The correct answer is b: cattle on rangeland. A point source of pollution occurs from a single identifiable and usually spatially narrow source. These sources of pollution are usually relatively easily to quantify and manage. In contrast, a non-point source of pollution, such as cattle on rangeland or irrigated agriculture, is variable on both spatial and temporal scales. These sources of pollution are difficult to quantify and manage.
The reason why the sets of proteins that are expressed in a
nerve is different from the sets of proteins that are expressed in a pancreatic
cell of the same individual is that nerve and pancreatic cells contain
different sets of regulatory proteins.
