"are there really enzymes in muscle tissue?"
That is what we learn! Enzymes are responsible for all metabolic reactions -- eg glycolytic enzymes, oxidative enzymes in mitochondria... both found in muscle cells responsible for creating ATP [energy to enable life to continue!] ... in fact CO2 is...
but using plate w/o treated water is control...indicative that bacteria was present in the sample + that the results of the independent variable are valid [that the tablet destroyed the bacteria]
I think that the population started at zero because one was born with a mutation...that was favourable + population of this new variety grew as the others declined b/c new variety were better competitors on something...
Plasma doesn't contain cellular components so the extra haemoglobin/O2 wouldn't necessarily be relevant but you're right about antibodies [which is what I think they wanted in the response] + also to increase blood volume I think