During the nineteenth century, sea otters were hunted almost to the point of extinction. when the number of sea otters became very low, it was noticed that the ecosystem of kelp bed "forests" was also disappearing. it was discovered that the sea otters were predators of sea urchins, which were, in turn, predators of the kelp. when sea otters declined, the sea urchin populations grew, destroying the kelp ecosystem and the many species that depended on it. what role did sea otters perform in this ecosystem?

They ensured that balance in the ecosystem was maintained. They ensure that the genetic diversity and species is maintained. Sea otters applied natural selection pressures on the sea urchins population hence maintaining their level such that they will not overgraze on the kelps. Overgrazing would severely affect the sea urchin population and consequently severely affect the sea otters population too.

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.