## 4 Discussion
Quinones in the ETC are more efficient at the functional level, showing higher QA reduction rates, which follows the mildly positive effects observed at the PS I level. On the other hand, there was a decrease in the percentage of EPA, usually abundant in all _P. tricrontutum_ membranes, which likely translates into an impairment in membrane-dependent reactions, such as transmembrane transport and thylakoid and mitochondrial electron transport. This could explain the lower culture growth rates at the highest glyphosate-based herbicide concentrations. Moreover, since EPA is an omega-3 fatty acid with key roles in vertebrate biochemistry, the decrease in its contents (reflected also in the omega-6/omega-3 ratio) is likely to negatively affect the nutritional quality of the diatom, inevitably impacting all the trophic web [77]. Nevertheless, because _P. tricrontutum_ showed tolerance to the lowest glyphosate-based herbicide concentrations (up to 100 \(\upmu\)g L\({}^{-1}\)) and is still able to remain alive in the highest concentrations, this can lead to biom magnification induced by glyphosate-based herbicides, leading to a possible vector of contamination and bioaccumulation. This should be addressed in future works due to the possibility of contamination within the trophic web. If, on one hand, photosynthetic and photoprotective antioxidant pigments increased, which may be also partly explained by the lack of changes in CAT and APX activities, on the other hand, the decreased activity of SOD can lead to the accumulation of lethal superoxide anions and consequent oxidation of several biological components, such as proteins, lipids, and EPA fatty acid [78]. However, a decrease in the energy transduction at the ETC, from Q\({}_{\text{A}}\) to plastoquinone, originated a lethal situation of increased redox accumulation in the affected photosystems [79]. Therefore, the energy reaching the PS I was lower, although the effectiveness of the energy transport from PQH\({}_{2}\) to the PS I was not affected (RE\({}_{0}\)/RC), and even increased under the highest glyphosate-based herbicide concentrations. Yet, a severe shift in the redox equilibrium between photosystems towards the PS II (\(\psi_{\text{E0}}/(1-\psi_{\text{E0}})\)) was still observed, decreasing the redox potential reaching the PS I, and thus impairing the light and dark reactions of photosynthesis and the renewal of substrates in the PS I [45]. Nevertheless, the available energy (Ea) increased in the highest glyphosate-based herbicide concentrations, particularly at 500 \(\mu\)g L\({}^{-1}\), probably due to an increase in lipid and protein concentrations. The increase in Ea has been observed in green algae, which accumulated energy reserves as a response to environmental stress [64; 80; 81]. A possible explanation could be related to the need for algae to counteract the increase in energy expenditure, as observed in the present study. Therefore, following a similar pattern as Ea, the energy consumption demonstrated by the mitochondrial ETS of _P. tricornutum_ increased significantly at the highest concentrations, reaching a 300% increase in the highest concentration relative to control. This increase in energy consumption has been observed in other microalgae [65]. Nonetheless, the Ea was higher than the ETS, which led to a slight increase of the CEA in the highest concentrations but only allowing a differentiation of the highest concentrations from the control and the lowest concentrations. This increase in CEA may reflect a higher impairment in mitochondria functioning relative to chloroplast functioning that can ultimately impact the latter due to biophysical disturbances [82]. While these energy balances appear to indicate an increase in the energy available for growth or cell division, the highest glyphosate-based herbicide concentrations inhibited diatom culture growth. Based on this data, stress forces the energy to shift from photosynthesis into energy consumption.