Tutor profile: Thomas S.
Subject: Music Theory
Q: While adhering to Common Practice Period conventions for harmony and voice leading, describe one strategy a composer could use to prepare a dominant (V) chord using nondiatonic harmony. Include any voice leading issues this may present.
Augmented sixth chords are a common nondiatonic predominant chord permissible under standard Common Practice Period conventions. These chords are built on a ♭VI-7 chord with the fifth omitted, which is spelled as ♭6, 1, #4 in the tonic key (this basis chord is termed the “Italian Sixth”). This resolves directly to the V chord by stepwise motion. Derivatives of the Italian Sixth add an additional note. These derivatives include the French Sixth (add a ♮2) and German Sixth (add a♭3 — note that this causes the chord to typically be resolved to a I-6/4 chord instead of V, as a direct resolution to V creates parallel fifths). Other derivations are possible but unusual.
What are the three sections of a piece in sonata-allegro form? What is the purpose of each section?
Pieces composed in sonata-allegro form typically contain exposition, development, and recapitulation sections. The exposition introduces the primary thematic material of the piece, allowing the audience to become familiar with the movement’s musical ideas. The section invariably modulates to a new key (typically V in a major-mode piece or III in a minor-mode piece). The development section takes the ideas from the exposition and modifies them, often providing a sense of journey. Keys are frequently transient or unstable, and circle-of-fifths modulations are commonplace. Finally, the recapitulation revisits the exposition’s material while staying in a stable key, providing the piece with a sense of completion. The section is typically composed entirely in the tonic key, though it can sometimes begin in a related key.
In the light-dependent reactions of photosynthesis, two different types of photosystems are involved in electron transport. What is a photosystem, and what is the functional difference between the two types?
Photosystems are enzyme complexes found in the thylakoid membranes of chloroplasts that convert light energy from the sun into chemical energy in the form of excited electrons. During the light-dependent reactions, the plant must produce NADPH and ATP for use in the light-independent reactions. After an electron is evolved from water and excited in Photosystem II, its travels to cytochrome b6f, where its energy is used to power a proton pump (the proton gradient cytochrome b6f creates will be used to make ATP). However, this process depletes the electron's extra energy before NADPH can be made; therefore, Photosystem I is needed to re-excite the electron, allowing NADPH to be synthesized.
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