The reversibility of enzyme reaction is scarcely described in Japanese upper secondary school students’ textbooks.

In the present study, I developed a new experimental method for high school students to show the reversibility of enzyme reaction visually using succinate dehydrogenase. It is well-known that dehydrogenases can use oxidized methylene blue (Mb), which is blue-color, as a hydrogen acceptor and reduced Mb (colorless) as a hydrogen donor. Succinate dehydrogenase catalyzes succinate oxidation (dehydrogenation) and its reverse reaction, fumarate reduction (hydrogenation). The optimum pH of this enzyme is about pH 7 for succinate oxidation and pH 8-9 for fumarate reduction.

The succinate oxidation activity of this enzyme could be detected by decolorization of Mb at pH 7. 4 in an evacuated Thunberg tube and, thereafter, the fumarate reduction activity could be detected by coloring of Mb in the same tube when a NaOH solution was transferred from the subchamber of the tube to the main chamber, changing pH of the reaction mixture to pH 8-9.

This method can be applied to observing the reversible reaction of lactate dehydrogenase. Thus, this simple method would enhance students’ understanding of the reversibility of enzyme reaction.

A practical lesson, “students discussing the dignity of life, after killing and eating hens”, was prepared as one of the lessons in a teacher training course in my university. One of the educational purposes in this lesson was to allow the students to recognize by themselves the fact that human beings live by killing numerous kinds of animals, and at the same time by making them do the above-mentioned practical work to allow them to realize the dignity of life of every living thing by themselves. From the contents of students’ reports on this practical lesson, it was assumed that the present lesson was useful for allowing them to recognize the dignity of life.

A new microcomputer-aided auxanometer was developed for plant growth physiology in the student laboratory. The elongation of plant roots and stems is semi-automatically measured by the machine (TRZ-8) that was made for the student laboratory by improving the previously invented machine (Tanimoto and Watanabe, Plant Cell Physiol. 27: 1475-1487, 1986). The structure and function of TRZ-8 will be described in this report, and the practical examples of student experiments will be described in the next report (pp.214-220).

The new apparatus has four major advantages when compared to the other methods of growth measurements. (1) It can detect O. lmm scale of elongation every lOmin with minimal mechanical contact with plants. (2) It records the elongation of all 8 plants simultaneously, and students can learn deviations of means by calculating standard errors of 8 specimens. (3) After the plant materials are placed in the machine, the measurements are performed semi-automatically without the plant materials being touched. This avoids injuring plant materials during the continuous recording of the elongation growth. (4) During the experiment, the roots or stems are alternatively kept in aerated mineral solution or in humid air for a minimum of two minutes. This process may be repeated depending on the length of the experiment.

Some technical improvements and development of new experiments were discussed.

The new experiments of plant growth physiology were carried out in the student laboratory by using a new auxanometer (TRZ-8). Promotive effect of auxin (indole-3- acetic acid) on the elongation of stem segments of pea (Pisum sativum L.) was detected within a 2-hr measurement. The effect of the auxin on the root elongation was also confirmed in the 2-hr measurement. The effect of acid pH on the elongation of the root segments was examined in the pea. The rapid increase in the elongation rate (acid growth) was observed but the rapid elongation ceased after 30min. The data of the elongation growth was obtained by the average data of 8 plants with standard errors. Some students, however, failed to detect such effects of auxin or acid pH due to the fluctuation of the obtained data. The major reason was ascribed to incorrect operation of the machine and careless treatment of the plant materials. Some technical points for avoiding such errors and improving the accuracy of the growth measurements were suggested and discussed. Other possible subjects for students’ laboratory work were also presented. This included the observation of the toxic effect of aluminum ion on root growth and the quantitative measurement of extension and shrinkage of roots by changing the osmotic concentration of environmental solutions.

It is important for secondary level students to understand the skeleton structure for studying the classification and development of vertebrates. In this parer, I reported a double staining technique which was modified for making skeletal specimens of vertebrates. The usefulness of the skeletal specimens for biological education was also discussed.