Answer: Alan is shifting from familiar to newer information
Step-by-step explanation:
According to the question, Alan is linking the concept of photosynthesis with requirement of plant for sunlight and then telling synthesization of food in plant with help of water and carbon dioxide following the rest topic.
He is making these connections among certain parts to which student are familiar with so that he can teach them about related new information.Student know basic information to which he is adding more detailed information through transitioning to make them understand concept .