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Andalusia PAU Biology study materials
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Andalusia 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 physical property of water allows it to absorb or release large amounts of heat energy with minimal change in its own temperature?

  1. High specific heat capacity Correct answer.
  2. High surface tension
  3. Low heat of vaporization
  4. Maximum density at 0 °C

Explanation

Water has a high specific heat capacity because a significant amount of heat energy is required to break the extensive hydrogen-bonding network between water molecules before kinetic energy can increase. This buffers organisms and aquatic environments against rapid temperature fluctuations. Other options describe surface tension, latent heat of vaporization, or density anomalies.

Question 14Biochemistry

When a plant cell is placed in a hypertonic solution, water leaves the vacuole and cytoplasm, causing the plasma membrane to pull away from the rigid cell wall. What is this phenomenon called?

  1. Plasmolysis Correct answer.
  2. Turgor
  3. Hemolysis
  4. Crenation

Explanation

Plasmolysis occurs when plant cells lose water in a hypertonic environment, causing the protoplast to shrink away from the rigid cell wall. Turgor refers to the outward pressure against the cell wall in a hypotonic medium. Hemolysis and crenation apply to animal cells (specifically red blood cells).

Question 15Biochemistry

Which of the following monosaccharides is classified as a ketohexose?

  1. D-Fructose Correct answer.
  2. D-Glucose
  3. D-Galactose
  4. D-Ribose

Explanation

D-Fructose is a ketohexose because it contains six carbon atoms and a ketone functional group at carbon-2. D-Glucose and D-Galactose are aldohexoses, while D-Ribose is an aldopentose.

Question 16Biochemistry

What type of chemical reaction links two monosaccharides together to form a disaccharide, releasing a molecule of water?

  1. Condensation (dehydration synthesis) Correct answer.
  2. Hydrolysis
  3. Oxidative decarboxylation
  4. Phosphorylation

Explanation

Condensation or dehydration synthesis involves the covalent coupling of two hydroxyl groups from monosaccharides to form an O-glycosidic bond, releasing one molecule of water. Hydrolysis is the reverse cleavage reaction requiring water.

Question 17Biochemistry

Why do unsaturated fatty acids with cis double bonds generally have lower melting points than saturated fatty acids of equivalent chain length?

  1. Cis double bonds introduce kinks that prevent tight molecular packing Correct answer.
  2. Unsaturated fatty acids form stronger ester bonds with glycerol
  3. Saturated fatty acids contain fewer hydrocarbon hydrogen atoms
  4. Cis double bonds increase non-polar van der Waals interactions

Explanation

Cis double bonds create rigid bends (kinks) in the hydrocarbon tail of fatty acids. These kinks interfere with close, crystalline molecular packing, weakening intermolecular van der Waals forces and lowering the melting point.

Question 18Biochemistry

A peptide bond forms between which two functional groups of adjacent amino acids?

  1. The carboxyl group of one amino acid and the amino group of another Correct answer.
  2. The hydroxyl group of one amino acid and the phosphate group of another
  3. The R-group side chains of two cysteine residues
  4. The carbonyl oxygen and the alpha-carbon atom

Explanation

A peptide bond is a covalent amide linkage (-CO-NH-) formed by a condensation reaction between the alpha-carboxyl group of one amino acid and the alpha-amino group of the next amino acid.

Question 19Biochemistry

What structural feature of a protein remains intact when it undergoes reversible denaturation caused by mild heat or pH changes?

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

Explanation

Denaturation disrupts non-covalent interactions (hydrogen bonds, ionic bonds, hydrophobic interactions) and disulfide bridges, altering secondary, tertiary, and quaternary structures. The primary structure (covalent peptide backbone) remains intact.

Question 20Biochemistry

According to Chargaff's rules for double-stranded DNA, which relationship between nitrogenous bases is always true?

  1. A + G = T + C Correct answer.
  2. A + T = G + C
  3. A / G = 1.0
  4. A + C = 100%

Explanation

Chargaff's rules state that in double-stranded DNA, Adenine equals Thymine (A = T) and Guanine equals Cytosine (G = C). Therefore, the sum of purines (A + G) equals the sum of pyrimidines (T + C).

Question 21Biochemistry

Why is water an excellent solvent for polar molecules and ionic salts?

