201. Which statement about new evolutionary types in a population is correct?
ⓐ. They appear only when all individuals mutate in the same direction at once.
ⓑ. They can arise gradually as successful variants increase generation after generation.
ⓒ. They arise only through use and disuse of organs in adults.
ⓓ. They appear only after a population stops reproducing.
Correct Answer: They can arise gradually as successful variants increase generation after generation.
Explanation: A recognizable new type may emerge when certain variants consistently leave more descendants over many generations. The population then shifts in character because those variants become common. This does not require a sudden simultaneous change in all individuals. Gradual increase of more successful variants is enough to alter the population noticeably.
202. Which scenario best illustrates the population-level action of natural selection?
ⓐ. A single deer becomes stronger after repeated running.
ⓑ. A tree grows taller during its own lifespan.
ⓒ. In a population of insects, a pre-existing resistant variant becomes common after repeated exposure to an insecticide.
ⓓ. One bird learns a new feeding habit and passes it directly to all offspring.
Correct Answer: In a population of insects, a pre-existing resistant variant becomes common after repeated exposure to an insecticide.
Explanation: The key idea is a shift in the proportion of heritable variants within a population. If a resistant variant already exists and survives exposure better, it leaves more offspring and increases in frequency. The result is evolutionary change at the population level. Individual strengthening or learning does not demonstrate the same process.
203. Assertion: Natural selection is better described at the population level than at the level of a single individual.
Reason: Selection changes the proportion of heritable variants across generations rather than transforming one organism during its lifetime.
ⓐ. Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
ⓑ. Both Assertion and Reason are true, but the Reason does not explain the Assertion.
ⓒ. Assertion is true, but Reason is false.
ⓓ. Assertion is false, but Reason is true.
Correct Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
Explanation: Selection has lasting evolutionary significance only when it changes the relative frequency of variants in later generations. A single organism may survive or die, but the broader evolutionary outcome is seen in the population. The reason directly explains why the population is the correct level of description. Evolution is therefore a generational population process, not a lifetime event in one body.
204. Which statement is incorrect about biological evolution through natural selection?
ⓐ. It depends on heritable variation already present in a population.
ⓑ. It can make some variants more common because they leave more offspring.
ⓒ. It is observed as a population-level change over generations.
ⓓ. It means each individual organism changes genetically during its own lifetime in order to adapt.
Correct Answer: It means each individual organism changes genetically during its own lifetime in order to adapt.
Explanation: Natural selection does not mean that each organism genetically reshapes itself during life in response to need. The process works because populations already contain heritable differences, and some variants reproduce more successfully than others. Over generations, those successful variants become more frequent. The change is therefore population-based and generational.
205. In the classic example of industrial melanism in peppered moths, the frequency of dark-coloured moths increased mainly because
ⓐ. soot-darkened tree trunks made them less visible to predators
ⓑ. dark moths were always produced in greater numbers than light moths
ⓒ. light moths changed their colour during life into dark moths
ⓓ. predators preferred feeding only in unpolluted forests
Correct Answer: soot-darkened tree trunks made them less visible to predators
Explanation: Industrial melanism is explained through differential survival under changed environmental conditions. When tree trunks became darkened by soot, dark moths were better camouflaged against the background. Birds could spot light moths more easily, so dark moths survived and reproduced more successfully. The increase in dark moths was therefore an effect of natural selection.
206. Which condition most strongly favoured light-coloured peppered moths before large-scale industrial pollution?
ⓐ. tree trunks were darkened by heavy soot deposits
ⓑ. tree trunks were comparatively light and lichen-covered
ⓒ. predators could not see moths at all in daylight
ⓓ. dark moths were completely absent from the population
Correct Answer: tree trunks were comparatively light and lichen-covered
Explanation: Before industrial pollution, the background on tree trunks was relatively light, often because of lichens. On such surfaces, light-coloured moths were harder for predators to detect. Better camouflage increased their chances of survival and reproduction. This made the light form more common under cleaner environmental conditions.
207. Which statement best explains industrial melanism as an example of natural selection?
ⓐ. Moths consciously chose the colour that matched the tree bark.
ⓑ. Pollution created a need, and all moths changed colour together.
ⓒ. Dark moths appeared suddenly only after industries developed.
ⓓ. Predation favoured the colour variant that was less conspicuous in a given environment.
Correct Answer: Predation favoured the colour variant that was less conspicuous in a given environment.
