AP Biology - Advanced Concepts and Analysis

Front

How does water's high specific heat capacity contribute to homeostasis in organisms?

Back

Water's high specific heat (4.18 J/g·°C) means it absorbs or releases large amounts of energy with minimal temperature change. This provides thermal stability for aquatic organisms and helps terrestrial organisms regulate internal temperatures through evaporative cooling and blood-based heat distribution.

Front

Predict the effect of a noncompetitive inhibitor on enzyme kinetics (Km and Vmax).

Back

A noncompetitive inhibitor binds to an allosteric site, changing enzyme shape and reducing activity. Vmax decreases because fewer functional enzymes exist. Km remains unchanged because substrate affinity at active sites is unaffected. Graphically, this appears as a lower plateau with unchanged x-intercept on a Lineweaver-Burk plot.

Front

Explain why the modern estimate for total aerobic respiration ATP yield is 30-32 ATP per glucose, not 36-38.

Back

Modern calculations account for: (1) NADH yields ~2.5 ATP (not 3) and FADH2 yields ~1.5 ATP (not 2) due to proton leakage and incomplete coupling; (2) ATP cost for transporting pyruvate and phosphate into mitochondria. Substrate-level phosphorylation: glycolysis (2 ATP) + Krebs (2 ATP). Oxidative phosphorylation contributes ~26-28 ATP, totaling 30-32 ATP.

Front

A plant cell in a hypertonic solution initially plasmolyzes but then recovers turgor. Propose a mechanism.

Back

The cell initially loses water via osmosis, causing plasmolysis (membrane detaches from wall). Recovery suggests the cell actively transported solutes (K+, sugars) into the cytoplasm using ATP-driven pumps. This decreases water potential inside the cell, drawing water back in and restoring turgor pressure against the rigid cell wall.

Front

How does the proton-motive force drive ATP synthesis in oxidative phosphorylation?

Back

The electron transport chain pumps H+ from the mitochondrial matrix to the intermembrane space, creating an electrochemical gradient (proton-motive force). This stores potential energy as both a pH gradient and electrical potential. H+ flow back through ATP synthase's Fo channel rotates the complex, catalyzing ADP + Pi → ATP in the F1 unit.