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Basque Country PAU Biology Examination — UPV/EHU (2º Bachillerato 2026) practice questions are available now; exam metadata is being verified.
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2026 Statistics
Key Facts: Basque PAU Biology Exam
90 Minutes
Exam time duration
UPV/EHU PAU Commission
EUR 86.33
Ordinary registration fee
UPV/EHU 2026 PAU
0–10 Scale
Grading scale for Bachillerato and PAU exams
Spanish Ministry of Education & UPV/EHU
5 Core Blocks
Biomolecules, Cell Biology, Metabolism, Molecular Genetics, Microbiology & Immunology
2º Bachillerato Biology Syllabus
100 Questions
Practice bank size in OpenExamPrep
OpenExamPrep
Basque Country PAU Biology (UPV/EHU 2026) is a 90-minute university entrance exam assessing 2º Bachillerato syllabus domains.
Sample Basque PAU Biology Practice Questions
Try these sample questions to test your Basque PAU Biology exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.
1Why does liquid water have an exceptionally high specific heat capacity compared to other small covalent molecules?
A.Extensive intermolecular hydrogen bonding absorbs thermal energy before increasing kinetic movement.
B.Covalent bonds within water molecules continuously break and reform at room temperature.
C.Water molecules form ionic complexes that retain thermal kinetic energy efficiently.
D.High molecular mass allows water to store vast amounts of rotational kinetic energy.
Explanation: Water possesses a high specific heat capacity (4.184 J/g°C) because a significant portion of absorbed heat energy goes into disrupting hydrogen bonds between adjacent molecules rather than increasing their translation kinetic speed. This property prevents sudden temperature fluctuations in biological fluids and organismal tissues, stabilizing metabolic environments.
2Which physical property of water enables continuous sap transport against gravity in xylem vessels of tall plants?
A.Low surface tension and high compressibility
B.High cohesion and adhesion combined with high tensile strength
C.Maximal density at 4 degrees Celsius and low viscosity
D.High dielectric constant and low specific heat capacity
Explanation: Cohesion (hydrogen bonding between adjacent water molecules) and adhesion (hydrogen bonding between water and xylem cell wall components like cellulose) allow water to form a continuous column under tension. Transpiration pull pulls this cohesive column upward without breaking.
3What happens to a plant cell when it is placed into a hypertonic salt solution?
A.Water enters the vacuole causing the cell to burst via osmotic lysis.
B.Sodium ions enter the cell via simple diffusion until turgor pressure stabilizes.
C.Water leaves the central vacuole causing the plasma membrane to detach from the cell wall (plasmolysis).
D.Solute equilibrium is maintained with no net movement of water across the membrane.
Explanation: In a hypertonic environment, the solute concentration outside the cell exceeds that in the cytoplasm. Osmotic pressure drives net water flow out of the central vacuole and cytoplasm, shrinking the protoplast and pulling the plasma membrane away from the rigid cell wall—a process termed plasmolysis.
4Which functional group distinction differentiates an aldose monosaccharide like D-glucose from a ketose like D-fructose?
A.An aldose cannot form D and L enantiomeric isomers, whereas a ketose can.
B.An aldose has carboxylic acid groups, whereas a ketose contains ester linkages.
C.An aldose forms ring structures with five atoms, whereas a ketose forms rings with seven atoms.
D.An aldose contains a carbonyl group at carbon-1 (aldehyde), whereas a ketose contains a carbonyl at carbon-2 (ketone).
Explanation: Aldoses possess an aldehyde functional group (-CHO) located at the terminal carbon (C-1). Ketoses possess a ketone functional group (C=O) located at an internal carbon atom, typically carbon-2 (C-2). Both glucose and fructose are hexoses with the chemical formula C6H12O6.
5Why is sucrose considered a non-reducing disaccharide, unlike maltose and lactose?
A.The glycosidic bond involves the anomeric carbons of both glucose (alpha-1) and fructose (beta-2), leaving no free anomeric hydroxyl group.
B.Sucrose lacks hydroxyl groups capable of participating in oxidation-reduction reactions.
C.Sucrose is composed exclusively of beta-D-galactose monomers joined by beta-1,4-bonds.