  1. Water molecules form hydration shells around charged ions due to dipoles Correct answer.
  2. Water molecules form non-polar hydrophobic interactions with solutes
  3. Water has a low dielectric constant that stabilizes ionic bonds
  4. Water reacts chemically with solutes to form covalent hydrates

Explanation

Water is a polar molecule with a partial negative charge on oxygen and partial positive charges on hydrogen. It surrounds cations with oxygen atoms and anions with hydrogen atoms, forming hydration shells that screen electrostatic charges and dissolve polar/ionic substances.

Question 22Biochemistry

In human blood plasma, which buffer system plays the primary role in maintaining physiological pH around 7.4?

  1. Carbonic acid / bicarbonate buffer system Correct answer.
  2. Acetic acid / acetate buffer system
  3. Ammonia / ammonium buffer system
  4. Lactic acid / lactate buffer system

Explanation

The carbonic acid / bicarbonate system (H2CO3 / HCO3-) is the principal extracellular buffer in human blood. It regulates pH by equilibrating dissolved CO2 gas in lungs with bicarbonate ions excreted by kidneys.

Question 23Biochemistry

Why is sucrose considered a non-reducing disaccharide, unlike maltose and lactose?

  1. Its glycosidic bond involves both anomeric carbons (C-1 of glucose and C-2 of fructose) Correct answer.
  2. It lacks oxygen atoms capable of undergoing oxidation-reduction
  3. It consists of two fructose molecules linked by an alpha-1,4 bond
  4. It cannot be hydrolyzed by digestive disaccharidase enzymes

Explanation

Sucrose is formed by an alpha-1,beta-2-glycosidic bond linking C-1 of alpha-D-glucose and C-2 of beta-D-fructose. Because both anomeric carbon atoms participate in the bond, no free hemiacetal or hemiketal group remains to reduce Fehling's or Benedict's reagent.

Question 24Biochemistry

Which structural difference explains why humans can digest starch but cannot digest cellulose?

  1. Starch contains glucose units joined by alpha-glycosidic bonds, whereas cellulose has beta-1,4-glycosidic bonds Correct answer.
  2. Starch is composed of galactose monomers, whereas cellulose is made of glucose
  3. Cellulose is highly branched with alpha-1,6 linkage nodes
  4. Cellulose contains nitrogenous amino groups attached to C-2

Explanation

Starch (amylose and amylopectin) consists of D-glucose monomers linked by alpha-1,4 (and alpha-1,6) glycosidic bonds, which human amylases can cleave. Cellulose consists of beta-1,4-glycosidic bonds forming linear unbranched fibers that humans lack enzymes (cellulase) to hydrolyze.

Question 25Biochemistry

What products are generated when a triacylglycerol undergoes alkaline hydrolysis (saponification) with sodium hydroxide (NaOH)?

  1. Glycerol and three sodium salts of fatty acids (soaps) Correct answer.
  2. Three sphingosine molecules and one glucose molecule
  3. Glycerol-3-phosphate and three choline molecules
  4. Cholesterol and three inorganic phosphate ions

Explanation

Saponification is the base-catalyzed ester hydrolysis of a triglyceride (triacylglycerol) using a strong alkali like NaOH, producing one molecule of glycerol and three fatty acid sodium salts (soaps).

Question 26Biochemistry

What architectural feature makes glycerophospholipids ideal structural components of biological membranes?

  1. Amphipathic structure with a hydrophilic polar head and two hydrophobic non-polar tails Correct answer.
  2. Completely non-polar hydrophobic hydrocarbon rings
  3. Covalent cross-linking between adjacent phosphate groups
  4. Ability to form rigid, crystalline triple-helical fibers

Explanation

Glycerophospholipids are amphipathic. They possess a polar, hydrophilic head (glycerol + phosphate + alcohol moiety) and two non-polar, hydrophobic fatty acid tails. In aqueous solution, they spontaneously assemble into lipid bilayers.

Question 27Biochemistry

To which class of non-saponifiable lipids does cholesterol belong?

  1. Steroids Correct answer.
  2. Terpenes
  3. Eicosanoids
  4. Prostaglandins

Explanation

Cholesterol is a steroid, a non-saponifiable lipid characterized by a cyclopentanoperhydrophenanthrene ring core (four fused carbon rings). It modulates cell membrane fluidity and serves as a precursor for steroid hormones and bile salts.

Question 28Biochemistry

What is the net electrical charge of an amino acid at its specific isoelectric point (pI)?

  1. Zero (zwitterionic state) Correct answer.
  2. +1 (fully protonated cation)
  3. -1 (fully deprotonated anion)
  4. +2 (dicationic state)

Explanation

At its isoelectric point (pI), an amino acid exists predominantly as a dipolar zwitterion where the positive charge on the protonated amino group (-NH3+) balances the negative charge on the carboxylate group (-COO-), yielding a net charge of zero.

