Isotonic Concentration of Lettuce and Chinese Cabbage

Determination of the Isotonic Concentration of Sodium Chloride Solution to Lettuce (Lactuca Sativa) and Chinese Cabbage (Brassica rapa)¹

• Josua Alvarez
• Ann Justine Marzo
• Patrick Ocampo
• Paula Tiongson

ABSTRACT

The isotonic concentration of lettuce and Chinese cabbage to sodium chloride was determined by obtaining a thin layer from the midrib of each of the freshly harvested leaves and then was cut to four. Each cut for each vegetable was then distributed to four glass slides and then labeled A, B, C, D respectively with NaCl solutions of 0.05 M, 0.15M, 0.30 M, and distilled water as control. After each was compared under the microscope, results showed that isotonic concentration was observed in both set-up B with 0.15 M of NaCl solution in both the Chinese cabbage and lettuce because the cells were alike with the control group. Both also observed hypotonic concentration in set-up A with 0.05 M and hypertonic concentration in set-up C with 0.30 M of NaCl solution because the cells showed an increased and decreased in size respectively. Therefore, the isotonic concentration of both Chinese cabbage and lettuce were observed in 0.15 M of NaCl solution.

INTRODUCTION

Vegetables are edible parts of plants or the whole plant itself that is intended for human cooking or eating raw (Vainio and Bianchini, 2003). Vegetables have a particular role in the diet of humans because they contain different vitamins and minerals necessary for the wellness of the human body. In order to prolong the life of vegetables, which are living tissues, techniques for increasing the shelf life of vegetables such as rapid post-harvest cooling is being done since it minimizes respiratory rates and inhibits the growth of decaying microorganism (Kohli, 2008).

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Lettuce (Lactuca sativa) and Chinese cabbage (Brassica rapa) are leafy types of vegetables. Lettuce contains different vitamins and minerals such as calcium, phosphorus, iron and vitamin C. It is mostly and easily produced on regions under relatively cool and mild temperatures (Ryder, 1999). Chines cabbage locally known as Pechay Wambok on the other hand, is the most important vegetable being grown in China. However, due to trade and exchanges, it has been also being grown in different parts of the world. This vegetable is also known to contain different vitamins and minerals like calcium, potassium, and vitamins C and A (Tatekar and Griggs, 1981).

Osmosis is defined to be as the cellular or artificial diffusion of free water across a selectively permeable membrane like the cell. In studying this, it is necessary to know the solute concentration and membrane permeability thus leading to tonicity, the ability of the cell membrane to gain or lose water. The medium at which the cell is exposed can be classified as isotonic, hypertonic and hypotonic. Hypertonic means the cell has a lower concentration than the medium while hypotonic refers to the higher concentration of the cell than that of its medium. Isotonic concentration on the other hand, means equal concentration of both cell and the medium (Campbell et.al. 2011).

In this paper, lettuce and Chinese cabbage w exposed to sodium chloride of different concentrations. Thus this study aimed to determine the isotonic concentration of sodium chloride to lettuce and Chinese cabbage. The specific objectives were:

1. to compare all the media whether they are hypotonic, hypotonic or isotonic to lettuce and Chinese cabbage and;
2. to differentiate the isotonic concentrations of lettuce and Chinese cabbage.

This study was conducted on November 17, 2014 at Room C-117 of the Institute of Biological Sciences, University of the Philippines, Los Baños.

MATERIALS AND METHODS

Thin layer from the midrib of the freshly harvested Chinese cabbage (Brassica rapa) was obtained. The layers were cut into four and were placed in four different glass slide and label as PA (Pechay A), PB (Pechay B), PC (Pechay C) and PD (Pechay D).

Figure 1. Chinese cabbage specimens.

Few drops of 0.05 M NaCl solution was added to the glass slide labeled Pechay A and place a coverslip to the slide while 0.15 M NaCl solution was used on the glass slide labelled Pechay B. On the glass slide labelled Pechay C, 0.30 M NaCl solution was added. Distilled water was dropped on the glass slide labelled Pechay D to serve as control. To prevent the specimen from drying, few more drops of each solution and the control were added to their respective glass slides to avoid extraneous results.

