Algae that do not require sunlight and can obtain energy through utilizing sugars manufactured by plants are

Heterotrophs

Explanation:

Heterotrophs are organisms that are not able to form their own source of energy and are dependent on others to gain energy. Most of the algae are autotrophs which uses light energy to make organic energy source.  

Some algae are heterotrophs that do not require sunlight and pigments as they do not make their food on their own and utilize sugars manufactured by other plants and algae.  

They are also called colorless algae as they do not possess pigments. These heterotrophic algae are consumers, not producers. Therefore the correct answer is heterotrophs.

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.