CENEVAL EGEL Plus Biología (EGEL Plus BIO)

In phylogenetic systematics, which type of taxonomic group includes an ancestral species and all of its descendants?

• AMonophyletic group (clade)
• BParaphyletic group
• CPolyphyletic group
• DPolytypic grade

Which set of shared derived characteristics (synapomorphies) distinguishes Embryophyta (land plants) from their charophyte green algal ancestors?

• AChlorophylls a and b, starch storage in plastids, and flagellated sperm
• BAlternation of generations, multicellular dependent embryos, and walled spores with sporo…
• CVascular tissue with xylem tracheids, secondary xylem, and lignin deposition
• DDouble fertilization, ovules enclosed within a carpel, and companion cells

A researcher tests whether fertilizer runoff increases algal biomass by adding fertilizer to one pond and leaving a second pond untreated, then collects 30 water samples from each pond. What is the main weakness of this design?

• AUsing an untreated pond as a control introduces bias, so both ponds should have received…
• BThe 60 samples are pseudoreplicates: with only one pond per treatment, pond-to-pond diffe…
• CThirty samples per pond are too many; one sample per pond would give a cleaner comparison
• DThere is no weakness, because a large number of samples guarantees statistical independen…

In the conventional textbook comparison of embryonic development, what distinction is commonly drawn between Protostomia and Deuterostomia?

• AIn protostomes the blastopore becomes the mouth, whereas in deuterostomes it becomes the…
• BIn protostomes the blastopore closes completely, whereas in deuterostomes it develops dir…
• CIn protostomes the blastopore becomes the anus, whereas in deuterostomes it forms the pri…
• DIn protostomes radial cleavage directs blastopore invagination, whereas in deuterostomes…

In a cladistic analysis based on the principle of maximum parsimony, how is homoplasy defined and handled?

• AA trait shared exclusively by two sister taxa that defines an uncontested synapomorphy
• BA shared character state that arose independently through convergence or evolutionary rev…
• CAn ancestral character state retained unchanged across all in-group taxa
• DA character state uniquely derived in a single terminal taxon that provides no phylogenet…

A field project asks whether shade-grown coffee plots host more bird species than sun-grown coffee plots. Which statement is the appropriate null hypothesis for this comparison?

• AShade-grown plots host more bird species than sun-grown plots
• BMean bird species richness does not differ between shade-grown and sun-grown plots
• CBird species richness depends on the altitude of the plots
• DSun-grown plots host no bird species at all

Which biochemical characteristic of the plasma membrane distinguishes Archaea from both Bacteria and Eukarya?

• AUnbranched fatty acid chains linked to D-glycerol by ester bonds
• BBranched isoprenoid hydrocarbons linked to L-glycerol by ether bonds
• CPhospholipids containing hopanoid steroids embedded in a rigid peptidoglycan layer
• DSphingolipids and cholesterol molecules organizing into fluid lipid rafts

Plots for a restoration trial lie along a steep soil-moisture gradient running from a riverbank up a hillside. How should four seed-mix treatments be assigned so that the moisture gradient does not bias the comparison among mixes?

• AAssign each seed mix to its own moisture zone so that every mix experiences uniform condi…
• BPlace all plots of the most promising mix on the wettest ground to maximize seedling surv…
• CDivide the site into blocks of similar moisture and assign all four mixes at random withi…
• DSow all four mixes together in the same plot to save space and labour

Which combination of four morphological features defines the phylum Chordata at some point during their ontogeny?

• AVentral solid nerve cord, dorsal heart, hemocoel, and spiracles
• BNotochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail
• CVertebral column, cranium, paired limbs, and closed double circulation
• DWater vascular system, pentaradial symmetry, tube feet, and endoskeleton

In an experiment on bean germination, seeds from a single seed lot are kept at 15, 20, 25 and 30 °C with the same light and watering, and the percentage that germinate after seven days is recorded. Which is the independent variable?

