Why cell wall is only found in plant cells

Which mantle is under the crust the upper mantle or the lower mantle i think it's upper let me know if i'm right

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.

In iceland, the mid atlantic ridge runs through the center of the contry. what can you conclude about the apperence of iceland many thousands of years from now?