Answer:
The structure of each cell type's wall.
Explanation:
The basis of Gram stain is differentiating cells in two different categories depending on the composition of the cell wall. Gram positives fixate a KI and Crystal Violeta complex in their peptidoglycan wall, but otherwise, gram negatives don't have a thick layer of this, and therefore, when the wash process happens it takes away all the pigments leaving the cells blank for the last pigment (pink).
Low-head dams are dangerous structures that basically extend from one side of a riverbank to the other. Low-head dams block the water way partially and the water moving over the dam produces a strong circular current at the lower part of the dam. Low-head dams are dangerous to small boats and paddle craft because the strong circular current below the dam can trap small boats and paddle craft and pull them under the dam.
