Samacheer Kalvi Class 10 Science Solutions Chapter 19 Origin and Evolution of Life

I. Choose the Correct Answer.

Question 1. Biogenetic law states that:
(a) Ontogeny and phylogeny go together
(b) Ontogeny recapitulates phylogeny
(c) Phylogeny recapitulates ontogeny
(d) There is no relationship between phylogeny and ontogeny
Answer: (b) Ontogeny recapitulates phylogeny
In simple words: The biogenetic law means that how an animal grows from an embryo shows its evolutionary history.

🎯 Exam Tip: Remember that 'ontogeny recapitulates phylogeny' is the key phrase for Biogenetic law, meaning individual development mirrors evolutionary history.

Question 2. The 'use and disuse theory' was proposed by:
(a) Charles Darwin
(b) Ernst Haeckel
(c) Jean Baptiste Lamarck
(d) Gregor Mendel
Answer: (c) Jean Baptiste Lamarck
In simple words: Lamarck came up with the idea that if animals use a body part a lot, it gets stronger, and if they don't, it gets weaker. These changes could then be passed to their children.

🎯 Exam Tip: Lamarckism is specifically associated with the 'use and disuse' concept and the inheritance of acquired characteristics.

Question 3. Paleontologists deal with:
(a) Embryological evidences
(b) Fossil evidences
(c) Vestigial organ evidences
(d) All of the options
Answer: (b) Fossil evidences
In simple words: Paleontologists study old bones and prints in rocks, which are called fossils, to learn about animals and plants from a long, long time ago.

🎯 Exam Tip: Remember that 'paleontology' comes from 'paleo' (ancient) and 'ontos' (being), specifically focusing on life through fossil records.

Question 4. The best way of direct dating fossils of recent origin is by:
(a) Radio-carbon method
(b) Uranium lead method
(c) Potassium-argon method
(d) Both (a) and (c)
Answer: (a) Radio-carbon method
In simple words: To find out how old recent fossils are, the best way is to use a special method called radio-carbon dating.

🎯 Exam Tip: Radiocarbon dating is effective for fossils up to about 50,000 to 60,000 years old, while other methods like uranium-lead or potassium-argon are for much older samples.

Question 5. The term Ethnobotany was coined by:
(a) Khorana
(b) J.W. Harshberger
(c) Ronald Ross
(d) Hugo de Vries
Answer: (b) J.W. Harshberger
In simple words: J.W. Harshberger was the first person to use the word Ethnobotany, which means studying how different groups of people use plants.

🎯 Exam Tip: Ethnobotany is a blend of anthropology and botany, focusing on the cultural uses of plants by indigenous people.

II. Fill in the Blanks.

Question 1. The characters developed by the animals during their life time, in response to the environmental changes are called ............
Answer: acquired characters
In simple words: When animals get new traits during their life because of their surroundings, these are called acquired characters.

🎯 Exam Tip: Acquired characters, like a scar or strong muscles from exercise, are not inherited by offspring.

Question 2. The degenerated and non-functional organs found in an organism are called ....................
Answer: vestigial organs
In simple words: Body parts that used to work in older animals but no longer have a use in new animals are called vestigial organs.

🎯 Exam Tip: Examples of vestigial organs in humans include the appendix and wisdom teeth, showing evolutionary remnants.

Question 3. The forelimb of bat and human are examples of ................ organs.
Answer: homologous
In simple words: Bat wings and human arms are homologous organs because they have a similar basic design, meaning they came from a shared ancestor, even if they do different jobs now.

🎯 Exam Tip: Homologous structures indicate divergent evolution from a common ancestor, showcasing shared ancestry despite functional differences.

Question 4. The theory of natural selection for evolution was proposed by ............
Answer: Charles Darwin
In simple words: Charles Darwin proposed the theory of natural selection, which explains how animals and plants change over many years to better fit their environment.

🎯 Exam Tip: Natural selection is often summarized as 'survival of the fittest,' where organisms best adapted to their environment are more likely to survive and reproduce.

