The model organism used to study growth, differentiation, cytoplasmic streaming and function of cytoskeleton belongs to

Explanation

Slime molds are often used as model organisms because they exhibit fascinating behaviors such as cytoplasmic streaming, which is crucial for nutrient distribution and cellular processes. They serve as excellent models for studying the cytoskeleton's role due to their dynamic morphological changes during their life cycle. The other options, Zooflagellates, Desmids, and Radiolarians, do not prominently feature in studies related to cytoplasmic streaming and the cytoskeleton, making Slime molds the correct choice.