The standard system on wikipedia is for each article to be assigned two grades: one for completeness and another for significance. These grades can be easily assigned to articles by installing the Rater tool. Ratings can also edited manually by adding and/or updating the {{WPMOLBIO|class= |importance= }} template on that article's talk page. If you have improved an article, you may adjust the entry in the template yourself, or you may simply put a remark in the talk page that improvements have been done.
Class is determined by how well written an article is based on completeness, clarity and referencing. Articles typically are slowly improved up the levels until they reach A-Class, at which point they go through a more thorough review process with strict criteria to become Good Articles (GA) and Featured Articles (FA). The quality level is set using the |class= attribute in the {{WPMOLBIO}} template in the article's talk page.
A — Excellent articles of a length suitable for the subject that provide a well-written, reasonably clear and complete description of the topic.
B — Articles that contain most of the necessary material but have significant gaps, missing elements or references.
C — Articles that are missing important content, contains irrelevant material, or are poorly referenced.
Start — Articles that have a meaningful amount of good content, but are still weak in many areas, possibly lacking a key element such as a standard infobox.
Stub — Articles that are either very short or rough collections of information that will need much work.
Article significance is based loosely on how aware the general population is of the topic, and therefore how likely they are to consult Wikipedia. Importance is set using the |importance= attribute in the {{WPMOLBIO}} template in the article's talk page. You can additionally set the importance to a specific taskforce (details here).
Top — Subjects that are first closely examined in high school or earlier (bacteria, amino acid), or that receive significant attention in the media (stem cell).
High — Subjects that are generally examined at university (RNA polymerase) or are briefly mentioned at the high school level (endoplasmic reticulum).
FA
GA