Angola 12th Grade National Examination — Biology (Biologia)

Which statement correctly represents a core tenet of the classical Cell Theory formulated by Schleiden, Schwann, and Virchow?

• AAll living organisms are composed of one or more cells, and all cells arise from pre-exis…
• BCells can spontaneously generate from non-living organic matter under anaerobic condition…
• CAll cells possess a membrane-bound nucleus and compartmentalized membrane organelles.
• DViruses represent the most primitive independent cellular life forms capable of autonomou…

According to the Fluid Mosaic Model proposed by Singer and Nicolson, how is the eukaryotic plasma membrane organized?

• AA rigid protein monolayer sandwiched between two continuous carbohydrate sheets
• BA phospholipid bilayer with hydrophobic tails facing inward and proteins embedded or atta…
• CA solid crystalline grid of cholesterol molecules surrounded by fixed peripheral glycopro…
• DA double layer of nucleic acids coated with structural polysaccharides and fibrous lipids

How does simple diffusion differ fundamentally from facilitated diffusion across a biological membrane?

• ASimple diffusion requires ATP hydrolysis, whereas facilitated diffusion operates without…
• BSimple diffusion moves solutes against their concentration gradient, whereas facilitated…
• CSimple diffusion moves non-polar solutes directly through the lipid bilayer, whereas faci…
• DSimple diffusion only occurs in plant cells, whereas facilitated diffusion is restricted…

When a plant cell is placed in a strongly hypertonic sucrose solution, what physiological change is observed?

• AWater enters the vacuole, causing the cell to swell and eventually lyse.
• BSolutes rapidly enter the cell, increasing turgor pressure against the primary cell wall.
• CThe cell wall degrades completely due to osmotic pressure, turning the cell into an anima…
• DWater exits the protoplast by osmosis, causing the plasma membrane to pull away from the…

What is the stoichiometric action and primary biological consequence of the plasma membrane Na+/K+ ATPase pump?

• APumps 3 Na+ out of the cell and 2 K+ into the cell per ATP hydrolyzed, maintaining negati…
• BPumps 2 Na+ into the cell and 3 K+ out of the cell per ATP hydrolyzed, depolarizing the c…
• CPumps 3 Na+ and 3 K+ out of the cell simultaneously without using ATP, equilibrating elec…
• DPumps 1 Na+ and 1 K+ in opposite directions by passive cotransport coupled with glucose d…

Which bulk transport mechanism enables human macrophages to engulf whole bacterial pathogens into specialized phagosomes?

• APinocytosis
• BPhagocytosis
• CReceptor-mediated exocytosis
• DFacilitated diffusion through porins

What is the correct sequential pathway of a newly synthesized secretory protein through the eukaryotic endomembrane system?

• ASmooth ER → Nucleus → Lysosome → Plasma membrane
• BGolgi apparatus → Rough ER → Peroxisome → Secretory vesicle
• CRough ER → Transport vesicle → Golgi apparatus cis-to-trans face → Secretory vesicle → Pl…
• DFree cytosolic ribosome → Mitochondria matrix → Transport vesicle → Exocytosis

How do lysosomes and peroxisomes differ in their internal enzymatic machinery and primary metabolic functions?

• ALysosomes carry out ATP synthesis via oxidative phosphorylation, whereas peroxisomes synt…
• BLysosomes break down hydrogen peroxide into oxygen and water, whereas peroxisomes digest…
• CLysosomes are double-membraned semi-autonomous organelles, whereas peroxisomes lack any l…
• DLysosomes contain hydrolytic enzymes active at acidic pH for digestion, whereas peroxisom…

Which cytoskeletal component is primarily responsible for forming the mitotic spindle apparatus and guiding chromosome separation during cell division?

• AMicrotubules composed of alpha and beta tubulin heterodimers
• BActin microfilaments
• CKeratin intermediate filaments
• DCollagen fibrils embedded in the extracellular matrix

Which piece of biological evidence most strongly supports the Endosymbiotic Theory for the evolutionary origin of mitochondria and chloroplasts?

• AThey are enclosed in a single phospholipid monolayer synthesized by the host Golgi appara…
• BThey possess their own circular DNA, 70S ribosomes, and replicate via binary fission-like…
• CThey share identical linear chromosomes with eukaryotic host nuclei.
• DThey lack internal membranes and synthesize proteins using 80S eukaryotic cytoplasmic rib…

During which subphase of interphase does semiconservative replication of nuclear DNA take place?

