3. Two body systems work together to help remove waste products from blood. What are these two systems?
a. Respiratory and excretory
b. skeletal and digestive
c. circulatory and reproductive
d. nervous and excretory

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.

What organelle other than the nucleus houses dna in a eukaryotic cell?

Explain how scientists use geologic time to determine the age of landforms.