GSEB Class 12 Biology Solutions Chapter 7 Evolution

Gujarat Board Textbook Solutions Class 12 Chapter 7 Evolution

GSEB Class 12 Biology Evolution Text Book Questions and Answers

Question 1. Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
Answer: Darwin's theory suggests that the overuse of antibiotics or drugs has led to the rapid selection of resistant variants. These resistant organisms or cells emerge within a timeframe of months or years, rather than centuries. This phenomenon illustrates evolution driven by human activities (anthropogenic action), rather than purely natural processes.
In simple words: When antibiotics are used too much, bacteria quickly evolve to become resistant, showing human actions can speed up evolution.

🎯 Exam Tip: Understanding antibiotic resistance in the context of Darwinian selection is crucial for explaining rapid evolutionary changes and the impact of human activity.

Question 2. Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
Answer:
(i) A fossil of a small terrestrial dinosaur was discovered, notable for having feathers covering its limbs and body (e.g., *Archaeopteryx lithographica*).
(ii) The *Mesohippus*, an ancient horse intermediate in size to a goat, featured three toes on each foot and molar teeth with serrations.
In simple words: Recent findings include feathered dinosaurs and early horses with unique features, providing insights into evolutionary pathways.

🎯 Exam Tip: Fossil discoveries provide direct evidence for evolution, illustrating transitional forms and the progression of life through geological time.

Question 3. Attempt giving a clear definition of the term species.
Answer: According to Dobzhansky, species generally comprise Mendelian populations that share a common gene pool. Mayr defined species as groups of natural populations that are actually or potentially capable of interbreeding and are reproductively isolated from other such groups.
In simple words: A species is typically defined as a group of organisms that can naturally breed with each other to produce fertile offspring, and they are distinct from other such groups.

🎯 Exam Tip: Knowing the biological species concept by Mayr is fundamental for understanding taxonomy and evolutionary isolation.

Question 4. Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
Answer: Students are encouraged to browse the internet to trace the various components of human evolution.
In simple words: Researching online can help trace how humans evolved, focusing on changes in brain, bones, and diet.

🎯 Exam Tip: Active research and critical thinking are essential for exploring complex topics like human evolution, which involve multiple interconnected factors.

Question 5. Find out through internet and popular science articles whether animals other than man has self-consciousness.
Answer: Students are advised to browse the internet to discover if animals other than humans exhibit self-consciousness.
In simple words: Look online to find out if animals other than humans show signs of self-awareness.

🎯 Exam Tip: Understanding consciousness in animals is a frontier in biology and psychology, requiring a multidisciplinary approach.

Question 6. List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.
Answer: Students should utilize internet resources to identify 10 modern animals and their corresponding ancient fossil records, naming both.
In simple words: Use the internet to find 10 living animals and the names of their ancient fossil relatives.

🎯 Exam Tip: Connecting modern species to their fossil ancestors is a powerful way to demonstrate evolutionary lineage and change over time.

Question 7. Practise drawing various animals and plants.
Answer: This task is not necessary for theoretical evaluation but serves as a practical exercise.
In simple words: Drawing animals and plants helps with visual understanding, but isn't required for grading.

🎯 Exam Tip: While not directly graded, sketching biological forms enhances observational skills and understanding of anatomical structures, which can aid in conceptual recall.

Question 8. Describe one example of adaptive radiation.
Answer: Adaptive radiation involves the formation of diverse new species from a common ancestor, with each species adapting to different geological niches. A classic example is Darwin's finches found on the Galapagos Islands, which originated from mainland finches. These birds diversified, evolving distinct beak shapes and sizes, dietary preferences, and feather patterns to suit various ecological roles.
In simple words: Adaptive radiation is when one ancestral species evolves into many different species, each specialized for a unique environment, like Darwin's finches evolving different beaks for different foods.

🎯 Exam Tip: Darwin's finches are a hallmark example; clearly outlining the ancestral origin, diverse adaptations, and geographical context will earn full marks.

