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I had the following question on an exam of mine and I got the points for the question, but I am wondering if someone could please explain why it is correct, or rather, if it is correct at all:

As living organisms grow, they increase in complexity and decrease in entropy. How does this relate to the second law of thermodynamics?

(A) Living organisms, like everything else in the universe, spontaneously decrease in entropy over time.

(B) The increase in entropy of the universe exactly balances out the decrease in entropy as the organism grows.

(C) Energy cannot be created or destroyed, so the energy used for growth is later used to increase entropy.

(D) The resulting increase in entropy of the universe is greater than the decrease in entropy associated with the growth.

I answered D, as it seemed like the most likely answer out of all of them, and I got the points.

According to the 2nd Law of Thermodynamics, the entropy of the universe will increase with time.

Please correct me if I am wrong, but from my understanding this only applies to closed systems--so how exactly would it apply to organisms (which are open systems)? Is it because organisms release heat through chemical reactions and thus add to the entropy of the universe while decreasing their own entropy?

Thank you!

-Aleksandr

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You are correct. Anything within the universe is part of the closed system of the universe. Therefore, they must also increase the entropy of the universe. You are correct, they do release a lot of heat. Plus, while making ATP, the major source of cellular energy, they convert a complex molecule, glucose, to simpler molecules, H2O and CO2, increasing entropy as they release these chemicals.

Also, the key fact is that to lower entropy in their body, organisms must use up energy. Energy is required to avoid the entropy from increasing (which actually means they actually expend energy to prevent equilibrium; high entropy means reaching equilibrium). So they would follow the 2nd law of thermodynamics. Which reminds me of a joke!

Old chenists never die, they just reach equilibrium!

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I would say D.) too.

The resulting increase in entropy of the universe is greater than the decrease in entropy associated with the growth.

We can argue that the cells and the universe together are a closed system and entropy increases in a closed system by time. So the sum of their entropy changes must be always positive.

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