Texas Biology STAAR EOC Hub

A nucleotide is made up of which three components?

1. AAn amino acid, a ribosome, and a protein
2. BA phosphate group, a deoxyribose sugar, and a nitrogenous base
3. CA chromosome, a gene, and an allele
4. DA capsid, genetic material, and an envelope

One Strand of a DNA Molecule

Based on complementary base pairing, which sequence represents the other strand of this DNA molecule?

1. AA-T-G-G-C-A (identical to the first strand)
2. BT-A-C-C-G-T
3. CU-A-C-C-G-U
4. DG-C-A-A-T-G

The RNA world hypothesis proposes that early self-replicating RNA molecules existed before DNA-based life. A student claims, "Since this is called a hypothesis, scientists have already proven it is correct." Which statement best evaluates this claim?

1. AThe claim is correct — once something is named a hypothesis, it has been proven.
2. BThe claim is incorrect — a hypothesis is a proposed explanation that is still being tested and refined with evidence, not a proven conclusion.
3. CThe claim is correct, because RNA has been directly observed in fossils from the time period in question.
4. DThe claim is incorrect, but only because hypotheses can never be supported by any evidence.

During which process is mRNA used as a template to assemble a chain of amino acids?

1. ATranscription
2. BTranslation
3. CDNA replication
4. DMitosis

Partial Codon Chart

An mRNA strand reads: AUG–UUU–GGC–UAA. What sequence of amino acids will this mRNA produce?

1. AGlycine–Phenylalanine–Methionine
2. BMethionine–Phenylalanine–Glycine, then translation stops
3. CMethionine–Phenylalanine–Glycine–Stop (all four codons code for amino acids)
4. DNo protein is produced because the sequence contains a stop codon.

A gene's DNA sequence is altered so that the mRNA codon at one position changes from GGC (glycine) to GAC (aspartic acid), while every other codon stays the same. Which statement best predicts the effect on the resulting protein?

1. AThe protein will be completely different, with every amino acid changed.
2. BThe protein will have the same overall length, but one amino acid (glycine) will be replaced with a different amino acid (aspartic acid) at that position, which may or may not change the protein's function depending on that amino acid's role.
3. CNo protein will be produced at all, since any change to mRNA prevents translation.
4. DThe protein will become longer because a new codon was added.

Which type of mutation is most likely to have NO effect on the resulting protein?

1. AFrameshift mutation
2. BNonsense mutation
3. CSilent mutation
4. DInsertion of ten nucleotides

Effects of Four Mutations on a Gene's Protein

Based on the table, which mutation is a frameshift mutation?

1. AMutation 1
2. BMutation 2
3. CMutation 3
4. DMutation 4

Two mutations occur in different genes. Mutation X is a substitution in the third position of a codon that does not change the amino acid produced. Mutation Y is a deletion of one nucleotide near the beginning of a gene. A student claims both mutations are equally likely to significantly affect the organism. Which statement best evaluates this claim?

1. AThe claim is correct — all mutations have the same significance regardless of type or location.
2. BThe claim is incorrect — Mutation X is silent and likely has no effect, while Mutation Y is a frameshift mutation near the start of the gene and is likely to drastically alter or destroy the protein's function.
3. CThe claim is incorrect, but only because Mutation X occurred in DNA while Mutation Y occurred in RNA.
4. DThe claim is correct, because both mutations involve only one nucleotide.

What is the main outcome of meiosis?

1. ATwo genetically identical diploid daughter cells
2. BFour genetically varied haploid gametes
3. COne diploid cell with double the original chromosome number
4. DTwo haploid cells that immediately fuse back together

Chromosome Number at Stages of Meiosis in a Cell with 8 Chromosomes (4 Pairs)

Based on the table, which statement is best supported?

1. AMeiosis II reduces the chromosome number from 4 to 2.
2. BMeiosis I is the division that reduces chromosome number from diploid (8) to haploid (4); meiosis II separates sister chromatids without further reducing the number.
3. CThe starting cell and the final gametes have the same chromosome number.
4. DMeiosis doubles the chromosome number at each stage.

A student observes that two full siblings (same parents) are noticeably different in several inherited traits. The student claims this can only be explained by new mutations occurring in each sibling. Which statement best evaluates this claim?

1. AThe claim is correct — without new mutations, siblings from the same parents would be genetically identical.
2. BThe claim is incorrect — crossing over and independent assortment during meiosis can produce gametes with many different allele combinations, so siblings can differ significantly without any new mutations.
3. CThe claim is incorrect, but only because siblings always have identical DNA regardless of meiosis.
4. DThe claim is correct, because meiosis always produces identical gametes unless a mutation occurs.

