Practice Questions

Water adheres to the polar -OH groups of cellulose/glass. This adhesion pulls water up the sides, creating a concave meniscus and generating the upward force for capillary action. If cohesion were dominant (like mercury), a convex meniscus and depression would result.

Water molecules experience a net inward pull due to unbalanced cohesive forces at the surface. This surface tension forces the droplet to assume the shape with the smallest possible surface area-to-volume ratio, which is a perfect sphere in the absence of gravity.

Antidiuretic hormone (ADH) increases the water permeability of the collecting duct by inserting aquaporins. Water then moves passively by osmosis down the osmotic gradient created by the counter-current multiplier system in the hypertonic medullary interstitium.

The dissolution process involves energy input to break the crystal lattice (lattice energy) and energy release from forming hydration shells (hydration energy). If the lattice energy is greater than the hydration energy, the net process is endothermic, absorbing heat from the surroundings and making the solution cold.

Viscosity is the internal resistance to flow. Water has a relatively low viscosity compared to other liquids like oils. This property allows blood (a water-based fluid) to be pumped efficiently through the cardiovascular system with minimal energy loss due to friction.

When a plant cell is in a hypotonic environment, water enters by osmosis, causing the protoplast to swell and press against the rigid cell wall. This hydrostatic pressure, called turgor pressure, provides structural support to non-woody plants.

In hydrolytic enzymes, a water molecule, often activated by a base in the active site, acts as a nucleophile. It attacks an electrophilic carbon in the peptide or glycosidic bond, leading to bond cleavage. The enzyme precisely orients this catalytic water molecule.

H₂S cannot form significant hydrogen bonds due to sulfur's lower electronegativity. Water's ability to form a 3D network of strong intermolecular H-bonds requires considerably more thermal energy to separate the molecules into a gaseous state, thus resulting in a liquid state at room temperature.

The descending limb is permeable to water. The medullary interstitium has a high solute concentration (low water potential). Water moves out of the descending limb by osmosis down this water potential gradient, concentrating the urine.

The ocean absorbs vast amounts of solar heat during the day/summer with a small temperature rise and releases it slowly at night/winter. This large thermal inertia moderates the temperature of the adjacent land, keeping coastal areas cooler in summer and warmer in winter.