Acids vs. bases in aqueous biology: what is the core difference? Choose the statement that best describes the fundamental Brønsted–Lowry difference between an acid and a base in water (physiology/biochemistry context).

Introduction / Context:
Understanding acids and bases under the Brønsted–Lowry framework is foundational for biochemistry, physiology, and pharmaceutical sciences. In aqueous systems such as blood plasma or cytosol, hydrogen ion (proton) transfer controls enzyme activity, buffer behavior, and membrane transport.

Given Data / Assumptions:

• Medium is water (aqueous solutions relevant to biology).
• We compare acids and bases using Brønsted–Lowry definitions.
• We assume normal physiological temperature and ionic strength.

Concept / Approach:
Brønsted–Lowry acid: proton donor. Brønsted–Lowry base: proton acceptor. In water, an acid increases the concentration of hydronium (H3O+), while a base decreases it by accepting a proton (often from water) to form species like NH4+ from NH3. This view generalizes the Arrhenius idea and fits complex biological buffers.

Step-by-Step Solution:
Define acid: a species that donates H+ to another species.Define base: a species that accepts H+ from another species.Map to water: HA + H2O → A− + H3O+ (acid donates), and B + H2O → BH+ + OH− (base accepts).Select the statement that matches: acids donate H+ in water; bases accept H+.

Verification / Alternative check:
Common biochemical buffers (for example, H2PO4−/HPO4^2−, bicarbonate/carbonic acid) behave according to this donor–acceptor model, confirming the rule across physiological pH.

Why Other Options Are Wrong:
Polarity alone does not define acid–base properties; some acids and bases are both polar. Saying bases donate H+ reverses the definition. Claiming both donate H+ contradicts proton balance.

Common Pitfalls:
Confusing Lewis and Brønsted–Lowry definitions; assuming acidity strictly correlates with molecular polarity.

Final Answer:
Acids donate hydrogen ions in water while bases accept hydrogen ions.