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Q1. Evolutionary relationships are studied by
Going backwards in timeEvolutionary relationships (phylogeny) are studied by analyzing shared characteristics, fossils, and DNA sequences to trace common ancestry backwards in time. Looking forward in time is not possible; measuring size alone is insufficient; random guessing is unscientific.
Q2. In different environments, natural selection
Operates differentlyNatural selection acts on traits relative to the specific environment. Different environments favor different traits (e.g., thick fur in cold climates, thin fur in hot climates). It does not operate identically, stop, or fail to operate; it is context-dependent.
Q3. Natural selection differs from genetic drift because it is
Advantage-basedNatural selection is non-random and advantage-based: traits that increase survival and reproduction become more common. Genetic drift is random and not based on advantage. Both are not temporary by definition; accidental and random describe drift, not selection.
Q4. Independent populations evolving separately lead to
SpeciationWhen populations are isolated and evolve independently, they accumulate genetic differences over time. Eventually, they may become reproductively isolated and form new species (speciation). Extinction is possible but not guaranteed; stability and uniformity are opposite outcomes.
Q5. Hierarchical classification means
Grouping based on increasing complexityHierarchical classification (Linnaean system) organizes organisms into nested levels: domain, kingdom, phylum, class, order, family, genus, species. Each level includes groups that share more characteristics as you move down. It is based on evolutionary relationships and shared traits, not alphabetical or random order.
Q6. The Miller–Urey experiment suggested that life could arise from
Inorganic moleculesThe Miller-Urey experiment (1953) demonstrated that organic molecules (amino acids) could form abiotically from inorganic precursors (water, methane, ammonia, hydrogen) under simulated early Earth conditions (sparks for lightning). It did not use DNA, existing organic matter, or living cells.
Q7. Less basic characteristics are shared by
Some organismsLess basic (more derived) characteristics are shared by fewer organisms because they evolved later. For example, hair is shared by mammals but not all vertebrates. Basic characteristics (e.g., cellular organization) are shared by all life. The pattern is hierarchical: basic = shared by many; derived = shared by few.
Q8. Unicellular and multicellular distinction is based on
Cell organisationUnicellular organisms consist of a single cell; multicellular organisms have many cells that differentiate into tissues/organs. This distinction is based on cell organization (level of cellular complexity). Habitat, color, and nutrition are not the defining criteria.
Q9. Asexually reproducing organisms show limited speciation because
There is little genetic variationAsexual reproduction produces clones (genetically identical offspring except for rare mutations). Low genetic variation reduces the potential for populations to diverge and form new species. Speciation is more common in sexual populations with recombination. Mutation frequency is generally low; reproduction speed varies; migration increases gene flow.
Q10. The process of formation of new species is called
SpeciationSpeciation is the evolutionary process by which populations evolve to become reproductively isolated and form distinct species. Mutation is a source of variation; adaptation is a trait that improves fitness; evolution is the broader change over time.
Q11. Brother and sister are closely related because they share
Same parentsSiblings share approximately 50% of their nuclear DNA because they inherit genes from the same two parents. Shared environment, behavior, or school may influence some traits but are not the reason for genetic relatedness.
Q12. Cell is the basic unit of
LifeThe cell is the fundamental structural and functional unit of all living organisms (basic unit of life). The basic unit of heredity is the gene; classification groups organisms; evolution operates on populations.
Q13. Amino acids are the building blocks of
ProteinsAmino acids link together via peptide bonds to form polypeptides, which fold into functional proteins. Carbohydrates are made of monosaccharides; DNA is made of nucleotides; lipids are made of fatty acids and glycerol.
Q14. Evolutionary classification helps us understand
Relationships among organismsEvolutionary classification (phylogenetic systematics) groups organisms based on common ancestry, revealing evolutionary relationships. It does not primarily study respiration, growth rate, or nutrition (though these may be correlated).
Q15. Behavioural isolation occurs when organisms
Do not mate with each otherBehavioural isolation is a prezygotic reproductive barrier where species have different mating rituals, calls, or behaviors, so they do not recognize each other as mates. Size differences and geographical separation are other isolation types; diet differences are ecological isolation.
Q16. Evolutionary trees are based on
Structural similaritiesEvolutionary trees (phylogenies) are constructed using homologous structural similarities (morphology), DNA sequences, and shared derived characteristics. Colour, behaviour alone, and habitat are too variable and not reliable for establishing deep evolutionary relationships.
Q17. Gene flow refers to
Movement of genes between populationsGene flow (migration) is the transfer of genetic material (alleles) between populations through interbreeding. It reduces genetic differences between populations. Mutation creates new alleles; DNA copying is replication; loss of genes is gene deletion.
