Heredity and Evolution

Correct answer: A. Homologous organs

The governing concept is homology, in which organs retain a similar underlying structural plan because of common ancestry, even when their functions differ. The human arm is adapted mainly for manipulation, while a bird wing is adapted for flight, but both contain corresponding bones such as the upper arm, forearm and hand elements. Therefore option A is correct. They are not analogous, acquired or fossil organs.

Correct answer: A. Analogous organs

The governing concept is the distinction between analogous and homologous organs. A bird wing and an insect wing perform the same function, flying, but their internal structures and evolutionary origins are different. Organs with similar functions but different basic structures and origins are called analogous organs. Homologous organs share a basic structural plan, while genes and sex chromosomes are genetic terms, not organ types. Therefore, option A is correct.

Correct answer: A. Speciation

The governing concept is speciation, a major process in evolution. Within a population, variations can accumulate over many generations, especially when groups become separated or experience different environments. If the differences become sufficiently large and reproductive separation develops, a new species may arise. Respiration and excretion are life processes, while germination is seed growth. Hence, option A, speciation, is correct.

Correct answer: A. It helps some organisms survive in changing environments

The governing concept is the role of variation in natural selection and survival. Environmental conditions may change because of climate, disease, food availability, or competition. Individuals with inherited features that suit the new conditions may survive and reproduce more successfully than others. Their useful traits can then become more common in the population. Therefore option A is correct; the other statements contradict the biological importance of variation.

Correct answer: A. From both parents

The governing concept is inheritance of traits through genes. In sexual reproduction, an offspring receives one set of genetic information from the mother and another from the father. These genes influence traits such as certain aspects of appearance and body function, although the environment can also affect how some traits are expressed. Food and water support growth but do not solely carry the inherited instructions. Thus option A is correct.

Correct answer: A. On chromosomes

The governing concept is the organisation of hereditary information. A gene is a segment of DNA that helps determine a particular trait or protein-related function. Genes are arranged at specific positions, called loci, on chromosomes. Chromosomes are thread-like structures present in the nucleus of most cells. Bones, the outside of the skin, and blood cells are not the structures on which genes are located. Therefore option A is correct.

Correct answer: A. Similarity in basic structure

The governing concept is comparative anatomy and homologous organs. If two organisms have body parts with a similar basic structural plan, even when those parts perform different functions, the similarity may have been inherited from a common ancestor. Such structures are called homologous organs and provide evidence of divergent evolution. Food colour, lifespan, and sound loudness do not establish evolutionary relationships. Hence option A is correct.

Correct answer: A. Because organisms can evolve in different directions

The governing concept is the branching nature of evolution. Evolution does not represent a straight climb from primitive organisms to one perfect or superior endpoint. Populations adapt to different environments, and their lineages can diverge in several directions; some may also become extinct. A branching evolutionary tree therefore represents relationships more accurately than a ladder. Option A is correct, while the other statements deny or distort evolutionary change.

Correct answer: A. Possibility of common ancestry

The governing concept is evolutionary relationship: organisms sharing important structural, biochemical, or genetic similarities may have inherited them from a common ancestral population. Humans and chimpanzees are not the same organism, and neither is a plant. Their similarities therefore support the scientific possibility of common ancestry, although they represent separate species that followed different evolutionary paths.

Correct answer: A. Strong muscles due to exercise

An acquired trait develops during an organism’s lifetime because of activity, practice, environment, or experience rather than being directly inherited through reproductive genes. Regular exercise can enlarge and strengthen muscles, so this is the correct example. Natural eye colour, blood group, and inherited height potential are associated mainly with genetic information received from parents, not with exercise or later experience.

Correct answer: A. Blood group

An inherited trait is determined by genetic information transmitted from parents to offspring through reproductive cells. Blood group is controlled by inherited alleles, so it is the correct example. Cutting hair, learning to read, and temporary or environmentally induced skin darkening are acquired changes or experiences; they do not normally alter the inherited genetic information passed to the next generation.

Correct answer: A. Because recessive information can come from both parents

A recessive allele is expressed in the phenotype only when a person receives two copies of it, one from each parent. It may remain hidden in a heterozygous first-generation individual because a dominant allele masks it. During the next cross, two recessive alleles can unite in an offspring, allowing the trait to reappear. Therefore option A is correct.

Correct answer: A. It can increase

Natural selection explains why a favourable variation can improve survival. If a variation helps an organism obtain food, avoid predators, tolerate conditions, or reproduce more successfully, that organism may leave more offspring than others. The advantage does not guarantee survival, but it can increase the probability. Thus option A is correct; the other choices are absolute and biologically unsupported.

