<p>This study presents a comprehensive numerical investigation of steady two-dimensional flow and heat transfer in a Carreau nanofluid embedded with quantum dots (QDs) and motile microorganisms, over a stretching sheet under the influence of an induced magnetic field. The physical model incorporates key transport mechanisms including Brownian motion, thermophoresis, thermal radiation, bioconvection, and activation energy—forming a robust multiphysics framework. The governing nonlinear partial differential equations are transformed into a set of similarity-based ordinary differential equations, which are solved using a dual-approach via MATLAB’s bvp5c and ode15s solvers. The excellent agreement between both solvers confirms the reliability and accuracy of the numerical scheme. Parametric analyses reveal distinct quantitative impacts of QD-related parameters on wall transport quantities. For instance, increasing the photothermal parameter reduces the Nusselt number by about 31% but enhances the Sherwood number by nearly 100%. Similarly, raising the length-scale parameter decreases heat transfer by 24%, while boosting solutal transport and bioconvective strength by 200% and 77%, respectively. The magnetic interaction parameter exerts little influence on heat or mass transfer but amplifies the microorganism density number by over 600%. Most strikingly, the nanoparticle interaction parameter increases the Nusselt number by more than 330%, yet suppresses the Sherwood number and microorganism density number by approximately 550% and 77%, respectively. These findings highlight that different quantum-dot parameters can be strategically tuned to optimize thermal regulation, solutal mixing, or bioconvective activity in advanced thermal systems such as microfluidic coolers, photothermal medical devices, and solar energy collectors.</p>