LEARNING BIOLOGY THROUGH THE EYEPIECE

Choosing the right microscope and preparing meaningful activities for the students can be difficult tasks, so our purpose is to help the teacher who is planning to use microscopes in class for the first time. Although there are other types, in this paper we propose the use of a compound light microscope; because it is capable of high magnification, and although the preparation of specimens is more demanding than in the case of dissecting microscopes, the opportunities offered make it worthwhile. We describe the main parts of a typical compound light microscope, and some of its characteristics and basic techniques to operate it, including how to focus to avoid damaging the sample, how to prepare a wet mount or how the field of view and working distance reduce as magnification is increased. Finally, we describe two simple activities, the estimation of the number of cells in a certain volume and the study of osmosis in plant cells that can be used to get the students familiar with the optical microscope. In the first one, we measure the size of a cork cell, and repeat the estimation of the number of cork cells in a cubic inch made by Robert Hooke in the XVII century. In the second one, we alter the external medium of onion cells to demonstrate osmosis, and as a bonus, we can see the difference between the cell membrane and the cell wall.