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100+ Free Castilla y León PAU Biology Practice Questions
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2026 Statistics
Key Facts: Castilla y León PAU Biology Exam
90 min
Exam Time Limit
Comisión Organizadora PAU Castilla y León
0–10
Grading Scale
Junta de Castilla y León
4.0
Min. Access Phase Score
USAL / UVA / UBU / ULE
EUR 76-90
Base Registration Fee
Junta de Castilla y León
5 Blocks
Curriculum Content Areas
2º Bachillerato Biology Syllabus
The Castilla y León PAU Biology exam (Biología) is administered by the public universities of Castilla y León (USAL, UVA, UBU, ULE) and the Junta de Castilla y León for students completing 2nd Bachillerato. The exam lasts 90 minutes and is graded on a 0–10 scale (minimum 4.0 required in the Access Phase). Note that local questions on this platform are an English-language MCQ study adaptation created to help students master the underlying 2nd Bachillerato curriculum.
Sample Castilla y León PAU Biology Practice Questions
Try these sample questions to test your Castilla y León 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 physical property of water allows it to absorb or release large quantities of thermal energy with minimal change in its own temperature, buffering biological organisms against environmental thermal fluctuations?
A.High specific heat capacity
B.High surface tension
C.Low latent heat of vaporization
D.Maximum density at 0 °C
Explanation: Water possesses a high specific heat capacity (4.184 J/g·°C) due to its extensive intermolecular hydrogen-bonding network. Heat energy supplied to water is predominantly consumed in breaking hydrogen bonds before increasing the kinetic energy of individual water molecules, thus moderating internal body temperatures and aquatic habitats.
2When a red blood cell (erythrocyte) is placed in a hypertonic NaCl solution, water rapidly flows out of the cell across the plasma membrane. What is this cellular response termed in animal cell physiology?
A.Crenation
B.Plasmolysis
C.Hemolysis
D.Turgor
Explanation: In animal cells lacking a cell wall, placement in a hypertonic environment causes osmotic loss of intracellular water, leading to cell shrinkage and a spiky surface appearance known as crenation. In plant cells with rigid cell walls, the equivalent protoplast detachment is termed plasmolysis.
3Which of the following monosaccharides is classified structural-chemically as a ketohexose?
A.D-Fructose
B.D-Glucose
C.D-Galactose
D.D-Ribose
Explanation: D-Fructose is a 6-carbon monosaccharide (hexose) containing a ketone functional group at carbon 2, classifying it as a ketohexose. D-Glucose and D-Galactose are aldohexoses, whereas D-Ribose is an aldopentose.
4Maltose is a disaccharide produced by starch hydrolysis. Which glycosidic linkage connects the two glucose units in maltose?
A.alpha(1 -> 4) glycosidic bond
B.beta(1 -> 4) glycosidic bond
C.alpha(1 -> 2) glycosidic bond
D.alpha(1 -> 6) glycosidic bond
Explanation: Maltose consists of two D-glucopyranose units linked by an alpha(1 -> 4) glycosidic bond formed via a condensation reaction between the anomeric hydroxyl of alpha-D-glucose (C1) and the C4 hydroxyl of another glucose molecule.
5Cellulose serves as a structural component in plant cell walls, whereas starch serves as energy storage. What structural feature accounts for the mechanical rigidity and resistance of cellulose to human digestive enzymes?
A.Linear unbranched chains of D-glucose linked by beta(1 -> 4) glycosidic bonds forming microfibrils
B.Branched polymer chains of D-glucose linked by alpha(1 -> 4) and alpha(1 -> 6) bonds
C.Coiled helical chains of D-glucose linked exclusively by alpha(1 -> 4) bonds
D.Heteropolysaccharide composition containing alternating units of N-acetylglucosamine
Explanation: Cellulose is composed of unbranched linear chains of D-glucose connected by beta(1 -> 4) glycosidic linkages. This geometry allows parallel glucose chains to form extensive interchain hydrogen bonds, creating insoluble microfibrils with high tensile strength that human alpha-amylases cannot hydrolyze.
6Which of the following lipid classes is non-saponifiable because it lacks fatty acid components connected by ester linkages?
A.Steroids (e.g., cholesterol)
B.Triacylglycerols (triglycerides)
C.Glycerophospholipids (phosphatidylcholine)
D.Sphingolipids (sphingomyelin)
Explanation: Steroids are non-saponifiable lipids derived from a tetracyclic cyclopentanoperhydrophenanthrene ring structure. Because they contain no esterified fatty acids, they do not undergo alkaline hydrolysis (saponification) to yield soap (fatty acid salts).
7Phospholipids self-assemble into lipid bilayers when introduced into an aqueous environment. What molecular property drives this spontaneous formation?
A.Amphipathic structure with hydrophilic polar heads and hydrophobic non-polar fatty acid tails
B.Complete hydrophobicity across all regions of the hydrocarbon skeleton
C.High solubility in polar solvents mediated by ionic carboxylate groups
D.Covalent cross-linking between adjacent fatty acid tails
Explanation: Phospholipids are amphipathic molecules containing a polar hydrophilic head (phosphate and attached group) and two non-polar hydrophobic tail regions (fatty acid chains). In water, hydrophobic interactions drive the non-polar tails inward away from water while hydrophilic heads face the aqueous environment, yielding a stable bilayer.
8Oleic acid is a monounsaturated 18-carbon fatty acid with a cis double bond at carbon 9. How does the presence of this cis double bond affect its physical melting point compared to stearic acid (saturated 18C)?
A.It lowers the melting point by creating a kink in the hydrocarbon chain that disrupts intermolecular packing
B.It increases the melting point by enhancing van der Waals packing density
C.It elevates the melting point due to increased molecular weight
D.It has no effect on physical melting temperature
Explanation: A cis double bond introduces a rigid bend (kink) in the fatty acid hydrocarbon chain. This prevents tight, parallel van der Waals packing among acyl chains, lowering the thermal energy required to disrupt the lattice and resulting in a lower melting point (liquid at room temperature).
9At physiological pH (~7.4), a standard amino acid lacking an ionizable side chain exists predominantly in which ionic state?
A.Zwitterion (dipolar ion with protonated -NH3+ and deprotonated -COO-)
B.Fully protonated cation (+1 charge)
C.Fully deprotonated anion (-1 charge)
D.Uncharged neutral non-polar molecule
Explanation: At physiological pH (~7.4), which is between the carboxyl pKa (~2.0) and amino pKa (~9.5), the alpha-carboxyl group loses a proton (-COO-) while the alpha-amino group retains a proton (-NH3+). The amino acid exists as a zwitterion with a net electrical charge of zero.
10Which of the following characteristics accurately describes the chemical nature of the peptide bond joining adjacent amino acid residues in proteins?
A.Planar amide linkage with partial double-bond character that restricts free rotation around the C-N bond
B.Flexible single covalent bond allowing unrestricted 360-degree rotation
C.Weak non-covalent hydrogen bond easily broken by mild temperature increases
D.Ionic interaction formed between positively and negatively charged side chains
Explanation: The peptide bond (-CO-NH-) is a covalent amide linkage formed by condensation. Resonance delocalization of electron pairs between the carbonyl oxygen and amide nitrogen imparts a ~40% double-bond character to the C-N bond, freezing the six backbone atoms in a rigid planar trans conformation.
About the Castilla y León PAU Biology Practice Questions
Verified exam format metadata for Castilla y León PAU Biology (Biología 2º Bachillerato) is pending. The practice questions above remain available while official exam length, timing, passing score, fee, and administrator details are reviewed.