Question 9. Can we call human evolution adaptive radiation?
Answer: No, human evolution is distinct and not classified as adaptive radiation, as it follows a different evolutionary pattern compared to the diversification seen in other animal groups.
In simple words: Human evolution is unique and doesn't fit the pattern of adaptive radiation seen in many other species.

🎯 Exam Tip: Differentiate between adaptive radiation and other evolutionary patterns; human evolution involves complex factors beyond simple niche diversification.

Question 10. Using various resources such as your school library or the internet and discussions with your teacher, trace the evolutionary stages of any animal, say horse.
Answer: Students should browse the internet, consult library resources, and discuss with their teachers to trace the evolutionary stages of an animal like the horse.
In simple words: Research online or in the library, and talk to your teacher, to learn about how animals like horses have evolved over time.

🎯 Exam Tip: Tracing evolutionary lineages, like that of the horse, demonstrates evidence of gradual change and adaptation, a key concept in evolution.

GSEB Class 12 Biology Evolution Additional Important Questions and Answers

Question 1. To support the Big Bang theory, an experiment was done in 2008.
a. Name the experiment.
b. Where is it done?
Answer:
(a) The experiment was named the Large Hadron Collider.
(b) It was conducted underground, spanning the border between Switzerland and France.
In simple words: The Large Hadron Collider experiment, done in 2008 at the Swiss-French border, aimed to provide evidence for the Big Bang theory.

🎯 Exam Tip: Accurately naming the experiment and its location is important for demonstrating knowledge of scientific milestones related to cosmic origins.

Question 2. What are fossils?
Answer: Fossils are the preserved remnants or traces of ancient organisms that existed in the geological past. They serve as crucial evidence for tracing biological evolution.
In simple words: Fossils are the remains or traces of old living things found in rocks, showing us how life changed over time.

🎯 Exam Tip: A precise definition of fossils, emphasizing their role as evolutionary evidence, is key to a good answer.

Question 3. It is possible to make a living cell with the help of methane, ammonia, water, and hydrogen. Do you agree with this statement?
Answer: Yes, this statement is accurate. The Urey-Miller experiment in 1953 confirmed this possibility. The experiment yielded simple organic compounds, including amino acids like glycine, alanine, and aspartic acid, along with fatty acids and urea. Since amino acids are the fundamental building blocks of proteins and fatty acids form the basis of lipids, it is indeed feasible to construct a basic living cell from these elements.
In simple words: Yes, it's possible. The Urey-Miller experiment showed that basic chemicals like methane and ammonia can form amino acids and fatty acids, which are the main ingredients for creating life.

🎯 Exam Tip: Recalling the Urey-Miller experiment and its products (amino acids, fatty acids) is vital for explaining the chemical origin of life on Earth.

Question 4. This is a type of adaptive radiation seen in one part of the world.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र मार्सुपियल स्तनधारियों के अनुकूलन विकिरण को दर्शाता है, जिसमें एक साझा पूर्वज से विभिन्न मार्सुपियल जैसे तस्मानियाई भेड़िया, बाघ बिल्ली, मार्सुपियल तिल, वोम्बैट और मार्सुपियल चूहा कैसे विकसित हुए, यह दिखाया गया है। यह ऑस्ट्रेलिया में एक ही भौगोलिक क्षेत्र में हुए विकास को प्रदर्शित करता है जहाँ ये जीव विभिन्न पारिस्थितिक niches के अनुकूल हुए।

a. Identify the type of adaptive radiation. Where is it seen?
b. Give the difference between convergent evolution and divergent evolution.
Answer:
(a) This exemplifies marsupial radiation, which is observed in Australia.
(b) The distinctions between convergent and divergent evolution are:
Convergent evolution occurs when multiple adaptive radiations appear in different habitats or geographically isolated regions, leading to similar traits in unrelated species due to similar environmental pressures.
Divergent evolution, also known as adaptive radiation, is the process where different species evolve from a single common ancestor within a particular geographical area, spreading out and adapting to various habitats.
In simple words: The diagram shows marsupial radiation in Australia. Convergent evolution is when different species develop similar features independently due to similar environments, while divergent evolution (adaptive radiation) is when one species splits into many new species, each adapting to a different niche.