An organism with the genotype "Bb" is described as which of the following?

1. AHomozygous dominant
2. BHeterozygous
3. CHomozygous recessive
4. DCodominant

Punnett Square for a Cross Between Two Heterozygous Pea Plants (Tt × Tt), where T (Tall) is dominant over t (short)

Based on the Punnett square, what is the expected ratio of tall to short offspring?

1. A1 tall : 1 short
2. B3 tall : 1 short
3. C1 tall : 3 short
4. DAll offspring will be tall

A parent with blood type A (genotype AO) and a parent with blood type B (genotype BO) have a child. A student claims the child cannot have blood type AB, because neither parent has type AB blood. Which statement best evaluates this claim?

1. AThe claim is correct — a child's blood type can never differ in category from both parents' blood types.
2. BThe claim is incorrect — the child could inherit the A allele from one parent and the B allele from the other, resulting in genotype AB and, due to codominance, blood type AB.
3. CThe claim is incorrect, but only because blood type is determined by a single allele, not multiple alleles.
4. DThe claim is correct, because the O alleles from each parent would dominate and the child would have type O blood.

The bones in a human arm, a bat wing, and a whale flipper have a similar arrangement but different functions. What type of evidence does this represent?

1. ABiogeography
2. BAnatomical homology
3. CThe fossil record
4. DMolecular homology

Percent DNA Sequence Similarity to Species X

Based on the data, which conclusion is best supported?

1. ASpecies W shares the most recent common ancestor with Species X.
2. BSpecies Y likely shares a more recent common ancestor with Species X than Species W does.
3. CDNA similarity provides no information about evolutionary relationships.
4. DSpecies X and Species Y cannot be related because their DNA is not identical.

Whales have small, non-functional pelvic bones embedded in their bodies, similar in position to the pelvic bones that support hind limbs in other mammals. A student claims these bones serve no purpose and therefore provide no scientific information. Which statement best evaluates this claim?

1. AThe claim is correct — structures with no current function cannot be used as evidence.
2. BThe claim is incorrect — as vestigial structures, these reduced pelvic bones are evidence that whales share ancestry with land mammals that used such bones to support hind limbs.
3. CThe claim is incorrect, but only because the bones are actually still used for swimming.
4. DThe claim is correct, because vestigial structures always disappear completely within one generation.

What must a scientific explanation be, in order to be considered scientific?

1. AAccepted by the public without question
2. BTestable and supported by evidence
3. CPermanent and never subject to revision
4. DBased only on a single observation

Comparing Mitochondria to Bacteria and to the Rest of the Eukaryotic Cell

Which conclusion is best supported by this data?

1. AMitochondria are identical to bacteria in every way.
2. BMitochondria share more features with bacteria than with the rest of the eukaryotic cell, consistent with the endosymbiotic theory.
3. CMitochondria have no DNA of their own.
4. DThe data shows mitochondria are unrelated to both bacteria and eukaryotic cells.

A student says, "The endosymbiotic theory is 'just a theory,' so it could be completely wrong and replaced by a totally different explanation tomorrow." Which statement best evaluates this claim?

1. AThe claim is correct — in science, "theory" means an unproven guess that could be discarded at any time.
2. BThe claim is incorrect — in science, a theory is a well-substantiated explanation supported by multiple independent lines of converging evidence; while details could be refined with new evidence, it is unlikely to be "completely wrong" or abruptly replaced.
3. CThe claim is incorrect, but only because scientific theories are voted on and cannot be changed once accepted.
4. DThe claim is correct, because no evidence currently supports the endosymbiotic theory.

Natural selection most directly results in a change in which of the following?

1. AThe traits of a single individual during its lifetime
2. BThe frequency of traits or alleles in a population across generations
3. CThe number of chromosomes in a species' cells
4. DThe location of genes on a chromosome within one generation

Frequency of Dark-Colored Moths in a Population Over Time

Based on the data, which statement is best supported?

1. AIndividual moths are changing color as they age.
2. BThe frequency of the dark-color trait in the moth population is increasing across generations, suggesting it provides a survival or reproductive advantage in this environment.
3. CThe total number of moths is decreasing over time.
4. DDark coloration provides no advantage, since the percentage changed.

A student writes: "Giraffes evolved long necks because individual giraffes kept stretching their necks to reach high leaves, and this stretching was passed on to their offspring." Which statement best evaluates this claim?

