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Galicia PAU Biology study materials
Galicia PAU Biology study resources

Galicia PAU Biology practice questions

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Question 1Biological inquiry and interpretation of evidence

A researcher predicts that tomato plants given a nitrogen-enriched fertilizer will produce more fruit than plants given a standard fertilizer. In this study, the amount of fruit produced is best described as which of the following?

  1. The hypothesis
  2. A controlled variable
  3. The dependent variable Correct answer.
  4. The independent variable

Explanation

The dependent variable is the measured outcome that responds to the manipulation, which here is fruit yield. The fertilizer type is the factor the researcher deliberately changes, so it is the independent variable rather than the measured result.

Question 2Biological inquiry and interpretation of evidence

A student measures the mass of the same sample five times and obtains nearly identical values, but the balance was never zeroed and reads 2.0 g too high. How should these measurements be described?

  1. Both accurate and precise
  2. Precise but not accurate Correct answer.
  3. Accurate but not precise
  4. Neither accurate nor precise

Explanation

Precision refers to how closely repeated measurements agree with one another, while accuracy refers to how close they are to the true value. Because the readings cluster tightly but are systematically offset by the unzeroed balance, they are precise but inaccurate.

Question 3Biological inquiry and interpretation of evidence

Which of the following best distinguishes a scientific hypothesis from a scientific theory?

  1. A hypothesis is a testable proposed explanation, while a theory is a well-supported explanatory framework built from extensive evidence Correct answer.
  2. A hypothesis is always correct once tested, while a theory remains an untested guess
  3. A hypothesis is a broad framework, while a theory is a single testable prediction
  4. A hypothesis applies only to biology, while a theory applies only to physics

Explanation

In science, a hypothesis is a testable proposed explanation for a specific observation, whereas a theory is a broad, well-substantiated explanation supported by many lines of evidence. The common usage of theory as a mere guess is incorrect in scientific contexts.

Question 4Biological inquiry and interpretation of evidence

A scientist repeats an experiment several times and obtains consistent results. Which conclusion is most justified?

  1. The findings are reliable and reproducible under the tested conditions Correct answer.
  2. The results now apply to all organisms everywhere
  3. The hypothesis has been proven true beyond any doubt
  4. The experiment has no remaining sources of error

Explanation

Reproducible results indicate reliability, meaning the procedure yields consistent outcomes under the tested conditions. Science does not establish absolute proof, and replication does not eliminate error or guarantee universal applicability.

Question 5Biological inquiry and interpretation of evidence

A graph plots plant height on the y-axis against days of growth on the x-axis. Which statement correctly identifies the placement of these variables?

  1. Days of growth is the independent variable on the x-axis, and height is the dependent variable on the y-axis Correct answer.
  2. Both variables are dependent and should share the x-axis
  3. Days of growth is the dependent variable because it is measured over time
  4. Height is the independent variable on the y-axis, and days of growth is the dependent variable on the x-axis

Explanation

By convention, the independent variable is placed on the x-axis and the dependent variable on the y-axis. Height responds to elapsed time, so time is independent and height is dependent.

Question 6Biological inquiry and interpretation of evidence

A student notices that mold grows on bread left in a warm, humid place but not on bread stored in a dry, cool place. Which of the following is the most appropriate next step in the scientific process?

  1. Formulate a testable hypothesis and design a controlled experiment to test it Correct answer.
  2. Conclude immediately that warmth and moisture cause mold growth
  3. Publish the observation as a confirmed scientific law
  4. Discard the observation because it was not made in a laboratory

Explanation

An observation generates questions that should be framed as a testable hypothesis and examined through a controlled experiment. Reaching a firm causal conclusion from a single uncontrolled observation is premature.

Question 7Biochemistry

Which property of water is most directly responsible for its ability to moderate temperature in living organisms and large bodies of water?

  1. Its low specific heat
  2. Its inability to form hydrogen bonds
  3. Its nonpolar covalent bonds
  4. Its high specific heat Correct answer.

Explanation

Water has a high specific heat because hydrogen bonds must absorb or release substantial energy before water molecules change temperature. This allows water and water-rich organisms to resist large temperature swings, helping maintain homeostasis.