🎯 Exam Tip: Clearly distinguishing between convergent and divergent evolution, with relevant examples like marsupial radiation, is crucial for evolutionary biology questions.

Question 5. The above-shown pictures are of a type of bird seen on an island near South America.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र डार्विन की फिंच की चार प्रजातियों को दर्शाता है, जिनमें उनकी चोंच के विभिन्न आकार दिखाए गए हैं। ये पक्षी गैलापागोस द्वीपों पर पाए जाते हैं और विभिन्न खाद्य स्रोतों के अनुकूलन के कारण विकसित हुए हैं, जो अनुकूलन विकिरण का एक उत्कृष्ट उदाहरण प्रस्तुत करते हैं।

a. Identify the island.
b. What is the significance of these birds in evolution?
Answer:
(a) The islands are the Galapagos Islands, a chain of 14 islands located approximately 960 km off the west coast of South America in the Pacific Ocean.
(b) These birds are famously known as Darwin's finches, serving as a classic illustration of adaptive radiation, a concept significantly advanced by Charles Darwin.
In simple words: These birds are Darwin's finches from the Galapagos Islands, a perfect example of how one species can evolve into many to suit different environments, a key idea in evolution.

🎯 Exam Tip: Darwin's finches are central to understanding adaptive radiation and natural selection; remember their location and the specific evolutionary phenomenon they illustrate.

Question 6. The diagrammatic representation shows the operation of natural selection. Give suitable heading for these curves.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र प्राकृतिक चयन के तीन विभिन्न प्रकारों को दर्शाता है। (a) एक स्थिरकारी चयन (stabilizing selection) वक्र को प्रस्तुत करता है, जहाँ मध्यवर्ती लक्षण वाले व्यक्ति अनुकूल होते हैं। (b) दिशात्मक चयन (directional selection) को दर्शाता है, जहाँ एक चरम लक्षण को प्राथमिकता दी जाती है। (c) विखंडनात्मक चयन (disruptive selection) को दर्शाता है, जहाँ दोनों चरम लक्षण अनुकूल होते हैं, और मध्यवर्ती लक्षण कम होते जाते हैं।

Answer:
(a) Stabilizing curve
(b) Directional curve for character value
(c) Disruptive curve, where more individuals acquire peripheral character values at both ends of the distribution curve.
In simple words: The curves represent different ways natural selection acts: (a) stabilizing selection favoring the average, (b) directional selection favoring one extreme, and (c) disruptive selection favoring both extremes.

🎯 Exam Tip: Being able to identify and explain the three types of natural selection (stabilizing, directional, disruptive) from graphical representations is a common and important exam requirement.

Question 7. Give the names of
a. biggest reptile,
b. first mammal
c. first fossil of human evolution.
d. first fossil of horse evolution.
Answer:
(a) The biggest reptile was *Tyrannosaurus rex*.
(b) The first mammal was the Shrew.
(c) The first fossils linked to human evolution were *Dryopithecus* and *Ramapithecus*.
(d) The earliest fossil in horse evolution was *Eohippus*.
In simple words: The largest reptile was T. rex, the first mammal was the Shrew, early human ancestors were Dryopithecus and Ramapithecus, and Eohippus was the first horse.

🎯 Exam Tip: Remembering key examples for evolutionary firsts or superlatives helps reinforce understanding of major groups and their timelines.

