S'identifier

A living cell's primary tasks of obtaining, transforming, and using energy to do work may seem simple. However, the second law of thermodynamics explains why these tasks are harder than they appear. None of the energy transfers in the universe are completely efficient. In every energy transfer, some amount of energy is lost in a form that is unusable. In most cases, this form is heat energy. Thermodynamically, heat energy is defined as the energy transferred from one system to another that is not work. For example, some energy is lost as heat energy during cellular metabolic reactions.

An important concept in physical systems is that of order and disorder. The more energy that is lost by a system to its surroundings, the less ordered and more random the system is. Scientists refer to the measure of randomness or disorder within a system as entropy. High entropy means high disorder and low energy. Molecules and chemical reactions have varying entropy as well. For example, entropy increases as molecules at a high concentration in one place diffuse and spread out.

Living things are highly ordered, requiring constant energy input to be maintained in a state of low entropy. As living systems take in energy-storing molecules and transform them through chemical reactions, they lose some amount of usable energy in the process because no reaction is completely efficient. They also produce waste and by-products that are not useful energy sources. This process increases the entropy of the system's surroundings. Since all energy transfers result in the loss of some usable energy, the second law of thermodynamics states that every energy transfer or transformation increases the entropy of the universe. Even though living things are highly ordered and maintain a state of low entropy, the entropy of the universe in total is constantly increasing due to the loss of usable energy with each energy transfer that occurs. Essentially, living things are in a continuous uphill battle against this constant increase in universal entropy.

This text is adapted from Openstax Biology 2e, Section 6.3 The Laws of Thermodynamics.

Tags

EntropyEnergy TransferThermodynamicsSecond Law Of ThermodynamicsDisorderOrderUsable EnergyHeat EnergyCellular MetabolismChemical ReactionsLiving SystemsUniversal Entropy

Du chapitre 3:

article

Now Playing

3.4 : Entropy within the Cell

Énergie et catalyse

10.2K Vues

article

3.1 : La première loi de la thermodynamique

Énergie et catalyse

5.3K Vues

article

3.2 : La seconde loi de la thermodynamique

Énergie et catalyse

4.9K Vues

article

3.3 : Enthalpie au sein de la cellule

Énergie et catalyse

5.7K Vues

article

3.5 : Une introduction à l'enthalpie libre

Énergie et catalyse

8.0K Vues

article

3.6 : Réactions endergoniques et exergoniques dans la cellule

Énergie et catalyse

14.2K Vues

article

3.7 : La constante d'équilibre des liaisons et la force des liaisons

Énergie et catalyse

8.9K Vues

article

3.8 : Énergie libre et équilibre

Énergie et catalyse

6.0K Vues

article

3.9 : Les conditions hors équilibre dans la cellule

Énergie et catalyse

4.1K Vues

article

3.10 : Oxydation et réduction des molécules organiques

Énergie et catalyse

5.8K Vues

article

3.11 : Introduction aux enzymes

Énergie et catalyse

16.7K Vues

article

3.12 : Enzymes et énergie d'activation

Énergie et catalyse

11.4K Vues

article

3.13 : Introduction à la cinétique enzymatique

Énergie et catalyse

19.4K Vues

article

3.14 : Constante catalytique et efficacité

Énergie et catalyse

9.7K Vues

article

3.15 : Enzymes parfaites

Énergie et catalyse

3.8K Vues

See More

JoVE Logo

Confidentialité

Conditions d'utilisation

Politiques

Recherche

Enseignement

À PROPOS DE JoVE

Copyright © 2025 MyJoVE Corporation. Tous droits réservés.