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Oxygenic photosynthesis supports the majority of life on Earth through the capture of energy from sunlight and the assimilation of CO2 into basic building blocks of cells. Microalgae are fast growing and account for about half of global photosynthesis. In addition, they can be cultivated and their metabolism can be redirected to generate additional useful products ranging from biofuels to pharmaceuticals. However, the efficiency of metabolite production is severely impacted by the slow diffusion of CO2 through water and the high energetic costs of harvesting microalgae from liquid cultures. Microalgae grow in open water, but they also form biofilms that require less energy to harvest. However, the impact of these different growth forms on rates of photosynthesis is poorly understood. The work in this dissertation explores the importance of growth form on photosynthesis by examining CO2 assimilation of the green microalga, Chlamydomonas reinhardtii, within three different states: as a liquid suspension, as a simple filtered two-dimensional artificial biofilm, and within a silica sol-gel encapsulation matrix as an example of a more complex biofilm. The rates of CO2 assimilation were decreased within the simple filtered biofilm and further decreased within the silica sol-gel matrix. The decrease is thought to be due to the diffusional limitations to CO2 imposed by the biofilm forms. Estimated rates of assimilation of CO2 were also calculated from chlorophyll fluorescence values of both biofilms and were more similar to the measured liquid suspension rates, suggesting a persistent energetic imbalance between light and CO2 capture in biofilms. This effort required development of new empirical corrections to correctly assess CO2 exchange rates, and novel approaches to collect data that could be directly compared between the three forms.