Explanation: The key idea in industrial melanism is not conscious choice or simultaneous change. A population already contained colour variants, and predation acted differently on them depending on background conditions. The better-camouflaged form survived more often and left more offspring. This is a direct demonstration of natural selection acting on existing variation.
208. If industrial pollution decreases and tree trunks again become lighter, which result is most likely over generations?
ⓐ. both dark and light moths will disappear completely
ⓑ. light-coloured moths may again gain a survival advantage
ⓒ. dark moths will always remain favoured because they were once common
ⓓ. predators will stop influencing moth populations
Correct Answer: light-coloured moths may again gain a survival advantage
Explanation: Natural selection depends on the environment in which organisms live. If the background becomes lighter again, light-coloured moths would become less visible to predators than dark moths. Over generations, this could increase their reproductive success and frequency in the population. The example shows that selection can reverse when environmental conditions change.
209. Which factor linked predation with colour frequency in peppered moths most directly?
ⓐ. degree of contrast between the moth and the tree trunk background
ⓑ. amount of food available to the moth larvae in winter
ⓒ. ability of moths to change colour after being attacked
ⓓ. rate at which industries produced smoke each day
Correct Answer: degree of contrast between the moth and the tree trunk background
Explanation: Predators detect prey more easily when it contrasts strongly with the background. In peppered moths, the colour that blended better with the tree trunk was less likely to be eaten. This changed which form survived and reproduced more often. The contrast with the resting surface therefore played a central role in the selection process.
210. A student says that industrial melanism proves that individual moths become dark because they need protection. Which correction is best?
ⓐ. Moths become dark mainly because soot directly stains their wings permanently.
ⓑ. Dark colour appears because predators teach moths to hide better.
ⓒ. Industrial melanism involves change in population frequency of pre-existing variants, not purposeful colour change in individuals.
ⓓ. All moths first become light and then some later become dark after reproduction.
Correct Answer: Industrial melanism involves change in population frequency of pre-existing variants, not purposeful colour change in individuals.
Explanation: Industrial melanism is a population-level evolutionary change, not a purposeful adjustment within one lifetime. The moth population already includes colour variation, and selection changes how common each form becomes. Individuals do not darken because they decide to adapt. The environment simply favours one existing variant over another.
211. Assertion: Industrial melanism is considered a strong example of natural selection in action.
Reason: Environmental change altered which colour variant was more easily seen by predators.
ⓐ. Both Assertion and Reason are false.
ⓑ. Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
ⓒ. Assertion is true, but Reason is false.
ⓓ. Assertion is false, but Reason is true.
Correct Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
Explanation: Industrial melanism directly connects environmental change with differential survival. When the visual background changed, predator detection also changed, so one colour variant gained an advantage over the other. This led to a shift in the population over generations. The reason therefore explains exactly why the example demonstrates natural selection.
212. Which observation would best support the explanation of industrial melanism?
ⓐ. Dark and light moths always survive equally well in every habitat.
ⓑ. Moth colour has no effect on visibility to birds.
ⓒ. The colour form that matches the resting background is attacked less frequently by predators.
ⓓ. Only polluted air, and not predation, determines which moths survive.
Correct Answer: The colour form that matches the resting background is attacked less frequently by predators.
Explanation: The explanation of industrial melanism depends on differential predation. If the better-camouflaged moth is attacked less often, it will survive and reproduce more successfully than the contrasting form. Repeated over generations, this changes colour frequency in the population. Such an observation directly supports the natural selection model.
213. The rise of antibiotic-resistant bacteria is best explained as
ⓐ. bacteria intentionally changing to survive the drug
ⓑ. bacteria becoming resistant because they are exposed to antibiotics once
ⓒ. natural selection favouring pre-existing resistant variants in the bacterial population
ⓓ. bacteria losing all variation after contact with the antibiotic
Correct Answer: natural selection favouring pre-existing resistant variants in the bacterial population
Explanation: A bacterial population may already contain some variants that are less affected by a particular antibiotic. When the drug is used, susceptible bacteria die more readily, while resistant ones survive and reproduce. Over time, the resistant type becomes more common in the population. This is a clear example of natural selection acting on existing variation.
214. Which statement about insecticide resistance in insects is correct?
ⓐ. Resistant insects survive chemical exposure better and leave more offspring.
ⓑ. All insects become resistant at the same time after one spray.
ⓒ. Insecticide resistance develops only in fossils, not in living populations.
ⓓ. Resistant insects arise only because they choose to adapt.