III. State True Or False. Correct The False Statements.

Question 1. The use and disuse theory of organs' was postulated by Charles Darwin.
Answer: False – The use and disuse theory of organs' was postulated by Jean Baptiste Lamarck. Lamarck believed that traits acquired during an organism's life could be passed on.
In simple words: This is false. Jean Baptiste Lamarck came up with the idea of 'use and disuse', not Charles Darwin.

🎯 Exam Tip: Distinguish between Lamarck's acquired characteristics and Darwin's natural selection; they are foundational but distinct evolutionary theories.

Question 2. The homologous organs look similar and perform similar functions but they have different origin and developmental pattern.
Answer: False – The analogous organs look similar and perform similar functions but they have different origin and developmental pattern. Homologous organs share a common origin.
In simple words: This is false. Analogous organs are the ones that look and work alike but come from different starting points, while homologous organs come from the same starting point.

🎯 Exam Tip: Homologous structures share common ancestry (e.g., human arm, bat wing), while analogous structures have similar function but different origins (e.g., bird wing, insect wing).

Question 3. Birds have evolved from reptiles.
Answer: True. Scientific evidence supports the idea that birds evolved from a group of feathered dinosaurs, which are a type of reptile. This shows a clear evolutionary link.
In simple words: This is true. Birds came from reptiles a very long time ago.

🎯 Exam Tip: Archaeopteryx is a classic example of a transitional fossil, displaying both reptilian (teeth, bony tail) and avian (feathers, wings) features.

IV. Match the Following.

Answer:
A. (iii)
B. (i)
C. (iv)
D. (ii)
E. (vi)
F. (v)
This matching exercise connects evolutionary concepts and examples with their correct descriptions. Atavism refers to the reappearance of ancestral traits, vestigial organs are non-functional remnants, analogous organs have similar functions but different origins, and homologous organs share a common structure from a common ancestor. Wood park refers to Thiruvakkarai, known for its petrified wood, and W.F. Libby is famous for developing radiocarbon dating.
In simple words: We match terms about how living things change over time with their right meanings or examples. For instance, atavism means old traits coming back, and vestigial organs are body parts that no longer work fully.

🎯 Exam Tip: Understand the core definitions of evolutionary terms like atavism, homologous, and analogous to correctly match them with their examples.

II. Fill in the Blanks.

Question 1. Branch of biology which deals with fossils is ....................
Answer: Palaeontology
In simple words: Palaeontology is the part of biology that studies old fossils.

🎯 Exam Tip: Palaeontology is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene Epoch, through the study of fossils.

Question 2. Archaeopteryx is connecting link between reptiles and ....................
Answer: Birds
In simple words: Archaeopteryx links reptiles and birds, showing how birds might have evolved from reptiles.

🎯 Exam Tip: Archaeopteryx is a classic example of a transitional fossil, showing a blend of features from two different groups.

Question 3. Darwin explained origin of species through ....................
Answer: Natural selection
In simple words: Darwin explained how new kinds of animals and plants came to be through a process called natural selection.

🎯 Exam Tip: Darwin's theory of natural selection highlights variation, inheritance, high population growth, and differential survival and reproduction.

Question 4. The ship on which Darwin worked as naturalist was ....................
Answer: H.M.S. Beagle
In simple words: Darwin worked as a scientist on a ship named H.M.S. Beagle.

🎯 Exam Tip: The voyage of the H.M.S. Beagle, particularly the stop at the Galapagos Islands, greatly influenced Darwin's observations on species variation.

Question 5. The book Origin of Species was published in the year ....................
Answer: 1859
In simple words: Darwin's famous book, 'Origin of Species', came out in the year 1859.

🎯 Exam Tip: Darwin's 'Origin of Species' is a landmark in scientific literature, laying the foundation for modern evolutionary biology.

Question 6. Mutation can be artificially induced by ....................
Answer: Radiation
In simple words: We can make mutations happen on purpose using radiation, like X-rays.

🎯 Exam Tip: Mutagens like radiation or certain chemicals can induce mutations, which are the ultimate source of genetic variation.

Question 7. Extraterrestrial states that units of life called ....................
Answer: Panspermia (spores)
In simple words: The idea of Panspermia says that small living things, like spores, came to Earth from space.