Question 29Biochemistry

Which chemical bonds stabilize the alpha-helix and beta-pleated sheet patterns of protein secondary structure?

  1. Hydrogen bonds between polypeptide backbone carbonyl oxygens and amide nitrogens Correct answer.
  2. Disulfide bridges between non-adjacent cysteine side chains
  3. Covalent peptide bonds between alpha-carbon atoms
  4. Hydrophobic interactions between non-polar aliphatic R-groups

Explanation

Protein secondary structure (alpha-helices and beta-sheets) is stabilized by hydrogen bonding between the peptide backbone amide N-H group and carbonyl C=O group of peptide bonds. Side chain interactions stabilize tertiary structure.

Question 30Biochemistry

Which covalent interaction contributes directly to stabilizing the tertiary structure of globular proteins such as antibodies?

  1. Disulfide bonds (-S-S-) between cysteine residues Correct answer.
  2. Glycosidic linkages between serine side chains
  3. Phosphodiester bonds between lysine residues
  4. Peptide bonds between alanine R-groups

Explanation

Disulfide bridges (-S-S-) are covalent bonds formed by the oxidation of sulfhydryl (-SH) groups of two cysteine residues. They provide strong structural stabilization for tertiary and quaternary protein folding.

Question 31Biochemistry

What is meant by describing the two complementary strands of a B-DNA double helix as 'antiparallel'?

  1. One strand runs in the 5'-to-3' direction while the complementary strand runs in the 3'-to-5' direction Correct answer.
  2. One strand consists of purines while the complementary strand consists exclusively of pyrimidines
  3. The strands rotate in opposite directions around separate central axes
  4. One strand is composed of ribose sugars while the other contains deoxyribose

Explanation

Antiparallel means the phosphodiester backbones of the two strands run in opposite chemical polarities: one strand oriented 5'-carbon to 3'-carbon, and the complementary strand oriented 3'-carbon to 5'-carbon.

Question 32Biochemistry

Which set of features correctly distinguishes RNA from DNA?

  1. Ribose pentose sugar, Uracil base, typically single-stranded Correct answer.
  2. Deoxyribose pentose sugar, Thymine base, double-stranded helix
  3. Ribose pentose sugar, Thymine base, double-stranded helix
  4. Deoxyribose pentose sugar, Uracil base, single-stranded

Explanation

RNA contains ribose (with a hydroxyl group at C-2'), the pyrimidine base Uracil (instead of Thymine), and functions primarily as a single-stranded nucleic acid molecule.

Question 33Biochemistry

A sample of human erythrocytes is suspended in an aqueous solution of 0.05 M NaCl (isotonic blood plasma NaCl concentration is ~0.15 M). What will happen to the red blood cells?

  1. Water enters the cells by osmosis, causing them to swell and burst (hemolysis) Correct answer.
  2. Water leaves the cells by osmosis, causing them to shrink (crenation)
  3. Solutes leave the cells by active transport until intracellular concentration reaches 0.05 M
  4. No net water movement occurs because cell membranes are impermeable to water

Explanation

0.05 M NaCl is hypotonic relative to erythrocyte cytoplasm (~0.15 M NaCl equivalent). Water moves down its osmotic gradient into the cells, leading to swelling and membrane rupture (hemolysis).

Question 34Biochemistry

What structural difference distinguishes alpha-D-glucopyranose from beta-D-glucopyranose in aqueous solution?

  1. The orientation of the C-1 anomeric hydroxyl group relative to the ring plane Correct answer.
  2. The position of the aldehyde functional group at C-6
  3. The inversion of configuration at C-4 making it a galactose isomer
  4. The presence of a five-membered furanose ring instead of a hexose

Explanation

Alpha and beta anomers of D-glucopyranose differ in configuration at C-1 (the anomeric carbon formed upon ring closure). In the Haworth projection, the C-1 hydroxyl is trans to the C-5 CH2OH group in the alpha-anomer and cis in the beta-anomer.

Question 35Biochemistry

Which component forms the structural backbone of sphingomyelin, a lipid abundant in the myelin sheath of nerve cell axons?

  1. Sphingosine (an 18-carbon amino alcohol) Correct answer.
  2. Glycerol-3-phosphate
  3. Isopentenyl pyrophosphate
  4. Cyclopentanoperhydrophenanthrene

Explanation

Sphingomyelin is a sphingolipid containing a sphingosine backbone (an 18-carbon amino alcohol) linked to a fatty acid via an amide bond (forming a ceramide) and a phosphocholine head group.

