The enzyme rubisco, used by the Calvin-Benson cycle to fix CO2 during photosynthesis, is probably the most abundant enzyme on the planet. Its properties are remarkably identical in all photosynthetic organisms, from bacteria to flowering plants. However, rubisco has properties that severely limit its efficiency under certain conditions. In the discussion that follows, we will identify and explore some of these limitations and see how evolution has constructed metabolic bypasses around them. First we'll look at photorespiration, a process in which rubisco reacts with O2 instead of CO2, lowering the overall rate of CO2 fixation. Then we'll examine some biochemical pathways and features of plant anatomy that compensate for the limitations of rubisco.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.