There are many reasons to why slaves were essential in the colonial economy:
Slaves were generally used more in the south, because large plantations were found there, which meant that the need for large amounts of workers.
Slaves provided cheap labors, and as they were not "citizens" of the US, they were not allowed their rights.
Slaves were also relatively easy to buy and replace, however, their survival rates were not that good after they traveled long distance.
etc.
hope this helps
diffusion is the movement of molecules or stuff through the cell membrane
osmosis is the movement of water
water move from high contration to lower concentration
the there is salt outside of the cells the water will move out of the cell membrane and if there is salt inside the cells the water will move into the cell
I believe the answer is receptor sites, but correct me if I'm wrong.
Hope this helps!
D the car is accelerating