Explore how to use a light microscope to observe onion and cheek cells. This KS3 simulation guides students through positioning and securing a prepared slide, selecting a low-power objective, adjusting the light and bringing the image into focus using the coarse- and fine-focus controls. Students can then increase magnification and investigate how staining makes cell structures easier to distinguish. Side-by-side comparisons show the effects of iodine on onion cells and methylene blue on cheek cells, while a cell explorer supports identifying and comparing visible structures. Guided and free-practice modes make the tool suitable for teacher demonstrations, preparation for practical work and independent revision. simopsis