Question 8Cell structure, membranes and division

Which structure is found in a typical plant cell but NOT in a typical animal cell?

  1. Mitochondrion
  2. Nucleus
  3. Ribosome
  4. Cell wall made of cellulose Correct answer.

Explanation

Plant cells have a rigid cell wall composed primarily of cellulose that surrounds the plasma membrane, providing structural support. Animal cells lack a cell wall, relying on the cytoskeleton and extracellular matrix instead.

Question 9Genetics, inheritance and molecular information

Meiosis differs from mitosis in that meiosis produces

  1. Two genetically identical diploid cells
  2. One diploid cell with double the chromosomes
  3. Two haploid cells identical to the parent
  4. Four genetically varied haploid cells Correct answer.

Explanation

Meiosis consists of two divisions that produce four haploid gametes, each with half the chromosome number of the parent. Crossing over and independent assortment generate genetic variation, distinguishing meiosis from the identical-diploid products of mitosis.

Question 10Metabolism

An enzyme lowers the activation energy of a reaction. Which statement best describes how this affects the reaction?

  1. It increases the reaction rate without being consumed in the reaction Correct answer.
  2. It changes the overall free-energy difference between reactants and products
  3. It supplies the energy needed to make an endergonic reaction exergonic
  4. It permanently binds to the product to stop the reaction

Explanation

Enzymes are biological catalysts that lower activation energy, speeding up reactions without being consumed. They do not change the net free-energy difference (delta G) between reactants and products; they only make the reaction reach equilibrium faster.

Question 11Microbiology Immunology

Gram-positive bacteria differ structurally from Gram-negative bacteria in their cell wall composition. Which characteristic feature distinguishes Gram-positive bacterial cell walls upon Gram staining?

  1. Thick multi-layered peptidoglycan meshwork retaining crystal violet-iodine complex (purple) Correct answer.
  2. Thin single layer of peptidoglycan enclosed by an outer membrane containing lipopolysaccharide (LPS)
  3. Absence of peptidoglycan, composed entirely of chitin
  4. Lipid envelope derived from host plasma membrane

Explanation

Gram-positive bacteria possess a thick, multi-layered peptidoglycan (murein) cell wall rich in teichoic and lipoteichoic acids. This dense structure dehydrates during alcohol decolorization, trapping the crystal violet-iodine complex and staining purple. Gram-negative cell walls have thin peptidoglycan and an outer LPS membrane (staining pink with safranin).

Question 12Biotechnology

The polymerase chain reaction, or PCR, is mainly used to do what?

  1. Amplify a selected DNA sequence Correct answer.
  2. Destroy all proteins in a sample
  3. Make plant roots bend downward
  4. Measure animal breathing rate directly

Explanation

PCR uses primers, DNA polymerase, nucleotides, and temperature cycling to make many copies of a target DNA region. It is widely used in testing and research.

Question 13Biochemistry

Which property of liquid water explains its high specific heat capacity and high heat of vaporization?

  1. Covalent peptide bonds
  2. Intermolecular hydrogen bonding network Correct answer.
  3. Ionic cross-linking
  4. Van der Waals dispersion forces

Explanation

Water molecules form a dense network of hydrogen bonds between partial negative oxygen and partial positive hydrogen atoms. Breaking these bonds requires substantial energy input, resulting in a high specific heat capacity and high heat of vaporization that help regulate thermal homeostasis in living organisms.

Question 14Biochemistry

When human red blood cells are placed in a hypertonic sodium chloride solution, what phenomenon occurs?

  1. Turgor pressure expansion
  2. Cellular crenation due to osmotic efflux of water Correct answer.
  3. Osmotic lysis due to rapid water entry
  4. Plasmolysis of the cell wall

Explanation

In a hypertonic environment, water moves out of the cell across the semipermeable plasma membrane by osmosis toward the higher solute concentration. This water loss causes the erythrocyte to shrink and form spikes, a process called crenation.

Question 15Biochemistry

Which extracellular buffer system is primarily responsible for maintaining human arterial blood pH near 7.40?

