
In simple words: 1. Traits are features of a living thing. 2. Inherited traits come from parents (like eye color), while acquired traits are learned or developed during life (like a scar) and aren't passed down. 3. Speciation is when new types of living things form, caused by genes not mixing, random gene changes, groups not breeding together, and nature picking certain traits.

Exam Tip: Clearly define "trait" and "speciation." For inherited and acquired traits, provide distinct definitions and examples for each. When listing factors for speciation, ensure you mention at least three key mechanisms.

 

Questions On High Orderer Thinking Skills (Hots)

 

Question 1. Study the given diagram and answer the questions.

(i) Why do we find all bottom row individuals different from each other?
(ii) What is similar in all the individuals?
Answer:
(i) The differences among all bottom row individuals arise from two main sources: the inheritance of acquired traits from their respective parents and the natural variation that occurs due to inheritance when parents themselves are genetically distinct. Each generation accumulates minor changes, making later descendants unique.
(ii) All the individuals in the diagram share a similar basic body design. Despite the variations that accumulate over generations, the fundamental structural blueprint remains consistent, indicating their common ancestry.
In simple words: (i) The individuals at the bottom are all different because they inherit small changes from their parents, and each new generation adds new variations. (ii) Even with differences, all the individuals in the diagram have the same basic body shape.

Exam Tip: For diagrams illustrating variation, explain that differences arise from inherited variations and cumulative changes over generations, while underlying similarities point to common ancestry.

 

Question 2. Male individual has 23 pairs of chromosomes, female individual has 23 pairs of chromosomes. Then why don't an offspring have 46 pairs of chromosomes which is obtained by the fusion of these two eggs.
Answer: While both male and female individuals have 23 pairs of chromosomes (a total of 46 chromosomes), the gametes (sperm in males and eggs in females) are formed through a process called meiotic cell division. Meiosis reduces the chromosome number by half, so each gamete contains only 23 single chromosomes, not pairs. Specifically, a male sperm carries 23 chromosomes, and a female egg carries 23 chromosomes. When these two gametes fuse during fertilization, they combine their chromosomes to form a zygote that has 23 pairs of chromosomes (a total of 46 chromosomes). This mechanism ensures that the offspring maintains the correct species-specific chromosome number, preventing it from doubling with each generation.

In simple words: Offspring don't have 46 pairs because eggs and sperm only carry half the number of chromosomes (23 each) after a special cell division. When an egg and sperm join, they combine to make 23 pairs, so the total stays at 46 chromosomes.

Exam Tip: Emphasize the role of meiosis in halving the chromosome number in gametes (sperm and egg) to ensure the correct number is restored during fertilization.

 

Question 3. Study the given figure and say what information it gives you.
Answer: The figure shows the process of sex determination in human beings. It illustrates that females contribute an X chromosome through their eggs, while males can contribute either an X or a Y chromosome through their sperm. The combination of these sex chromosomes from the parents determines the sex of the offspring. An XX combination results in a female child, and an XY combination results in a male child. This highlights that the male parent's sperm is the deciding factor for the child's sex.
In simple words: The figure explains how a baby's sex is decided. Females give an X, males give either an X or a Y. If it's XX, it's a girl; if it's XY, it's a boy. So, the father's sperm decides.

Exam Tip: Explain the key components of the diagram: parental sex chromosomes, gamete formation, and the resulting offspring's sex based on chromosome combination.

 

Question. Variations in a population – inherited and otherwise.
Answer: This question is an instruction for you to observe and apply concepts about variation in populations. It asks you to consider how traits are passed down (inherited) versus how they are developed during an organism's lifetime (otherwise, or acquired). You should analyze how diverse characteristics appear within a group of organisms, noting which ones are genetic and which are influenced by the environment or individual experiences. The visual representation accompanying this question likely depicts different individuals within a population showing various traits, prompting you to identify and categorize these differences based on their origin.
In simple words: This question tells you to think about how living things in a group are different. Some differences come from their parents (inherited), and some happen during their life (acquired). You need to look at the picture and think about these two types of variations.

Exam Tip: When analyzing diagrams about variation, distinguish between inherited traits (passed genetically) and acquired traits (developed during life) and understand their implications for population diversity.

