CRH Nanfeng high school

I am a rural middle school teacher. In the teaching process, I insist on leading every student to carry out practical activities of collecting and making plant specimens, hoping to improve students' interest in learning. In practice, I found some defects in the method of making leaf specimens used in teaching materials, which affected the effect of practical activities. Specifically, it is mainly manifested in the following aspects:

(1) The manufacturing process takes a long time:

It takes about a week from the completion of collection to the completion of specimen production. Long drying time, slow speed, plants are easy to turn yellow, wither and lose their primary colors.

(2) red tape:

It is necessary to repeatedly replace absorbent papyrus, arrange specimens, dry papyrus and other corresponding operations.

(3) Plants are easily damaged:

In the process of changing toilet paper, the leaves, flowers and fruits of the specimen will fall off and be damaged.

(4) poor practicality:

Even the finished product will inevitably be damaged by external forces such as flowers, leaves and fruits falling off due to transfer and other operations during use. The visual effect of the specimen is also not good.

(5) Other aspects:

It is almost impossible to make specimens of drought-tolerant cactus and Sedum plants. For example, Portulaca oleracea, I found that even after two weeks of repeated drying, the stems were as fresh as ever, while the leaves, flowers and seeds almost completely fell off, leaving only bare stems. In addition, as mentioned above, it is difficult to finish the finishing steps before making the pinnate compound leaves of mimosaceae plants because of dehydration and closure.

The main purpose of our teaching practice is to let students collect specimens:

(1) Master the method of making leaf specimens; (2) Improving students' interest in biology; (3) Know several common plants.

Improving students' interest in biology is of great significance to the follow-up teaching of undergraduate courses, which is also the main purpose of teachers' activities. However, due to the shortcomings of the specimen making method used in textbooks, such as long time-consuming, complicated procedures and unsatisfactory making effect. On the contrary, it will make students feel difficult and depressed, thus affecting their interest in making plant specimens, and then affecting their interest in learning biology. In order to overcome the shortcomings of traditional methods of making plant specimens, after years of teaching practice, I have explored a set of methods of making plant specimens for your reference.

First, the characteristics:

(1) Rapid production:

If the weather is fine, it only takes 5-8 hours from the collection of specimens to the completion of production, while the actual hands-on operation time is only about 10 minutes.

(2) The manufacturing procedure is simple:

Only three steps are needed: collecting, manufacturing and removing water. There is no need to replace or dry toilet paper.

(3) The finished product has good practicability;

The finished product can be reused and is not easy to be damaged. And is easy to store and not easy to be mildewed and eaten by insects. Most of them can keep the original color of plants, and some fern specimens can even keep green for more than two years.

(4) Wide scope of application:

Except for a few plant species such as mimosa, it is difficult to make specimens of almost all other plants, and it is also easy to make specimens of wax leaves of Portulaca oleracea, a succulent drought-tolerant plant. Even compared with mechanical film pressing method, this method has its advantages.

(5) Low cost:

The transparent tape used is not expensive, and it costs about 0.07 yuan to make each specimen.

Second, the production method:

I. Materials and tools:

(1) materials and tools

Collecting box, cutting branches, digging roots, shovel, tweezers, pen, paper cutter, 20cm plastic ruler, wooden board, sponge, hand-held watering can.

A roll of scotch tape, about 10cm wide and about 0.8cm wide.

Proper amount of table paper

(2) Description of some materials and tools:

(a) All tools are one set;

(b) The pen is used for writing labels; Paper cutter is used as fine cutting specimen; Plastic ruler is used to help lay transparent tape; Hand watering can be used to clean the soil on the surface of plants.

(c) The reference parameter of the board is 40×40× 1.4 (unit: cm). Used as a workbench for field work to complete plant specimens that must be covered with plastic film on site. Composite plate can be used for cutting in the market.

(d) The parameters of the sponge are: 15× 15× 10 (unit: cm). It can be used to make the force of pressing samples evenly distributed, and it can also be used to remove the residual water when cleaning plants.

(e) One side of the table paper should be white and the other side should be black. In practice, there are shirts lined with cardboard and horse manure cardboard to protect the textbooks purchased by schools.