Correct Answer: Resistant insects survive chemical exposure better and leave more offspring.
Explanation: Insect populations may include inherited differences in sensitivity to a chemical. When an insecticide is applied, susceptible individuals are eliminated more heavily, while resistant ones survive and reproduce. As those survivors contribute more descendants, resistance becomes common. The change is therefore evolutionary and population-based.
215. Which feature makes microbes especially useful examples of rapid evolutionary change?
ⓐ. They do not show heritable variation.
ⓑ. They cannot be affected by natural selection.
ⓒ. They evolve only after millions of years.
ⓓ. They have short generation times, so selection can change populations quickly.
Correct Answer: They have short generation times, so selection can change populations quickly.
Explanation: Microbes reproduce very rapidly, so many generations can pass in a short time. Because natural selection acts across generations, changes in population composition can appear quickly in such organisms. This makes resistance evolution especially easy to observe in bacteria and other microbes. Short life cycle and fast reproduction therefore speed up visible evolutionary change.
216. Fill in the blank in the most accurate way:
Under continued antibiotic use, susceptible bacteria are removed more often, while resistant bacteria are ______.
ⓐ. transformed into non-living particles
ⓑ. favoured by selection
ⓒ. forced to stop reproducing
ⓓ. unable to survive in any environment
Correct Answer: favoured by selection
Explanation: Antibiotics create a selection pressure in the bacterial population. Variants that can survive the drug are more likely to persist and reproduce, whereas susceptible ones are removed. The result is an increase in the resistant form over generations. This is why resistant bacteria are said to be favoured by selection.
217. A student says that antibiotics directly create resistance in every bacterium they contact. Which correction is best?
ⓐ. Antibiotics mainly select resistant variants already present rather than creating resistance in all bacteria at once.
ⓑ. Antibiotics affect only human cells and not bacteria.
ⓒ. Resistance appears only if bacteria stop reproducing.
ⓓ. Antibiotics convert all susceptible bacteria into viruses.
Correct Answer: Antibiotics mainly select resistant variants already present rather than creating resistance in all bacteria at once.
Explanation: Natural selection works on variation that is already present in a population. When antibiotics are used, susceptible bacteria are killed more effectively, while resistant ones survive and multiply. The drug therefore changes the frequency of variants rather than instantly producing the same change in all individuals. This distinction is central to understanding resistance evolution.
218. Which situation best illustrates evolution by natural selection in a microbial population?
ⓐ. All bacteria in a culture remain equally sensitive to a drug over many generations.
ⓑ. A single bacterial cell grows larger after absorbing extra nutrients.
ⓒ. Bacteria stop dividing permanently after one chemical treatment.
ⓓ. After repeated use of an antibiotic, resistant bacteria become increasingly common in the culture.
Correct Answer: After repeated use of an antibiotic, resistant bacteria become increasingly common in the culture.
Explanation: Evolution in this context means a change in the composition of the population across generations. If resistant bacteria become more common after repeated antibiotic exposure, natural selection has altered the population. The shift is not simply growth of one individual cell. It is a generational increase in the frequency of a successful variant.
219. Which statement correctly links resistance evolution with natural selection?
ⓐ. Resistance evolution proves that acquired characters are always inherited.
ⓑ. Resistance evolution shows that selection can rapidly alter populations when heritable variants differ in survival.
ⓒ. Resistance evolution means every member of a population adapts equally.
ⓓ. Resistance evolution can occur only in large animals with long lifespans.
Correct Answer: Resistance evolution shows that selection can rapidly alter populations when heritable variants differ in survival.
Explanation: Resistance examples are powerful because they make population change visible in a relatively short time. When some variants survive treatment better than others, they contribute more offspring to future generations. This changes the population quickly, especially in short-lived organisms. The phenomenon therefore strongly supports natural selection.
220. Assertion: The repeated use of an insecticide can lead to an increase in resistant insects in a population.
Reason: The insecticide removes many susceptible insects, allowing resistant individuals to contribute proportionally more offspring.
ⓐ. Both Assertion and Reason are false.
ⓑ. Assertion is true, but Reason is false.
ⓒ. Both Assertion and Reason are true, but the Reason does not explain the Assertion.
ⓓ. Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
Correct Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
Explanation: Insecticide application creates a strong selection pressure. Susceptible insects are reduced more heavily, while resistant ones survive and reproduce. Over generations, the proportion of resistant individuals rises in the population. The reason directly explains why the assertion is correct.