• AGermination percentage after seven days
• BIncubation temperature
• CThe seed lot used
• DThe light and watering regime

A mining company must show whether a new tailings dam affects the aquatic macroinvertebrate community of a river. Which sampling design provides the strongest evidence about the dam's impact?

• ASample only downstream of the dam after it has been built
• BSample the impact site before and after construction, with no other site
• CSample both the impact site and an upstream control site, before and after construction
• DCompare the impact site after construction with published values from a river in another…

How are the body cavities of flatworms (Platyhelminthes), roundworms (Nematoda), and segmented worms (Annelida) categorized based on their mesodermal lining?

• APlatyhelminthes are coelomate, Nematoda are pseudocoelomate, and Annelida are acoelomate
• BPlatyhelminthes are acoelomate, Nematoda are pseudocoelomate, and Annelida are eucoelomate
• CPlatyhelminthes are pseudocoelomate, Nematoda are acoelomate, and Annelida are hemocoelous
• DAll three phyla are eucoelomates that differ only in whether they form by enterocoely or…

A tree-density survey of a watershed must cover pine-oak forest (60% of the area), cloud forest (25%) and grassland (15%). Which sampling scheme best ensures that each vegetation type is represented in proportion to its area?

• AStratified random sampling, allocating plots to each vegetation type in proportion to its…
• BSimple random sampling of a few plots anywhere in the watershed
• CConvenience sampling of plots located next to the main road
• DSystematic sampling along the river channel only

Which of the following is the best-formulated specific objective for a conservation project?

• AImprove the environmental conditions of the region
• BConserve biodiversity for future generations
• CReduce buffelgrass cover in the 40-hectare study area from 30% to below 10% by December 2…
• DCarry out actions to protect the local ecosystem

While planning a study, a researcher expects only a small difference in mean body mass between two lizard populations, and individual body mass is highly variable. What should she do to reduce the risk of a Type II error?

• ALower the significance level from 0.05 to 0.01
• BIncrease the sample size, using a power analysis to estimate how many lizards are needed
• CDecide after collecting the data to call any result with p < 0.10 significant
• DMeasure fewer lizards so that each one can be weighed more carefully

In molecular phylogenetics and comparative genomics, why is distinguishing orthologous genes from paralogous genes essential for inferring species trees?

• AParalogs result from speciation events and therefore track species divergence directly
• BOrthologs diverge following a speciation event and reflect phylogenetic history, whereas…
• COrthologs are non-coding pseudogenes that accumulate mutations neutrally, whereas paralog…
• DParalogs are transferred horizontally between unrelated bacterial taxa while orthologs ar…

In a research article organized in the IMRaD format (Introduction, Methods, Results and Discussion), in which section should the authors interpret their findings and compare them with previous studies?

• AMethods
• BResults
• CDiscussion
• DIntroduction

A project report must show how mean leaf area (cm²) changes with altitude (m), measured at 25 sites. Which figure is the most appropriate?

• AA pie chart showing each site's share of the total leaf area
• BA scatter plot with altitude on the x-axis and mean leaf area on the y-axis
• CA bar chart with one bar per site, ordered alphabetically by site name
• DA single table listing the 25 site names without the measurements

Which content belongs in the abstract of a research article on a biological project?

• AA brief statement of the objective, the methods, the main quantitative results and the co…
• BThe complete raw data tables so that readers can check every measurement
• CAn extended literature review citing all the sources used in the article
• DAcknowledgements to funding agencies and field assistants

While writing the introduction of a technical report, a biologist copies two sentences word for word from a published article. What must she do?

• ANothing, because published scientific facts are in the public domain
• BPlace the sentences in quotation marks and cite the source, or paraphrase them and still…
• CMention the article only in the acknowledgements section
• DChange a few words so that a citation is no longer needed

The heart rate of the same 20 frogs is measured before and after exposure to a sublethal pesticide dose. Which statistical test is appropriate to compare mean heart rate before and after exposure?