• AG1 phase (First Gap)
• BG2 phase (Second Gap)
• CS phase (Synthesis)
• DG0 phase (Quiescence)

In which mitotic phase do sister chromatids synchronously separate and move toward opposite poles of the dividing cell?

• AProphase
• BMetaphase
• CTelophase
• DAnaphase

What cytological event occurs during the pachytene stage of Prophase I in meiosis that generates new combinations of alleles?

• ACrossing-over (homologous recombination) between non-sister chromatids of a bivalent
• BCentromere division of sister chromatids
• CDegradation of homologous maternal chromosomes by endonucleases
• DFusion of two haploid nuclei into a tetraploid zygote

For a diploid organism with 2n = 6 chromosomes, how many genetically distinct gamete combinations can be produced solely through independent assortment in Meiosis I (excluding crossing-over)?

• A3
• B8
• C6
• D64

Which comparison between mitotic cell division and meiotic cell division is biologically accurate?

• AMitosis involves two successive nuclear divisions, whereas meiosis consists of a single e…
• BMitosis creates gametes for sexual reproduction, whereas meiosis facilitates somatic tiss…
• CMitosis produces two genetically identical diploid (2n) daughter cells, whereas meiosis p…
• DMitosis reduces the chromosome number by half, whereas meiosis preserves the ploidy level.

How do biological enzymes accelerate the rate of cellular chemical reactions?

• ABy increasing the temperature and kinetic energy of the whole cell
• BBy permanently binding to substrates and becoming consumed as reactants
• CBy shifting endergonic reactions into exergonic reactions by adding extra thermal calories
• DBy lowering the activation energy barrier without altering the overall free energy change…

In enzyme kinetics, how does a reversible competitive inhibitor alter the apparent Km and Vmax of the reaction?

• AIncreases apparent Km while leaving Vmax unchanged at sufficiently high substrate concent…
• BDecreases apparent Km and decreases Vmax proportionally
• CReduces Vmax while leaving apparent Km completely unchanged
• DIncreases Vmax and decreases apparent Km by permanently modifying the active site

What molecular mechanism explains the sharp decline in human enzyme activity when temperature rises significantly above 45 °C?

• ACovalent peptide bonds in the primary structure are instantly cleaved.
• BThermal agitation disrupts hydrogen bonds and tertiary structural folding, leading to den…
• CEnzyme molecules are converted into nucleic acid chains.
• DSubstrate molecules freeze and lose all kinetic energy.

Which property of adenosine triphosphate (ATP) explains its role as the immediate energy currency of living cells?

• AIt stores the genetic blueprint for assembling amino acids in ribosomes.
• BIt acts as a permanent structural lipid in the outer mitochondrial membrane.
• CHydrolysis of its high-energy phosphoanhydride bonds releases readily usable free energy…
• DIt contains indestructible covalent bonds that never break during metabolic reactions.

What is the primary function of the photolysis of water in Photosystem II (PSII) during the light-dependent reactions of photosynthesis?

• ATo produce atmospheric CO2 for fixation in the Calvin cycle
• BTo directly synthesize glucose in the thylakoid lumen without enzymes
• CTo neutralize acidic pH by consuming protons inside the chloroplast stroma
• DTo supply replacement electrons to the oxidized P680 reaction center and release protons…

During non-cyclic photophosphorylation in chloroplasts, what is the ultimate electron acceptor that receives energized electrons at the end of the electron transport chain?

• ANADP+ (forming NADPH)
• BMolecular Oxygen (O2)
• CRibulose-1,5-bisphosphate (RuBP)
• DCytochrome c oxidase

Which key enzyme in the chloroplast stroma catalyzes the fixation of atmospheric carbon dioxide to ribulose-1,5-bisphosphate (RuBP)?

• AATP Synthase
• BRuBisCO (Ribulose-1,5-bisphosphate carboxylase-oxygenase)
• CPyruvate Dehydrogenase
• DPhosphofructokinase

What is the net yield of ATP and reduced coenzymes produced per single molecule of glucose during glycolysis in the cytoplasm?

• ANet 4 ATP and 4 FADH2
• BNet 36 ATP and 6 CO2
• CNet 2 ATP and 2 NADH
• DNet 0 ATP and 2 NADPH

During the link reaction (pyruvate oxidation) inside the mitochondrial matrix, what chemical conversion occurs prior to the Krebs cycle?

