Heredity and Evolution

Fossils provide a time-ordered record of organisms and can reveal changes in forms that lived in the past. Homologous organs have a similar basic structural plan, even when their functions differ, suggesting common ancestry. When both types of evidence are considered together, they support change over generations and relationships among organisms. Thus option A is correct; the other choices confuse evolutionary evidence with feeding, acquired traits, or sex determination.

Evolution concerns changes in inherited characteristics of populations across generations. A colour difference can be useful, but it contributes to evolution only if the genetic information responsible for it can pass through reproductive cells to offspring. A change acquired during an individual’s lifetime is generally not inherited merely because it is useful. Therefore option A is correct; options B, C and D prevent the trait from being reliably transmitted between generations.

Natural selection depends on the interaction between existing variation and environmental conditions. Different environments present different challenges, such as temperature, food availability, predators or disease. A trait that improves survival or reproduction in one environment may provide little benefit, or even a disadvantage, in another. Over generations, selection can therefore increase different heritable traits in the two populations. Hence option A is correct; the other options deny variation or misunderstand selection.

Homologous organs are identified by a common basic structural plan and evolutionary origin, not by identical present-day use. The bones of the human forelimb and bird forelimb correspond in arrangement, but natural selection has modified them for different functions. A human hand is mainly adapted for grasping and manipulation, whereas a bird wing is adapted for flight. Therefore option A is correct; homology does not require functional identity.

The governing concept is that inherited information must be present in the genetic material of reproductive cells, such as sperm or eggs. During reproduction, these cells transmit genes to the offspring. Therefore, a change confined to body cells cannot normally enter the next generation. Option A is correct; B is false because body cells do not form offspring, C ignores the difference between acquired and inherited changes, and D is false because reproductive cells do contain chromosomes.

The governing principle is the distinction between acquired traits and inherited traits. Exercise can enlarge or strengthen muscles during an individual’s lifetime, but this bodily change does not normally alter the DNA of sperm or eggs. Since offspring receive hereditary information through reproductive cells, the exercise-developed muscle is not directly transmitted. Option A is correct; B confuses tissue with chromosomes, C is scientifically false, and D is false because offspring inherit genes.

The governing concept is genetic recombination in sexual reproduction. A child receives hereditary material from two parents, and the combination of their alleles is not an exact copy of either parent. Independent assortment and the random union of gametes can produce new combinations, increasing variation among offspring. Option A is correct; B describes copying rather than sexual reproduction, while C and D are biologically incorrect.

The governing concept is that asexual reproduction usually produces genetically similar offspring from one parent, but copying DNA is not perfectly error-free. Occasional small mutations or copying errors can create differences in the genetic material. Environmental effects may also influence appearance, but the biological source of inherited variation here is copying error. Option A is correct; B describes sexual reproduction, C is false because chromosomes are present, and D is not a genetic explanation.

The governing concept is chromosome-number maintenance through haploid gametes and fertilisation. In normal sexual reproduction, each sperm or egg has half the species-specific chromosome number. If both reproductive cells carried the full number, their fusion would add two complete sets and double the chromosome number in the offspring. Repeating this in each generation would cause continual increase. Option A is correct; the other choices do not follow from fertilisation.

The governing concept is that the mother normally contributes X through every egg, while the father’s sperm contributes either X or Y. An XX combination results when an X-bearing sperm fertilises the egg, and an XY combination results when a Y-bearing sperm does so. Therefore, repeatedly having daughters is not scientifically the mother’s fault. Option A is correct; the other options refer to biological factors that should be understood, not unfairly blamed.

Natural selection acts on heritable variation when some individuals survive and reproduce more successfully than others. A colour that provides camouflage helps an organism escape predators, so its carriers may leave more offspring. If the colour is inherited, its frequency can increase over generations. Therefore option A directly shows selection, whereas identical organisms, no reproduction, or no environmental pressure provide no effective basis for selection.

In undisturbed sedimentary rock, deeper layers are generally older than layers above them. Fossils from these successive layers provide a relative sequence of past life. Comparing their structures and types can reveal that organisms appeared, changed or disappeared through geological time, providing evidence for evolution. It cannot tell only today's temperature, food taste or a common age for all organisms. Therefore A is correct, while B, C and D are unrelated or false.

Fossils are preserved remains, impressions or traces of organisms from the past, so they reveal earlier forms and the sequence of biological change. However, fossilisation requires special conditions, such as protection from rapid decay, and many organisms leave no preserved record. The fossil record is therefore incomplete and must be interpreted with comparative anatomy, embryology, genetics and other evidence. Option A captures both its value and limitation; B, C and D are false.

