stable isotope in studies in microbial ecology?

It is simple to grind up a plant and then extract and measure all of the chemical elements present, but this does not tell us which elements are essential. Why not?

Define the element based on its composition. I am currently in biolgy 141 general biology.

Complete the chart below looking at levels of nitrogenous bases in different species.

Why does PET use different isotopes than that of nuclear medicine exams with gamma cameras? What makes PET isotopes different?

The role microbes play in the environment is an important question to microbiologists.   Explain how a firm understanding of chemical bonds and chemical reactions is crucial to answering this question.

A person (70kg) eating locally caught fish from water contaminated with 100ppb TCE and 100ppb aniline. The bioconcentration value for TCE and aniline in fish is the same at 1.06mg TCE (or aniline) per kg fish, respectively. Fish is only exposed to these contaminants in its environment. About 54g of fish is consumed in 350days/yr for 30years. Assume bioavailability value of 1. The potency factor for TCE is 1.1 × 10$# kg.day/mg and reference dose is 1.00 × 10$% mg/kg.day. Whereas the potency factor for aniline is 5.7 × 10$* kg.day/mg and reference dose (based on drinking water) is 1.60 × 10$& µg/L. Unlike aniline, TCE is not a carcinogenic compound. There are 70yrs in a lifetime and 365day/yr. a) Using chronic daily intake calculation, determine the non-cancer risk (number of people in one million) for the above case. b) Calculate the cancer risk (number of people in million) for the above case.

a 139 ng sample of radioactive material has a half life of 4.2 days how many ng of radioactive material is left after 3 half lives ?

How do organisms obtain Hydrogen and Oxygen elements from a Microbiology perspective?

Trace elements are required by organisms in only minute quantities (less than 0.01% of mass). Which of the following is a trace element that is required by humans and other vertebrates? potassium calcium phosphorus iodine nitrogen