Heredity and Evolution

The governing concept is natural selection acting on variation in a population. If green insects are more visible to birds, they are more likely to be eaten, while brown insects may survive and reproduce more successfully because they are better camouflaged. Across generations, the proportion of brown insects may therefore increase. Option A is correct; the other choices are too absolute or incorrectly deny selection.

Fossils are preserved remains, impressions or traces of organisms that lived in the past. Comparing fossils from different rock layers and geological periods shows which forms existed earlier and how body structures changed over time. This historical sequence supports the idea that present organisms developed from earlier forms. Option A is correct; fossils are not records of weather or food quantity, and they can reveal relationships among organisms.

The relevant geological principle is superposition: in an undisturbed sequence of sedimentary rock, lower layers were generally deposited before the layers above them. Consequently, fossils preserved in deeper layers are usually relatively older than fossils in higher layers. The word “may” is important because folding, faulting and disturbance can alter the original order. Thus A is the scientifically careful answer.

Analogous organs perform a similar function but arise from different structural plans and evolutionary origins. Bird wings are modified vertebrate forelimbs containing bones, whereas insect wings develop as extensions of the insect body wall and do not have the same skeletal arrangement. Both enable flight, but that shared function does not show common ancestry for the wings themselves. Therefore A is correct.

The key comparison is structure versus function. Homologous organs share a similar basic structural plan, often because of common ancestry, even when their functions differ. Analogous organs perform similar functions but have different underlying structures and evolutionary origins, such as bird and insect wings. Thus option A states the essential distinction. The remaining options are biologically false or deny a well-defined difference.

Variation means that individuals of the same species differ in their inherited features. Natural selection acts on these differences: if a variation helps an organism survive or reproduce in a particular environment, that organism may leave more offspring. Over many generations, the favourable inherited trait can become more common. Thus A is correct; selection does not remove every variation and does not transmit acquired traits directly.

Inheritance depends on genetic information carried by reproductive cells, such as sperm or egg cells, because these cells contribute to the formation of the next generation. A change limited to a body cell may affect only that individual and is not normally copied into its reproductive cells. Therefore A is correct. Body cells do contain chromosomes, and not every acquired change is inherited.

Evolution explains similarity through common ancestry: related organisms can inherit features from an earlier shared population. It also explains differences because mutations, recombination, selection and environmental conditions can lead related populations along different paths. Thus A combines both ideas correctly. B denies change, C denies common ancestry, and D incorrectly limits evolution to humans.

Evolution is not a fixed ladder in which every organism progresses toward one final form. A population may split into separate lineages, and different environments, variations and selection pressures can produce different adaptations in those lineages. These divergences are represented by branches of an evolutionary tree, so A is correct. The other options incorrectly assume human-directed progress, value judgments about age, or absence of branching.

Biological similarities between humans and chimpanzees, including features of anatomy and genetics, support the inference that their lineages share an ancestral population in the past. This does not mean that modern humans evolved directly from modern chimpanzees; both have followed separate evolutionary paths since their lineages diverged. Therefore B is correct, while A, C and D are scientifically false.

The governing concept is homology in evolution. Organs such as the forelimbs of humans, whales and bats may have different functions, yet their underlying bone arrangement is similar because they were inherited from a common ancestral structure. Therefore, option A is correct. Analogous organs have similar functions but different structural origins, while acquired traits and food habits do not explain this anatomical pattern.

The governing concept is analogy in evolution. When structures perform a similar function, such as flying, but arise from different ancestral origins and have different basic designs, they are called analogous organs. Thus, option B is correct. Homologous organs share a basic structural plan despite different functions, whereas genes and chromosomes are hereditary units or structures, not categories of organs.

Fossils preserve evidence about organisms that lived in the past, while living organisms show forms present today. By comparing their structures, scientists can identify similarities, differences and gradual changes across geological time. Therefore, option A correctly explains their value as evidence for evolution. Food taste, weather change and chromosome destruction have no logical connection with fossil comparison.

