What is a density-dependent factor? a) floodb) firec) natural disasterd) space

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.

Describe the response the kidneys have to dehydration and excessive water intake. what happens to the concentration of urine in each case ?

Which type of respiration takes place when there is no oxygen present