  1. Phosphate buffer system (HPO4^2- / H2PO4-)
  2. Bicarbonate buffer system (HCO3- / H2CO3) Correct answer.
  3. Histidine protein buffer system
  4. Ammonium buffer system (NH4+ / NH3)

Explanation

The carbonic acid-bicarbonate buffer system is the primary extracellular buffer in blood plasma. Carbon dioxide produced by cellular respiration reacts with water to form carbonic acid, which dissociates into bicarbonate ions and protons to cushion against pH alterations.

Question 16Biochemistry

Which structural feature distinguishes alpha-D-glucose from beta-D-glucose in aqueous solution?

  1. The orientation of the hydroxyl group on the anomeric carbon C1 Correct answer.
  2. The carbon position of the carbonyl group in open-chain form
  3. The presence of an amino group at carbon C2
  4. The molecular formula and total molecular weight

Explanation

Alpha-D-glucose and beta-D-glucose are anomers that differ in the stereochemical configuration at carbon C1 (the anomeric carbon). In the Haworth projection of alpha-D-glucose, the hydroxyl group at C1 is trans to the CH2OH group (pointing down), whereas in beta-D-glucose it is cis (pointing up).

Question 17Biochemistry

Which polysaccharide functions as the primary energy storage molecule in animal liver and muscle tissues?

  1. Amylose
  2. Cellulose
  3. Glycogen Correct answer.
  4. Chitin

Explanation

Glycogen is a highly branched polymer of alpha-D-glucose linked by alpha-1,4-glycosidic bonds with alpha-1,6-glycosidic branch points occurring every 8 to 12 glucose residues. This architecture allows rapid enzymatic mobilization of glucose in liver and muscle cells.

Question 18Biochemistry

What type of chemical linkage connects glycerol to fatty acids in a triglyceride molecule?

  1. Ester bond Correct answer.
  2. Glycosidic bond
  3. Phosphodiester bond
  4. Peptide bond

Explanation

Triglycerides consist of one glycerol backbone molecule esterified to three fatty acid molecules. The reaction between a carboxyl group of a fatty acid and a hydroxyl group of glycerol produces an ester bond along with the release of a water molecule.

Question 19Biochemistry

Which lipid class is amphipathic and forms the lipid bilayer matrix of biological membranes?

  1. Triacylglycerols
  2. Phospholipids Correct answer.
  3. Waxes
  4. Steroid esters

Explanation

Phospholipids possess a hydrophilic polar head group (glycerol, phosphate, and an alcohol moiety) and two hydrophobic nonpolar fatty acid tails. This amphipathic nature causes them to spontaneously assemble into lipid bilayers in aqueous environments.

Question 20Biochemistry

Which level of protein structure is held together predominantly by hydrogen bonds between backbone peptide carbonyl oxygens and amide hydrogens?

  1. Primary structure
  2. Secondary structure Correct answer.
  3. Tertiary structure
  4. Quaternary structure

Explanation

Secondary structure refers to localized repeating conformations of the polypeptide backbone, such as alpha-helices and beta-pleated sheets. These structures are stabilized by periodic hydrogen bonds between peptide backbone carbonyl oxygens and amide nitrogens.

Question 21Biochemistry

What is the zwitterionic form of an amino acid at its isoelectric point (pI)?

  1. A net positively charged cation with protonated carboxyl and amino groups
  2. A net negatively charged anion with deprotonated carboxyl and amino groups
  3. A dipolar ion with a negatively charged carboxylate group and a positively charged amino group Correct answer.
  4. An uncharged molecule with no ionized functional groups

Explanation

At its isoelectric point (pI), an amino acid exists as a zwitterion: the alpha-carboxyl group is deprotonated (-COO-) and the alpha-amino group is protonated (-NH3+), yielding a molecule with equal positive and negative charges and a net electrical charge of zero.

Question 22Biochemistry

How does a competitive enzyme inhibitor affect the kinetic parameters Vmax and Km?