Q18. Gene flow decreases mainly due to
Geographical isolationGeographical isolation (physical barriers like mountains, rivers, oceans) prevents populations from interbreeding, reducing or eliminating gene flow. Mutation and natural selection do not directly decrease gene flow; reproduction can occur within populations but not between isolated ones.
Q19. Miller–Urey experiment was conducted in the year
1953Stanley Miller and Harold Urey conducted their famous experiment at the University of Chicago in 1953. 1929 is Haldane’s primordial soup proposal; 1945 and 1965 are incorrect.
Q20. When isolated populations can no longer reproduce, they become
New speciesWhen isolated populations evolve to the point where they cannot interbreed and produce fertile offspring (reproductive isolation), they are considered distinct species. This is the biological species concept. Hybrids result from cross-breeding; adaptations are traits; variants are variations within a species.
Q21. A girl and her cousin are
Less closely relatedFirst cousins share about 12.5% of their DNA (one set of grandparents). Siblings share about 50% of their DNA. Thus, cousins are less closely related than siblings but still related. They are not unrelated, more closely related, or equally related as siblings.
Q22. Oxygen was
Added laterEarly Earth had little to no free oxygen (reducing atmosphere). Oxygen began accumulating significantly about 2.4 billion years ago after the Great Oxidation Event, due to photosynthetic cyanobacteria. It was not present initially; it was added later.
Q23. Evolutionary classification connects
Heredity and evolutionEvolutionary classification (phylogenetics) uses hereditary traits (genetic information) to understand evolutionary relationships. It connects the study of inheritance (how traits are passed) with evolution (how populations change over time). Growth, ageing, behaviour, habitat, reproduction, and nutrition are not the primary connections.
Q24. At the end of one week, about ___ of carbon was converted into organic compounds
10%In the Miller-Urey experiment, after approximately one week of continuous sparking, about 10-15% of the carbon from methane was converted into organic compounds, primarily amino acids. 10% is the commonly cited approximate figure. 50% is too high; 5% and 15% are close but 10% is standard.
Q25. Speciation requires
Isolation and variationSpeciation requires: (1) variation (genetic differences) within a population, and (2) isolation (geographical, behavioural, or reproductive) to prevent gene flow. Over time, isolated populations diverge. Nutrition, reproduction alone, or mutation alone are insufficient.
Q26. Genetic drift affects populations more strongly when populations are
SmallGenetic drift (random changes in allele frequencies) has a stronger effect in small populations because chance events can significantly alter allele frequencies. Large populations buffer against random fluctuations. Stability and age are not directly relevant.
Q27. Presence of nucleus in cells is a
Fundamental characteristicThe presence of a nucleus distinguishes prokaryotes (no nucleus) from eukaryotes (have nucleus). This is a fundamental, deep-level characteristic used in high-level classification (domain and kingdom levels). It is not temporary, behavioural, or minor.
Q28. The atmosphere simulated in the Miller–Urey experiment contained
Ammonia, methane and hydrogen sulphideMiller and Urey simulated early Earth’s reducing atmosphere using a mixture of methane (CH₄), ammonia (NH₃), hydrogen (H₂), and water vapor. Some variations included hydrogen sulfide (H₂S). They deliberately excluded oxygen. The correct answer includes ammonia, methane, and hydrogen-related gases.
Q29. The simple organic compounds formed included
Amino acidsThe Miller-Urey experiment produced several amino acids (glycine, alanine, etc.), which are the building blocks of proteins. Lipids, vitamins, and sugars were not the primary identified products, though other similar experiments have produced some sugars and lipids.
Q30. Closely related species share
Recent common ancestorsClosely related species share a recent common ancestor (e.g., humans and chimpanzees). Distantly related species share a more ancient common ancestor (e.g., humans and fish). Different ancestors or no ancestors would mean no evolutionary relationship.
Q31. Photosynthesis is a characteristic used to classify
Multicellular organismsPhotosynthesis is used to classify plants, algae, and some bacteria (cyanobacteria). It distinguishes autotrophs from heterotrophs. It is not used for viruses (non-living), only animals (animals do not photosynthesize), or all organisms (many do not photosynthesize). Within multicellular organisms, it distinguishes plants from animals/fungi.
Q32. Formation of new species occurs when populations
Cannot reproduce with each otherAccording to the biological species concept, new species form when populations become reproductively isolated—they cannot interbreed to produce fertile offspring. Sharing habitats, becoming identical, or rapid growth alone do not cause speciation.
Q33. Organisms without a nucleus are
BacteriaBacteria are prokaryotes; they lack a membrane-bound nucleus and other organelles. Plants, animals, and fungi are eukaryotes with a true nucleus. This is a fundamental classification distinction.
Q34. A large river separating populations causes
Increased isolationA large river acts as a geographical barrier, preventing interbreeding between populations on opposite sides. This increases reproductive isolation, reduces gene flow, and can lead to speciation over time. It does not reduce isolation or increase gene flow.
