Why is humus important? A) It increases soil porosity.
B) It decreases soil acidity.
C) It increases soil basicity.
D) It decreases water movement.

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.

Which organisms have pharyngeal arches that develop from all three germ layers and go through the same development stages as embryos? 1.bird 2.ladybug 3.starfish 4.snake

Which of the following was not a major animal on land during the carboniferous period? amphibians insects both a and b none of the above