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Cantabria PAU Biology Examination — UNICAN (Biología 2º Bachillerato 2026) practice questions are available now; exam metadata is being verified.
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2026 Statistics
Key Facts: Cantabria PAU Biology Exam
90 Minutes
Official examination duration
UNICAN PAU Regulations
Min 4.0
Minimum Access Phase score required
UNICAN PAU Guidelines
6 Blocks
Official saberes: biomolecules, molecular genetics, cell biology, metabolism, biotechnology, immunology
UNICAN Criterios de Corrección PAU Biología 2026
EUR 71.09
Base registration fee for PAU Access Phase
UNICAN Fees
100
Practice questions available in this question bank
OpenExamPrep
Cantabria PAU Biology (UNICAN 2026) is a 90-minute Spanish written exam across six official blocks (biomolecules, molecular genetics, cell biology, metabolism, biotechnology, immunology). This English-language MCQ bank is a study adaptation, not a format simulation.
Sample Cantabria PAU Biology Practice Questions
Try these sample questions to test your Cantabria PAU Biology exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.
1Which physicochemical property of water allows homeothermic organisms to keep a stable body temperature through evaporation of sweat?
A.High heat of vaporization due to intermolecular hydrogen bonds.
B.Low boiling point caused by nonpolar covalent bonds.
C.Higher density in the solid state than in the liquid state.
D.Low surface tension that favors hydrophobic cohesion.
Explanation: Water has a high heat of vaporization (about 540 cal/g at 100 °C) because a large amount of thermal energy is needed to break its dense network of intermolecular hydrogen bonds before molecules enter the gas phase. That energy absorption cools the body efficiently when sweat evaporates from the skin.
2What happens to a human erythrocyte placed in a saline solution that is hypertonic relative to its cytoplasm?
A.It takes up water by osmosis until it undergoes lysis or hemolysis.
B.It loses water by osmosis to the external medium and undergoes crenation (shriveling).
C.It takes up Na+ ions by simple diffusion, increasing cell volume.
D.It remains unchanged because the membrane is completely impermeable to water.
Explanation: In a hypertonic medium, solute concentration is higher outside than inside the erythrocyte. Water therefore leaves the cell by osmosis down the water-potential gradient, shrinking cytoplasmic volume and producing the wrinkled appearance called crenation.
3What is the main function of the bicarbonate buffer system (HCO3− / H2CO3) in human blood plasma?
A.To catalyze hydrolysis of plasma proteins during physiological exercise.
B.To raise osmotic pressure by irreversibly precipitating calcium phosphate salts.
C.To keep plasma pH within physiological limits (about 7.35–7.45).
D.To transport dietary triglycerides directly to adipose tissue.
Explanation: The bicarbonate buffer dampens pH swings in blood plasma. When proton concentration rises, HCO3− binds H+ to form H2CO3, which dissociates into CO2 and H2O, helping keep physiological pH stable.
4How do the α and β anomers of D-glucopyranose differ structurally in aqueous solution?
A.In the total number of carbon atoms in the hydrocarbon chain.
B.In having a ketone group instead of an aldehyde group in the open-chain form.
C.In the ability to form peptide bonds with aromatic amino acids.
D.In the spatial orientation of the hydroxyl (–OH) attached to the anomeric carbon (C1).
Explanation: When D-glucose cyclizes to glucopyranose, carbonyl carbon C1 becomes a new asymmetric anomeric carbon. If the C1 –OH points down in the Haworth projection (trans to C6), the sugar is the α anomer; if it points up (cis to C6), it is the β anomer.
5Why does sucrose (α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside) lack reducing power toward Fehling’s reagent?
A.Because both anomeric carbons (C1 of glucose and C2 of fructose) are involved in the glycosidic bond.
B.Because it contains only galactose units linked by β(1→4) bonds.
C.Because its structure completely lacks hydroxyl groups on the furanose rings.
D.Because it denatures rapidly at room temperature, releasing carbon monoxide.