  1. Vmax decreases while Km remains unchanged
  2. Km increases while Vmax remains unchanged Correct answer.
  3. Both Vmax and Km decrease proportionally
  4. Both Vmax and Km increase

Explanation

A competitive inhibitor binds reversibly to the active site of the free enzyme, competing directly with the substrate. Increasing substrate concentration can outcompete the inhibitor, so the maximum reaction velocity (Vmax) is unchanged, but a higher substrate concentration is needed to reach half-Vmax, increasing the apparent Km.

Question 23Biochemistry

Which nucleotide base pair in double-stranded DNA is held together by three hydrogen bonds?

  1. Adenine and Thymine
  2. Guanine and Cytosine Correct answer.
  3. Adenine and Uracil
  4. Guanine and Adenine

Explanation

Guanine pairs specifically with Cytosine via three hydrogen bonds, whereas Adenine pairs with Thymine (in DNA) via two hydrogen bonds. The higher hydrogen-bond density of G-C pairs provides greater thermal stability to double-stranded DNA.

Question 24Biochemistry

What type of covalent bond connects the 3'-hydroxyl group of one nucleotide to the 5'-phosphate group of the next nucleotide in a polynucleotide chain?

  1. Phosphodiester bond Correct answer.
  2. Glycosidic bond
  3. Peptide bond
  4. Disulfide bond

Explanation

Nucleotides in DNA and RNA are linked into linear chains by 3',5'-phosphodiester bonds. The phosphate group esterified to the 5'-carbon of one pentose sugar forms a second ester linkage with the 3'-hydroxyl group of the adjacent pentose sugar.

Question 25Biochemistry

Which of the following is a non-reducing disaccharide?

  1. Maltose
  2. Lactose
  3. Sucrose Correct answer.
  4. Cellobiose

Explanation

Sucrose consists of alpha-D-glucose and beta-D-fructose linked by an alpha-1,beta-2-glycosidic bond. Because the glycosidic linkage involves the anomeric carbons of both monosaccharides (C1 of glucose and C2 of fructose), no free anomeric aldehyde or ketone group remains to reduce oxidizing reagents.

Question 26Biochemistry

Which unsaturation character distinguishes oleic acid from stearic acid?

  1. Oleic acid contains one cis double bond, whereas stearic acid is fully saturated Correct answer.
  2. Stearic acid contains two trans double bonds, whereas oleic acid is saturated
  3. Oleic acid is a branched-chain amino acid
  4. Stearic acid contains a cyclic cyclopentane ring

Explanation

Oleic acid (18:1 cis-9) is a monounsaturated fatty acid possessing one double bond with cis stereochemistry at carbon 9. Stearic acid (18:0) is a fully saturated 18-carbon fatty acid containing only single carbon-carbon bonds.

Question 27Biochemistry

Which amino acid residue is unique because its side chain forms a covalent ring with its own backbone alpha-amino group?

  1. Glycine
  2. Proline Correct answer.
  3. Cysteine
  4. Histidine

Explanation

Proline is a cyclic imino acid whose pyrrolidine side chain folds back to bind covalently to the backbone alpha-amino group. This rigid cyclic structure imposes conformational constraints on polypeptide chains and frequently introduces turns or disrupts alpha-helices.

Question 28Biochemistry

Which RNA molecule carries amino acids to the ribosome during protein synthesis and features an anticodon loop?

  1. Messenger RNA (mRNA)
  2. Transfer RNA (tRNA) Correct answer.
  3. Ribosomal RNA (rRNA)
  4. Small nuclear RNA (snRNA)

Explanation

Transfer RNA (tRNA) functions as an adaptor molecule during translation. It possesses a 3'-CCA acceptor stem where a specific amino acid is covalently attached and an anticodon loop that base-pairs with the complementary codon on mRNA inside the ribosome.

Question 29Biochemistry

What occurs during the irreversible denaturation of a globular protein?

  1. Peptide bonds are hydrolyzed into free amino acids
  2. The non-covalent tertiary and secondary structures unfold, causing loss of biological activity Correct answer.
  3. Primary structure sequence is altered
  4. Disulfide bonds spontaneously multiply

Explanation

Denaturation destroys the non-covalent native folding of a protein (secondary, tertiary, and quaternary structures) due to heat, extreme pH, or denaturing chemicals. The protein unfolds into a disordered chain and loses its biological function, while covalent peptide bonds remain intact.

