We say ; There is a lot of sugar (There is a lot of ...uncountable)
There are a lot of apples ( There are a lot of plural countables)
There are lots of apples
Some examples:
There is a lot of pizza left over after the party.
There are a lot of slices of pizza left from the party.
There is lots of left-over pizza if you�re hungry. (uncountable) lots of tells you how much.
There is a lot of sugar spilled on the table.
There is lots of sugar left in the bowl.
There are a lot of bags of sugar in the cupboard.
There are lots of flowers in the garden.