Cell specialization is the differentiation of cells to perform very specific function. At the stage of cellular differentiation, the generic cells are transformed into very specialized cells.
Multicellular organisms have very complex body systems. They carry many different tasks. They have to move, find food, excrete, maintain balance within their body system and the environment etc.
To perform these tasks, cells must have specific functions because they would be in need of different materials to carryout the functions.
A unicellular organism performs very simple functions of life. They do not require complex biological processes to manufacture their food and carry out life activities.
Chloroplasts are the food producers of the cell. The organelles are only found in plant cells and some protists such as algae. Animal cells do not have chloroplasts. Chloroplasts work to convert light energy of the Sun into sugars that can be used by cells.
