188 EXERCISE 1 the cytoplasm (cyclosis), and the formation of an- other vacuole

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188 EXERCISE 1 the cytoplasm (cyclosis), and the formation of an- other vacuole begins. Food vacuoles travel in a de- Aned route through the organism (Fig 16-3) They lue first pass posteriorly, then anteriorly, and finally posteriorly to the region of the oral groove where ein the undigestible contents are eliminated through What simfarity is there between the pHof the food the cytopyge (anal pore). vacuole as it passes through this anirmal and that of Locate a food vacuole. Observe that when it is first formed, the vacuole is bright red-orange. Closely observe the vacuole as it moves through the protozoan. You will see that during digestion, its contents change from red-orange to blue-green to yellow-green to yellow and fnally back to red- orange (Fig. 16-3). The reason for this color change is that Congo red is an indicator dye that changes color with pH: it is blue-green in acidic conditions and red-orange in alkaline conditions. What does this indicate about the pH of the food vacuole as it moves through the organismi the mouth, stomach, and intestines in human beings? c. Reproduction Play-a The most common type of reprod uction in proto- zoa is binary fission. In this type of asexual rep:o- duction, the cell divides into two geneticallyidenti- cal daughter cells. In flagellates, the plane of division is longitudinal; in ciliates, the parent cell divides transversely. Examine demonstration ANTERIOR Yelow-green f Paramecium showing the various stages of binary fission (Fig. 16-4) Occasionally, paramecia reproduce sexually by conjugation (Fig. 16-5), in which micronuclei are exchanged. You can observe conjugation in Para mecium by carrying out the follo wing procedure. For this study, you will use mating strains of Para- mecium bursaria, which is symbiotic with a green alga. Supplement yoùr observations by examining commercially prepared slides showing various Yellow (alkaline) Orange Red-orange Put a small drop of one of the two mating strains oopye (anal pore) into the depression of a deep-well slide. While ob- serving the paramecia with a stereoscopic micro- scope, add a drop of the second mating strain. You should observe, almost immedia tely, the aggluti- nation (or clumping) of opposite mating strains which brings the cells together for the transfer of nuclear material. Place the slide in a covered petri dish containing moist flter paper to prevent dessi cation of the culture. Examine periodically. Conja- gating paramecia can be seen for up to 48 hours after which few or no conjugants are found. Wasto Food vacuole forming (red) Red-orange facid) 2. Other Ciliates

Explanation / Answer

1) the change in colour of the food vacuole suggests that the vacuole , when without food, has an alkaline pH while as it moves through the body of paramoecium, and engulfs food it happens to uptake H+ ions from the surrounding which causes a drop in the pH of the vacuole which would be facilitating the digestion of the food inside it. As the nutrients are absorbed and wastes are excreted, the pH of the vacuole and again comes back to an alkaline one.

2) the similarity in the pH of this organism and that of the human gut is the cycle of changes in the pH (alkaline -> acidic -> alkaline). In the mouth it is alkaline, in the stomach it drops due to HCl secretion by the parietal cells and in the intestine the intestinal juices bring it back to an alkaline one.

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