Introduction to Photosynthesis: Overview

<h1>Text Preview</h1> <p>Why are leaves green? Why do they change color in the fall? The answers to these questions lie inside the leaves. </p> <p>Leaves are like little food factories. They manufacture glucose out of water and carbon dioxide. The leaves contain pigments—molecules that absorb the energy of visible light. Photosynthetic organisms use light energy to drive the synthesis of compounds such as glucose. The primary pigment in leaves is chlorophyll. Chlorophyll gives leaves their green color. Leaves also contain accessory pigments, such as carotenoids and anthocyanins.</p> <p>As the days begin to shorten and temperatures drop, chlorophyll production slows down, and the brilliant yellows and oranges of the carotenoid pigments are revealed. The anthocyanins are the pigments responsible for the red colors. These pigments are produced only in the fall, when the levels of nutrients such as phosphorous drop. Anthocyanins are also responsible for the red color of cranberries, red apples, cherries, and strawberries.</p> <p>The light-absorbing pigments are essential components of plants as well as some bacteria and protists that use sunlight, water, and carbon dioxide to manufacture molecular oxygen, glucose, and other compounds. The process of converting light energy to chemical energy is called photosynthesis. In plants and algae, photosynthesis takes place in special organelles called chloroplasts. Chloroplasts have an outer membrane and an inner membrane, which encloses the fluid-filled stroma and a system of thylakoids that look like stacks of disks. The photosynthetic pigments are embedded in the thylakoid membranes.</p> <p>During photosynthesis, absorbed light energy is converted into the chemical energy of ATP and the reduced coenzyme NADPH. Because they are coupled to the energy obtained from sunlight, the reactions that produce ATP and NADPH are referred to as the light reactions.</p> <p>In a second process, carbon dioxide is captured and incorporated, or “fixed,” into carbohydrates such as glucose. This light-independent process is known as carbon fixation. Because the reactions of carbon fixation don’t require sunlight, they are sometimes referred to as the dark reactions. </p> <p>In this activity, we’ll learn how light energy is used to synthesize sugars from carbon dioxide and water. We’ll look at the light-dependent reactions of photosynthesis that produce ATP and NADPH, as well as the light-independent process of carbon fixation. We’ll finish with a short demonstration to illustrate the principles of photopigments. In addition, we’ll analyze the pigments in leaves by paper chromatography.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>