1. AThe claim is correct — traits acquired through an individual's behavior during its lifetime are passed directly to offspring.
2. BThe claim is incorrect — neck-stretching during an individual's lifetime does not change its offspring's genes; instead, giraffes with genes for longer necks would have had a survival/reproductive advantage, increasing the frequency of those genes in the population over generations.
3. CThe claim is incorrect, but only because giraffes do not stretch their necks.
4. DThe claim is correct, as long as enough giraffes stretch their necks at the same time.

Which best defines an adaptation?

1. AAny trait an organism develops during its lifetime in response to its environment
2. BA heritable trait, shaped by natural selection, that increases an organism's fitness in its environment
3. CA trait that all members of a species share, regardless of environment
4. DA random mutation with no effect on survival

Beak Shape and Primary Food Source in Three Related Bird Species on Different Islands

All three species descended from a common ancestor. Based on the table, which conclusion is best supported?

1. AThe three species are unrelated and evolved completely independently.
2. BEach species' beak shape is an adaptation suited to its primary food source, consistent with divergence from a common ancestor through adaptive radiation.
3. CAll three species eat the same food, so beak shape does not matter.
4. DBeak shape is unrelated to diet in birds.

Dolphins (mammals) and sharks (fish) are not closely related, yet both have streamlined, torpedo-shaped bodies and fins. A student claims this similarity must mean dolphins and sharks share a very recent common ancestor. Which statement best evaluates this claim?

1. AThe claim is correct — any shared physical trait indicates a recent common ancestor.
2. BThe claim is incorrect — the similar body shapes likely arose through convergent evolution, as both species independently evolved adaptations suited to moving efficiently through water, despite not being closely related.
3. CThe claim is incorrect, but only because sharks cannot have adaptations.
4. DThe claim is correct, because all aquatic animals are closely related by definition.

Which statement best explains how a bacterial population can become resistant to an antibiotic?

1. AThe antibiotic causes every bacterium to develop resistance at the same time.
2. BSome bacteria already carry resistant alleles; the antibiotic kills susceptible bacteria, allowing resistant bacteria to survive and reproduce, increasing their frequency.
3. CResistance only develops if no bacteria are killed by the antibiotic.
4. DBacteria cannot become resistant to antibiotics.

Percent of a Bacterial Population Resistant to an Antibiotic After Repeated Treatments

Based on the data, which statement is best supported?

1. AThe antibiotic is becoming more effective with each treatment round.
2. BRepeated antibiotic treatments act as a selective pressure that increases the proportion of resistant bacteria in the population over time.
3. CResistant bacteria existed only after treatment round 3.
4. DThe data shows no relationship between antibiotic treatment and resistance.

A student claims, "The antibiotic caused the bacteria's DNA to mutate, creating new resistance genes that didn't exist before the antibiotic was used." Which statement best evaluates this claim?

1. AThe claim is correct — antibiotics directly cause beneficial mutations to appear in response to the threat.
2. BThe claim is incorrect — resistant alleles typically already exist at low frequency in the population due to ongoing genetic variation; the antibiotic does not create them but instead selects for individuals who already have them.
3. CThe claim is incorrect, but only because bacteria cannot have any genetic variation.
4. DThe claim is correct, because resistance only appears after the first exposure to an antibiotic.

Which evolutionary mechanism involves random changes in allele frequency that are especially significant in small populations?

1. ANatural selection
2. BGenetic drift
3. CGene flow
4. DRecombination

Allele Frequency Change After One Generation in Two Populations

Based on the data, which conclusion is best supported?

1. ABoth populations show the same type and magnitude of allele frequency change.
2. BThe large change in Population 2 is consistent with genetic drift, which has a much greater effect in small populations than in large ones.
3. CPopulation 1's small change shows it is more affected by genetic drift than Population 2.
4. DAllele frequency cannot change in a single generation.

A small population of beetles, isolated on a remote island for one generation, shows a large increase in the frequency of a particular shell-color allele. There is no evidence this allele provides any survival or reproductive advantage on the island. Which evolutionary mechanism best explains this change?

1. ANatural selection, because any allele frequency change must be due to a fitness advantage.
2. BGenetic drift, because the change occurred in a small population and is not linked to any fitness advantage — consistent with a random shift, possibly amplified by a founder effect if the island population began from few individuals.
3. CGene flow, because the beetles migrated to a new island.
4. DMutation, because a new allele must have just appeared.

A tapeworm lives inside the digestive tract of a dog, absorbing nutrients and harming the dog's health. Which type of relationship does this describe?

