Final answer:
Chloroplasts primarily function in photosynthesis, where they convert light energy, water, and carbon dioxide into sugars/carbohydrates and oxygen, which serve as energy sources and structural materials for the plant.
Step-by-step explanation:
The primary function of chloroplasts in plant cells is photosynthesis. Chloroplasts capture light energy from the sun and use it, along with water and carbon dioxide, to produce sugars/carbohydrates and oxygen. This process can be represented by the equation: 6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂. Thus, the correct answer to the student's question is c) Photosynthesis. Glucose produced by photosynthesis is a vital source of energy for the cell, which can be stored in more complex carbohydrates such as starch or used to create structural compounds like cellulose.