🎯 Exam Tip: Panspermia is a hypothesis suggesting that microscopic life forms or their precursors can survive the vacuum of space and seed new planets.

Question 8. The idea of chemical evolution of life was developed by ....................
Answer: Oparin and Haldane
In simple words: Oparin and Haldane came up with the idea that life started from simple chemicals on the early Earth.

🎯 Exam Tip: The Oparin-Haldane hypothesis suggests a primordial soup where organic compounds formed and then self-assembled into early life forms.

Question 9. Living being able to reproduce more individuals and form the own progeny is called ....................
Answer: Over production
In simple words: When living things make many babies, more than can actually live, it's called overproduction.

🎯 Exam Tip: Overproduction is a fundamental concept in Darwin's theory, driving the competition for resources and survival.

Question 10. .................... is the raw material which plays an important role in evolution.
Answer: Variation
In simple words: Differences between living things, called variation, are very important for evolution to happen.

🎯 Exam Tip: Genetic variation is crucial for evolution, allowing populations to adapt to changing environments through natural selection.

III. Match the Following.

Answer:
A. (ii)
B. (iv)
C. (i)
D. (v)
E. (iii)
This matching activity connects important concepts and figures in evolutionary biology. The Biogenetic law is related to the recapitulation theory. Archaeopteryx is recognized as a fossil bird, linking reptiles and birds. The 'Use and Disuse theory' is attributed to Lamarckism. H.M.S. Beagle is the ship on which Darwin made his famous voyage, contributing to his evolutionary theories. Ethnobotany involves traditional knowledge about plants.
In simple words: We match important ideas and names in evolution. For example, the Biogenetic law is about how development repeats evolution, and Archaeopteryx is an old bird fossil.

🎯 Exam Tip: Ensure you know the key scientists and their associated theories (e.g., Lamarck and use/disuse, Darwin and Beagle) and central concepts (Biogenetic law, Ethnobotany).

IV. State Whether True Or False. If False Write The Correct Statement.

Question 1. De Vries is called as the Father of Palaeontology.
Answer: False – Leonardo da Vinci is called as the Father of Palaeontology. Leonardo da Vinci is widely recognized as the Father of Palaeontology for his early observations and interpretations of fossils. De Vries is known for his work on mutation theory.
In simple words: This is false. Leonardo da Vinci is known as the Father of Palaeontology, not De Vries.

🎯 Exam Tip: Leonardo da Vinci made early significant contributions to palaeontology, while Hugo de Vries is noted for rediscovering Mendel's laws and introducing the concept of mutation.

V. Answer in a word or sentence.

Question 1. Who proposed the theory of Natural selection?
Answer: Charles Darwin came up with the idea of Natural Selection. Natural selection is a key concept that explains how living things change over time to fit their environment better.
In simple words: The theory of Natural Selection was introduced by Charles Darwin.

🎯 Exam Tip: Remember Charles Darwin as the central figure for the theory of natural selection and evolution.

Question 2. What do you understand by evolution?
Answer: Evolution is the process where new types of living things come into being. This happens because of small changes in their features across many generations, often in response to natural selection. It shows how life on Earth has changed and adapted over millions of years.
In simple words: Evolution means new species form over many generations due to changes in traits, often driven by natural selection.

🎯 Exam Tip: Define evolution clearly by mentioning the formation of new species, changes in characters, and the role of natural selection over generations.

Question 3. How do embryological studies provide evidences for evolution?
Answer: Studies of embryos show that many different animals, from fish to mammals, look very similar in their first stages of growth. Their unique features only appear later. This similarity in early development suggests that all these animals might share a common ancestor. This idea, known as 'ontogeny recapitulates phylogeny', highlights developmental similarities that suggest common ancestry.
In simple words: Early embryos of different animals, like fish and humans, look alike. This sameness points to a shared origin in evolution.

🎯 Exam Tip: Focus on the similarity of early embryonic stages across diverse species as key evidence for shared ancestry in evolution.

