Heredity and Evolution

Cutting a mouse's tail is a physical change acquired during its lifetime. It affects the body cells and does not normally alter the genes in the sperm or eggs that form the next generation. Consequently, the offspring inherit the genes for normal tail development and are not born tailless merely because parental tails were cut. Therefore option A is correct; B, C, and D do not explain heredity.

An acquired trait develops after birth as a result of an individual's activities, environment, or experiences. Muscles becoming stronger through regular exercise are an example because training changes the body during life and is not normally encoded as a new inherited trait in gametes. Thus option A is correct. Natural eye colour, blood group, and inborn hair colour are primarily determined by inherited genetic information, so B, C, and D are not suitable examples.

An inherited trait is influenced by genetic information received from parents and can be transmitted through reproductive cells. Blood group is determined by alleles inherited from the parents, so option A is correct. Learning to ride a bicycle and learning a language are acquired abilities shaped by practice and environment. Cutting hair is a temporary physical change, not a genetic characteristic; therefore B, C, and D are incorrect.

Fossils are preserved remains, impressions, or other traces of organisms that lived in the past. By studying their structure, age, and position in rock layers, scientists learn which organisms existed earlier and how living forms have changed over geological time. Therefore option A is correct and fossils are important evidence for evolution. Fresh food, modern machines, and weather alone are not what fossils directly document.

The governing concept is fossil preservation as evidence of evolution. When organisms die, their remains may be buried by sediments and, over very long periods, become preserved or leave impressions in sedimentary rock layers. Therefore, option A is correct. Fresh milk, air, and human blood are not normal geological places where fossils are preserved; those choices confuse biological materials with rock deposits.

Homologous organs are structures that share a similar basic plan because of common ancestry, although they may perform different functions in different organisms. For example, the forelimbs of humans, whales, and bats have related skeletal patterns but are used differently. Thus option A is correct. Colour, occurrence only in plants, and digestion do not define homology.

The governing concept is homology: structures inherited from a common ancestral body plan can retain similar bones even when their functions diverge. A human hand is mainly used for grasping, whereas a bird wing is adapted for flight, but both contain corresponding limb bones. Therefore option A is correct. Analogous organs share function without the same basic structure, and the other choices describe unrelated functions.

Analogous organs perform similar functions but arise from different basic structural plans and evolutionary origins. The wings of a bird and an insect both support flight, yet their internal construction is very different. Thus option A is correct. Homologous organs, represented by the distractor idea of identical structure and function, are defined by shared basic structure rather than merely similar use; the remaining choices are unrelated.

The governing idea is analogy, in which different structures independently perform a similar function. Both a bird wing and an insect wing enable flight, but a bird wing contains bones and is a modified forelimb, whereas an insect wing is an outgrowth of the body wall. Hence option A is correct. They are not homologous, respiratory, or secretory organs.

Homologous organs can indicate common ancestry because organisms may inherit a similar underlying structural plan from an ancestral form. Their present functions may differ as populations adapt to different conditions, but the corresponding arrangement of parts remains evidence of relationship. Therefore option A is correct. Shared colour, food, or location alone does not reliably establish ancestry and cannot replace structural or genetic evidence.

Fossils are preserved remains, impressions, or traces of organisms that lived in the past. Comparing fossils from different geological layers can reveal the appearance, disappearance, and gradual modification of life forms through time. This historical evidence helps scientists study evolution, so option A is correct. Fossils are not used to taste food, predict current weather, or measure a heartbeat.

In school-level biology, a species is a group of similar organisms that can generally interbreed with one another and produce fertile offspring. This reproductive connection helps distinguish one species from another and is important for classification and evolution. Therefore option A is correct. A food name, a geographical place, or a colour describes neither reproductive compatibility nor biological classification.

Genetic drift is a change in the frequency of inherited traits caused by chance rather than by a trait’s usefulness. Its effect is especially strong in a small population, where the accidental survival or reproduction of only a few individuals can alter the proportion of alleles in later generations. Thus, option A is correct. Options B, C, and D describe food movement, evaporation, and blood clotting, which are unrelated biological processes.

Natural selection operates through the interaction between inherited variation and environmental conditions such as food availability, temperature, disease, and predators. A trait that improves survival or reproduction in one environment may be less useful in another. Therefore, option A is correct: the environment influences which existing variations are advantageous. It does not make organisms identical, erase genes, or provide immortality, so B, C, and D are incorrect.

Charles Darwin is most closely associated with the theory of evolution by natural selection. He explained that individuals in a population show heritable variations, and those with variations better suited to their surroundings are more likely to survive and reproduce. Over generations, useful variations become more common. Thus, option A is correct. Blood circulation, electric current, and photosynthesis are important topics, but they are not Darwin’s central scientific contribution.

A dominant allele is expressed in the phenotype even when it is paired with a contrasting recessive allele. In pea plants, a plant with genotype Tt is tall because the tall allele masks the dwarf allele; the dwarf trait appears phenotypically only in tt plants. Therefore, option A is correct. Dominance does not mean that a trait is found only in leaves or that it makes food, so C and D are unrelated, while B is opposite to the observation.

A recessive trait is expressed when an individual has two recessive alleles, commonly represented by aa. If a dominant allele is present, it usually masks the recessive allele in the phenotype, although the recessive allele can still be inherited. Thus, option A is correct. Option B describes the situation in which the dominant trait is expressed, while C and D have no valid genetic connection with recessive expression.

Evolution is a population-level change in inherited characteristics across successive generations. It usually results from many small variations, selection, and reproductive differences accumulating over long periods, often far beyond a human lifetime. Consequently, a person generally cannot watch a complete evolutionary change directly, although fossils, comparative anatomy, embryology, and genetic evidence reveal it. Option A is correct; B, C, and D are scientifically irrelevant or contradictory.

A useful variation is an inherited difference that improves an organism’s suitability to particular environmental conditions. For example, better camouflage or resistance to a disease may increase the probability of surviving and reproducing. Natural selection can then make such a variation more common in later generations, though usefulness depends on the environment and is not guaranteed. Therefore, option A is correct. B, C, and D describe impossible or harmful effects, not adaptive variation.

Homology is determined mainly by common basic structural plan and evolutionary origin, not merely by outward appearance. Homologous organs may perform different functions, such as the forelimbs of humans, whales, and bats, yet share underlying structural features. Conversely, organs can look similar or perform similar functions while having different origins and structures. Therefore, option A is correct; colour, digestion, and occurrence only in humans are not criteria for homology.