D.Sucrose spontaneously hydrolyzes into free carboxylic acids in aqueous solution.
Explanation: A reducing sugar requires a free anomeric carbon (C-1 in aldoses, C-2 in ketoses) capable of opening into an open-chain aldehyde or ketone to reduce Benedict's or Fehling's reagents. In sucrose, the O-glycosidic bond links C-1 of alpha-D-glucose directly to C-2 of beta-D-fructose, tying up both anomeric carbons.
6What structural difference explains why humans can digest starch but cannot digest structural cellulose?
A.Starch is composed of D-glucose monomers, whereas cellulose is composed of L-galactose monomers.
B.Starch consists of alpha-1,4 and alpha-1,6 glycosidic bonds, whereas cellulose consists of unbranched beta-1,4 glycosidic bonds.
C.Starch contains nitrogenous amino groups, whereas cellulose contains phosphate ester linkages.
D.Starch is a linear protein complex, whereas cellulose is a branched lipid polymer.
Explanation: Human digestive enzymes like alpha-amylase specifically recognize and hydrolyze alpha-1,4 glycosidic bonds found in amylose and amylopectin (starch). Cellulose consists of linear chains of beta-D-glucose joined by beta-1,4 glycosidic bonds, which human enzymes cannot cleavage due to substrate specificity.
7Which heteropolysaccharide serves as a major structural component of animal extracellular matrix and synovial fluid?
A.Amylopectin
B.Glycogen
C.Hyaluronic acid
D.Inulin
Explanation: Hyaluronic acid (hyaluronan) is a non-sulfated glycosaminoglycan (heteropolysaccharide) composed of repeating disaccharide units of D-glucuronic acid and N-acetyl-D-glucosamine. It forms high-viscosity gels in animal extracellular matrices, cartilage, and synovial fluid.
8How does the introduction of cis double bonds into hydrocarbon chains affect the melting point of fatty acids?
A.It eliminates hydrophobic interactions, rendering the fatty acid fully water-soluble.
B.It increases molecular linearity, promoting tight hydrophobic stacking and raising the melting point.
C.It enables ionic bonding between chains, converting liquid oils into solid crystalline fats.
D.It introduces kinks that disrupt van der Waals packing, lowering the melting point.
Explanation: Naturally occurring unsaturated fatty acids feature cis double bonds, which introduce fixed 30-degree bends ('kinks') in the hydrocarbon acyl chain. These kinks hinder compact parallel packing of adjacent molecules, weakening intermolecular van der Waals forces and lowering the melting point.
9Which structural feature grants glycerophospholipids their amphipathic property in biological membranes?
A.A hydrophilic polar head group (phosphate + alcohol) attached to a hydrophobic backbone of two fatty acyl chains
B.Three saturated fatty acid chains attached to a polar spherical carbohydrate ring
C.A steroid nucleus esterified to four hydrophilic polypeptide subunits
D.A single non-polar hydrocarbon chain attached to a polar peptide bond
Explanation: Glycerophospholipids possess a glycerol molecule esterified to two non-polar, hydrophobic fatty acid tails and one polar, hydrophilic phosphate group bound to an amino alcohol (like choline or ethanolamine). This amphipathic dual polarity drives spontaneous lipid bilayer self-assembly in aqueous solutions.
10Which parent molecule serves as the biochemical precursor for steroid hormones, vitamin D, and bile salts in animals?
A.Sphingomyelin
B.Cholesterol
C.Triacylglycerol
D.Phosphatidylcholine
Explanation: Cholesterol is an essential amphipathic sterol containing a fused four-ring steroid nucleus (cyclopentanoperhydrophenanthrene). In animal biochemistry, cholesterol is the direct biosynthetic precursor for steroid hormones (cortisol, aldosterone, estrogen, testosterone), vitamin D3, and bile acids.
About the Basque PAU Biology Practice Questions
Verified exam format metadata for Basque Country PAU Biology Examination — UPV/EHU (2º Bachillerato 2026) is pending. The practice questions above remain available while official exam length, timing, passing score, fee, and administrator details are reviewed.