Energetics of Symport Suppose you determined experimentally that a cellular transport system for glucose, driven by symport of Na1, could accumulate glucose to con-centrations 25 times greater than in the external medium, while the external [Na1] was only 10 times greater than the intracellular [Na1]. Would this violate the laws of thermody-namics? If not, how could you explain this observation?

No

Explanation:

The symport may be able to transport more than one equivalents of glucose per sodium ion. This is because most symports acts in this way hence the laws of thermodynamics will not be violated.

NO

Explanation:

One implication of the second law of thermodynamics is that in order for a process to happen, it must somehow increase the entropy of the universe. This may immediately raise some questions for you when you think about living organisms such as yourself. After all, aren’t you a pretty ordered collection of matter? Every cell in your body has its own internal organization; the cells are organized into tissues, and the tissues into organs; and your entire body maintains a careful system of transport, exchange, and commerce that keeps you alive. Thus, at first glance, it may not be clear how you, or even a simple bacterium, can represent an increase in the entropy of the universe.

To clarify this, let’s look at the energy exchanges that take place in your body – say, when you are going for a walk. As you contract the muscles of your legs to move your body forward, you are using chemical energy from complex molecules such as glucose and converting it into kinetic energy (and, if you’re walking uphill, potential energy). However, you’re doing this with pretty low efficiency: a large fraction of the energy from your fuel sources is simply transformed into heat. Some of the heat keeps your body warm, but much of it dissipates into the surrounding environment.

Cartoon of person walking, with a hamburger in his hand. The person is taking in complex macromolecules in the hamburger, and releasing them as carbon dioxide and water molecules, increasing entropy. He is also walking forward (converting chemical energy from macromolecules into kinetic energy), but much of the energy released is lost as heat (also increasing entropy).

Cartoon of person walking, with a hamburger in his hand. The person is taking in complex macromolecules in the hamburger, and releasing them as carbon dioxide and water molecules, increasing entropy. He is also walking forward (converting chemical energy from macromolecules into kinetic energy), but much of the energy released is lost as heat (also increasing entropy).

This transfer of heat increases the entropy of the surroundings, as does the fact that you’re taking large, complex biomolecules and converting them into a lot of small, simple molecules, such as carbon dioxide and water, as you metabolize fuel to power your walk. This example uses a person in motion, but the same would be true for a person, or any other organism, at rest. The person or organism will maintain some basal rate of metabolic activity, causing the breakdown of complex molecules to smaller and more numerous ones and the release of heat, thus increasing the entropy of the surroundings.

Stated more generally, processes that locally decrease entropy, such as those that build and maintain the highly organized bodies of living things, can indeed take place. However, these local decreases in entropy can occur only with an expenditure of energy, where some of that energy is converted into heat or other non-usable forms. The net effect of the original process (local decrease in entropy) and the energy transfer (increase in entropy of surroundings) is an overall increase in the entropy of the universe.

To sum up, the high degree of organization of living things is maintained by a constant input of energy, and is offset by an increase in the entropy of the surroundings.

baby baby baby oh over and over again