Correct answer: A. Variation

Variation means differences in characteristics among individuals belonging to the same species. If members of one species show different body colours, colour is a variable characteristic and therefore an example of variation. Digestion and respiration are life processes, while fertilisation is a reproductive event; none of these terms describes the difference in colour itself. Therefore option A is correct.

Correct answer: A. Their relationships and evolution

Comparative study uses similarities to identify possible relationships and differences to trace changes among populations over time. Together, these observations provide evidence for common ancestry and evolutionary diversification. They are not limited to taste, weight, or colour change alone. Therefore the broad and scientifically meaningful conclusion is that such study helps us understand relationships among organisms and their evolution, making option A correct.

Correct answer: A. Relationships and common ancestry

In biology, a family-tree-like or evolutionary-tree diagram represents relationships among organisms or groups. Branching patterns can indicate which groups share a more recent common ancestor and how lineages diverged over time. Such a diagram is not designed to show only food quantity, weather, or sound. Thus option A is correct because it describes the evolutionary information represented by the branches.

Correct answer: A. Because small changes accumulate over many generations

Speciation is generally a gradual process. Small heritable variations arise and may accumulate in populations over many generations. Natural selection, genetic drift, and reproductive isolation can progressively increase differences until groups can no longer interbreed successfully. Food does not instantly create a species, organisms do not all change in one day, and chromosomes are not absent. Therefore option A is correct.

Correct answer: A. Heredity maintains similarities, while variation produces differences among offspring

Heredity is the transmission of genetic information and traits from parents to offspring, so it creates continuity and resemblance between generations. Variation means differences that arise among offspring because of genetic recombination, mutation, or environmental influence. Thus, heredity explains similarity, whereas variation explains differences. Options B, C, and D incorrectly deny these biological meanings.

Correct answer: A. Transmission of traits, variation, and changes in organisms over time

The chapter combines two connected ideas. First, heredity explains how genetic traits pass from parents to offspring. Second, variation explains why offspring are not completely identical. When inherited variations accumulate over many generations, populations may change and diversify; this long-term biological change is evolution. The other options belong to unrelated areas of science.

Correct answer: A. Both gene forms will be recessive

The governing concept is dominance in a Mendelian genotype. A recessive phenotype appears only when the individual has two recessive alleles, commonly written aa. If one dominant allele, A, were present in Aa, it would usually mask the recessive allele and produce the dominant phenotype. Therefore option A is correct. Options B and C would normally produce a dominant appearance, while D is biologically impossible because a trait requires genetic information.

Correct answer: A. The dominant trait will appear

The governing concept is complete dominance. A plant with one dominant allele and one recessive allele is heterozygous, for example Tt. The dominant allele determines the phenotype, so the plant generally appears tall if T represents tallness, even though the recessive allele is still present and can be passed to offspring. Hence option A is correct. The recessive phenotype requires two recessive alleles, and heterozygosity does not prevent reproduction.

Correct answer: A. Eye colour received from parents

The governing concept is heredity: an inherited trait is transmitted from parents to offspring through genetic information. Eye colour may be determined partly by genes received from both parents, so it is an appropriate example of an inherited trait. Learning to cycle is a learned behaviour, while a wound and exercise-built muscles are acquired changes that are not normally passed genetically to children.

Correct answer: A. Darkening of skin in sunlight

The governing concept is the difference between inherited and acquired traits. Darkening of skin after exposure to sunlight develops during an individual’s lifetime because of an environmental influence, so it is an acquired change. Blood group and genetically controlled eye colour are inherited characteristics, while chromosome number is a genetic feature rather than a lifetime-acquired trait. Sun tanning normally does not alter reproductive-cell DNA in a heritable way.

Correct answer: A. Genes carry information for traits

The governing concept is heredity through genes. A gene is a segment of genetic material that contains information involved in producing a particular characteristic or trait, often by directing the formation of a functional protein or RNA. Therefore option A correctly connects genes with inherited traits. Genes do not digest food, make only blood, or exist outside the organism; their information operates within cells as part of the genetic material.

Correct answer: A. Two recessive alleles

According to Mendel’s principle of dominance, a recessive phenotype appears only when both copies of the relevant gene are recessive. Using T for tallness and t for dwarfness, a dwarf pea plant must have the genotype tt. A Tt plant is tall because the dominant T masks t, while TT is also tall. Therefore option A is correct; the plant still has genes and chromosomes.