Entropy within the Cell

Living cells follow the second law of thermodynamics, which states that systems tend to proceed from low entropy-ordered states to high entropy-disordered states without outside input.

For example, the passive transport of concentrated oxygen from the lungs to the less oxygenated blood disperses the oxygen molecules, increasing the entropy of the system.

Cells derive energy from the breakdown of molecules such as glucose. The by-products of the reaction – carbon dioxide, water, and heat are released into the surroundings, raising its entropy.

Cell survival depends upon highly ordered systems such as DNA and proteins. The formation of these ordered structures causes a decrease in the entropy of the system, which must be accompanied by an equal or greater increase in the entropy of the surroundings.

Single DNA strands are disordered, and their entropy decreases when they reanneal into an ordered double helix structure.

At the same time, energy is released into the surroundings during double helix formation. This energy makes the surroundings more disordered and increases its entropy.