Q35. Large populations are less affected by
Genetic driftIn large populations, random fluctuations in allele frequencies (genetic drift) have minimal effect because chance events average out. Natural selection, reproduction, and mutation occur in all population sizes regardless of size.
Q36. Speciation is driven by
Genetic drift and natural selectionSpeciation is driven by evolutionary forces: natural selection (adaptive divergence) and genetic drift (random changes), especially when populations are isolated. Nutrition, growth alone, or reproduction only are insufficient drivers.
Q37. Characteristics are defined as
Appearance or behaviourIn classification, characteristics refer to observable features of an organism, including morphology (appearance), physiology, and behaviour. Population size, habitat preference, and “genetic material only” are not the standard definition; genetic material is used but characteristics include many levels.
Q38. Skeleton inside or outside the body distinguishes
AnimalsAnimals are broadly classified into vertebrates (internal skeleton – endoskeleton) and invertebrates (external skeleton – exoskeleton or no skeleton). Plants, algae, and bacteria do not have skeletons in this sense. This is a key characteristic for animal classification.
Q39. Genetic drift is mainly caused by
Random eventsGenetic drift is caused by random events such as natural disasters, accidental death, or chance differences in reproduction (founder effect, bottleneck effect). Advantageous traits and environmental selection drive natural selection, not drift. Adaptation is an outcome, not a cause.
Q40. The gases were passed through electric sparks to simulate
LightningIn the Miller-Urey experiment, electric sparks were used to simulate lightning, which was a likely energy source on early Earth. Lightning provides energy to drive chemical reactions. Earthquakes, solar radiation (UV was present but not simulated by sparks), and volcanic heat are different energy sources.
Q41. Self-pollinating plants show speciation less due to
Lack of geographical isolation effectSelf-pollinating plants reproduce with themselves, so gene flow between populations is already minimal. Geographical isolation has less effect because there is little gene flow to begin with. Speciation is still possible but occurs via other mechanisms (e.g., polyploidy). Rapid gene flow would increase mixing, not decrease speciation.
Q42. The experiment explaining origin of life was conducted by
Miller and UreyThe Miller-Urey experiment (1953) provided experimental evidence for the chemical origin of life (abiogenesis). Darwin and Mendel worked on evolution/inheritance; Haldane proposed the theory but did not conduct the experiment; Lamarck and Wallace are also evolution scientists.
Q43. The temperature of the experimental setup was maintained
Just below 100°CIn the Miller-Urey apparatus, water was boiled (100°C) in one flask, and the vapor condensed in another flask that was kept at a lower temperature. The system cycled; the boiling flask was at 100°C, but the overall setup included temperatures just below 100°C in the condensation chamber. The best answer is “just below 100°C.”
Q44. Change in chromosome number can prevent
Fusion of germ cellsChanges in chromosome number (e.g., polyploidy) can cause reproductive isolation because gametes with different chromosome numbers cannot fuse properly to form a viable zygote. Feeding, photosynthesis, and growth may be affected but are not directly prevented by chromosome number changes.
Q45. Small changes within a species are referred to as
Micro-evolutionMicro-evolution refers to small-scale evolutionary changes within a species or population, such as changes in allele frequency over generations. Macro-evolution refers to large-scale changes (speciation, new body plans). Mutation is a mechanism; speciation is an outcome.
Q46. Classification is based on
CharacteristicsBiological classification is based on a wide range of characteristics: morphological, anatomical, physiological, genetic, and evolutionary relationships. Habitat, colour only, or size alone are insufficient and often misleading (convergent evolution). Characteristics is the broad, correct answer.
Q47. Fundamental characteristics are shared by
Most organismsFundamental characteristics (e.g., cellular organization, DNA as genetic material, basic metabolic processes) are shared by most or all living organisms because they evolved early and are conserved. Derived characteristics are shared by fewer organisms. Only plants or only animals is incorrect.
Q48. Species sharing more characteristics are
More closely relatedIn evolutionary classification, the more characteristics two species share (especially derived homologous traits), the more recently they shared a common ancestor, and thus the more closely related they are. Fewer shared characteristics indicate more distant relationship.
Q49. Evolutionary classification is possible because
Traits are inheritedEvolutionary classification relies on the fact that traits are inherited from ancestors. Shared inherited traits (homologies) reflect common descent. DNA is stable (not unstable); species are not identical; environment is not fixed. Inheritance is the basis.
Q50. The main aim of classification is to
Simplify study of organismsThe primary purpose of biological classification is to organize the vast diversity of life into hierarchical groups, making it easier to study, identify, and understand relationships among organisms. It does not aim to change traits, increase species, or stop evolution.