Question 8. Correct the flowchart of vertebrae according to the geological period. Old to new.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र कशेरुकियों के विकासवादी क्रम का एक सही प्रवाह चार्ट प्रस्तुत करता है, जिसे सबसे पुराने से सबसे नए भूवैज्ञानिक कालक्रम के अनुसार व्यवस्थित किया गया है। यह दर्शाया गया है कि कैसे शुरुआती सरीसृपों से स्तनधारियों तक विभिन्न समूह क्रमिक रूप से विकसित हुए।

Answer: The correct evolutionary flowchart for vertebrates from old to new geological periods is:
Early reptiles
\( \implies \) Synapsids
\( \implies \) Pelycosaurs
\( \implies \) Thecodonts
\( \implies \) Therapsids
\( \implies \) Dinosaurs
\( \implies \) Mammals
In simple words: The correct order of vertebrate evolution, from oldest to newest, is Early reptiles, then Synapsids, Pelycosaurs, Thecodonts, Therapsids, Dinosaurs, and finally Mammals.

🎯 Exam Tip: Understanding the correct sequence of evolutionary lineages, especially for major animal groups, is fundamental to evolutionary biology. Pay attention to the transitions.

Question 9. Find out the odd one in each group.
a. Cat's paw, insect wings, horse foot, bat's wing, human hand.
b. Industrial melanism, mutation, genetic drift, gene migration.
c. Vermiform appendix, plica semilunaris, spleen, pelvic girdle of python, cervical fistula.
d. Coenozoic, mesozoic, palaeozoic, proterozoic, holozoic
e. Isolation, recombination, genetic drift, gene migration, natural selection, mutation, speciation.
Answer:
(a) The odd one out is insect wings (analogous structure), while others are homologous structures.
(b) The odd one out is Industrial melanism (an example of natural selection), while others are mechanisms causing genetic variation or change in gene frequency.
(c) The odd one out is spleen (a functional organ), while others are vestigial organs or embryonic remnants.
(d) The odd one out is Holozoic (a mode of nutrition), while others are geological eras.
(e) The odd one out is Isolation (a mechanism leading to speciation, but not a direct source of genetic variation or a process within selection itself in the same vein as the others), while others are direct factors affecting gene pools or evolutionary processes.
In simple words: In group (a), insect wings are different as they are analogous; in (b), industrial melanism is an outcome, not a cause; in (c), the spleen is a working organ, unlike vestigial ones; in (d), holozoic refers to feeding, not a geological era; and in (e), isolation is a condition for evolution, not a direct genetic change mechanism like the others.

🎯 Exam Tip: Distinguishing between homologous/analogous structures, causes/examples of evolution, functional/vestigial organs, and geological/biological terms is key for such categorization questions.

Question 10. Give reasons for the following.
a. Frog tadpole excretes ammonia, adult frog excretes urea.
b. The chemical composition of DNA in almost all animals is similar.
c. For energy production all animals depend upon glycolysis and Kreb's cycle.
e. Change in germ cells is heritable.
f. Genetic drift is also known as bottleneck phenomenon.
Answer:
(a) Ammonia excretion necessitates a significant amount of water, whereas urea excretion requires only a minimal quantity of water.
(b) The similarity in DNA composition across most animals indicates a common ancestry among them.
(c) All animals depend on glycolysis and the Krebs cycle for energy production due to their common ancestry, reflecting a conserved metabolic pathway.
(d) (Implicitly related to connecting links from the source text context) Certain animals, like *Archaeopteryx*, exhibit characteristics of both aves (birds) and reptiles, serving as crucial connecting links in evolution.
(e) Genetic information within germ cells is passed on to subsequent generations, making these changes heritable, unlike changes in somatic cells.
(f) Genetic drift can significantly reduce gene frequencies within a population, which is why it's also referred to as the bottleneck phenomenon.
In simple words: Tadpoles excrete ammonia because they live in water, while adult frogs excrete urea to save water. Similar DNA shows common ancestors. Glycolysis and Krebs cycle are universal for energy due to shared evolution. Germ cell changes are inherited, unlike somatic cell changes. Genetic drift is like a bottleneck because it drastically reduces genetic variety.

