Heredity and Evolution

An inherited trait is determined substantially by genetic information received from parents through reproductive cells. Human blood group is an example because it is genetically controlled. Learning to swim results from practice, training and experience during life, so it is an acquired trait rather than a directly inherited one. Thus option A correctly pairs the examples; the other options reverse or misclassify them.

Natural selection favours heritable variations that improve an organism’s ability to survive and reproduce in a particular environment. Such organisms are more likely to obtain resources, avoid dangers, reach reproductive age and leave offspring carrying the favourable variation. Being largest is not automatically advantageous, and organisms that produce no offspring cannot pass traits on. Therefore option A best describes success in natural selection.

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.

A gene is a segment of DNA that carries information for a particular characteristic or functional product. Genes are arranged at specific positions, called loci, on chromosomes. Chromosomes are long DNA-protein structures found mainly in the cell nucleus. Hence B correctly states the relationship. A reverses the relationship, while C and D are unrelated statements about biological structures.

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.

External appearance or function alone may be misleading because analogous organs can perform similar functions while having different basic structures and evolutionary origins. Reliable relationships are assessed using deeper anatomy, embryology, fossils and molecular evidence together. Therefore A expresses the relevant caution. B is too absolute, C wrongly dismisses function, and D is false because fossils provide important evidence of evolutionary history.

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.