Heredity and Evolution

The governing concept is genetic drift, in which allele frequencies change because of chance rather than because a trait is necessarily advantageous. When a sudden event leaves only a small number of survivors, their genetic composition may not represent the original population. This bottleneck effect can make their traits more common in later generations by chance. Therefore option A is correct; photosynthesis, osmosis, and transpiration are physiological processes, not population-level changes in inherited variation.

The governing concept is homology. Organs that share a similar basic structural plan, even when they perform different functions, are called homologous organs. Their structural similarity is best explained by inheritance from a common evolutionary ancestor, followed by modification in different lineages. Thus option A is correct. Food, body colour, and the presence of genetic material do not determine whether organs have a shared structural origin.

The governing concept is analogy and convergent evolution. Analogous organs carry out similar functions but arise from different basic structures and evolutionary origins, often because unrelated organisms face similar environmental demands. For example, wings of a bird and an insect serve flight but are built differently. Therefore option A is correct. Identical function and structure would suggest homology, while analogous organs are not fossils and are not restricted to humans.

An acquired trait develops during an individual’s lifetime because of practice, use, environment, or experience. A blacksmith’s stronger arm muscles result from repeated physical work and are not ordinarily encoded as an inherited change in the reproductive cells. Thus option A is correct. Bark-like colour and camouflage may improve survival through natural selection, while an advantageous inherited trait becoming more common across generations is itself a population-level evolutionary pattern.

The governing concept is genetic recombination in sexual reproduction. The offspring receives genetic material from two parents, and the combination of alleles is newly formed rather than copied from only one parent. Meiosis and the random union of gametes contribute to variation, so offspring resemble their parents while showing differences. Option A is correct. Options B, C, and D are wrong because offspring possess genetic material from both parents, not none or just one parent.

Asexual reproduction usually involves one parent and produces genetically similar copies, but copying genetic material is not perfectly error-free. Small replication errors or mutations can alter DNA and create slight differences in the offspring. Therefore option A is correct. The union of two parents describes sexual reproduction, whereas complete absence of chromosomes would prevent normal development, and producing no offspring cannot create variation in a population.

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.

Natural selection changes a population only when heritable variation affects survival or reproduction and is transmitted to descendants. A useful trait in an organism that leaves no offspring cannot be inherited by the next generation, so its frequency cannot rise through that organism’s reproduction. Option A is correct. The trait need not be recessive, become a fossil, or dissolve in blood; those statements do not explain population-level inheritance.

The governing concept is speciation through isolation. When populations remain separated for a long period, mutations, recombination, drift, and selection can produce differences between them. If reproductive isolation develops, members can no longer exchange genes successfully, allowing the populations to become separate species. Thus option A is correct. Frequent mixing prevents divergence, identical food is not sufficient by itself, and an individual injury is not a mechanism of speciation.

The governing biological concept is the reproductive definition of a species. Organisms are generally placed in the same species when they can naturally interbreed and produce fertile offspring, meaning their genetic material can continue through subsequent generations. Differences in appearance alone do not necessarily establish separate species. Therefore option A is correct; the other choices confuse visible variation with kingdoms, fossils, or absence of genetic material.

The governing concept is fossil evidence of past life. A fossil is a preserved remain, impression, mould, cast, or other trace of an organism that lived in the past; it may be found in sedimentary rock or preserved in another natural material. Such evidence helps scientists infer the forms and changes of earlier organisms. Therefore option A is correct. Food, present blood, and a fresh flower are parts or products of living organisms, not fossils.

The governing concept is comparative evidence in evolution. Genetic material stores inherited information, and organisms with more similar DNA sequences often share a more recent common ancestor than organisms with greater genetic differences. This similarity supports an inference of a closer evolutionary relationship, although scientists consider multiple kinds of evidence and do not treat it as proof that the organisms are identical. Therefore A is correct; B, C, and D contradict basic genetics.

The governing concept is common ancestry inferred from biological similarity. Humans and chimpanzees share many anatomical and genetic features, so the evidence supports the conclusion that their lineages diverged from a common ancestor in the past. Evolution does not state that modern humans came directly from modern chimpanzees; both species have continued evolving along separate branches. Hence option A is correct, while B is a common misconception and C and D are plainly false.

The governing concept is natural selection through differential reproductive success. If a heritable useful trait helps organisms survive or reproduce, individuals carrying it may leave more offspring. Those offspring can inherit the trait, increasing its frequency in the population over several generations. The change is not guaranteed to be immediate because environment, chance, and inheritance patterns also matter. Thus A is correct; B, C, and D do not follow from increased reproduction.

Heredity explains how genetic information and traits pass from parents to offspring, while evolution explains how inherited variation changes in populations across many generations. Natural selection can preserve useful variations, causing population-level change over time. Thus option A correctly connects the two subjects. The other options incorrectly restrict both ideas to digestion, one lifetime, or no relationship.

In a simple Mendelian example, tallness is treated as the dominant trait and dwarfness as recessive. If T represents tallness and t represents dwarfness, a tall plant may have TT or Tt. In both combinations, at least one dominant T allele is present and the tall phenotype appears. Only tt produces a dwarf plant, so option B is correct; the other choices either describe the recessive condition or are biologically impossible.

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.

Human somatic, or body, cells are diploid and normally contain 46 chromosomes arranged in 23 pairs. Human reproductive cells, or gametes, are haploid and contain 23 chromosomes, one from each pair. This reduced number allows sperm and egg to fuse and restore 46 chromosomes in the zygote. Therefore option B is correct; options A, C and D contradict the normal human chromosome counts.

During sexual reproduction, one sperm and one egg fuse during fertilisation. If each gamete has half the diploid number, 23 + 23 gives the normal human zygote number of 46. Meiosis produces these haploid gametes, and fertilisation restores diploidy. This prevents chromosome number from doubling in every generation, so option A is correct; the other choices misrepresent the purpose of meiosis.

Muscle development caused by exercise is an acquired modification that occurs in body tissues during an individual’s lifetime. It does not ordinarily change the DNA information carried by that person’s reproductive cells, so it is not transmitted directly to offspring. Inherited traits arise from genetic information passed through gametes. Therefore option A is correct; muscles are tissues, not genes, and children do have chromosomes.