Evolution across generations depends on heritable changes that can pass from parents to offspring. Acquired traits, such as increased muscle strength from exercise, generally affect body cells and do not alter the genetic information of reproductive cells. Hence they are usually not inherited in that form, making option A correct. The other options incorrectly claim that acquired traits are always inherited, never occur, or are chromosomes.

Natural selection changes the frequency of heritable variations according to their effects on survival and reproduction. A variation that gives no advantage may be passed on less often, especially if it reduces reproductive success, so its frequency can remain low or decline over generations. Thus, option A is correct. It is not guaranteed to spread, create a species immediately, or be beneficial in every environment.

Genetic drift is the random change in the frequency of alleles or traits within a population. Its effect is especially strong in small, isolated populations, where chance events can make a trait common or remove it even when the trait provides no survival advantage. Therefore, option A is correct. Digestion, respiration and photosynthesis are life processes, not mechanisms that explain random changes in inherited traits.

Natural selection is a non-random process in which heritable variations that improve survival or reproduction tend to become more frequent. Genetic drift, in contrast, changes trait or allele frequencies through chance events, particularly in small populations, whether or not a trait is advantageous. Therefore, option A correctly identifies the difference. The other options confuse an evolutionary mechanism with a life process or deny the role of variation.

In sexual reproduction, the offspring receives genetic information from both parents. For many traits, one allele or form is contributed by the mother and another by the father, producing a pair of alleles in the offspring. Thus, option A is correct. The other options wrongly exclude one parent or deny the presence of genetic information. Dominant and recessive relationships may determine which form is expressed.

Dominance describes expression, not destruction of an allele. When a dominant allele is paired with a recessive allele, the dominant phenotype is usually visible, while the recessive allele remains present in the genotype but is masked. Therefore, option A is correct. The recessive form is not automatically destroyed or converted into a dominant form, and it cannot destroy a chromosome.

A useful heritable variation can increase an organism’s survival or reproductive success. If individuals carrying it leave more offspring, the variation may become more frequent in successive generations. Over a long period, this change in frequency can alter the overall characteristics of the population and contribute to evolution. Thus, option A is correct; the other choices contradict inheritance and population change.

The governing concept is that heredity transmits genetic information from parents to offspring, while evolution describes changes in populations over many generations. Heritable variations can be passed on, and advantageous variations may become more common through natural selection. Therefore, option A correctly connects heredity with evolution. Acquired skills are generally not inherited genetically, evolution is not completed in one generation, and the two concepts are clearly related.

The chapter focuses on how traits are transmitted, how differences arise, and how populations change over long periods. Heredity explains the transfer of genetic information, variation describes differences among individuals, and evolution is the gradual change that can result when inherited variations are selected across generations. Thus option A presents the three connected ideas. The other choices belong to life processes, mechanics, or chemistry rather than this chapter.

The governing concept is dominance and recessiveness. A dominant allele can mask the expression of a recessive allele in a heterozygous condition, such as Aa. A recessive phenotype appears only when both alleles are recessive, represented by aa, because no dominant allele is present to mask it. Therefore option A is correct; option B gives a dominant phenotype, while C also expresses dominance and D is biologically impossible.

The governing distinction is between somatic changes and heritable changes. Exercise can enlarge or strengthen muscle cells in the individual’s body, but this acquired modification usually does not alter the DNA in the sperm or ova that form the next generation. Since it is not encoded in gametes, it is not directly transmitted to offspring. Therefore option A is correct; B is false, and C and D make unsupported or impossible claims.

The governing concept is natural selection acting on heritable variation. An adaptive trait gives some organisms an advantage in survival or reproduction under particular environmental conditions. Those organisms are more likely to leave offspring, so the associated trait may become more common over generations. Natural selection does not create every adaptation instantly or remove useful traits; therefore option A correctly describes the relation.