You can use your outdoor classroom to explain this yearly phenomenon. Its blood dripped down to earth making the leaves red. The leaves receive their yellow color from the bear dripping fat while it was being cooked. The Scientific Explanation Different factors control when and how deeply leaves change colors. The photo period is the amount of sunlight a region receives during the year.
Plants use sunlight in a process called photosynthesis to survive.
With sunlight, they use chlorophyll, a substance found in their leaves, to absorb water and nutrients. When the days become shorter and the temperatures cool, the food making process is reduced. When chlorophyl production is reduced, the deep green begins to fade. The other colors were always in the leaf but concealed by the green of the chlorophyl. With it now gone, you can see the other shades.