PLANT GROWTH & PHYSIOLOGY. (Part 5)There are three classes of plants. Each of these classes metabolize in a different way. The first class are succulent plants called CAM. These plants like low light and high humidity levels and so thrive indoors, in bathrooms and kitchen areas.The second class of plants is called C4. These plants grow in hot arid regions and are very efficient at using both Carbon Dioxide (CO2) and Sunlight. Most C4 plants are grasses.The third and last class of plants are.