Do not use someone else's words if it is not required. The only time you should quote is if the exact words themselves are important. The above example is heavily paraphrased from the original. This is a form of plagiarism. If you borrow heavily from someone else's work, it's no different than simply copying it.
Organization is critical.
If you understand something, you can come up with an original way to say it. The last sentence in the example is redundant with the second and third sentences. The citation for the source of the quote is incorrect. The entire reference should be listed in the bibliography. The first step in visual perception is transduction of light into an electrochemical signal.