Have any species (with the exceptions of humans) been observed to kill themselves purposefully?

Yes...one dog has been observed to kill themselves purposefully.

Bottlenose dolphins have been known to kill themselves

option a is correct i.e.

only sodium ions can pass through the membrane.

explanation:

in context to the membrane of nerve impulse, the outer membrane of neuron is semi permeable that is only sodium ions can pass through the membrane i.e. smaller ions can pass through the membrane while larger ions cannot pass through it.

The nurse should include dirahea, dry mouth, vomiting, decreased sex drive, lack of coordination, tingly feelings, impotence, or difficulty having an orgasm.. good luck