45 minutes. Place samples on microscope slides. Make sure that the
two samples do not mix with each other. Observe the granules
under both bright-field and polarized light.
5. Starch Granules: Response to Lugol’s Solution
Repeat experiment 4. Add Lugol’s solution to the control and experimental solutions. Observe the number of large, intermediate, and
small starch granules in the control and experimental solutions under
bright-field light. Compare the results to those of experiment 4. Once
again, do not use polarized light, because the stained granules are too
dark to observe structural details.
Additional Notes to Teachers
In keeping with Bloom’s taxonomy, this lab was designed so that it
can be adapted to different academic levels, ranging from high
school to college, based on the collection, quantitation, and analysis
of data and the synthesis of conclusions. The lab is also modular so
that the teacher can select some or all of the experiments, based on
time, lab resources, and skill levels of students.
Slight changes to the lab procedure can make it more suitable to
different academic levels. For example, small starch granules are
digested more rapidly than large granules. As a result, small granules
will disappear while the larger granules will remain. Students could
quantitate the difference in amylase breakdown rates between small
(length ≤15 µm), intermediate, and large (length ≥45 µm) granules
by making multiple observations (e.g., at 0, 15, 30, and 45 minutes
incubation). In addition, conducting the same experiment at both
room temperature and in an incubator (38°C) will demonstrate that
the higher temperature accelerates digestion. A sample worksheet for
this lab (as presented in a college sophomore-level cell biology class)
and student assessment questions are provided in the Appendix.
We thank Miranda Brown for help in preparing specimens for this
experiment, and Rakshak Adhikari for his advice and work in its
Hardin, J., Bertoni, G. & Kleinsmith, L.J. (2012). Becker’s World of the Cell,
8th ed. (p. 88). Boston, MA: Benjamin Cummings.
McMahon, K.A. (2004). Practical botany – the Maltese cross. In M.A.
O’Donnell (Ed.), Tested Studies for Laboratory Teaching, vol. 25
(pp. 352–357). Proceedings of the 25th Workshop/Conference of the
Association for Biology Laboratory Education.
Tamarkin, D.A. (2015). Exploring carbohydrates with bananas. American
Biology Teacher, 77, 620–623.
JAMES SANDERS ( email@example.com) is an Assistant Professor in the
Department of Chemistry and Physics at Troy University, Troy, AL 36082.
GLENN M. COHEN ( firstname.lastname@example.org) is Professor Emeritus, Department of
Biological and Environmental Sciences, Troy University.
Figure 1. Starch granules viewed under magnification with a
classroom microscope. The magnification and illumination
types are (A) 10× magnification under bright-field illumination,
(B) 10× magnification under crossed polarized illumination,
(C) 40× magnification under bright-field illumination, and
(D) 40× magnification with crossed polarized illumination.
These images were taken using the camera of a cell phone
mounted to a classroom microscope.