Cells and the Laws of Thermodynamics

Study Notes

The total amount of energy in the universe remains constant, and cells obey this law by converting energy from one form to another.
The ultimate source of energy for all life on Earth is the sun.

Plants obtain energy directly from sunlight through photosynthesis, storing it in chemical bonds of organic molecules.
Animals live on energy stored in chemical bonds of organic molecules by consuming plants or other animals that have eaten plants.
Energy is extracted from organic molecules by gradual oxidation, which involves adding oxygen atoms to a molecule.
Oxidation occurs in any reaction where electrons (e-) are transferred from one atom to another, essentially the removal of electrons.

Oxidation: adding O2 atoms to a molecule, or the removal of electrons from an atom.
Reduction: the reverse of oxidation, involving the addition of electrons to an atom.
Examples: photosynthesis (reduction of carbon dioxide to form glucose) and cellular respiration (oxidation of glucose to produce ATP).

Carbon in the atmosphere is constantly recycled: stored in glucose in plants, broken down by organisms, and sent back to the atmosphere.

Living things create order within themselves, but this requires energy and effort.
The universe tends towards disorder, known as entropy, where molecules move freely.
Cells maintain their structure by releasing enough energy into the surroundings, increasing the overall disorder of the environment.

Exergonic reactions: release energy, often involving oxidation events (e.g., cellular respiration).
Endergonic reactions: require energy, often involving reduction events (e.g., photosynthesis).