Hydrogen sulfide a. is produced when sulfur compounds are used as terminal electron acceptors. b. may react with iron to produce a black precipitate. c. is produced by desulfovibrio. d. has a rotten egg smell. e. all of the choices are correct.

The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-saharan africa than among those of african descent living in the united states. even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-saharan africa but absent in the united states. discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions.

Which of the following types of pollution is most responsible for large numbers of deaths worldwide because of unsafe drinking water? (a) nutrient pollution (b) thermal pollution (c) pathogen pollution (d) sediment pollution

Alexa is preparing for a presentation by creating note cards identifying keywords that describe various features of each type of plate boundary. which words apply to all three of the convergent boundaries?