• AGlucose (6C) is split directly into two molecules of oxaloacetate (4C).
• BLactate is converted into ethanol and ATP under anaerobic conditions.
• CCitrate is phosphorylated to generate RuBP and oxygen.
• DPyruvate (3C) is decarboxylated and oxidized to form Acetyl-CoA (2C), releasing CO2 and p…

In the Krebs cycle (citric acid cycle), what 4-carbon molecule combines with Acetyl-CoA (2C) to form the initial 6-carbon citrate?

• AOxaloacetate
• BAlpha-ketoglutarate
• CMalate
• DSuccinate

How does the mitochondrial electron transport chain couple electron transfer to ATP synthesis according to Peter Mitchell's Chemiosmotic Hypothesis?

• AElectrons pass directly through the central channel of ATP synthase, phosphorylating ADP…
• BProtons are pumped from the matrix into the intermembrane space, creating an electrochemi…
• CProtons are pumped out of the cell across the plasma membrane, causing the cytoplasm to b…
• DOxygen is converted to ozone in the outer membrane, which releases heat to synthesize ATP.

Under anaerobic conditions in vigorously exercising human skeletal muscle, what is the crucial metabolic purpose of reducing pyruvate to lactic acid?

• ATo produce 30 additional ATP molecules directly from lactate
• BTo generate oxygen gas internally for the mitochondria
• CTo regenerate NAD+ from NADH so that glycolysis can continue producing ATP
• DTo increase intracellular pH and prevent muscle fatigue

According to Chargaff's rules and Watson-Crick base pairing in double-stranded DNA, what complementary base pairing and hydrogen bond counts are correct?

• AAdenine pairs with Cytosine via 3 hydrogen bonds; Guanine pairs with Thymine via 2 hydrog…
• BAdenine pairs with Uracil via 3 hydrogen bonds; Guanine pairs with Adenine via 1 hydrogen…
• CAdenine pairs with Guanine via peptide bonds; Thymine pairs with Cytosine via ionic bonds.
• DAdenine pairs with Thymine via 2 hydrogen bonds; Guanine pairs with Cytosine via 3 hydrog…

What conclusive experimental finding from the classic Meselson-Stahl experiment (using 15N and 14N isotopes) supported the semiconservative model of DNA replication?

• AAfter one generation in 14N, all DNA consisted of an intermediate-density hybrid (15N-14N…
• BAfter one generation in 14N, DNA separated into one pure 15N heavy band and one pure 14N…
• CAfter ten generations, all DNA molecules broke down into single nucleotides without duple…
• DDNA replication was found to produce completely new double helices with no parental stran…

What is the specific enzymatic function of DNA topoisomerase (gyrase) during replication fork progression?

• ASynthesizes short RNA primers complementary to the DNA template
• BRelieves torsional strain and prevents positive supercoiling ahead of the advancing repli…
• CCatalyzes the formation of phosphodiester bonds between adjacent Okazaki fragments
• DUnzips hydrogen bonds between complementary nitrogenous bases to open the double helix

Why is the lagging strand synthesized discontinuously in short Okazaki fragments during DNA replication?

• AThe lagging strand template lacks adenine bases, preventing continuous base pairing.
• BTopoisomerase blocks RNA primase from binding on the lagging strand.
• CDNA polymerases can only add deoxynucleotides in the 5' to 3' direction, requiring synthe…
• DLagging strand synthesis occurs in the ribosome rather than the replication bubble.

If a DNA template strand has the sequence 3'-TAC GGC TTA CGA ACT-5', what will be the complementary sequence of the RNA transcript?

• A5'-ATG CCG AAT GCT TGA-3'
• B5'-UAC GGC UUA CGA ACU-3'
• C3'-AUG CCG AAU GCU UGA-5'
• D5'-AUG CCG AAU GCU UGA-3'

Which set of post-transcriptional processing events must occur in the eukaryotic nucleus to convert primary pre-mRNA into mature translatable mRNA?

• AAddition of a 5' 7-methylguanosine cap, addition of a 3' poly-A tail, and spliceosome exc…
• BRemoval of all exons, translation of introns, and attachment of lipid bilayers
• CBinding of DNA polymerase I, degradation of ribose sugars, and circularization of the tra…
• DPhosphorylation of all purines and conversion of Uracil into Thymine

Why is the genetic code described as 'degenerate' (redundant) and 'universal'?

• AEach single codon can code for multiple different amino acids depending on the organelle.
• BMultiple codons can specify the same amino acid, and nearly all living organisms utilize…
• CThe genetic code degrades after translation and differs completely in every biological ki…
• DCodons overlap with one another so that each nucleotide is read three separate times.

