The primary reason surplus carbohydrates in plants are stored as starch is because: the space they occupy as carbohydrates is needed for other macromolecules. if they were left as individual monosaccharides, water would enter the cell by osmosis. all of these choices represent equally important reasons why surplus carbohydrates in plants are stored as starch. they would otherwise be utilized as energy sources even if such energy were not needed at that time. energy is needed in the nucleus, and only starch is capable of being transported into the nucleus.