Certain species of aquatic organisms are particularly sensitive to environmental changes. Scientists often monitor the behavior, population size, and overall health of these so-called indicator species in order to evaluate the water quality in an ecosystem. Biological indicator species are important to water systems because
A.
they provide an early warning sign of degrading water quality in an ecosystem.

B.
they are used to control water quality by filtering out pollutants in an ecosystem.

C.
they can convert harmful pollutants into helpful nutrients in an ecosystem.

D.
they become healthier as water quality degrades and can replace weaker species.

Choose the incorrect statement (a) the motor end plate membrane is only capable of generating graded potentials, but it is contiguous with the skeletal muscle sarcolemma, which can generate action potentials. (b) propagation of an action potential through the t-tubules into the sarcoplasmic reticulum triggers the release of ca++ into the cytoplasm of a skeletal muscle fiber. (c) the generation of suprathreshold endplate potentials in multiple muscle fibers could be due to the increased frequency of action potential generation at the axon hillock of a single motor neuron. (d) a greater amount of ach would be found in the presynaptic vesicles of a motor unit that fired several action potentials after exposure to botulinum toxin, than in a motor unit that fired several action potentials after exposure to the venom of the krait snake (which contains α-bungarotoxin).