The glass slides were placed and examined under a microscope using the low power objective (LPO). The appearance of the cells in slides A-C were compared to the appearance of the cells on slide D. Using the comparison of the appearance of the cells, the isotonic, hypotonic and hypertonic concentration of sodium chloride solution to Chinese cabbage was determined.

The steps were repeated using the Lettuce (Lactuca sativa) leaf.

RESULTS AND DISCUSSION

The slides labeled with A, B, and C, contained 0.05, 0.15, 0.30 M NaCl, respectively. The slides labeled with D contained distilled water and is therefore the controlled set up. The slides labeled with P and C contained cabbage and lettuce, respectively.

The cell in the slide labeled P.A. was hypotonic with the slide labeled P.D. since the former was larger than the latter which can only mean that the cell was filled with water. An isotonic osmotic concentration was observed in the slide labeled P.B. since there was no change in appearance compared to the controlled experiment. A shrink in appearance was observed in the slide labeled P.C. in comparison to the slide with just distilled water and cabbage since the cell undergone plasmolysis. This is therefore hypertonic. As seen in table 1

In the next experiment, a hypotonic osmotic concentration was observed in the slide labeled C.A. since the cell had an increase in size compared to the controlled experiment since water was absorbed. The cell in the slide labeled C.B. was isotonic since it was identical to the cell in the slide labeled C.D. A decrease in size was observed with the slide that contained 0.30 M NaCl and lettuce in comparison to the slide that contained distilled water and the same substance. Thus, it is hypertonic (refer to table below).

Table 1. Figures of cells of lettuce and cabbage exposed in different media.

SUMMARY AND CONCLUSION

The isotonic concentration of sodium chloride to lettuce and Chinese cabbage was determined. Thin layer from the midrib of each of the freshly harvested leaves was obtained and cut into four. Per vegetable, the divided leaf was distributed to four glass slides and the slides were differentiated by labeling A, B, C, and D respectively. NaCl solutions of 0.05 M, 0.15 M, and 0.30 M were added to slides A, B, and C respectively while distilled water was added to slide D that served as the control group. The appearance of the cells in slides A, B, and C was compared in slide D.

Results showed that Chinese cabbage in 0.05 M NaCl solution was hypotonic because enlargement of the cells was observed when compared to the control. NaCl solution of 0.15 M was isotonic because the cells were alike to the control set up. Lastly, 0.30 M NaCl solution was hypertonic to Chinese cabbage because the cells were smaller compared to the control set up. As for the lettuce, 0.05 M NaCl was also hypotonic because there was an increase in the size of the cells. Sodium chloride solution of 0.15 M was isotonic to Lettuce because the cells were identical to the control set up. Lastly, 0.30 M NaCl solution was hypertonic because of a decrease in the size of the cells.

Therefore, the isotonic condition of both lettuce and Chinese cabbage to salt solution is 0.15 M.

However, due to lack of equipment, it is recommended to do this experiment again in a proper laboratory. Furthermore, the specimens shall be observed under an electron microscope to get quantitative results.

LITERATURE CITED

Campbell, N.A., J.B. Reece, et.al. 2011. Campbell Biology. 9^th ed. USA: Pearson. p. 133.

Tatekar, N.S. and T.D. Griggs. 1981. Chinese Cabbage: Proceedings of the First International Symposium. Taiwan, China: Hong Wen Printing Works. p. 1-9.

Ryder, E.J. 1999. Lettuce, Endive and Chicory. New York, USA: CABI Publishing. p. 1-13.

Vainio, H. and F. Bianchini. 2003. Fruits and Vegetables. IARC. p. 2.

Kohli, P. 2008. Fruits and Vegetables Post Harvest Care: The Basics. Crosstree Techno-visors. p. 3-5.