Question 30Biochemistry

Which class of non-saponifiable lipids is derived from five-carbon isoprene units and includes vitamins A, E, and K?

  1. Steroids
  2. Terpenes (Isoprenoids) Correct answer.
  3. Eicosanoid prostaglandins
  4. Sphingolipids

Explanation

Terpenes (isoprenoids) are non-saponifiable lipids synthesized by polymerizing 5-carbon isoprene (2-methyl-1,3-butadiene) building blocks. They include essential fat-soluble vitamins (A, E, K), carotenoid pigments, and essential oils.

Question 31Biochemistry

What is the term for non-protein organic molecules that bind tightly or loosely to enzymes and are required for catalytic activity?

  1. Apoenzymes
  2. Coenzymes Correct answer.
  3. Zymogens
  4. Isoenzymes

Explanation

Coenzymes are organic non-protein helper molecules (often derived from vitamins, such as NAD+, FAD, or Coenzyme A) that participate in enzymatic reactions by transferring chemical groups, electrons, or hydrogen atoms. The inactive protein component alone is called an apoenzyme.

Question 32Biochemistry

Why does ice float on liquid water?

  1. Ice has a higher density than liquid water due to compact ionic packing
  2. Hydrogen bonds in ice hold water molecules in a rigid open crystalline lattice that is less dense than liquid water Correct answer.
  3. Ice contains dissolved trapped gases that increase its buoyancy
  4. Covalent O-H bonds elongate upon freezing, increasing atomic mass

Explanation

As water freezes below 4 °C, each water molecule forms four stable hydrogen bonds with neighboring molecules, locking them into a hexagonal crystalline lattice. This open framework increases the volume and lowers the density of ice compared to liquid water, allowing ice to float.

Question 33Cell structure, membranes and division

Which molecular component of eukaryotic plasma membranes restricts membrane fluidity at high temperatures and prevents hyper-rigidity at low temperatures?

  1. Integral ion channel proteins
  2. Cholesterol Correct answer.
  3. Glycolipid carbohydrate chains
  4. Peripheral actin filaments

Explanation

Cholesterol acts as a membrane fluidity buffer. At warm temperatures, its rigid steroid ring structure restrains phospholipid hydrocarbon chain motion to reduce excessive fluidity; at cold temperatures, it breaks up dense phospholipid packing to prevent membrane freezing.

Question 34Cell structure, membranes and division

Which transport mechanism moves glucose into intestinal epithelial cells against its concentration gradient coupled to the downhill movement of sodium ions?

  1. Simple passive diffusion
  2. Primary ATP-driven active transport
  3. Secondary active transport (symport) Correct answer.
  4. Facilitated diffusion through GLUT transporters

Explanation

The Na+/glucose cotransporter (SGLT1) utilizes secondary active transport. The entry of Na+ down its electrochemical gradient (established by the primary Na+/K+ ATPase pump) provides the thermodynamic energy to transport glucose uphill into the cell.

Question 35Cell structure, membranes and division

Which eukaryotic organelle contains acid hydrolases and maintains an internal acidic pH (~4.5 - 5.0) for intracellular digestion?

  1. Peroxisome
  2. Lysosome Correct answer.
  3. Golgi apparatus
  4. Rough endoplasmic reticulum

Explanation

Lysosomes are membrane-enclosed organelles filled with acid hydrolases (nucleases, proteases, lipases) that function optimally in acidic environments. Membrane V-type H+ ATPases pump protons into the lumen to maintain the low internal pH required for autophagy and phagocytic degradation.

Question 36Cell structure, membranes and division

What structural arrangement characterizes the axoneme of eukaryotic cilia and flagella?

  1. 9+0 triplet microtubule pattern
  2. 9+2 doublet microtubule pattern Correct answer.
  3. 7+2 singlet microfilament pattern
  4. 13 parallel intermediate filaments

Explanation

The motile eukaryotic axoneme features a classic '9+2' arrangement consisting of nine outer doublet microtubules surrounding two central single microtubules, interconnected by dynein motor arms, nexin links, and radial spokes.

