📘 Welcome
Hi User, you have selected Read Mode. This is Time Free (Unlimited) for your ease to understand every question as per your Ease and Time.
Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main window designed with Exam Features.
Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main window designed with Exam Features.
Q1. Evolution explains
How life became complexEvolution explains the gradual change in populations over generations, leading to the diversity and complexity of life from simpler common ancestors. It does not explain the origin of life (abiogenesis) or DNA formation (biochemistry), nor does it primarily explain inheritance (genetics does that).
Q2. Darwin proposed evolution by
Natural selectionCharles Darwin proposed natural selection as the mechanism of evolution: individuals with advantageous traits survive and reproduce more, passing those traits to offspring. Genetic drift was later developed by population geneticists (Wright, Fisher). Mutation theory is associated with De Vries.
Q3. Survival advantage leads to
Natural selectionWhen certain individuals have traits that confer survival advantage in their environment, they are more likely to survive and reproduce. This differential reproduction is natural selection. Extinction is the opposite outcome; genetic drift is random; uniformity is not the result.
Q4. Changes in non-reproductive tissues
Are not inheritedChanges in somatic (non-reproductive) tissues—such as acquired traits from injury, exercise, or surgery—do not alter the DNA in germ cells (sperm/egg). Therefore, they are not passed to offspring and do not contribute to evolution. Only heritable changes in germ cells matter.
Q5. Mendel’s experiments explained
Inheritance of traitsGregor Mendel’s pea plant experiments established the basic laws of inheritance (segregation, independent assortment), showing how traits are passed from parents to offspring. He did not study evolution, origin of life, or nutrition.
Q6. Changes that do not alter DNA of germ cells are
Acquired traitsAcquired traits are characteristics developed during an organism’s life due to environment, use/disuse, or injury. They do not change the DNA in germ cells and are therefore not heritable. Recessive/dominant refer to allele expression; inherited traits are passed via DNA.
Q7. Genetic drift is more effective in
Small populationsGenetic drift is the random change in allele frequencies due to chance events (e.g., accidental death, founder effect). In small populations, random fluctuations have a larger proportional impact, leading to faster fixation or loss of alleles. Large populations buffer against random drift.
Q8. The increase of blue beetles in population was due to
Survival advantageIn the beetle example, blue beetles (or green in the classic version) increased because their colour provided camouflage, reducing predation. This survival advantage led to differential reproduction. Natural selection is the process; survival advantage is the immediate cause.
Q9. Acquired traits do not contribute to evolution because
They are not inheritedFor a trait to contribute to evolution, it must be heritable (passed via germ cell DNA). Acquired traits (e.g., muscles from exercise, surgically removed tails) do not alter the genetic code in gametes and are therefore not inherited. Dominance, weakness, or harm are not the primary reason.
Q10. In the first beetle situation, green colour spread because
It had survival advantageGreen beetles on green leaves were camouflaged from predators (crows). This survival advantage allowed them to live longer and reproduce more, increasing their frequency in the population. Dominance and order of appearance are not the reasons; it was selection, not accident.
Q11. Natural selection in the first situation was exerted by
CrowsIn the classic beetle example, crows are the predators that eat visible (red) beetles more easily. The crows exert the selective pressure: they remove less-camouflaged individuals, causing the better-camouflaged (green) beetles to increase. Plants, elephants, and beetles themselves do not exert this selection.
Q12. After returning to England, Darwin
Stayed at home and experimentedAfter the HMS Beagle voyage (1831-1836), Darwin returned to England, settled at his home in Down House, Kent, and conducted extensive experiments (on barnacles, pigeons, plants) while developing his theory of natural selection. He published On the Origin of Species in 1859.
Q13. A cross between a tall pea plant (TT) and a dwarf pea plant (tt) will produce tall plants in the F1 generation because
Tallness is the dominant traitIn pea plants, tall (T) is dominant over dwarf (t). The cross TT × tt produces all Tt heterozygotes, which express the dominant tall phenotype. Dwarfness is recessive; traits do not mix (blending) in Mendel’s inheritance.
Q14. First organisms were
PrimitiveThe first living organisms on Earth (around 3.5-4 billion years ago) were primitive, single-celled prokaryotes (similar to modern bacteria). They were simple in structure, not multicellular, not plants (which evolved much later), and not complex.
Q15. Evolution occurs due to
Many generationsEvolution is the change in allele frequencies in a population over successive generations. It is not observable in a single generation or lifetime (except in fast-reproducing organisms like bacteria). It requires accumulation of heritable changes across many generations.
Q16. Darwin lived during the period
1809–1882Charles Darwin was born in 1809 in Shrewsbury, England, and died in 1882. He published On the Origin of Species in 1859. Mendel (1822-1884) is a different scientist. 1900-1950 is the Modern Synthesis period; 1700-1750 is pre-Darwin.
Q17. Darwin is also known for studies on
Earthworms and soil fertilityIn addition to evolution, Darwin conducted extensive studies on earthworms, publishing “The Formation of Vegetable Mould through the Action of Worms” (1881), demonstrating their role in soil formation and fertility. He also studied barnacles and plants, but earthworms are a notable example.