During the elongation phase of translation, what happens at the ribosomal A (aminoacyl) and P (peptidyl) sites?

• AThe empty tRNA enters the A site and hydrolyzes the polypeptide chain into free amino aci…
• BThe ribosome synthesizes mRNA in the P site while DNA unzips in the A site.
• CAn incoming aminoacyl-tRNA binds to the A site, peptidyl transferase forms a peptide bond…
• DStop codons bind to the P site to recruit initiator tRNA-methionine.

Sickle cell anemia in humans is caused by a point mutation in the beta-globin gene that converts a GAG codon into GUG. What type of mutation is this?

• ASilent mutation
• BNonsense mutation introducing a premature stop codon
• CFrameshift deletion mutating all downstream amino acids
• DMissense mutation resulting in valine substituting for glutamic acid

What cytogenetic error during meiotic cell division leads to aneuploid conditions such as Down syndrome (Trisomy 21)?

• ANondisjunction of homologous chromosomes in Anaphase I or sister chromatids in Anaphase II
• BReciprocal translocation between non-homologous chromosomes without gene loss
• CInversion of the short arm of chromosome 21 during Prophase I
• DComplete replication of all maternal autosomes during G1 phase

In a classic Mendelian monohybrid cross between two heterozygous pea plants with yellow seeds (Yy x Yy), what phenotypic and genotypic ratios are expected in the F2 generation?

• APhenotypic ratio 1 yellow : 1 green; Genotypic ratio 1 YY : 1 yy
• BPhenotypic ratio 3 yellow : 1 green; Genotypic ratio 1 YY : 2 Yy : 1 yy
• CPhenotypic ratio 9 yellow : 3 green : 3 round : 1 wrinkled; Genotypic ratio 1:1
• DPhenotypic ratio all yellow; Genotypic ratio 3 YY : 1 yy

What is the primary genetic purpose of performing a testcross on an organism displaying a dominant phenotype?

• ATo induce artificial mutations in the coding region of the target gene
• BTo verify whether the gene is located in the mitochondrial circular DNA
• CTo determine whether the individual is homozygous dominant or heterozygous by crossing it…
• DTo produce polyploid offspring with superior agricultural traits

In a dihybrid cross between two individuals heterozygous for two independently assorting traits (AaBb x AaBb), what fraction of the offspring is expected to be homozygous recessive for both traits (aabb)?

• A3/16
• B9/16
• C1/4
• D1/16

When red snapdragon flowers (CRCR) are crossed with white snapdragon flowers (CWCW), all F1 offspring have pink flowers (CRCW). What mode of inheritance does this illustrate?

• AIncomplete dominance
• BComplete dominance
• CCodominance
• DEpistasis

A man with blood type AB marries a woman with blood type O. What are the possible blood types and phenotypic ratios among their biological children?

• A100% blood type AB
• B50% blood type A (IAi) and 50% blood type B (IBi)
• C25% A, 25% B, 25% AB, and 25% O
• D100% blood type O

Under what parental Rh blood group combination can Erythroblastosis Fetalis (Hemolytic Disease of the Newborn) develop in a second pregnancy?

• ARh-positive mother pregnant with an Rh-negative fetus
• BRh-negative mother pregnant with an Rh-negative fetus whose father is Rh-negative
• CRh-negative mother pregnant with an Rh-positive fetus after prior sensitization during a…
• DBoth parents are Rh-positive homozygous individuals

Why are X-linked recessive disorders (such as classic hemophilia and red-green color blindness) much more frequently expressed in human males than females?

• AThe Y chromosome contains multiple dominant alleles that actively activate X-linked disea…
• BX-linked recessive alleles cannot be transcribed in female cells due to Barr body formati…
• CMales possess two X chromosomes, doubling their probability of inheriting the mutant alle…
• DMales are hemizygous (XY) and express any recessive allele on their single X chromosome w…

Assume complete penetrance and no new mutation. A human pedigree shows that an unaffected mother and unaffected father have a daughter affected by a rare metabolic disorder. Which listed mode of inheritance best fits this pattern?

• AAutosomal recessive
• BAutosomal dominant
• CX-linked dominant
• DY-linked

In recombinant DNA technology, what specific role do restriction endonucleases play?

• AThey join Okazaki fragments together during DNA replication in bacteria.
• BThey recognize specific palindromic DNA sequences and cleave phosphodiester bonds to prod…
• CThey translate recombinant mRNA into therapeutic proteins inside the nucleus.
• DThey amplify single DNA molecules into millions of copies using thermal cycles.