Question 37Cell structure, membranes and division

Where within the eukaryotic cell are ribosomal RNA (rRNA) genes transcribed and ribosome subunits assembled?

  1. Smooth endoplasmic reticulum
  2. Nucleolus Correct answer.
  3. Peroxisomal matrix
  4. Centrosome

Explanation

The nucleolus is a dense subnuclear domain formed around nucleolar organizer regions (NORs). Ribosomal RNA (rRNA) is transcribed here by RNA polymerase I, processed, and assembled with imported ribosomal proteins into 40S and 60S subunit precursors.

Question 38Cell structure, membranes and division

Which structure is present in plant cells but absent in typical animal cells?

  1. Mitochondria
  2. Cell wall composed of cellulose Correct answer.
  3. 80S cytosolic ribosomes
  4. Golgi cisternae

Explanation

Plant cells possess a rigid extracellular cell wall primarily composed of cellulose microfibrils embedded in a matrix of hemicellulose and pectins, providing structural support and protection against osmotic lysis.

Question 39Cell structure, membranes and division

During which phase of mitosis do sister chromatids separate and move toward opposite spindle poles?

  1. Prophase
  2. Metaphase
  3. Anaphase Correct answer.
  4. Telophase

Explanation

During anaphase, cohesin complexes holding sister chromatids together are cleaved by separase. The sister chromatids separate into individual daughter chromosomes and are pulled toward opposite centrosomal poles by kinetochore microtubule shortening.

Question 40Cell structure, membranes and division

In which specific stage of meiotic prophase I does genetic crossing over (homologous recombination) take place?

  1. Leptotene
  2. Zygotene
  3. Pachytene Correct answer.
  4. Diplotene

Explanation

Crossing over occurs during pachytene of meiotic prophase I. Once the synaptonemal complex fully joins homologous chromosome pairs during zygotene, recombination nodules facilitate non-sister chromatid exchange of genetic material during pachytene.

Question 41Cell structure, membranes and division

What is the chromosomal number and DNA content of human gametes resulting from normal meiosis?

  1. Diploid (2n = 46) with 2c DNA content
  2. Haploid (n = 23) with 1c DNA content Correct answer.
  3. Haploid (n = 23) with 2c DNA content
  4. Tetraploid (4n = 92) with 4c DNA content

Explanation

Meiosis consists of one round of DNA replication followed by two nuclear divisions, reducing the diploid chromosome number (2n = 46) by half to produce haploid gametes (n = 23) containing a single copy of genome DNA (1c).

Question 42Cell structure, membranes and division

Which protein complex regulates the G1/S transition by phosphorylating retinoblastoma protein (Rb)?

  1. Cyclin D - CDK4/6 Correct answer.
  2. Cyclin B - CDK1 (MPF)
  3. Anaphase-Promoting Complex (APC/C)
  4. Caspae-3 endonuclease

Explanation

During G1 phase, mitogenic signals induce Cyclin D expression, activating CDK4 and CDK6. The Cyclin D-CDK4/6 complex phosphorylates the retinoblastoma protein (Rb), causing Rb to release E2F transcription factors that activate S-phase genes.

Question 43Cell structure, membranes and division

According to the endosymbiotic theory, which feature of mitochondria and chloroplasts supports their origin from free-living prokaryotes?

  1. Presence of linear chromosomes bound by eukaryotic histones
  2. 70S ribosomes and circular double-stranded DNA Correct answer.
  3. Single lipid monolayer membranes
  4. Ability to survive independently outside host eukaryotic cells indefinitely

Explanation

Mitochondria and chloroplasts contain 70S ribosomes (inhibited by bacterial antibiotics like chloramphenicol) and circular, naked double-stranded DNA genomes similar to modern alpha-proteobacteria and cyanobacteria, supporting their endosymbiotic prokaryotic origin.

Question 44Cell structure, membranes and division

Which cytoskeletal component is composed of actin filaments and mediates cytokinesis cleavage furrow formation in animal cells?

