Three processes that occur in cells are described in the box. Substances pass through the lipid bilayer of a cell from areas of high concentration to areas of low
concentration.
• Substances move through protein channels of the lipid bilayer of a cell from areas of high concentration to
areas of low concentration.
Substances move through the lipid bilayer of a cell from areas of low concentration to areas of high
concentration.

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 this experiment, the was intentionally manipulated. it is the independent variable. the dependent variables that were measured were the

Why zebra fish experience similar genetic disease as human