• AAn independent two-sample t-test
• BA paired t-test
• CA chi-square test of independence
• DA Pearson correlation between body mass and heart rate

What is the primary thermodynamic distinction between primary active transport and secondary active transport across cellular membranes?

• APrimary active transport requires channel proteins, whereas secondary active transport re…
• BPrimary active transport couples solute movement directly to ATP hydrolysis, whereas seco…
• CPrimary active transport only transports anions, whereas secondary active transport is re…
• DPrimary active transport operates strictly along electrochemical gradients, whereas secon…

A dihybrid cross yields 160 offspring distributed across four phenotypic classes as 96 : 28 : 26 : 10. The expected Mendelian ratio is 9 : 3 : 3 : 1 (expected counts 90 : 30 : 30 : 10). Which conclusion follows from a chi-square goodness-of-fit test at α = 0.05?

• Aχ² ≈ 1.07 with 3 degrees of freedom; it is below the critical value of 7.81, so the data…
• Bχ² ≈ 1.07 with 3 degrees of freedom; because it is larger than 0.05, the 9 : 3 : 3 : 1 hy…
• Cχ² = 56 with 3 degrees of freedom; it exceeds 7.81, so the 9 : 3 : 3 : 1 hypothesis is re…
• Dχ² ≈ 1.07 with 4 degrees of freedom; the critical value is 9.49, so the result is inconcl…

Population A has a mean wing length of 40 mm with a standard deviation of 4 mm; population B has a mean of 80 mm with a standard deviation of 6 mm. Which population shows greater relative variability?

• APopulation A, with a coefficient of variation of 10%
• BPopulation B, because its standard deviation is larger
• CNeither, because the two standard deviations differ by only 2 mm
• DPopulation B, with a coefficient of variation of 13.3%

Under Mexico's General Law of Ecological Equilibrium and Environmental Protection (LGEEPA), what is the ordenamiento ecológico?

• AThe permit SEMARNAT grants to each individual project before construction begins
• BAn environmental policy instrument that regulates or induces land use and productive acti…
• CThe official list of wild species at risk and their protection categories
• DA federal decree that creates a protected area divided into core and buffer zones

According to LGEEPA Article 19 Bis, through which four types of programs is the ordenamiento ecológico of Mexico's territory carried out?

• AFederal, state, municipal and ejido programs
• BUrban, rural, coastal and forest programs
• CGeneral del Territorio, Regional, Local and Marine programs
• DCore-zone, buffer-zone, restricted-use and sustainable-use programs

The technical studies for a regional ordenamiento ecológico program pass through four stages defined in LGEEPA's implementing regulation on ecological land-use planning. Which stage has the purpose of identifying and analysing the environmental conflicts in the study area, for example through land-aptitude analyses for each sector?

• ACaracterización
• BDiagnóstico
• CPronóstico
• DPropuesta

In the light reactions of oxygenic photosynthesis, where does the photolysis of water occur, and what inorganic catalytic cluster mediates this reaction?

• AOn the stromal side of Photosystem I; an iron-sulfur cluster [4Fe-4S]
• BOn the luminal face of Photosystem II; an oxygen-evolving manganese-calcium cluster (Mn4C…
• CWithin the cytochrome b6f complex; a Rieske [2Fe-2S] center
• DAt the F0 subunit of chloroplast ATP synthase; a magnesium-porphyrin ring

In land-use planning for a fragmented tropical forest, what is the main ecological purpose of establishing a biological corridor between two forest patches?

• ATo maintain habitat connectivity so that organisms can move and exchange genes between pa…
• BTo increase the proportion of edge habitat and its microclimatic effects
• CTo create a physical barrier that keeps all wildlife inside the larger patch
• DTo replace the need to protect the forest patches themselves

In *Escherichia coli* DNA replication, which enzyme is responsible for removing RNA primers and filling the resulting gaps with deoxyribonucleotides on the lagging strand?