Question 4. Mention three important features of fossils.
Answer: Fossils have several important features: 1. They help us group and classify different living things. 2. They are used to describe and compare the anatomy of ancient life forms. 3. They provide clues about the evolutionary history and relationships of organisms. By studying fossils, scientists can piece together the timeline of life on Earth and see how species have transformed.
In simple words: Fossils help us classify past life, compare their body parts, and understand how they changed over time.

🎯 Exam Tip: List specific ways fossils contribute to our understanding of biology, such as classification, comparative anatomy, and tracing evolutionary paths.

Question 5. Who is the Father of Indian Paleobotany? What is his contribution in this field.
Answer: Birbal Sahani is known as the Father of Indian Paleobotany. He made important contributions by researching two main areas: 1. He studied the internal structures and shapes of ancient ferns from the Paleozoic era. 2. He also researched the fossil plants found in the Gondwana rock formations in India. His work greatly advanced our understanding of prehistoric plant life in the Indian subcontinent.
In simple words: Birbal Sahani is the Father of Indian Paleobotany. He studied ancient ferns and fossil plants from India.

🎯 Exam Tip: Remember Birbal Sahani's name and his two key areas of research: paleozoic ferns and Gondwana plant fossils.

Question 6. List out the methods of Fossilization.
Answer: The common ways fossils are formed include: 1. Petrifaction: Where minerals replace the original organic material. 2. Molds and casts: Impressions left by the organism. 3. Carbonization: Where only a carbon film remains. 4. Preservation: When whole organisms are kept intact. 5. Compression: When organisms are flattened by pressure. 6. Infiltration: Where minerals fill in empty spaces. Each method leaves a distinct type of fossil, offering different levels of detail about ancient life.
In simple words: Fossils form through petrifaction, molds, casts, carbonization, preservation, compression, and infiltration, which are different ways organic material turns into rock.

🎯 Exam Tip: Briefly explain each method of fossilization, focusing on how the organism's remains are preserved.

Question 7. What are extremophiles?
Answer: Extremophiles are living things that can survive and thrive in very harsh conditions on Earth. These conditions can include extremely hot, cold, acidic, or salty environments. Their ability to adapt to such harsh conditions makes them subjects of interest in the search for extraterrestrial life.
In simple words: Extremophiles are organisms that live in extreme places, like very hot or very cold environments.

🎯 Exam Tip: Define extremophiles by their ability to live in extreme environments, providing a few examples of such conditions.

Question 8. What is Goldilock zone for life. Name the planet in the Goldilock zone.
Answer: The Goldilocks Zone is an area around a star where a planet can have the right temperature for liquid water to exist on its surface. This is because the planet is not too close (too hot) or too far (too cold) from its star, and it has enough mass to hold an atmosphere. In our solar system, Earth is the only planet located in the Goldilocks Zone. This zone is crucial for life as we know it, as liquid water is essential for all known biological processes.
In simple words: The Goldilocks Zone is the perfect distance from a star for a planet to have liquid water. Earth is the only planet in our solar system that is in this zone.

🎯 Exam Tip: Explain the Goldilocks Zone as the habitable zone around a star and identify Earth as the only planet in our solar system within this zone.

Question 9. What are the three types of struggle for existence?
Answer: The three main kinds of struggle for existence are: 1. Intraspecific struggle: Competition between individuals of the same species. 2. Interspecific struggle: Competition between individuals of different species. 3. Environmental struggle: Dealing with harsh environmental conditions like extreme weather or lack of resources. These struggles drive natural selection, where only the fittest survive and pass on their genes.
In simple words: Living things struggle against others of their own kind (intraspecific), against other species (interspecific), and against the environment itself.

🎯 Exam Tip: Clearly define and differentiate between intraspecific, interspecific, and environmental struggles for existence.

Question 10. What is Atavism?
Answer: Atavism is when an ancient trait, which was present in distant ancestors but has disappeared through evolution, reappears in an individual. An example of this is the presence of a small, undeveloped tail in some newborn babies. These occurrences are rare and often provide interesting insights into a species' evolutionary past.
In simple words: Atavism means an old trait from an ancestor shows up again in a modern animal or human. Like a small tail on a baby.

