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Conservation of mass and energy?

  1. Jun 27, 2005 #1
    conservation of mass and energy??????

    ok... i get the principle, but what about birth? Meaning what about when someone is born, where is that mass coming from? Where is the energy coming from? The only thing i can think of is the nurishment the mom takes and gives to the baby, but how can that possibly equate to a human? More fundatmental a question i guess would be how does physics deal with growth in humans? i know this question may be off the wall, but, well, im fairly odd, and ive been curious about this for a while..... any comments?
     
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  3. Jun 27, 2005 #2
    The energy of the food is broken down and transferred to the child. The child's developping body then uses that energy to grow. This is of course, a very basic explaination.

    The law of conservation of mass and energy states that both of these things can neither be created nor destroyed, only transferred. Do you see the transfer?
     
  4. Jun 28, 2005 #3

    Monique

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    A human does not have to conserve mass and energy, you eat. When more energy goes in than out, you grow bigger. Food is broken down and taken up from the bowel, it then circulates the blood; the fetus can take nutrients from the mother's blood and uses it to grow. Just remember that the blood circulation of the mother and fetus are not shared, there is a membrane barrier through which nutrients diffuse.
     
  5. Jun 28, 2005 #4
    surely you don't mean that mass/energy is not conserved in biology?

    thermodynamically, energy is conserved. the energy that you gain through feeding contributes to maintaining the negative entropy of the being. this negative entropy represents the highly-ordered state of a living system. if this were not the case, there would be no reason to feed - simply exchanging "atom for atom" does nothing. this thermodynamic process is not completely efficient though, so heat is also given off.
     
  6. Jun 28, 2005 #5

    Monique

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    I knew someone would fall over that comment. Sure mass/energy is conserved. I meant to say that the mass/energy of a human increases as we eat, it is not static. A baby does not come out of nothing, it feeds on the nutrition that the mother provides.
     
  7. Jun 28, 2005 #6

    selfAdjoint

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    In other words a human - or any live organism - is an open system, irretrievably linked to its environment and hence not a conservative system. Its entropy doesn't have to increase either; it can offload the increase to its environment, providing it can acquire some free energy, relative to that environment.

    Because all organisms try to sequester free energy, the best source of free energy is other organisms. Hence Original Sin.
     
  8. Jun 29, 2005 #7
    this is the way you become immortal, forever insure that you receive more than you give, recycle your own wastes(technically), cover all the letters in MRS. GREN... death is impractical, far more than birth, i suppose it is similar to cryogenic freezing...

    while an open system gives way for others to use the energy you once used, a closed system ensures that you allways receive the correct amount of energy...
     
    Last edited: Jun 29, 2005
  9. Jun 29, 2005 #8
    oh ok. now i understand how to be immortal.

    and to think it was right under my nose all this time!

    i have no idea what you just said
     
  10. Jun 29, 2005 #9

    selfAdjoint

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    Sorry, but in a closed system entropy increases to its max, at which time the available free energy becomes zero. Recycling can never be 100% efficient.
     
  11. Jun 29, 2005 #10
    sorry, i don't have a clue about some stuff, it just occured to me that death was the loss of energy, and through devices like nanites pehaps you could maintain a good stream of well controlled energy throughout your body, by having extra imputs, but i forgot about the aging gene, which i have no clue about atall...
     
  12. Jun 29, 2005 #11

    Phobos

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    Just to add to what's already been said...

    Your body is made of cells. Cells are made of molecules. Molecules are made of atoms. Nutrients (food) provide the building blocks (atoms, molecules) for new cells. When you digest food, you are breaking it down into a form usable to make new cells or to generate energy. Biochemistry makes things happen in a particular way (generation of necessary proteins, enzymes, etc.). DNA is the blueprint for putting these pieces together into a particular organisms like a human.
     
  13. Jun 29, 2005 #12
    this makes sense for something in a state of growth, which does require raw materials, but not so much after.

    a grown adult human does not make many new cells, but maintains the ones that exist. an adult human is the result of approximately 50 cell divisions (that is, ~2^50 cells total), after which cell senescence takes hold and cell division (in most cell types) comes to a halt.

    however, we still eat...the only explaination is one of thermodynamics. we need to maintain negative entropy, this requires energy. This energy comes from the high-energy bonds from the food that we eat. Another way of saying this is that to maintain our "order" we steal the "order" from other organisms.

    it has more to do with energy than providing raw materials.
     
  14. Jun 29, 2005 #13

    DaveC426913

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    "Another way of saying this is that to maintain our "order" we steal the "order" from other organisms."

    Which nicely defines the division between plants, herbivores and carnivores:
    - plants get their energy from the Sun
    - herbivores steal the somewhat concentrated energy stored in plants
    - carnvores steal the very concentrated energy stored in herbivores
     
  15. Jun 30, 2005 #14

    Moonbear

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    Adult humans (as well as children) are continuously regenerating new cells as older ones die.

    We also lose energy to the environment in other ways, such as heat transfer, for which we need to consume food to replace that lost energy.
     
  16. Jun 30, 2005 #15

    Monique

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    Not true, give someone chemotherapy directed against fast dividing cells and see how sick they get.

    You turn over a lot of cells in your skin, in your gastrointestinal tract and in your bone marrow. I think you'd be suprised about the quantities of cells that are replenished.

    If it were only energy, it would suffice to only take in ATP.. I think it is clear that such a diet would not sufficient: you need building materials to synthesize biologically active molecules in order to function.
     
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