1. AMutualism
2. BParasitism
3. CCommensalism
4. DCompetition

Predator and Prey Population Sizes Over Time

Based on the data, which statement is best supported?

1. APredator and prey populations change completely independently of each other.
2. BIncreases in the prey population tend to be followed by increases in the predator population, and predator increases tend to be followed by prey declines — a typical predator-prey cycle.
3. CThe predator population is always larger than the prey population.
4. DBoth populations only ever increase over time.

A bird species regularly removes and eats ticks from the backs of large grazing mammals. A student claims this must be parasitism because the bird benefits from the relationship. Which statement best evaluates this claim?

1. AThe claim is correct — any relationship where one species clearly benefits is parasitism.
2. BThe claim is incorrect — the bird benefits by gaining food, and the grazing mammal also benefits by having parasitic ticks removed, making this mutualism rather than parasitism.
3. CThe claim is incorrect, but only because birds cannot be parasites.
4. DThe claim is correct, because the grazing mammal is unaffected by the bird's actions.

Which of the following is an abiotic factor in an ecosystem?

1. AA population of deer
2. BSoil pH
3. CA predator-prey relationship
4. DA community of decomposers

Abiotic Measurements and Species Richness at Three Sites Along an Estuary

Based on the data, which conclusion is best supported?

1. ASalinity has no relationship to which species are present at each site.
2. BDifferent salinity levels (an abiotic factor) along the estuary are associated with different species communities (a biotic factor) at each site.
3. CThe mid-estuary site has the lowest salinity of the three sites.
4. DSpecies richness always decreases as salinity increases.

Two bird species live in the same forest and both eat insects. Researchers observe that Species A feeds mainly in the treetops while Species B feeds mainly on the forest floor. A student claims the two species must not be competing at all, since they coexist in the same forest. Which statement best evaluates this claim?

1. AThe claim is correct — species that live in the same forest never compete.
2. BThe claim oversimplifies the situation — the two species likely reduced competition through resource partitioning (feeding in different locations), which is a reason they can coexist, not evidence that competition never occurs between them.
3. CThe claim is incorrect, but only because both species eat insects.
4. DThe claim is correct, because niche differences always eliminate competition completely and permanently.

Which trophic level captures energy directly from sunlight?

1. APrimary consumers
2. BProducers
3. CSecondary consumers
4. DDecomposers

Energy Available at Each Trophic Level

Applying the 10% rule, approximately how much energy would be available at the tertiary consumer level?

1. A10,000 kcal
2. B100 kcal
3. C1,000 kcal
4. D100,000 kcal

A student claims, "If we want more energy available for top predators in an ecosystem, we should just remove the primary consumers, since they're 'wasting' energy that could go to the predators directly." Which statement best evaluates this claim?

1. AThe claim is correct — removing a trophic level always increases energy available to the level above it.
2. BThe claim is incorrect — top predators in this ecosystem rely on primary consumers as their food source (directly or through secondary consumers); removing primary consumers would eliminate the predators' energy source rather than redirect energy to them.
3. CThe claim is incorrect, but only because producers would also need to be removed.
4. DThe claim is correct, as long as the top predators can photosynthesize.

What does "carrying capacity" refer to?

1. AThe total number of species in an ecosystem
2. BThe maximum population size an environment can sustain given its available resources
3. CThe rate at which a population reproduces
4. DThe number of trophic levels in a food web

Deer Population in a Forest Over 10 Years

Based on the data, which statement is best supported?

1. AThe population will keep growing indefinitely at the same rate as years 1-5.
2. BThe population grew rapidly at first and is now leveling off near approximately 480-490, suggesting it is approaching the forest's carrying capacity.
3. CThe forest has no limiting factors affecting the deer population.
4. DThe deer population reached its maximum in year 1.

An invasive plant species is introduced to a Texas grassland and rapidly spreads, using water and soil nutrients that native grasses depend on. A student claims this will have no effect on the carrying capacity for native grazing animals, since the invasive plant doesn't directly interact with the animals. Which statement best evaluates this claim?

1. AThe claim is correct — only direct interactions between species can affect carrying capacity.
2. BThe claim is incorrect — by outcompeting native grasses for water and nutrients, the invasive plant can reduce the amount of native grass available as food, lowering the carrying capacity for native grazing animals even without any direct interaction.
3. CThe claim is incorrect, but only because invasive species always go extinct quickly.
4. DThe claim is correct, because carrying capacity is determined only by predator populations.