2. In this chapter, you learned that some pathogens must attach to host cells to cause disease. To accomplish this, molecules on their surface (adhesins or ligands) recognize and attach to molecules (receptors or integrins) on the surface on certain host cells.
So a chromatic note, is any note you play that is not in the scale you are playing. They are also a great way to practice, especially if you are going through the pentatonic scale. Try adding one of these outside chromatic notes to your scale, and see how it sounds above the chord you are playing over.
An octave, as the name suggest has the number 8 related with it. There are 7 major notes in music viz. C D E F G A B || C D E F G A || C D... As you further move ahead the pitch increases. The lower C has a lower pitch than the higher C, but the sound that the note creates is the same. The number of notes between the higher and lower C (Including the higher C), are 8. Thus an octave is difference between a particular note, and its higher or lower counterpart in terms of pitch.