🎯 Exam Tip: Provide concise, direct reasons for each statement. For biology questions, relate explanations to fundamental principles like adaptation, common ancestry, and genetic mechanisms.

Question 11. Birds are glorified reptiles. Justify the statement.
Answer: This statement is justified by the features observed in *Archaeopteryx*, a fossil regarded as a connecting link between birds and reptiles. *Archaeopteryx* possessed a combination of traits:
(a) A beak similar to birds, yet teeth characteristic of reptiles.
(b) Wings like birds, but also clawed digits typical of reptiles.
(c) Feathers, akin to birds, alongside scales, which are reptilian features.
(d) A feathery tail resembling birds, but with tail vertebrae like reptiles.
These combined features support the evolutionary transition from reptiles to birds, hence the description "glorified reptiles."
In simple words: Birds are called "glorified reptiles" because fossils like *Archaeopteryx* show a mix of bird features (feathers, wings) and reptile features (teeth, claws), suggesting birds evolved from reptiles.

🎯 Exam Tip: When justifying evolutionary relationships, providing specific anatomical features of transitional fossils (like *Archaeopteryx*) that demonstrate characteristics of both ancestral and descendant groups is highly effective.

Question 12. Write the names of two dinosaurs that lived early in geological history and two that lived later.
Answer:
Early in geological history:
- *Brachiosaurus*
- *Stegosaurus*
Later in geological history:
- *Triceratops*
- *Tyrannosaurus*
In simple words: Early dinosaurs included Brachiosaurus and Stegosaurus, while later ones were Triceratops and Tyrannosaurus.

🎯 Exam Tip: Knowing examples of dinosaurs from different geological periods helps illustrate the vast timeline and diversity of life on Earth.

Question 13. *Archaeopteryx* is considered as a connecting link between birds and reptiles. Justify the statement by giving two characters of each group.
Answer: Fossils serve as evidence for connecting links between different groups of organisms. *Archaeopteryx* is a prime example, displaying characteristics of both reptiles and birds. Its reptilian features include a toothed beak, clawed digits on its wings, scales, and tail vertebrae. Its avian (bird-like) features include feathers (modified scales) and wings. These combined traits strongly suggest that birds evolved from reptiles. Werner discovered this fossil bird in 1861, and its features validate Huxley's assertion that birds are indeed "glorified reptiles."
In simple words: *Archaeopteryx* is a connecting link because it has reptile traits like teeth and tail bones, but also bird traits like feathers and wings, showing the evolutionary transition between the two groups.

🎯 Exam Tip: For connecting link questions, always list specific shared characteristics from both groups to demonstrate evolutionary relationships clearly.

Question 14. Name one organ analogous to the wings of a bird. Why are they both analogous. Can you include wings of the bat also with them under the same category? Give reason.
Answer: Insect wings are analogous to bird wings. They are considered analogous because both perform the same function of flight but possess dissimilar structures and evolutionary origins. Insect wings are modified outgrowths of the body, lacking internal bones, whereas bird wings are modified forelimbs, containing bones. Bat wings, however, cannot be categorized with insect wings and bird wings as analogous structures in this context. Bat wings and bird wings are homologous organs; both are modified forelimbs, despite having distinct bone structures adapted for flight.
In simple words: Insect wings are analogous to bird wings because they both fly but are built differently. Bat wings, however, are homologous to bird wings because both are modified forelimbs, showing a common skeletal origin, even if adapted differently for flight.

🎯 Exam Tip: Clearly define analogous (similar function, different origin) and homologous (similar origin, different function) structures, and use distinct examples for each to avoid confusion.

Question 15. Mention the role of cyanobacteria in origin of life.
Answer: Cyanobacteria are thought to be among the earliest life forms to evolve on Earth. They were aerobic phototrophs, meaning they could produce their own food using sunlight and released oxygen. Fossil evidence suggests that ancient cyanobacteria were structurally similar to modern forms, playing a pivotal role in oxygenating Earth's early atmosphere, which was critical for the evolution of aerobic life.
In simple words: Cyanobacteria were early life forms that used sunlight to make food and released oxygen, crucially changing Earth's atmosphere and paving the way for other oxygen-breathing life.

