CHLOROPLASTS In those organisms that have chloroplasts, this is where the energy gathering occurs. The structure of a chloroplast is shown in figure 26:
One of the main structures inside chloroplasts are called thylakoids. These are folded cylindrical sheets of membranes that have a very large surface area so as to gather the most light possible. Bacteria that have no chloroplasts either use the cell membrane itself or bunched up pieces of cell membrane that are also called thylakoids. In algae and plants, there are ten to a hundred chloroplasts per cell. These are membranous structures that have an internal stroma that is filled with stacks of thylakoids, where photosynthesis takes place. Each thylakoid is membranous and has its own lumen, called the thylakoid space. Within the membrane, similar to the idea that inside mitochondrial cristae there are membrane-bound enzymes, there are membranebound protein complexes in these thylakoids that participate in the process of photosynthesis. There is a variety of pigments used in absorbing light as part of photosynthesis. By far the most important and abundant is chlorophyll. Other pigments used in photosynthesis are xanthophylls, carotenes, fucoxanthin, phycoerythrin, and 100
