Something I was puzzling over for a project of mine*—it can’t simply be the difference in mass between a 2.5 oz fetus and a 120 lb. adult. Even if you restricted nutritional intake to the subject to the barest possible for it to grow and stay alive, there’s surely some waste—plus whatever tissues the body normally sheds (skin cells, hair, etc), whatever the total water intake would be…I can’t even begin to think I’ve thought of everything.
Biology’s never really been my forté, I’m sad to say. Can anyone here help me figure this one out?
*No, I’m not doing anything horrifying with a basement laboratory, so’s you know.
Your question’s actually a bit fuzzy. Are you looking for the * minimum * mass necessary? Or the actual mass consumed in the process of growing up? Because if you’re really, really, really good at recycling and maybe have access to nano-technology, you could probably get by with a surprisingly small amount of mass.
If you’re looking for a good back of the envelope of mass input, then you could just figure out the average food/water/air intake per body mass per day, but it gets complicated because those are not constant values as the body grows. And if your subject is doing anything besides floating in a big test tube, then activity will change the amount of required input mass.
Yeah, I dig you…luckily, I’m looking for the minimum lying-in-a-gurney/floating-in-a-testtube level of activity input for the subject, and no nanites or anything—basically “how much mass would you have to feed to the subject through an umbilical tube” for it to survive and grow to maturity.
And I think I spent more effort trying to write that paragraph halfway intelligently than the makers of the movie that sparked the question did in dreaming up the scenario.
While I don’t claim to quite understand your question, there is a rule of thumb that says as you go from one level to the next in a food chain, about 10% of the original mass is carried onto the next level. For example, it takes about 10 pounds of corn to grow 1 pound of corn worm.
Doesn’t this depend on how fast the animal grows though? A human takes decades to reach maturity and eats way more than 1500 pounds of food, give or take, during that time, since most of that food goes towards basic body functions and energy and not growing bigger. If you take the numbers on this page as a guide, you eat about 10 times your body weight in food every year (of course, this includes water in the food, but not water by itself, and apparently not in soda, which is 53 gallons/441 pounds per year; for example, while milk is shown as the largest component of what we eat by weight, it is mostly water, thus contributes only about 10% of calories).
This is one of those thumb-rules that makes sense once you understand it, but is almost impossible to explain. It’s not that it ‘creates’ this much matter, it’s that it’s necessary to continuously support it. It starts from the ground up, I suppose - For any amount of vegetation, you have to dedicate X lbs of it, continuously, to support .1X lbs of herbivore - that is to say, there will be X lbs less of vegetation then there otherwise would be, sans herbivores, once you add in .1X lbs of herbivore. It goes down the list the same for carnivores - you need a broadly-sustainable system of X lbs worth of herbivores (comfortable, reproducing, and not subject to wild population shifts) in order to keep .1X lbs of carnivores in the same condition.