100+ Free European Baccalaureate Biology Practice Questions

Explanation: Water possesses a remarkably high specific heat capacity (4.184 J/g·°C) because a significant amount of heat energy must be absorbed to break its extensive intermolecular hydrogen bonds before the kinetic energy of individual molecules can increase. This thermal buffering capability stabilizes internal cellular temperatures and aquatic environments against sudden external temperature changes.

Explanation: Phospholipids are amphipathic molecules with a polar, hydrophilic phosphate-containing head group and two nonpolar, hydrophobic fatty acid tails. In water, hydrophobic interactions drive the nonpolar tails to face inward away from water, while the polar heads face outward toward the aqueous cytosol and extracellular fluid, creating a stable bilayer.

Explanation: Active transport pumps solutes against their electrochemical or concentration gradient (from lower to higher concentration) and requires metabolic energy (typically ATP hydrolysis or electrochemical gradient coupling). In contrast, facilitated diffusion is a passive process moving solutes down their concentration gradient through transmembrane channel or carrier proteins without ATP consumption.

Explanation: Secretory proteins are translated by ribosomes attached to the Rough Endoplasmic Reticulum (ER), where they enter the ER lumen for folding. They are packaged into transport vesicles that travel to the cis-face of the Golgi apparatus for glycosylation and sorting, exit the trans-Golgi in secretory vesicles, and fuse with the plasma membrane via exocytosis.

Explanation: A competitive inhibitor binds reversibly to the active site of an enzyme, competing directly with the substrate. This increases the apparent Km (meaning higher substrate concentration is needed to reach half-maximal velocity), but Vmax remains unchanged because high substrate concentrations can completely outcompete the inhibitor.

Explanation: ATP stores metabolic energy in high-energy phosphoanhydride bonds linking its three phosphate groups. Hydrolysis of the terminal phosphoanhydride bond (converting ATP to ADP + Pi) releases approximately 30.5 kJ/mol of free energy (ΔG°' = -30.5 kJ/mol) due to electrostatic repulsion relief and resonance stabilization of inorganic phosphate.

Explanation: Glycolysis occurs entirely within the cytosol of eukaryotic cells. It breaks down one 6-carbon glucose molecule into two 3-carbon pyruvate molecules, consuming 2 ATP during the investment phase and producing 4 ATP (via substrate-level phosphorylation) and 2 NADH, resulting in a net yield of 2 pyruvate, 2 NADH, and 2 net ATP.

Explanation: In the mitochondrial matrix, pyruvate dehydrogenase converts 3-carbon pyruvate into 2-carbon acetyl-CoA. This oxidative decarboxylation removes one carbon atom as CO2, oxidizes the remaining acetyl group while reducing NAD+ to NADH, and attaches coenzyme A to yield acetyl-CoA, which then enters the Krebs cycle by condensing with oxaloacetate.

Explanation: Electron transport chain complexes (I, III, and IV) pump protons (H+) from the mitochondrial matrix into the intermembrane space, generating a steep electrochemical gradient. Protons diffuse down this gradient back into the matrix through the F0 channel of ATP synthase, driving rotational conformational changes in the F1 catalytic subunit that phosphorylate ADP to ATP (chemiosmosis).

Explanation: In the absence of oxygen (the terminal electron acceptor in aerobic respiration), electron transport halts and NADH accumulates. Fermentation pathways transfer electrons from NADH back onto pyruvate or its derivatives (forming lactate or ethanol + CO2), regenerating free NAD+ so glycolysis can continue generating 2 net ATP per glucose via substrate-level phosphorylation.