Q18. J.B.S. Haldane proposed origin of life in the year
1929J.B.S. Haldane (British geneticist) independently proposed the “primordial soup” theory for the origin of life in 1929, suggesting that organic molecules formed abiotically in the early ocean. Aleksandr Oparin had proposed a similar idea in 1924. 1859 is Darwin’s Origin; 1882 is Darwin’s death; 1950 is later.
Q19. In the second situation, colour change gave
No survival advantageIn the second beetle scenario (often presented), a colour change occurs but does not provide any survival advantage (e.g., beetles change from red to purple but predators still see them equally). Without advantage, natural selection does not act, and the colour does not spread. Adaptation requires advantage.
Q20. The idea that acquired traits are not inherited disproves
LamarckismLamarck proposed that acquired traits (e.g., giraffe’s elongated neck from stretching) could be inherited and drive evolution. The discovery that acquired traits do not alter germ cell DNA disproved Lamarckism. Mendel, Darwin, and mutation theory are not disproved by this fact.
Q21. In humans, the sex of the child is determined by
The father’s sex chromosomeThe mother always contributes an X chromosome. The father contributes either X (producing a girl) or Y (producing a boy). Thus, the father’s sperm determines the sex of the child. While both contribute, the decisive factor is the father’s contribution.
Q22. Darwin could not explain evolution fully because he lacked knowledge of
Mechanism of inheritanceDarwin did not know about Mendelian genetics (rediscovered in 1900), DNA, or the mechanism by which traits are passed from parents to offspring. He knew fossils, natural selection, and environment well. The lack of a valid inheritance mechanism was a major gap in his theory.
Q23. Natural selection always leads to
AdaptationNatural selection results in populations becoming better adapted to their environments over generations (increased fitness). It does not always lead to extinction (that occurs when adaptation fails), genetic drift is random and separate, and uniform populations are not the outcome.
Q24. The combined understanding of Mendel and Darwin explains
Evolution with inheritanceThe Modern Synthesis (1930s-1940s) combined Darwin’s natural selection with Mendel’s genetics, explaining how heritable variations are selected and passed on, leading to evolution. Alone, each was incomplete. Digestion, growth, and respiration are unrelated.
Q25. Large populations are less affected by
Genetic driftGenetic drift (random changes in allele frequency due to chance) has a smaller effect in large populations because random fluctuations average out. In small populations, drift can cause significant changes. Reproduction, mutation, and selection occur in all population sizes.
Q26. A trait that is expressed in a hybrid even in the presence of the other trait is called
Dominant traitA dominant trait is expressed in heterozygotes (hybrids) even when the contrasting allele is present. Recessive traits are masked. Incomplete dominance produces an intermediate phenotype; co-dominance shows both traits simultaneously.
Q27. Organic molecules necessary for life formed by
Chemical synthesisAccording to the Oparin-Haldane hypothesis and Miller-Urey experiment (1953), organic molecules (amino acids, sugars) formed abiotically (by chemical synthesis) from inorganic precursors under early Earth conditions. Reproduction and mutation require existing life; biological processes came later.
Q28. Haldane suggested life arose from
Simple inorganic moleculesJ.B.S. Haldane proposed that the early Earth had a reducing atmosphere (methane, ammonia, water vapor). Simple inorganic molecules combined to form organic monomers (amino acids, sugars) via energy sources (UV, lightning), eventually forming protocells. Cells and DNA came later; “organic matter only” is not precise.
Q29. Removal of tail in mice does not affect progeny because
Germ-cell genes remain unchangedSurgically removing a mouse’s tail is an acquired alteration that does not change the DNA in its germ cells (sperm/egg). Therefore, offspring are born with normal tails. This disproves Lamarckian inheritance of acquired characteristics. Tail regrowth is incorrect (mice do not regrow tails).
Q30. Early earth conditions were
Very different from todayEarly Earth (4.5-4 billion years ago) had a reducing atmosphere (no free oxygen), high volcanic activity, intense UV radiation, and frequent impacts. It was very different from today’s oxidizing atmosphere, and while conditions were harsh, they were not entirely unfavourable for chemical evolution. Not “cold only.”
Q31. Origin of life is NOT explained by
MendelMendel’s work on inheritance (genetics) does not address how life originated. Natural selection (Darwin) explains how life diversifies after it begins, not its origin. Evolution as a whole studies change after life exists. The origin of life (abiogenesis) is a separate field; none of these fully explain it, but Mendel is the least relevant.
Q32. Since genes control traits, evolution can be described as change in
Gene frequencyThe Modern Synthesis defines evolution as a change in allele (gene) frequencies in a population over generations. Habitat, population size, and body size may change as a result, but the fundamental evolutionary change is at the genetic level.
Q33. Evolution depends on
Inherited variationsEvolution requires heritable variation (traits passed via DNA from parents to offspring). Experiences, behaviour, and acquired traits that do not alter germ-line DNA are not inherited and thus do not contribute to evolution (except through cultural evolution, which is separate).