🎯 Exam Tip: Highlight cyanobacteria's photosynthetic capability and its role in producing oxygen, which was a game-changer for early Earth's atmosphere and subsequent evolution.

Question 16. The universe had an explosive beginning'. Which theory proposes this?
Answer: This concept is proposed by the Big Bang theory.
In simple words: The Big Bang theory states that the universe started with a huge explosion.

🎯 Exam Tip: Basic knowledge of cosmological theories, especially the Big Bang, is essential for understanding the grand scale of universal origins before biological evolution.

Question 17. There are many unusual organisms reported in Australia because of some special evolution. Mention the speciality of evolution that have occurred for the past 38 million years.
Answer: The unique evolution observed in Australia over the past 38 million years is primarily attributed to geographical isolation.
In simple words: Australia's many unique animals are due to its long period of being isolated from other continents, allowing its species to evolve separately.

🎯 Exam Tip: Geographical isolation is a powerful driver of speciation and unique evolutionary pathways, especially evident in continent-sized landmasses like Australia.

Question 18. Match the following related things from B and C with column A

🎯 Exam Tip: Accurately associating scientists with their theories and core ideas is essential for demonstrating foundational knowledge in evolutionary history.

Question 19. Match the following related things from B and C with Column A.

🎯 Exam Tip: Memorizing the key geological eras, their associated periods, and the dominant life forms during those times is crucial for understanding Earth's history of life.

Question 20. Identify the following figures.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र घोड़े के विकासवादी इतिहास के विभिन्न चरणों को दर्शाता है, जिसमें सबसे शुरुआती रूप (a) से आधुनिक घोड़े (d) तक के क्रमिक परिवर्तनों को प्रस्तुत किया गया है। यह पैरों, शरीर के आकार और दांतों में परिवर्तनों के माध्यम से अनुकूलन को उजागर करता है।

Answer: The figures illustrate the evolutionary stages of the horse, providing concrete evidence of evolution over geological time. Fossils are critical in this regard, and their significance includes:
(i) Fossils are the preserved remains of past life forms.
(ii) They facilitate the study of the structure, characteristics, and behavior of extinct animals.
(iii) They offer insights into the forms and structures of organisms that no longer exist.
(iv) They aid in understanding the phylogeny (evolutionary history) of various animals, such as horses, camels, and humans. For instance, horse evolution shows a progression from *Eohippus* (a dog-like animal from 54 million years ago), through *Mesohippus* (38 million years ago) and *Merychippus* (25 million years ago), leading to the modern *Equus*. All earlier forms are extinct.
(v) Fossils also reveal connecting links between different groups. For example, *Archaeopteryx* exhibits features of both reptiles (toothed beak, clawed digits, tail vertebrae) and birds (feathers, modified scales), confirming birds evolved from reptiles. This supports Huxley's statement that birds are "glorified reptiles."
(vi) By analyzing the distribution of fossils in different rock strata, scientists can infer the historical periods when various species formed or became extinct.
In simple words: The figures show horse evolution, highlighting how fossils prove life changed over time. Fossils are dead remains that help us study extinct animals' forms, trace evolutionary trees like the horse's lineage (Eohippus to modern Equus), and identify links between groups, like Archaeopteryx bridging reptiles and birds. They also help date when species appeared or disappeared.

🎯 Exam Tip: For questions involving diagrams of evolutionary series, not only identify the sequence but also discuss the broader significance of such fossil records in proving evolutionary theory.

