Final answer:
When observing Euglena, the low-power objective is ideal for initial observation. To keep a left-swimming Euglena in view, the slide should be moved to the right due to the inverted image effect of the microscope's lenses.
Step-by-step explanation:
When observing a Euglena wet mount, starting with the low-power objective of the microscope is appropriate because it provides a wider field of view, making it easier to locate the swimming organisms. Once the Euglena are in view, it's important to remember that the optics of the microscope invert the image. Therefore, if the Euglena are swimming to the left, you should move your slide to the right to keep the organism in view.
The light microscope uses two sets of lenses, which results in an inverted image. This means that all movements of the slide will appear opposite through the eyepiece. If you wish to follow the movement of an organism under the microscope, move the slide in the opposite direction to where the organism appears to be moving.