• ADNA polymerase I
• BDNA polymerase III
• CDNA ligase
• DDnaB helicase

Under LGEEPA Articles 28 and 30, what must a developer submit to SEMARNAT to obtain environmental impact authorization for a new highway?

• AA municipal land-use certificate only
• BA manifestación de impacto ambiental describing the possible effects on ecosystems and th…
• CAn inventory of NOM-059 species registered with CONABIO
• DA payment to a state environmental fund in place of any study

In eukaryotic pre-mRNA processing, what consensus nucleotide sequence at the 5' splice site, 3' splice site, and branch point is recognized by the spliceosome?

• A5' GU... branch point adenosine... AG 3'
• B5' AG... branch point guanosine... GU 3'
• C5' TATA... branch point cytosine... AATAAA 3'
• D5' CCA... branch point thymine... GUGU 3'

Why is a high proportion of Ephemeroptera, Plecoptera and Trichoptera (EPT) larvae in a stream sample interpreted as a sign of good water quality?

• AEPT larvae feed on pollutants and actively clean the water
• BMost EPT taxa are sensitive to organic pollution and low dissolved oxygen, so their abund…
• CEPT taxa are pollution-tolerant and dominate degraded streams
• DEPT larvae occur only in still water, so they indicate a stable lake

Under what environmental conditions is the *lac* operon in *Escherichia coli* maximally transcribed?

• ALactose is present and glucose is absent
• BBoth lactose and glucose are present in high concentrations
• CBoth lactose and glucose are absent from the growth medium
• DGlucose is present and lactose is absent

How do histone acetylation and DNA methylation typically correlate with eukaryotic transcriptional activity?

• AHistone acetylation promotes open euchromatin and active transcription, whereas DNA methy…
• BHistone acetylation condenses chromatin into heterochromatin, whereas DNA methylation exp…
• CBoth histone acetylation and DNA methylation uniformly silence gene expression by displac…
• DBoth modifications uniformly promote active gene transcription by recruiting basal transc…

Runoff from fertilized fields carries excess nitrogen and phosphorus into a lake. Which sequence best describes the resulting cultural eutrophication?

• AThe nutrients directly poison fish, and algae then disappear because there are fewer herb…
• BThe nutrients lower the lake's pH, dissolving the shells of aquatic organisms
• CAlgal and cyanobacterial blooms develop; when the biomass dies, bacterial decomposition c…
• DThe nutrients reduce algal growth because algae compete with aquatic plants for them

How does Agrobacterium tumefaciens-mediated transformation introduce a transgene into plant cells?

• AThe transgene is placed between the T-DNA borders of a disarmed Ti plasmid, and bacterial…
• BShort electrical pulses open pores in the plant cell wall so that naked plasmid DNA can e…
• CThe bacterium fuses with the plant cell and releases its whole chromosome into the cytopl…
• DThe transgene replicates as an independent plasmid inside the chloroplasts without integr…

In a classic Mendelian dihybrid cross between two heterozygous pea plants (AaBb x AaBb) with independently assorting genes showing complete dominance, what proportion of the offspring is expected to display the dominant phenotype for the first trait and the recessive phenotype for the second trait?

• A3/16
• B9/16
• C1/16
• D6/16

A woman who is a heterozygous carrier of an X-linked recessive condition has children with a phenotypically normal male. What is the probability that their first son will be affected by the condition?

• A50%
• B25%
• C0%
• D100%

In a two-point testcross between a dihybrid female (AaBb) and a homozygous recessive male (aabb), 1,000 offspring are obtained: 420 AaBb, 430 aabb, 78 Aabb, and 72 aaBb. What is the estimated genetic distance between gene A and gene B?

• A15.0 centimorgans (cM)
• B7.5 centimorgans (cM)
• C30.0 centimorgans (cM)
• D42.5 centimorgans (cM)

In a real-time PCR (qPCR) assay with about 100% amplification efficiency, sample A reaches the threshold at cycle 22 (Ct = 22) and sample B at cycle 25 (Ct = 25). What does this indicate about the starting amounts of target DNA?

