Water percentage of an organism

**DragonPetter** · Jun18-09, 12:23 AM

I am curious, how do scientists come up with facts like a human is xx% water? I saw on a documentary recently that a jelly fish is 96% water. How is this measured and determined? What about other elements and materials?

**Andy Resnick** · Jun18-09, 09:55 AM

If you can believe it, simply by weighing the specimen before and after drying.

I have some old book with data of different human tissues (including bone), and the percentage is rather variable.

In terms of 'other materials', what can be done is to grind up tissues and perform analytical chemistry techniques to determine the concentration of Na, K, Ca, etc. etc. Subcellular fractionation techniques can be used to further distinguish between, for example, cytoplasm and nucleus. Membrane extraction can be used to determine the lipid constitution of membranes.

It's a ton of work- an unbelievable amount of grunt work.

**DragonPetter** · Jun18-09, 10:41 AM

Originally Posted by Andy Resnick

If you can believe it, simply by weighing the specimen before and after drying.

I have some old book with data of different human tissues (including bone), and the percentage is rather variable.

In terms of 'other materials', what can be done is to grind up tissues and perform analytical chemistry techniques to determine the concentration of Na, K, Ca, etc. etc. Subcellular fractionation techniques can be used to further distinguish between, for example, cytoplasm and nucleus. Membrane extraction can be used to determine the lipid constitution of membranes.

It's a ton of work- an unbelievable amount of grunt work.

Ah very interesting :D The drying up makes a lot of sense, but I wonder how accurate that is, as other compounds may decompose to other gases that take away from the mass of the organism which aren't water.

I also ran across this last night after I searched a little bit:
http://en.wikipedia.org/wiki/Body_water