Question 21. The population of grey coloured *Biston betularia*, were almost replaced by the black variety during the industrial revolution in England. Explain the mechanism involved.
Answer: The mechanism involved in the shift of *Biston betularia* population from grey to black during the Industrial Revolution is known as industrial melanism. This is a classic example of natural selection, where pollution darkened tree trunks, making the lighter moths more visible to predators, while the darker, melanic moths became camouflaged and thus survived and reproduced more effectively.
In simple words: The change from light to dark moths during the Industrial Revolution is called industrial melanism; darker moths survived better against sooty trees, a prime example of natural selection.

🎯 Exam Tip: Industrial melanism in peppered moths is a classic and frequently tested example of observable natural selection in action. Be able to explain the environmental change and selective pressure.

Question 22. Correct the following chart showing Darwinism.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र डार्विन के प्राकृतिक चयन सिद्धांत के सही प्रवाह चार्ट को दर्शाता है। यह अति-उत्पादन से शुरू होता है, जिसके कारण अस्तित्व के लिए संघर्ष होता है। इस संघर्ष से भिन्नताएँ उत्पन्न होती हैं, जो अनुकूल भिन्नताओं वाले व्यक्तियों को जीवित रहने और प्रजनन करने का अवसर देती हैं (योग्यतम की उत्तरजीविता)। अंततः, प्राकृतिक चयन के माध्यम से, नई प्रजातियों का उद्भव होता है, जबकि अनुपयुक्त व्यक्ति समाप्त हो जाते हैं।

Answer: The corrected flowchart depicting Darwinism is as follows:
Overproduction
\( \implies \) Struggle for existence
\( \implies \) Variations
\( \implies \) Survival of the fittest
\( \implies \) Favourable variation
\( \implies \) Origin of species
AND
\( \implies \) Unfavourable variations
\( \implies \) Perishes or eliminates
(Leading back to Natural selection encompassing both favorable and unfavorable outcomes).
In simple words: Darwinism starts with overproduction, leading to a struggle for existence where variations arise. Favorable variations lead to survival of the fittest and new species, while unfavorable ones are eliminated through natural selection.

🎯 Exam Tip: Accurately sequencing the components of Darwin's theory (overproduction, struggle, variation, natural selection, survival of fittest, origin of species) is fundamental for understanding evolutionary mechanisms.

Question 23. Aristotle believed that fishes originated from mud, insects from decaying meat, a frog from moist soil, etc. Do you agree with this statement? If no, give a reason.
Answer: No, this statement is incorrect. Louis Pasteur conclusively disproved the theory of spontaneous generation (abiogenesis), which Aristotle supported, through his renowned swan neck experiment. Pasteur demonstrated that life arises only from pre-existing life.
In simple words: No, Aristotle's idea that life spontaneously appears from non-living matter is wrong. Louis Pasteur's swan neck experiment proved that life only comes from existing life.

🎯 Exam Tip: Referencing Louis Pasteur's swan neck experiment is the definitive way to counter the theory of spontaneous generation in an exam setting.

Question 24. Give a detailed account of the theory of natural selection. Or Describe Darwin's opinion about the origin of new species of organisms.
Answer: Charles Darwin (1809-1882) elucidated the theory of evolution by natural selection in his seminal work, "Origin of Species." During a five-year voyage as a naturalist aboard the British warship 'Beagle,' Darwin explored the Galapagos Islands, collecting extensive evidence for evolution. He proposed natural selection as the primary mechanism for the origin of species. The key principles of Darwinism are:
1. **Over-production of offspring:** All living organisms have an inherent capacity to produce more offspring than can possibly survive in their environment.
2. **Struggle for existence:** Despite overproduction, population numbers remain relatively constant due to a continuous struggle for survival among individuals for resources like food, space, and mates, along with threats like disease.
3. **Survival of the fittest:** Individuals best adapted to their environment are more likely to survive and reproduce, passing on their advantageous traits. Fitness in this context refers to reproductive success.
4. **Variation:** Organisms within a population exhibit natural variations. In response to environmental pressures and the struggle for existence, these variations become crucial.
5. **Natural selection:** In the ongoing struggle for survival, individuals possessing favorable variations for their environment are more likely to thrive and pass on those traits. Conversely, individuals lacking beneficial variations are less likely to survive or reproduce.
6. **Origin of species:** Environmental changes drive natural selection, favoring well-adapted individuals. Through the inheritance of these favorable changes across successive generations, populations gradually transform, leading to the formation of new species.
In simple words: Darwin's theory of natural selection explains evolution through six points: living things overproduce, leading to a struggle for survival. Within this struggle, individuals with helpful variations are "fittest" and survive to reproduce, passing on those traits. Over time, this natural selection creates new species as populations adapt to their changing environments.

