AP Syllabus focus:
‘Life maintains high levels of order without violating thermodynamic laws by ensuring energy input exceeds energy loss.’
Living cells appear highly ordered, yet they obey thermodynamics. This page explains how organisms maintain and build biological order by continually acquiring, transforming, and dissipating energy.
Thermodynamics in Living Systems
Thermodynamics describes how energy moves and changes form. Cells are open systems: they exchange energy and matter with their surroundings, so cellular order must be understood in that environmental context.
The First Law: Energy Is Conserved
Practice Questions
FAQ
By exporting entropy to the surroundings.
Heat released from energy transformations increases environmental entropy.
Waste products carry dispersed energy/matter away from the organism.
Molecular energy transfers involve many steps with friction-like losses (random collisions).
Some energy inevitably spreads into random kinetic motion of molecules, which is heat, raising entropy.
Negative $\Delta G$ indicates a process is energetically favourable, not fast.
Reaction rate depends on kinetic factors (e.g., energy barriers and molecular rearrangements), so a favourable process may still proceed very slowly.
Increasing $T$ increases the magnitude of $T\Delta S$.
This can make entropy-increasing processes more favourable at higher temperatures, and entropy-decreasing processes less favourable unless compensated by energy changes elsewhere.
Biological order is local and maintained.
Organisms create structured arrangements (local order) while simultaneously increasing disorder externally through heat and exported products, so total entropy still rises.
