Evolution of photosynthesis symbiotic relationship with chloroplasts they capture from the algae in their diet and then store in their bodies. This allows the mollusks to survive solely by photosynthesis for several months at a time. Some of the genes from the plant cell nucleus have even been transferred to the slugs, so that the chloroplasts can be supplied with proteins that they need to survive. An even closer form of symbiosis may explain the origin of chloroplasts. Chloroplasts have many similarities with photosynthetic bacteria, including a circular chromosome, prokaryotic-type ribosomes, and similar proteins in the photosynthetic reaction center. The endosymbiotic theory suggests
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.