Bioenergetics terminology — exergonic reactions: In metabolism, an exergonic reaction is best defined as a process that releases free energy usable for cellular work and can occur spontaneously under appropriate conditions. Which option states this correctly?

Introduction / Context:
Exergonic reactions power life by providing free energy that cells harness to perform work, such as synthesizing macromolecules, pumping ions, and driving motion. Recognizing exergonic processes allows learners to understand how metabolic pathways are organized and why some steps are irreversible.

Given Data / Assumptions:

• An exergonic reaction has Delta G < 0 (negative free-energy change).
• Spontaneous in the thermodynamic sense does not mean fast; kinetics require enzymes.
• Cells capture released free energy in ATP, ion gradients, or reduced cofactors.

Concept / Approach:
Exergonic simply means that the products are at a lower free energy than the reactants. Consequently, energy is released that can be conserved. For instance, electron transport oxidizes reduced cofactors and uses the energy to pump protons, creating a gradient later used for ATP synthesis.

Step-by-Step Solution:
Match definition: Delta G < 0 means energy is released. Express in practical terms: usable for work (ATP synthesis, transport). Choose the statement that explicitly states energy release for work.

Verification / Alternative check:
Glucose oxidation overall is exergonic; cells harness it through stepwise redox reactions to maximize captured energy in ATP and reduced cofactors.

Why Other Options Are Wrong:

• Requires energy: That is endergonic, not exergonic.
• Gives off heat but cannot perform work: Misleading; in biology, energy is conserved in coupled forms, not only as heat.
• No free-energy change: Would be equilibrium, not exergonic.

Common Pitfalls:
Equating heat release with exergonic without considering whether free energy can be conserved for work; biology focuses on free-energy transformations, not just temperature changes.

Final Answer:
Releases energy for work.