Process of photosynthesis makes glucose. Excess glucose is stored as starch, or made into cellulose in cell walls.
The myelin sheath is the protective layer, which is present in the outer layer of the neural cells. This myelin sheath prevents the loss of electrical impulses, which are being conducted in the neurons. This also act as an insulator between neuron and its external environment.
This layer is mainly made up of the protein and fatty substance. The degeneration of the myelin sheath result in many neurological disorders.
Hence, the correct answer is myelin sheath.
Because gravity pulls towards the center of the earth evenly in all directions, giving earth a spherical shape.