You are a junior scientist at a research lab. Your supervisor hands you two microscope slides and says: 'One of these samples is from a human cheek swab. The other is from a piece of spinach leaf. Tell me everything you can figure out about these cells.' Under the microscope you notice: Slide A has cells with a clearly visible nucleus, no cell wall, no green structures, and irregular blobby shapes. Slide B has cells with a nucleus, a rigid rectangular shape, a thick outer wall, and bright green oval structures scattered inside. Identify which slide is which, name at least three organelles visible in each, and explain how you know.