Why did leaves turn yellow, orange, and other pretty colors in the fall before they fall off the trees? Well, all of those colors or pigments were there all along, but there was so much of another pigment present that it masked the other colors. This green pigment, called chlorophyll, is found in an organelle called the chloroplast. Chloroplasts are found in plants, algae, and even in some bacterial cells. Plants carry out an important process in the chloroplasts called photosynthesis. Photosynthesis converts carbon dioxide gas into sugar or food. This process requires sunlight as the energy source. What do we know about carbon dioxide? Well, you're breathing it out right now as you watch this video. It is, in fact, a waste product that your cells produce in order to use the nutrients in your food. As we learned in cellular respiration, cells must have ATP or energy to survive by making their own sugar. Plants supply fuel for cellular respiration in their cells.

Plants are called photoautotrophs because they use the sun to sell feed. In other words, they make their own food. Photoautotrophs are the base of the majority of food chains. This means we are dependent on plants. Without plants, we would not have a food source. Well, what about steak? Well, no grass, no cows, no steak. Let's get back to our question. Why do leaves change color in the fall? Well, during the fall, when temperatures drop and there is not as much sunlight, plants stop the food-making process. The chlorophyll molecules break down and voila, the other pigments can be seen. The chemical reaction for photosynthesis is carbon dioxide plus water. Yields glucose or sugar and oxygen. Does this look like it relates to something else you've learned? If you flip this reaction, you have cellular respiration. The products of one are the reactants of the other. Photosynthesis is an endothermic reaction because

it requires an input of energy. In this case, the energy is sunlight or else also called electromagnetic radiation. To review an endothermic reaction, click here. Back to our original pigment question, why do plants have other these other colored pigments, Xanthophylls which are yellows and carotenoids, which are orange are some examples. Well, white light that comes from the sun has all the colors of the rainbow. Roy G Biv [Red, orange, yellow, green, blue, indigo, violet]. Chlorophyll is only able to absorb the energy from certain colors or wavelengths of light. The other pigments each have particular wavelengths of light they can absorb. The more wavelengths of light a cell can absorb, the more energy it can obtain from the sun.

Photosynthesis overview

Photosynthesis overview