Q34. Darwin’s studies were mainly conducted in
South AmericaDuring the HMS Beagle voyage (1831-1836), Darwin spent most of his time exploring South America (Brazil, Argentina, Chile, Galápagos Islands, etc.). He collected fossils, observed biodiversity, and noted geographic variations that influenced his theory. Europe was his home base; Asia and Africa were not primary.
Q35. In the third situation, beetle weight decreased due to
Poor nutritionIn some beetle examples, a decrease in weight is caused by environmental factors (poor nutrition), not a genetic change. This is an acquired trait. If the reduced weight is not due to a heritable genetic change, it will not be passed to offspring. Selection, inheritance, and mutation are not the direct cause here.
Q36. Natural selection results in
AdaptationsNatural selection favors traits that increase survival and reproduction in a specific environment, leading to adaptations (features that enhance fitness). It does not always cause extinction (that occurs when adaptation fails). Variation remains; changes are not random (they are directed by environment).
Q37. Mendel and Darwin
Did not know each other’s workMendel published his work on pea plants in 1865, and Darwin published On the Origin of Species in 1859. They were contemporaries but unaware of each other’s work. Mendel’s work was largely ignored until 1900, after both had died. They never collaborated or criticized each other.
Q38. Change in frequency of inherited traits over generations is called
EvolutionEvolution is defined as the change in allele (or inherited trait) frequencies in a population over successive generations. Growth is increase in size; heredity is transmission of traits; nutrition is food intake. Evolution is the correct term.
Q39. Genetic drift provides
Diversity without adaptationGenetic drift causes random changes in allele frequencies, leading to genetic diversity (or loss) that is not necessarily adaptive. Unlike natural selection, drift does not produce adaptations (traits that improve survival). It can cause uniformity (if alleles fix) but primarily creates diversity without direction.
Q40. During DNA replication, the two strands of the DNA molecule separate because of
Breakdown of hydrogen bonds between nitrogenous basesThe two DNA strands are held together by hydrogen bonds between complementary base pairs (A-T, G-C). During replication, the enzyme helicase breaks these hydrogen bonds, causing strand separation. Phosphodiester bonds are within strands; RNA polymerase is for transcription; DNA ligase joins fragments.
Q41. The scientist who proposed chemical origin of life was
HaldaneJ.B.S. Haldane (1929) proposed the chemical (abiogenetic) origin of life theory, suggesting organic molecules formed from inorganic precursors in the “primordial soup.” Darwin focused on evolution of existing life; Lamarck on inheritance; Mendel on genetics.
Q42. The process by which traits are passed from parents to offspring is called
InheritanceInheritance (heredity) is the transmission of genetic traits from parents to offspring via DNA. Variation refers to differences among individuals; adaptation is a trait that improves fitness; evolution is change over generations.
Q43. Variation alone is not sufficient for evolution; it must be
InheritedFor variation to lead to evolution, it must be heritable (passed from parents to offspring via DNA). Non-heritable variations (acquired traits) do not change the genetic composition of a population over generations. Visibility and randomness are not the determining factors.
Q44. Reduction in beetle weight due to starvation is
AcquiredWeight reduction caused by starvation is an environmental effect, not a genetic change. It is an acquired trait (not encoded in DNA). It will not be passed to offspring unless it is accompanied by a genetic mutation. Dominant and genetic are incorrect; inherited is false.
Q45. Evolution requires variation that is
InheritedEvolution by natural selection requires heritable variation (differences in DNA that are passed to offspring). Behavioural variations can be inherited if genetically based; acquired and temporary variations that are not heritable do not contribute to evolutionary change.
Q46. Accidents affecting gene frequency in small populations lead to
Genetic driftRandom accidents (e.g., natural disaster, accidental death) that change allele frequencies, especially in small populations, are called genetic drift. This is different from natural selection (non-random, advantage-based). Speciation may eventually result but is not the direct immediate outcome.
Q47. Germ cells are formed in
Specialised reproductive tissuesGerm cells (sperm and eggs) are produced in specialized reproductive organs: testes in males (spermatogenesis) and ovaries in females (oogenesis). Nervous, non-reproductive, and digestive tissues do not produce germ cells.
Q48. Genetic drift differs from natural selection because it is
RandomGenetic drift is a random change in allele frequencies due to chance events. Natural selection is non-random; it favors alleles that confer survival or reproductive advantage. Environment-driven and adaptive describe selection; advantage-based also describes selection.
Q49. Darwin’s voyage lasted for
Five yearsThe HMS Beagle voyage began in December 1831 and ended in October 1836, lasting approximately five years. Darwin was 22 when he started and 27 when he returned. Ten, three, and two years are incorrect.
Q50. After food becomes plentiful again, beetle weight will
Increase againIf beetle weight decreased due to poor nutrition (acquired trait), it is not a genetic change. Once food becomes plentiful, beetles will return to normal weight because the environmental cause is removed. The acquired change is not permanent or heritable.