(f) It is ideal if the width of the transparent tape can be 25 cm. If not, it's about 10 cm. Of course, a little wider is better.

Second, the specific production steps:

(1) Specimen collection:

Except that some specimens were made in the field and were not brought back to the laboratory, most of the methods were the same as those in the textbook.

(2) Pretreatment of samples:

Pretreatment mainly includes: (a) cleaning the soil of plants with a hand-held watering can, and absorbing the residual water on the surface with a sponge. (b) pruning plants. That is, remove some repetitive, irrelevant, insect-damaged, damaged leaves and redundant leaves, fruits and flowers. You can cut off half of the back of the stem that is too thick (C) and shape it, that is, put the plant in a suitable position on the table paper and put the back of a proper amount of leaves outward. After plants are placed and shaped, stress and deformation will inevitably occur, and it is difficult to achieve the purpose of reasonable placement. The fresh plants on the table paper are not on the same plane. At this time, it is still not ideal to press them with a sponge. 0.8cm wide transparent tape can be used to fix the part that needs temporary fixing in the proper position of the table paper. (d) In addition, parts with plant characteristics can be displayed, such as elderberry bark with lenticels and obvious pith, and perilla stem with square cross section.

(3) Labeling:

In practice, you can use practice paper cut to an appropriate size as a label. In addition to some key information, the label should also have a general name and a brief introduction, such as purpose, specimen introduction, etc. This helps students to connect with practice, and also helps later scholars to understand this plant in practice. Now take wild soybean as an example to make an introduction:

Name: Wild Soybean (Leguminosae)

Common name: wild soybean, rattan soybean

Collection location: Huludun, Tongqing Village, Nanfeng Town

Collector: Chu Zhengchao

Acquisition time: August-May, 2003

Ecological environment: plain wasteland

Introduction: It is a national second-class protected plant, which is beneficial to improvement.

The genetic quality of soybean may be of great significance.

The ball at the root of the specimen is the nodule.

(4) film covering:

This is the key to this method. In fact, the essence of this method is to seal the plants on the table paper with transparent tape. In practice, the plants must be tightly sealed on the table paper, and no gaps can be left, otherwise it will easily lead to moth-eaten. Then the transparent rubber cloth, table paper and plants are pressed and bonded together by sponge. If there is enough space on the front, you can stick the label on the front of the table paper together with the plants, otherwise you can stick the label on the back.

(5) in addition to water:

Different from the drying method of wax leaf specimens contained in textbooks, this method does not use toilet paper to absorb all the water in the specimens, but exposes the specimens covered with plastic films to the scorching sun. But remember that the back of the specimen must face up, which is the key to this method, otherwise it will lead to the rejection of the specimen. Different plants have different water content and different drying time. When there is no water vapor condensation on the front tape of the specimen, the drying is basically completed, but it needs to be consolidated for a period of time (in order to speed up the drying of the specimen, the back of the white surface paper can be painted black).

(6) Late care:

The finished specimen should avoid the positive exposure of the specimen to the sun as much as possible; Dry them several times a year, try to keep them dry, and be sure to put your back up when drying; For a few insect-eaten specimens, it is necessary to deal with them in time to prevent them from being scrapped.

(7) Other aspects:

For the plants with kohane compound leaves mentioned above, if they are brought back to the laboratory for re-making, it will be difficult to finish the sorting work and make specimens because the plants lose water and the pinnate compound leaves are closed. For this method, the specimens of these plants should be completed in the field, and the wooden board should be used as the workbench for field operation. If possible, try to cover all the specimens on site.

The method of making wax leaf specimens contained in textbooks is difficult to make on the spot to avoid exposure. In this way, if you want to make high-quality works, you must use on-site production and exposure. After I introduced this method in teaching practice, many students showed great interest. They trial-produced some specimens, and the results were very good and successful, which greatly stimulated their interest in learning biology. It has also made great progress in my teaching achievements.

This method can not only make wax leaf specimens, but also make specimens of small arthropods such as butterflies and dragonflies in a similar way, and the effect is also very good.