Aweakened immune system may be caused by what?

Wich organism obtains its energy from dead or decaying matter

With regard to enzymes, key is to lock as a) substrate is to activation energy eliminate b) product is to substrate. c) enzyme is to active site. d) substrate is to active site.

There are fewer than 100 naturally occurring elements in the universe, but there are millions of different unified substances. explain how this can be true.