STAAR (State of Texas Assessments of Academic Readiness) Biology (STAAR EOC) Syllabus

What enzyme builds the new DNA strand during replication?

DNA polymerase.

What are the two main stages of protein synthesis and where does each occur?

Transcription (DNA -> mRNA) occurs in the nucleus; translation (mRNA -> protein) occurs at the ribosome in the cytoplasm.

What is a codon and how many nucleotides does it contain?

A codon is a sequence of three nucleotides (a triplet) on mRNA that codes for one amino acid.

What is the role of tRNA in translation?

tRNA carries specific amino acids to the ribosome and matches its anticodon to the mRNA codon, adding the correct amino acid to the growing protein chain.

Compare DNA and RNA in three ways.

DNA is double-stranded, uses deoxyribose, and contains thymine; RNA is single-stranded, uses ribose, and contains uracil instead of thymine.

State Mendel's law of segregation.

Each organism carries two alleles for a trait that separate during gamete formation, so each gamete receives only one allele.

State Mendel's law of independent assortment.

Alleles for different traits are distributed to gametes independently of one another.

Define the terms genotype and phenotype.

Genotype is the genetic makeup (alleles, e.g., Bb); phenotype is the observable physical trait (e.g., brown eyes).

In a cross between two heterozygous parents (Bb x Bb), what is the expected genotypic and phenotypic ratio?

Genotypic ratio 1 BB : 2 Bb : 1 bb; phenotypic ratio 3 dominant : 1 recessive.

What is incomplete dominance? Give an example.

Incomplete dominance is when the heterozygote shows a blended intermediate phenotype, e.g., red x white snapdragons producing pink flowers.

What is codominance? Give an example.

Codominance is when both alleles are fully and separately expressed in the heterozygote, e.g., AB blood type or roan coat color.

Explain sex-linked inheritance and why males are more often affected by X-linked recessive disorders.

Sex-linked genes are carried on the X chromosome; males (XY) have only one X, so a single recessive allele is expressed, making them more frequently affected (e.g., color blindness, hemophilia).

What is the result of mitosis and what is its purpose?

Mitosis produces two genetically identical diploid daughter cells; its purpose is growth, repair, and asexual reproduction.

What is the result of meiosis and how does it differ from mitosis?

Meiosis produces four genetically unique haploid gametes; unlike mitosis, it involves two divisions and reduces the chromosome number by half.

What is crossing over and why is it important?

Crossing over is the exchange of segments between homologous chromosomes during prophase I of meiosis; it increases genetic variation.

What is natural selection?

Natural selection is the process by which organisms with favorable heritable traits survive and reproduce at higher rates, passing those traits to offspring.

List the four conditions required for natural selection to occur.

(1) Overproduction of offspring, (2) genetic variation, (3) competition/struggle for survival, and (4) differential survival and reproduction (survival of the fittest).

How does genetic drift differ from natural selection?

Genetic drift is a random change in allele frequencies (strongest in small populations), whereas natural selection is non-random change driven by differential fitness.

List four major categories of evidence for evolution.

Fossil record, comparative anatomy (homologous and vestigial structures), embryology, and molecular/biochemical similarities (DNA and proteins).

What is the difference between homologous and analogous structures?

Homologous structures share a common evolutionary origin but may differ in function (e.g., whale flipper and human arm); analogous structures have similar function but different origins (e.g., bird and insect wings).

What are vestigial structures and what do they indicate?

Vestigial structures are reduced or functionless remnants of structures that were useful in ancestors (e.g., human appendix), providing evidence of common descent.

List the levels of the Linnaean classification system from broadest to most specific.

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Explain binomial nomenclature using an example.

Binomial nomenclature is a two-name Latin system using genus and species, e.g., Homo sapiens; the genus is capitalized and both names are italicized.

What are the three domains of life?

Bacteria, Archaea, and Eukarya.

What does a phylogenetic tree (cladogram) show?

It shows evolutionary relationships and common ancestry among organisms, with branch points (nodes) representing shared common ancestors.

On a cladogram, what does a shared derived characteristic indicate?

It indicates that the organisms sharing that trait descended from a common ancestor that first had it, grouping them on the same branch (clade).