🎯 Exam Tip: Define atavism as the reappearance of an ancestral trait and provide a clear example like the rudimentary tail in human babies.

VI. Short Answers Questions

Question 1. Distinguish between acquired and inherited trait with example.
Answer:

🎯 Exam Tip: Clearly state the definition and provide distinct examples for both acquired and inherited traits to score full marks.

Question 2. What are the aspects of ethnobotany?
Answer: Ethnobotany covers many important aspects: it helps with understanding nutrition, traditional health care, and life support systems. It also includes cultural beliefs about plants, supports small-scale industries, helps economic growth, protects diverse plant life, and promotes using plant resources in a way that can continue for a long time. This field bridges cultural studies with scientific understanding of plant uses, highlighting the deep connection between humans and the plant world.
In simple words: Ethnobotany looks at how people use plants for food, medicine, income, and cultural reasons, and how to protect them for the future.

🎯 Exam Tip: When explaining ethnobotany, cover its scope including health, economy, culture, and environmental conservation.

Question 3. What is the Geological Time Scale?
Answer: The Geological Time Scale is a system used to organize Earth's history into different time periods. It connects layers of rocks (geological strata) to specific dates and helps scientists like geologists and paleontologists understand when events happened and how they are related over Earth's long past. It is a fundamental tool for understanding the evolution of life and the planet itself.
In simple words: The Geological Time Scale is a calendar for Earth's history. It uses rock layers to show when different events happened over millions of years.

🎯 Exam Tip: Define the Geological Time Scale as a chronological dating system that correlates rock strata with time to describe Earth's history.

Question 4. Write a note on types of Germinal Variation.
Answer: Germinal variations are differences in traits that originate from changes in the genetic material (germ cells) and can be inherited. They are mainly divided into two types: 1. **Continuous variation:** These are small, gradual differences seen among individuals within a population. They are also called fluctuating variations and build up slowly over time. Examples include skin color, height, weight, and eye color in humans. 2. **Discontinuous variation:** These are sudden and distinct changes in an organism, often caused by mutations. They do not have intermediate forms. While sometimes leading to significant changes, such large variations might not always be helpful for evolution, such as the short legs in Ancon sheep or having extra fingers in humans. Both types of variation are essential for evolution, providing the raw material for natural selection to act upon.
In simple words: Germinal variations are inherited differences. Continuous variations are small, gradual changes (like height). Discontinuous variations are big, sudden changes (like extra fingers).

🎯 Exam Tip: Differentiate clearly between continuous and discontinuous variations, giving examples for each type.

Question 5. Explain the existence for astro biology.
Answer: Astrobiology explores the possibility of life beyond Earth. According to the theory, a planet can support life if it meets two crucial conditions: 1. It must have enough mass to hold onto an atmosphere, which protects life and maintains a stable environment. 2. It needs to orbit its star at a distance that is not too hot and not too cold, allowing liquid water to exist on its surface. This ideal zone is often called the Goldilocks Zone. These criteria help scientists focus their search for exoplanets that might harbor life.
In simple words: For life to exist on another planet, it needs enough mass for an atmosphere and must be in the 'Goldilocks Zone' where liquid water can exist.

🎯 Exam Tip: Highlight the two main criteria for a planet to potentially support life: sufficient mass for an atmosphere and being within the Goldilocks Zone for liquid water.

