Population density is calculated by
a. dividing the number of organisms in a region by the land area
b. multiplying the number of organisms in a region by the land area
c. dividing the land area by the number of organisms in the region
d. by subtracting the land area from the number of organisms in a region

Once an egg cell is fertilized by sperm, the cell then, as the embryo develops, it receives nourishment and eliminates wastes by transferring substances from its blood to its mother's blood. a. becomes a fetus immediately and exits the womb b. begins to divide and implants itself in the wall of the uterus c. remains in the uterus without dividing for several months d. travels back to the ovaries until the fetus is developed