Explanation: Reducing power depends on a free carbonyl (aldehyde or ketone) at an anomeric carbon. In sucrose, the dicarbonyl glycosidic link joins the anomeric C1 of α-D-glucose to the anomeric C2 of β-D-fructose, so both anomeric carbons are locked and no free reducing group remains.
6Which structural feature explains cellulose’s high mechanical strength and insolubility compared with starch?
A.Starch has β(1→4) linkages that form very compact branched helices.
B.Cellulose consists of linear β-D-glucose polymers joined by β(1→4) bonds that form interchain hydrogen bonds.
C.Cellulose contains N-acetylglucosamine monomers covalently joined by amide bonds.
D.Starch is a heteropolysaccharide with a strict alternating glucose–ribose pattern.
Explanation: Cellulose is a structural homopolysaccharide of β-D-glucose linked by β(1→4) bonds. That geometry yields straight parallel chains that pack tightly through interchain hydrogen bonds into strong, insoluble microfibrils.
7Why do unsaturated fatty acids with cis double bonds have lower melting points than saturated fatty acids of the same chain length?
A.Because saturated chains form additional hydrogen bonds with surrounding water molecules.
B.Because cis unsaturations completely remove the electrical charge of the terminal carboxyl group.
C.Because cis double bonds kink the hydrocarbon chain and hinder lipid packing.
D.Because unsaturated fatty acids spontaneously polymerize into high-density crystalline networks.
Explanation: Cis double bonds introduce a fixed bend in the hydrocarbon chain. That angular geometry prevents tight linear packing through van der Waals contacts, so less thermal energy is needed to melt them.
8What does saponification of a triacylglycerol (triglyceride) consist of?
A.Dehydrating condensation of three glycerol molecules with one long-chain fatty acid.
B.Catalytic oxidation of double bonds to produce volatile aldehydes and ketones.
C.Enzymatic addition of phosphate groups to glycerol hydroxyls to synthesize nucleotides.
D.Alkaline hydrolysis of the ester bonds between glycerol and fatty acids, releasing glycerol and sodium/potassium fatty-acid salts (soaps).
Explanation: Saponification is hydrolysis of triacylglycerol ester bonds by a strong base (NaOH or KOH). The esters break, releasing one glycerol (propanetriol) and three alkali fatty-acid salts commonly called soaps.
9Which structural property lets glycerophospholipids spontaneously organize into bilayers in water?
A.Their amphipathic nature: a hydrophilic polar head (phosphate and alcohol) and two hydrophobic nonpolar fatty-acid tails.
B.Peptide bonds covalently joining the fatty acids to the polar head.
C.Complete water solubility because they lack hydrocarbon chains longer than three carbons.
D.An exclusive ability to act as photosynthetic pigments that capture infrared light.
Explanation: Phospholipids are amphipathic: a hydrophilic head (glycerol, phosphate, and an amino alcohol) and a hydrophobic region (two fatty-acid tails). In water, tails face inward and polar heads face the aqueous phases, forming the lipid bilayer.
10What is cholesterol’s role in regulating plasma-membrane fluidity in animal cells?
A.It indefinitely increases permeability so large hydrophilic proteins pass freely.
B.It buffers fluidity: at high temperature it reduces lipid mobility, and at low temperature it hinders packing and freezing.
C.It blocks mitochondrial ATP synthesis by inhibiting active proton transport.
D.It completely replaces phospholipids in the outer leaflet of a cellulosic bilayer.
Explanation: Cholesterol acts as a dual fluidity buffer in animal plasma membranes. At higher physiological temperatures its rigid sterol ring restrains excessive fatty-acid motion; at lower temperatures it intercalates between chains and prevents tight packing and crystallization.
About the Cantabria PAU Biology Practice Questions
Verified exam format metadata for Cantabria PAU Biology Examination — UNICAN (Biología 2º Bachillerato 2026) is pending. The practice questions above remain available while official exam length, timing, passing score, fee, and administrator details are reviewed.