Question 36Biochemistry

How does an enzyme accelerate the rate of a biochemical reaction without altering its overall thermodynamic free energy change (delta G)?

  1. By lowering the activation energy (delta G transition state) of the reaction Correct answer.
  2. By increasing the temperature of the microenvironment inside the active site
  3. By shifting the chemical equilibrium constant (Keq) toward product formation
  4. By supplying external ATP energy to make endergonic reactions exergonic

Explanation

Enzymes act as biological catalysts by stabilizing the high-energy transition state, thus lowering the activation energy barrier (delta G transition state). They accelerate both forward and reverse rates equally without changing delta G or Keq.

Question 37Biochemistry

Which specific sequence is located at the 3'-terminus of all mature transfer RNA (tRNA) molecules, serving as the attachment site for a specific amino acid?

  1. 5'-CCA-3' Correct answer.
  2. 5'-AUG-3'
  3. 5'-UAA-3'
  4. 5'-TATA-3'

Explanation

All mature tRNAs end with the trinucleotide sequence 5'-CCA-3' at their 3'-unpaired acceptor stem. Aminoacyl-tRNA synthetase enzymes covalently attach the specific amino acid to the 3'-hydroxyl group of the terminal adenosine residue.

Question 38Cell structure, membranes and division

Which ribosome sedimentation coefficient characterizes cytoplasmic ribosomes in eukaryotic cells compared to prokaryotic cells?

  1. 80S in eukaryotic cytoplasm vs 70S in prokaryotes Correct answer.
  2. 70S in eukaryotic cytoplasm vs 50S in prokaryotes
  3. 60S in eukaryotic cytoplasm vs 40S in prokaryotes
  4. 100S in eukaryotic cytoplasm vs 80S in prokaryotes

Explanation

Eukaryotic cytoplasmic ribosomes are 80S (composed of 60S large and 40S small subunits). Prokaryotic ribosomes (as well as mitochondrial and chloroplast ribosomes) are 70S (composed of 50S large and 30S small subunits).

Question 39Cell structure, membranes and division

According to the fluid mosaic model proposed by Singer and Nicolson, how are proteins arranged in the plasma membrane?

  1. Integral and peripheral proteins are embedded in or associated with a fluid phospholipid bilayer Correct answer.
  2. Proteins form continuous solid layers covering both inner and outer surfaces of a static lipid core
  3. Proteins form rigid hollow tubes through which lipid molecules flow passively
  4. Lipids are covalently bonded to a rigid protein meshwork matrix

Explanation

The fluid mosaic model describes the membrane as a dynamic, two-dimensional fluid phospholipid bilayer in which integral proteins are embedded and peripheral proteins are non-covalently attached.

Question 40Cell structure, membranes and division

What key feature distinguishes facilitated diffusion from simple diffusion across a biological membrane?

  1. Facilitated diffusion requires specific transmembrane transport proteins (channels or carriers) Correct answer.
  2. Facilitated diffusion consumes metabolic energy in the form of ATP
  3. Facilitated diffusion transports solutes against their electrochemical gradient
  4. Facilitated diffusion occurs exclusively for non-polar gas molecules like oxygen

Explanation

Both simple and facilitated diffusion are passive transport processes moving solutes down concentration gradients without ATP. Facilitated diffusion requires transmembrane channel or carrier proteins for polar/charged molecules.

Question 41Cell structure, membranes and division

What is the primary function of the nucleolus located inside the eukaryotic cell nucleus?

  1. Synthesis of ribosomal RNA (rRNA) and assembly of ribosome subunits Correct answer.
  2. Replication of genomic DNA during S phase
  3. Synthesis of secretory proteins and membrane lipids
  4. Breakdown of cellular hydrogen peroxide

Explanation

The nucleolus is a non-membrane-bound nuclear region where rRNA genes are transcribed by RNA polymerase I and processed, and where rRNA combines with ribosomal proteins to assemble 40S and 60S ribosomal subunits.

Question 42Cell structure, membranes and division

Which organelle possesses membrane-bound ribosomes on its cytosolic surface and specializes in synthesizing proteins destined for secretion or membrane insertion?

  1. Rough Endoplasmic Reticulum (RER) Correct answer.
  2. Smooth Endoplasmic Reticulum (SER)
  3. Lysosome
  4. Peroxisome

Explanation

The Rough Endoplasmic Reticulum (RER) is studded with ribosomes on its outer cytosolic membrane. It synthesizes secretory proteins, lysosomal enzymes, and transmembrane proteins.