Homologous organs are identified mainly by similarity in basic structural plan and evolutionary origin, not by identical function. The human arm is used for grasping, while a bat wing is used for flight, yet both contain corresponding bones such as the upper arm, forearm and hand elements. This structural relationship suggests common ancestry, so option A is correct. Option B describes neither their actual functions nor homology; C is factually false; D describes analogous similarity incorrectly.

Analogous organs perform a similar function but arise from different basic structures and evolutionary origins. A bird wing is a modified forelimb containing bones, whereas an insect wing is an outgrowth of the exoskeleton and has no corresponding vertebrate bone plan. Both support flight, but that shared function does not establish close common ancestry. Therefore option A is correct. Option B confuses analogy with homology, C is false, and D makes an unjustified claim about ancestry.

External resemblance alone is not reliable evidence of close evolutionary relationship because unrelated groups can develop similar features when they face similar environmental demands. These are analogous similarities, produced by convergent evolution. Scientists therefore also compare internal anatomy, embryology, fossils and molecular evidence. Option A is correct because similar outward function may hide different origins. B and C are plainly false, while D wrongly treats every resemblance as proof of common ancestry.

Evolution is not a fixed ladder in which every organism climbs toward a supposedly superior form. Populations diverge from common ancestors, and different lineages undergo changes suited to their environments; some lineages may also become extinct. A branching tree represents these splits, relationships and multiple directions more accurately. Thus option A is correct. B and C incorrectly assume that humans are the goal of evolution, while D directly contradicts the evidence of divergent evolution.

Shared anatomical, genetic and biochemical features can indicate that two groups descended from a common ancestral population. Humans did not evolve directly from the chimpanzees alive today; instead, humans and chimpanzees represent separate lineages that diverged from an older common ancestor. Therefore option A expresses the scientifically correct conclusion. Option B reverses the meaning of common ancestry, C is unsupported, and D ignores substantial comparative evidence of relatedness.

Evolution does not follow a universal rule that organisms must become increasingly complex. Natural selection favours traits that improve survival and reproduction in a particular environment, and a relatively simple body plan can remain highly successful for a long time. Consequently, present simplicity does not mean evolutionary failure or inferiority. Option A is correct. B and C promote the ladder misconception, while D is false because simple organisms also possess genetic material.

An evolutionary tree is a diagram of inferred relationships among organisms or groups. When two branches join at a node that is relatively recent, the groups may share a more recent common ancestor than groups whose branches join farther back. This indicates relative relatedness, not necessarily identical species or complete similarity. Therefore option A is correct. B denies the purpose of the tree, C overstates the conclusion, and D is biologically false.

An acquired trait develops during an individual's lifetime because of practice, use, injury, nutrition, or environmental conditions; examples include increased muscle strength from exercise. An inherited trait is associated with genetic information and can be transmitted through reproductive cells, although its expression may also be influenced by the environment. Therefore option A gives the correct distinction. B is too absolute, C is the opposite of inheritance, and D ignores an important biological difference.

Variation gives a population a range of characteristics. When the environment changes, such as through a new climate, disease, or food shortage, some existing characteristics may provide better survival than others. If individuals are nearly identical, the same environmental threat may harm most or all of them, leaving little opportunity for adaptation through selection. Hence option A is correct. B and C deny the protective role of variation, and D incorrectly describes speciation.

Evolutionary relationships are reconstructed by comparing several independent lines of evidence. Body structures can reveal homologous patterns, fossils provide information about organisms and changes in the past, and similarities in DNA or proteins can indicate common ancestry. One feature alone may be misleading because unrelated organisms can resemble one another through similar adaptations. Therefore option A is the most reliable basis. Colour, habitat, or size alone cannot establish evolutionary relationships.

Natural selection depends on heritable differences among individuals. If every organism has the same relevant trait, environmental conditions cannot favour one individual over another for that trait. Consequently, differential survival and reproduction are limited, so the population cannot readily change through selection. Option A is correct; the other options describe processes unrelated to the requirement of variation.

Let T represent the dominant tall allele and t the recessive dwarf allele. A hybrid tall plant has genotype Tt, so the cross is Tt × Tt. The possible offspring are TT, Tt, Tt and tt. Only tt is dwarf, giving 1 out of 4 offspring, or 25%. Thus A is correct. The 3:1 ratio refers to tall:dwarf phenotypes, not to the dwarf proportion alone.