I'll give it my best shot for you:
ii) Prepared slides are an advantage when it comes to gathering information about the structure of nerounes due to the extremely small nature of them. Maginified images from microscopes of the slides allows for accurate scientific diagrams of the physical structure and scaled size of neurones to be made, it can also allow students to differentiate between motor, connector and sensory neurones if different slides are availible. Through viewing the slides students are also able to identify and learn the structure of various parts of neurons including the cell body (forming the grey matter in the CNS), dendrites which conduct nerves impulses towards the cell body, and Axon's which conduct impulses away from the cell body. However the disadvantage of slides is that often the finer details of the neurons are difficult to see, even through the use of appropriate dyes on the slide it can be hard to visibly locate different parts of the neurone.
(That sounds very contradictory now that I read over it lol). Its a hard question and not one that I like, sort of falls under the same stupid catagory as that question "assess the value of using models to represent biological processes".
ii). The threshold is the amount of positive change in a membrane potential which is required before an action potential is produced. The depolarisation which occurs from sodium ions entering the cell membrane must reach a threshold which is atleast 15 mV more positive then the resting potential of -70mV. Each stimulus produces either a full action potential or none at all, thus if depolarisation falls below this level then no action potential and thus no nerve impulse is produced. Each action potential is also a separate event. Therefore a cell cannot produce another action potential until this previous one is complete, this is another reason why an action potential may not occur at a particular point in time.
