Plant cell parenchyma cells, that covers the external surfaces of leaves, stems and roots. Several cell types may be present in the epidermis. Notable among these are the stomatal guard cells that control the rate of gas exchange between the plant and the atmosphere, glandular and clothing hairs or trichomes, and the root hairs of primary roots. In the shoot epidermis of most plants, only the guard cells have chloroplasts. Chloroplasts contain the green pigment chlorophyll which is needed for photosynthesis. The epidermal cells of aerial organs arise from the superficial layer of cells known as the "tunica" (L1 and L2 layers)
Fractionation of carbon isotopes in oxygenic photosynthesis activity, and variations in cell growth and geometry. The isotopic fractionations of different photosynthetic pathways are uniquely characterized by these factors, as described below. A C3 plant uses C3 carbon fixation, one of the three metabolic photosynthesis pathways which also include C4 and CAM (described below). These plants are called "C3" due to the three-carbon compound (3-Phosphoglyceric acid, or 3-PGA) produced by the CO fixation mechanism in these plants. This C3 mechanism is the first step of the Calvin-Benson cycle, which converts CO and RuBP into 3-PGA. C3 plants are the most common type of plant, and typically thrive under