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 RuBisCO-dependent cell growth rate, and the cell geometry and surface area. The use of bicarbonate and carbon concentrating mechanisms in phytoplankton distinguishes the isotopic fractionation from plant photosynthetic pathways. The difference between intracellular and extracellular CO concentrations reflects the CO demand of a phytoplankton cell, which is dependent on its growth rate. The ratio of carbon demand to supply governs the diffusion of CO into the cell, and is negatively correlated with the magnitude of the carbon fractionation by phytoplankton. Combined, these relationships allow the fractionation between CO and phytoplankton biomass to be used to estimate the phytoplankton growth rates.