Plant type Ferredoxins (Fds) are small soluble electron carriers within the chloroplast of photosynthetic eukaryotes. During oxygenic photosynthesis, linear electron flow (LEF) collects electrons from water and ultimately transfers them towards various Fds isoforms in the chloroplast stroma, where their clients await reduction. Fd–NADP+ oxidoreductase (FNR), reducing NADP+ to NADPH, is the major recipient of electrons from Fds, and NADPH in turn is used predominantly in the Calvin-Benson cycle (CBC) for the assimilation of CO2. Intriguingly, multiple essential pathways within the chloroplast require electrons from Fds, including key proteins in N and S assimilation, chlorophyll and fatty acid biosynthesis, redox regulation and H2 production. Accordingly, multiple, highly diverse Fds isoforms have evolved and are found within the chloroplasts of eukaryotic algae and land plants. The fact that multiple Fd isoforms are often expressed together in the same chloroplast at the same time raises questions about how electron flow towards different metabolic pathways is controlled. We want to understand, and ultimately manipulate, the totality of photosynthetic electron distribution in the chloroplast, its dynamics and regulation, and the properties of the individual Fds that control its individual reactivities and substrate specificity. For this purpose, we chose to investigate the pool of Fds in a single eukaryotic reference system, the unicellular green alga Chlamydomonas reinhardtii. Chlamydomonas is an ideal system to study Fd heterogeneity, as the alga developed a rich, flexible metabolism balancing many different Fd-dependent processes in its single chloroplast. Additionally, Chlamydomonas is a facultative phototroph, allowing to inactivate otherwise essential photosynthetic processes, and has a rich history as a photosynthetic model system, enabling critical research via a plethora of tools and resources.