🎯 Exam Tip: Master Darwin's six core tenets of natural selection (over-production, struggle, variation, survival of fittest, natural selection, origin of species) as they are foundational to evolutionary theory and frequently tested.

Question 25. Is there any population in Kerala having sickle cell anaemia? What is the reason for this genetic defect? Does it help the people in preventing any other diseases like malaria?
Answer: Yes, certain populations, including those residing in high altitude areas (as per the provided text, though typically linked to malaria-prone regions), can have sickle cell anemia. This genetic defect is characterized by red blood cells (RBCs) that assume a sickle shape due to the presence of abnormal hemoglobin (Hb).
In simple words: Yes, some populations in Kerala can have sickle cell anemia, a genetic problem causing red blood cells to be sickle-shaped due to faulty hemoglobin.

🎯 Exam Tip: When discussing genetic disorders like sickle cell anemia, focus on the genetic basis (abnormal hemoglobin) and its effect on cells (sickle shape). Note: The connection to malaria resistance is a well-known aspect but was not provided in the original answer; only paraphrase what is given.

Question 26.
ℹ️ चित्र व्याख्या (Diagram Explanation): इस चित्र में दो प्रसिद्ध जीवविज्ञानी और विकासवादी सिद्धांतकार दिखाए गए हैं। बाईं ओर चित्र (A) जीन-बैप्टिस्ट लैमार्क का है, और दाईं ओर चित्र (B) चार्ल्स डार्विन का है, जिन्होंने विकास के अध्ययन में महत्वपूर्ण योगदान दिया।

a. Identify the personalities shown above.
b. Briefly give about their contributions to evolution.
Answer:
(a) Personality A is Jean-Baptiste Lamarck, and Personality B is Charles Darwin.
(b) Their contributions to evolution are:
Lamarck proposed Lamarckism, known as the theory of Inheritance of Acquired Characters, suggesting traits acquired during an organism's lifetime could be passed to offspring.
Darwin put forward Darwinism, or the theory of Natural Selection, which explains evolution through the survival and reproduction of individuals best adapted to their environment.
In simple words: A is Lamarck, known for his theory that acquired traits are inherited. B is Darwin, famous for his theory of natural selection, where beneficial traits help survival and reproduction.

🎯 Exam Tip: Accurately identifying key historical figures in evolution and concisely stating their primary contributions (e.g., Lamarckism vs. Darwinism) is a common exam question.

Question 27. The national geographic channel selected you to interview Lamarck, the famous evolutionist. Prepare some questions to be asked.
Answer: To conduct an interview with Lamarck, one could prepare questions about his personal life history, his theory of Lamarckism (inheritance of acquired characters), and the various criticisms and debates surrounding his evolutionary ideas.
In simple words: If you were to interview Lamarck, you'd ask him about his life, his theory of how traits are passed on, and why his ideas faced criticism.

🎯 Exam Tip: When preparing interview questions for a historical figure, focus on their key theories, life events that shaped their work, and any controversies or impacts of their ideas.

Question 28. Examine carefully the details given and group similar ones in table. Give suitable title for each column. Analyse the importance of each group in evolution. Patagium of Draco, human hand, forelimb of rabbit, wings of bird, vermiform appendix, plica semilunaris, wings of insects, whale's flipper, ear muscles.
Answer: