What distinguishes the melodic minor scale from the natural minor scale?

The distinction of the melodic minor scale from the natural minor scale lies in its unique structure when ascending and descending. Specifically, the melodic minor scale features a raised 6th and 7th scale degree when played in an ascending context, which provides a leading tone effect that is essential in establishing a stronger sense of resolution to the tonic. When descending, however, the melodic minor scale reverts to the natural minor scale, incorporating the lowered 6th and 7th degrees. This characteristic makes the melodic minor scale particularly useful in melodic contexts, where it can enhance both harmonic progressions and melodic lines, creating different emotional effects compared to the natural minor scale, which maintains the same notes throughout its ascent and descent.

The other answer options do not accurately describe the melodic minor scale. The first option incorrectly states that it includes all twelve notes of an octave, which does not apply to the scale structure being discussed. The third option suggests that the scale consistently has lowered degrees, which does not reflect the behavior of the melodic minor scale when ascending. Lastly, the fourth option presents an incorrect structure, as the melodic minor scale is characterized by a combination of whole and half steps, not composed solely of whole steps.