VII. Long Answer Questions.

Question 1. Explain the various methods of Fossilization.
Answer: Fossilization is the process by which the remains or traces of ancient organisms are preserved in rock. Several methods contribute to this process: 1. **Petrifaction:** In this method, minerals like silica slowly soak into and replace the original organic tissues, forming a rock-like fossil. Hard and soft parts, especially bones and wood, can become petrified. 2. **Mold and Cast:** When an organism is buried in soft sediment, its body dissolves over time, leaving a hollow space called a mold. If minerals then fill this mold, it creates a cast, which is a replica of the organism's original shape but without internal structure. 3. **Preservation:** Sometimes, original remains are kept intact, for example, in ice or tree sap (amber). These methods protect the organisms from decay, preserving the entire plant or animal. 4. **Compression:** This happens when an organism dies, and its hard parts settle at the bottom of a water body. Over time, layers of sediment cover it, and the pressure flattens the organism, forming a fossil. 5. **Infiltration or Replacement:** This process involves minerals precipitating and filling the cell walls of an organism. Elements such as silica, calcium carbonate, and magnesium carbonate dissolve the original hard parts and replace them with new minerals. These diverse methods allow scientists to study various aspects of ancient life, from detailed cellular structures to overall body shapes.
In simple words: Fossilization happens in different ways, like petrifaction (minerals replacing parts), molds and casts (imprints), preservation (whole body saved), compression (flattened by layers), and infiltration (minerals filling cells).

🎯 Exam Tip: Describe each fossilization method accurately, noting the type of preservation and the resulting fossil's characteristics.

Question 2. Explain the principles of Lamarckism.
Answer: Lamarckism, proposed by Jean-Baptiste Lamarck, suggests that organisms change over time based on certain principles: 1. **Internal Vital Force:** Lamarck believed that all living things and their body parts naturally tend to increase in size continuously throughout their lives. This growth comes from an inner drive within the organisms. 2. **Influence of Environment and New Needs:** When an organism's environment changes, it creates new needs for the organism. In response to these new needs, the organism develops specific adaptive traits or new body parts to better suit its changing surroundings. 3. **Use and Disuse Theory:** This principle states that if an organ or body part is used often, it becomes stronger and more developed. Conversely, if an organ is not used for a long time, it becomes weaker and eventually degenerates or shrinks. The example of the long neck of a giraffe, which Lamarck believed grew longer from continuous stretching, illustrates this point. 4. **Inheritance of Acquired Characters:** Lamarck thought that the characteristics an organism develops or changes during its lifetime (acquired characters) could be passed on to its offspring. This means that if a parent developed a certain trait, their children would inherit that improved trait. Although largely disproven by modern genetics, Lamarck's ideas were among the first to propose a mechanism for evolution.
In simple words: Lamarckism says living things grow, change based on their environment, develop parts they use a lot (and lose parts they don't), and pass these new traits to their children.

🎯 Exam Tip: List and briefly explain each of Lamarck's four principles: internal vital force, environmental influence, use and disuse, and inheritance of acquired characters.

VIII. Higher Order Thinking Skills (HOTS).

Question 1. What is the relationship between mutation and variation?
Answer: Mutation and variation are closely linked processes crucial for evolution. A **mutation** is a sudden, random change in an organism's DNA, often caused by errors during DNA copying or by harmful factors like UV rays or chemicals. These mutations then lead to **variation**, which means differences in traits among individuals within a population. So, mutations are the raw source of new variations, which then can be acted upon by natural selection. Without mutations creating new variations, evolution would not be possible as there would be no new traits for natural selection to favor or eliminate.
In simple words: Mutations are changes in DNA. These changes cause variations, which are the differences we see in living things. So, mutations create variations.

🎯 Exam Tip: Explain that mutations introduce new genetic material, which in turn generates phenotypic variations that are critical for evolution.

Question 2. (i) Name the phenomenon responsible for the structure marked (a) in the Figure.
Answer: The phenomenon responsible for the structure marked as (a) in the figure (which represents a rudimentary tail) is Atavism. This appearance of an ancestral trait is a rare but fascinating biological event.
In simple words: The structure (a) is an example of Atavism.

🎯 Exam Tip: Identify the reappearance of an ancestral trait as atavism when analyzing diagrams showing such features.

Question 2. (ii) Give the definition of the phenomenon responsible for the development for the structure marked.
Answer: The phenomenon is Atavism, which is the reappearance of an ancestral trait in an individual, a trait that was present in distant ancestors but had disappeared through evolutionary processes. Such genetic throwbacks provide strong evidence for the evolutionary history of species.
In simple words: Atavism is when an old trait from an ancestor shows up again in a modern animal or human.

🎯 Exam Tip: Define atavism as the re-emergence of an ancestral characteristic that was absent in intermediate generations.