Question 43Cell structure, membranes and division

Which organelle contains acid hydrolase enzymes operating at optimal pH ~5.0 for intracellular digestion of worn-out cellular parts (autophagy) or phagocytosed material?

  1. Lysosome Correct answer.
  2. Golgi apparatus
  3. Peroxisome
  4. Centrosome

Explanation

Lysosomes are membrane-bound organelles containing acid hydrolases (phosphatases, nucleases, proteases) maintained at acidic pH (~5.0) by membrane proton pumps. They digest internal organelles (autophagy) and extracellular endocytosed material.

Question 44Cell structure, membranes and division

What is the function of the infoldings (cristae) of the inner mitochondrial membrane?

  1. To increase surface area for electron transport chain complexes and ATP synthase Correct answer.
  2. To store calcium ions required for muscular relaxation
  3. To synthesize ribosomal RNA subunits for export to the cytosol
  4. To physically anchor the outer nuclear envelope

Explanation

Cristae are deep invaginations of the inner mitochondrial membrane that greatly expand the surface area available to house respiratory electron transport chains and ATP synthase complexes.

Question 45Cell structure, membranes and division

During which phase of interphase does genomic DNA undergo complete replication?

  1. S phase Correct answer.
  2. G1 phase
  3. G2 phase
  4. M phase

Explanation

During the S (Synthesis) phase of interphase, the cell replicates its entire nuclear genome, duplicating each chromosome into two sister chromatids joined at the centromere.

Question 46Cell structure, membranes and division

What is the stoichiometric ion transport ratio of the primary active Na+/K+-ATPase pump for each molecule of ATP hydrolyzed?

  1. 3 Na+ ions pumped out of the cell, 2 K+ ions pumped into the cell Correct answer.
  2. 2 Na+ ions pumped out of the cell, 3 K+ ions pumped into the cell
  3. 3 Na+ ions pumped into the cell, 3 K+ ions pumped out of the cell
  4. 1 Na+ ion pumped out of the cell, 1 K+ ion pumped into the cell

Explanation

The Na+/K+-ATPase pump hydrolyzes one ATP molecule to actively transport 3 Na+ ions out of the cytoplasm and 2 K+ ions into the cell, both against their respective concentration gradients, maintaining membrane potential.

Question 47Cell structure, membranes and division

Which coat protein is recruited to the cytosolic face of the plasma membrane to form coated pits during receptor-mediated endocytosis?

  1. Clathrin Correct answer.
  2. Kinesin
  3. Tubulin
  4. Actin

Explanation

Receptor-mediated endocytosis relies on clathrin triskelions assembling into a polyhedral coat on the cytosolic surface of the membrane, inducing invagination to form clathrin-coated vesicles.

Question 48Cell structure, membranes and division

Which face of the Golgi apparatus receives transport vesicles arriving from the Rough Endoplasmic Reticulum?

  1. Cis (forming) face Correct answer.
  2. Trans (maturing) face
  3. Medial cisternae
  4. Secretory granule face

Explanation

The Golgi apparatus exhibits structural and functional polarity. Transport vesicles from the RER dock at and fuse with the cis (forming) face. Modified proteins exit via secretory vesicles at the trans (maturing) face.

Question 49Cell structure, membranes and division

What is the catalytic function of catalase inside peroxisomes?

  1. Decomposition of toxic hydrogen peroxide into water and oxygen Correct answer.
  2. Phosphorylation of ADP to generate ATP during glycolysis
  3. Synthesis of peptide bonds during protein translation
  4. Hydrolysis of glycogen into glucose-1-phosphate

Explanation

Peroxisomes carry out oxidative reactions (such as beta-oxidation of fatty acids) that generate hazardous hydrogen peroxide (H2O2). Catalase decomposes H2O2 into water and oxygen (2 H2O2 -> 2 H2O + O2).

Question 50Cell structure, membranes and division

Which protein polymer constitutes eukaryotic microtubules, forming spindle fibers and structural doublets in cilia and flagella?

  1. Tubulin (alpha and beta dimers) Correct answer.
  2. Actin
  3. Keratin
  4. Myosin

Explanation

Microtubules are hollow cylindrical polymers composed of heterodimers of alpha-tubulin and beta-tubulin. They form mitotic spindle apparatuses, centrioles, and cilia/flagella axonemes (9+2 structure).