What effect can fertilizer runoff have on an aquatic ecosystem?
a. increased plant growth leading to a decrease in fish populations
b. increased plant growth leading to an increase in fish populations
c. decreased plant growth leading to a decrease in fish populations
d. decreased plant growth leading to an increase in fish populations

a. increased plant growth leading to a decrease in fish populations. Fertilizer runoff degrades aquatic system by promoting growth of algae, phytoplanktons and other aquatic plants. A phenomenon called 'algal bloom' will take place, increasing oxygen consuming bacteria and lessening the available oxygen for plants and animals in the area.

Since diffusion moves materials from an area of higher concentration to the lower, it is described as moving solutes "down the concentration gradient." The end result of diffusion is an equal concentration, or equilibrium, of molecules on both sides of the membrane. At equilibrium, movement of molecules does not stop.