  1. Microtubules
  2. Microfilaments (Actin filaments) Correct answer.
  3. Intermediate filaments
  4. Keratin fibers

Explanation

Microfilaments (actin filaments) interact with myosin II motor proteins to form a contractile ring beneath the plasma membrane during late anaphase and telophase. Contracting this ring pinches the cytoplasm to achieve cytokinesis in animal cells.

Question 45Cell structure, membranes and division

Which process describes the selective uptake of specific macromolecules via clathrin-coated pits following binding to cell-surface transmembrane receptors?

  1. Pinocytosis
  2. Phagocytosis
  3. Receptor-mediated endocytosis Correct answer.
  4. Exocytosis

Explanation

Receptor-mediated endocytosis allows selective uptake of specific extracellular ligands (such as low-density lipoproteins or transferrin). Binding of the ligand to its specific transmembrane receptor triggers intracellular recruitment of clathrin adaptors and clathrin coat assembly to form invaginated coated vesicles.

Question 46Cell structure, membranes and division

What is the primary function of the Golgi apparatus in eukaryotic cells?

  1. Synthesis of genomic DNA
  2. Post-translational modification, sorting, and packaging of ER-derived proteins Correct answer.
  3. Generation of ATP via oxidative phosphorylation
  4. Primary fatty acid beta-oxidation

Explanation

The Golgi apparatus receives proteins and lipids synthesized in the rough ER at its cis-face. It modifies N-linked glycans, performs O-linked glycosylation, phosphorylates, and sorts these biomolecules into specific vesicles at the trans-Golgi network destined for lysosomes, plasma membrane, or secretion.

Question 47Cell structure, membranes and division

How does plant cell cytokinesis differ fundamentally from animal cell cytokinesis?

  1. Plant cells divide by forming a contractile actin ring
  2. Plant cells form a cell plate (phragmoplast) by fusing Golgi-derived vesicles from the center outward Correct answer.
  3. Plant cells undergo binary fission similar to prokaryotes
  4. Plant cells do not divide cytoplasm and remain multinucleated

Explanation

Because of their rigid cell wall, plant cells cannot form a cleavage furrow. Instead, micro-tubule-guided phragmoplast structures direct Golgi-derived vesicles carrying cell wall precursors to the equatorial plane, where they fuse from the center outward to build a new cell plate and cell wall.

Question 48Cell structure, membranes and division

What role does tumor suppressor protein p53 play in response to severe DNA damage during G1 phase?

  1. Promotes immediate entry into S phase to bypass DNA repair
  2. Induces expression of p21 to arrest the cell cycle or triggers apoptosis if damage is unrepairable Correct answer.
  3. Degrades repair enzymes via proteasomal cleavage
  4. Phosphorylates Cyclin B to initiate mitosis

Explanation

When DNA damage is detected, p53 is stabilized and activated as a transcription factor. It upregulates p21 (a CDK inhibitor) to arrest the cell cycle in G1 and allow repair; if DNA damage is extensive and unrepairable, p53 transactivates pro-apoptotic genes (Bax, Puma) to trigger programmed cell death.

Question 49Cell structure, membranes and division

Which lipid modification facing the cytosolic leaflet of the plasma membrane serves as an early marker for phagocytic recognition during apoptosis when flipped to the outer leaflet?

  1. Phosphatidylcholine
  2. Phosphatidylserine Correct answer.
  3. Sphingomyelin
  4. Cholesterol palmitate

Explanation

In healthy cells, flippases actively maintain phosphatidylserine on the inner cytosolic leaflet of the plasma membrane. During apoptosis, scramblases expose phosphatidylserine on the outer leaflet, serving as an 'eat-me' signal for macrophage recognition and phagocytosis.

Question 50Cell structure, membranes and division

Which lumenal organelle is responsible for post-translational protein folding, N-linked glycosylation initiation, and calcium ion storage in muscle cells?

  1. Endoplasmic reticulum Correct answer.
  2. Mitochondrial matrix
  3. Peroxisome
  4. Lysosome

Explanation

The endoplasmic reticulum (ER) processes nascent secretory and membrane proteins through chaperones (BiP, calnexin) for proper folding and initial N-glycosylation. In muscle tissue, the specialized sarcoplasmic reticulum stores and releases Ca2+ ions to regulate contraction.