List the levels of biological organization in an ecosystem from smallest to largest.

Organism, population, community, ecosystem, biome, biosphere.

What is the difference between a population and a community?

A population is all members of one species in an area; a community is all the different populations (species) interacting in that area.

What are the functions of xylem and phloem in plants?

Xylem transports water and minerals upward from the roots; phloem transports sugars (food) made in the leaves to the rest of the plant.

What is transpiration in plants?

Transpiration is the loss of water vapor through the stomata of leaves, which helps pull water up through the xylem.

Define homeostasis and give an example in animals.

Homeostasis is the maintenance of a stable internal environment; for example, humans regulating body temperature near 37 degrees C through sweating or shivering.

What is negative feedback in homeostasis? Give an example.

Negative feedback is a response that reverses or counteracts a change to restore balance, e.g., insulin lowering blood glucose after a meal.

Why are viruses considered nonliving by most biologists?

Viruses are not made of cells, cannot carry out metabolism or reproduce on their own, and must hijack a host cell's machinery to replicate.

Describe the basic structure of a virus.

A virus consists of genetic material (DNA or RNA) enclosed in a protein coat called a capsid; some also have a lipid envelope.

In an energy pyramid, approximately how much energy is transferred from one trophic level to the next?

About 10 percent; the remaining ~90 percent is lost as heat through metabolic processes.

Distinguish producers, consumers, and decomposers in an ecosystem.

Producers (autotrophs) make their own food via photosynthesis; consumers (heterotrophs) eat other organisms; decomposers break down dead matter and recycle nutrients.

What is the difference between a food chain and a food web?

A food chain shows a single linear path of energy flow; a food web shows the interconnected, overlapping feeding relationships of many organisms.

Describe the key steps of the carbon cycle.

Carbon moves from the atmosphere (CO2) into producers via photosynthesis, through food chains, and returns to the atmosphere via respiration, decomposition, and combustion of fossil fuels.

What role do bacteria play in the nitrogen cycle?

Nitrogen-fixing bacteria convert atmospheric N2 into usable ammonia/nitrates; decomposers and denitrifying bacteria return nitrogen to the soil and atmosphere.

What is carrying capacity?

Carrying capacity is the maximum population size an environment can support indefinitely given available resources.

Contrast exponential and logistic population growth.

Exponential growth produces a J-shaped curve with unlimited resources; logistic growth produces an S-shaped curve that levels off at carrying capacity due to limiting factors.

Differentiate density-dependent and density-independent limiting factors.

Density-dependent factors (e.g., disease, competition, predation) intensify as population density rises; density-independent factors (e.g., natural disasters, weather) affect populations regardless of size.

Define a keystone species.

A keystone species has a disproportionately large effect on its ecosystem; its removal causes major changes in community structure (e.g., sea otters controlling sea urchins).

What is the difference between primary and secondary ecological succession?

Primary succession begins on bare rock/lifeless areas with no soil (e.g., after a volcano); secondary succession occurs where a disturbance left soil intact (e.g., after a fire or farming).

What is a pioneer species and give an example?

A pioneer species is the first organism to colonize a barren area and begin soil formation, such as lichens and mosses.

What is a climax community?

A climax community is the relatively stable, mature stage of ecological succession that persists until a major disturbance occurs.

Compare symbiotic relationships: mutualism, commensalism, and parasitism.

Mutualism: both species benefit (+/+); commensalism: one benefits and the other is unaffected (+/0); parasitism: one benefits at the other's expense (+/-).

What is the role of the cell membrane and what model describes it?

The cell membrane controls what enters and leaves the cell (selective permeability); it is described by the fluid mosaic model of a phospholipid bilayer with embedded proteins.

How does a mutation in DNA potentially affect a protein?

A change in the DNA base sequence can alter the mRNA codons, changing the amino acid sequence and possibly the structure and function of the resulting protein.

What is the central dogma of molecular biology?

The flow of genetic information: DNA -> RNA -> protein (replication, transcription, then translation).

What is biodiversity and why is it important to ecosystem stability?

Biodiversity is the variety of species in an ecosystem; greater biodiversity increases stability and resilience, helping the ecosystem recover from disturbances.