• ASample B contained about 8 times more starting template than sample A
• BSample A contained about 3 times more starting template than sample B
• CSample A contained about 8 times more starting template than sample B
• DBoth samples contained the same amount, because both eventually crossed the threshold

What is the biochemical rationale for utilizing a thermostable DNA polymerase (such as *Taq* polymerase from *Thermus aquaticus*) in the Polymerase Chain Reaction (PCR)?

• AIt resists thermal denaturation during the high-temperature (94–98 °C) strand separation…
• BIt contains an intrinsic 3' to 5' proofreading exonuclease that prevents all misincorpora…
• CIt synthesizes DNA in both 5' to 3' and 3' to 5' directions simultaneously without requir…
• DIt selectively amplifies methylated eukaryotic genomic DNA while ignoring unmethylated ba…

In chain-termination DNA sequencing (Sanger sequencing), what specific structural feature of dideoxynucleotide triphosphates (ddNTPs) causes termination of DNA strand elongation?

• ALack of a 3'-hydroxyl group (-OH) on the deoxyribose ring, preventing the formation of a…
• BSubstitution of the purine or pyrimidine nitrogenous base with a fluorescent fluorophore…
• CPresence of a bulky sulfate group on the 5'-carbon preventing alpha-phosphate nucleophili…
• DConversion of the phosphodiester backbone into an unstable phosphorothioate linkage

In plasmid cloning with blue-white screening, what molecular event explains why recombinant bacterial colonies containing a foreign DNA insert appear white on agar containing X-gal and IPTG?

• AInsertional inactivation of the *lacZ* alpha-peptide coding sequence within the multiple…
• BThe cloned insert encodes a competitive inhibitor of beta-galactosidase that prevents X-g…
• CIPTG binds irreversibly to the ampicillin resistance gene, suppressing beta-lactamase sec…
• DThe foreign DNA prevents plasmid replication, diluting the beta-galactosidase enzyme acro…

In CRISPR-Cas9 genome editing, what short nucleotide sequence motif adjacent to the target genomic DNA is strictly required for Cas9 binding and double-strand DNA cleavage?

• AProtospacer Adjacent Motif (PAM), canonically 5'-NGG-3' for *Streptococcus pyogenes* Cas9
• BPribnow box consensus sequence (5'-TATAAT-3')
• CShine-Dalgarno ribosomal recruitment motif (5'-AGGAGG-3')
• DInternal ribosome entry site (IRES) polypyrimidine tract

During the depolarization phase of a neuronal action potential, what ionic conductance change drives the membrane potential toward positive values?

• ARapid opening of voltage-gated sodium (Na+) channels, producing an inward sodium current
• BEfflux of potassium (K+) ions through voltage-gated delayed rectifier channels
• CInactivation of the electrogenic Na+/K+ ATPase pump
• DOpening of ligand-gated chloride (Cl-) channels generating an inhibitory postsynaptic cur…

Which Spanish sentence from a field report shows correct subject-verb agreement?

• ALos resultados del muestreo indican que la riqueza de especies disminuyó en las parcelas…
• BEl análisis de las muestras de suelo revelaron una alta concentración de nitratos.
• CSe analizó las muestras de agua en el laboratorio de la estación biológica.
• DLos datos obtenidos en el transecto sugiere un marcado efecto de borde.

In skeletal muscle excitation-contraction coupling, what molecular event directly exposes the myosin-binding sites on actin thin filaments?

• ABinding of calcium ions (Ca2+) to troponin C, inducing a conformational shift in tropomyo…
• BHydrolysis of ATP by the myosin head while detached from actin
• CDepolarization of the T-tubule membrane activating the sarcoplasmic Ca2+-ATPase pump
• DPhosphorylation of the regulatory light chain of myosin by myosin light-chain kinase