Teaching Microscopy Using Plants

This article from Dr Chris Graham (Visiting Teacher at SAPS), published in the November 2024 issue of School Science Review, suggests readily available plant material that can be used to help students of any age become confident and enthusiastic users of microscopes as well as skilled interpreters of what they see. The specimens discussed require minimal preparation and no staining, allowing students to spend more time using microscopes and less time preparing slides. What is viewed under the microscope is also easily relatable to what students can see with the naked eye, thereby minimising the conceptual leap needed to interpret what is being viewed under the microscope.

Download the article

The article explores:

• the concepts of depth of field, focal plane, and field of view
• how the leaves of Tradescantia zebrina (silver inch plant) and the pondweed Egeria densa can be used to build students’ understanding of these concepts
• how using a dandelion seed (Taraxacum sp.) can show that a microscope creates an optical slice through a specimen.

These specimens also help students gain a sense of scale while using the microscope to transition from the ‘just visible with the naked eye’ to ‘only visible with a microscope’.

The associated PowerPoint presentation contains high resolution images you can use in your teaching. Download here.

The videos below demonstrate two of the specimens suggested in the article.

This video starts by focusing though the full depth of a leaf of the pondweed Egeria densa. The leaf is two cells thick and the first part of the video focuses from the top of the leaf to the bottom and back up again to allow the viewer to build up an understanding of the 3D structure of the leaf. (Note: these sections have been sped up slightly.)

The video then shows the movement of chloroplasts at two different depths within the leaf (in real time).

Firstly, chloroplasts are seen moving across the uppermost layer of cytoplasm in the lower layer of cells, and secondly chloroplasts are seen streaming around the edge of the cells in the thin layer of cytoplasm between the plasma membrane and the vacuole. This cytoplasmic streaming is thought to help these large cells overcome the limitations of diffusion by constantly stirring the contents of the cell. It also shows that cells are dynamic, living things and not just static objects.

This video was created by focussing through the pappus (the filamentous parachute-like structure) of a dandelion seed (Taraxacum sp.).

It was filmed by securing a dandelion seed horizontally in some Blu Tack on a slide without a coverslip. You can see this setup in the first part of the video.

It shows that only part of a specimen is in focus at any one time and that objects just out of focus are noticeable but blurry whereas objects that are far away from the focal plane are not noticeable at all.