 

Question 4. Dead remains of two species A and B were buried. Later only A's body was found to be a fossil but not B's given reason.
Answer: Species A's body was likely found as a fossil because it possessed hard tissues, such as bones or shells, which are more resistant to decomposition and better preserved over long periods. In contrast, species B's body probably lacked these hard tissues. Organisms composed mainly of soft tissues decompose quickly, making fossilization a rare occurrence for them, as their remains do not last long enough to undergo the mineralization process required for fossil formation.
In simple words: Species A became a fossil because it had hard parts like bones, which don't rot easily. Species B didn't become a fossil because it mostly had soft body parts that quickly broke down.

Exam Tip: Explain that the presence of hard body parts (bones, shells) significantly increases the likelihood of fossilization, as soft tissues decay too rapidly.

 

Question 5. Species A shares ten characteristics with species B, species C share fifteen characteristics with D which of the two pairs share closer relation.
Answer: The pair that shares closer relation is species C and D. This is because they share a greater number of common characteristics (fifteen) compared to species A and B, which share only ten. A higher number of shared traits generally indicates a more recent common ancestor and thus a closer evolutionary relationship between the species.
In simple words: Species C and D are more closely related because they share 15 features, which is more than the 10 features shared by species A and B. More shared features usually means they are closer relatives.

Exam Tip: Remember that a greater number of shared characteristics between species suggests a closer evolutionary relationship and a more recent common ancestor.

 

Question 6. After the death of two insects, one of the insect was hurried in hot mud and the other in usually found mud. Which of the two is more likely to be preserved better and why?
Answer: The insect buried in hot mud is more likely to be preserved better. This is because hot mud can quickly dehydrate and seal the organism, creating an anaerobic (oxygen-free) environment that slows down or prevents decomposition by bacteria and fungi. In such conditions, the body's impression or even some organic material can be preserved for a longer time, increasing the chances of fossilization. In contrast, "usually found mud" might allow for faster decomposition due to the presence of oxygen and decomposers.
In simple words: The insect in hot mud will be preserved better. Hot mud stops it from rotting quickly because it seals it off from air and germs, making it more likely to become a fossil.

Exam Tip: Focus on the conditions that inhibit decomposition (anaerobic environment, rapid burial) as key factors for better preservation and fossilization.

 

Question 7. Green and red coloured seeds are recessive and dominant trait respectively. Out of F1 and F2, in which generation will the green seed appear, if both parents are not hybrid.
Answer: If green seeds are a recessive trait and red seeds are a dominant trait, and both parents are not hybrid (meaning they are purebred), then the green seed will appear in the F2 generation.
Here’s why:
Let R be the dominant allele for red seeds and r be the recessive allele for green seeds.
Parental Generation (P):
Purebred Red (RR) \( \times \) Purebred Green (rr)
Gametes: R from one parent, r from the other.
F1 Generation:
All offspring will be Rr (heterozygous). Since red (R) is dominant, all F1 seeds will be red in color. The green trait (r) is present but masked.
F2 Generation:
When F1 generation plants (Rr) are self-pollinated or crossed with another F1 plant (Rr \( \times \) Rr), the F2 generation will produce a phenotypic ratio of 3 Red : 1 Green. The genotypes will be 1 RR : 2 Rr : 1 rr.
The 'rr' genotype represents green seeds, which will appear in the F2 generation.
In simple words: If green is recessive and red is dominant, and the first parents are purebred (not mixed), then green seeds will only show up in the F2 generation. All the F1 generation seeds will be red, but they carry the green gene.

Exam Tip: Remember that recessive traits, when starting with purebred parents, will only reappear in the F2 generation at a specific ratio (typically 1 out of 4) due to the segregation of alleles.

 

Question 8. With the help of an example explain how “Genes control characteristics or traits"?
Answer: Genes control characteristics or traits by providing instructions for making proteins, which then influence an organism's features. For example, consider the tallness of a plant. Plant height is a characteristic that depends on the amount of a specific hormone secreted, which promotes growth. A gene carries the code for producing this hormone. If this gene has an alteration (a mutation) that makes the hormone less efficient or reduces its production, then the plant will be short, even if it has the potential for tallness. This clear link demonstrates that the specific genetic information (the gene) directly controls the production of substances (hormones) that, in turn, determine an observable trait (tallness or shortness).
In simple words: Genes control traits by telling the body how to make things like hormones. For example, a gene makes a hormone that controls plant height. If the gene is faulty, the plant makes less hormone and stays short, showing how genes directly manage features.

Exam Tip: Use a clear example (like plant height and hormones) to illustrate how genes provide the instructions for protein synthesis, which ultimately determines an observable trait.