Why can't plants and animals use the nitrogen directly from the atmosphere?
answer
a. there is not enough of it in the air.
b. nitrogen gas contains the element in an inert, unusable state.
c. they do use it directly from the atmosphere.
d. plants and animals do not need nitrogen for their life processes.

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.

The reactions that occur in the ribosome, where amino acids are combined to form proteins are anabolic or catabolic?

The concept of keystone species is controversial among ecologists because most organisms are highly interdependent. if each of the trophic levels is dependant on all others how can we say one is most important