Cells grown in culture are often used to investigate the role of organelles. As culture conditions can be easily manipulated, cells can be subjected to different chemicals and their responses studied and analyzed. In one such experiment, mouse cells were incubated in the presence of high concentrations of sucrose. The cells were examined under the microscope. Crystals of sucrose were found in the lysosomes of all the cells. When sucrose was depleted from the culture medium, the sucrose crystals in the lysosomes persisted for many days, but did not affect the growth of the cells. Eventually, the sucrose crystals disappeared. The rate of disappearance is shown in the graph below (note: all graphs are the same scale).
Researchers performed two additional experiments:
Immediately after sucrose was removed from the culture medium, the enzyme invertase was added. Invertase catalyzes the cleavage of sucrose into monosaccharides. The cells were then examined for the presence of sucrose crystals. The results are shown below.
Mouse cells grown in the presence of invertase (cell type A) were mixed with cells grown in the presence of sucrose (cell type B). A reagent that fuses cells was also added to the culture. After fusion, the cells (cell type AB) were grown in the absence of sucrose. The cells were then examined for the presence of sucrose crystals. The results are shown below.
From the results in Experiment 1, what can you conclude about invertase?
|A||It irreversibly inhibits sucrose production.|
|B||It catalyzed the break down of sucrose in the medium.|
|C||It was internalized by the lysosomes.|
|D||It changes the pH of the cytoplasm to catalyze sucrose.|
Since the sucrose crystals appeared in the lysosomes of the cell, the invertase had to have been internalized in order to catalyze the reaction of the crystals into monosaccharides. Given the circumstances, none of the other answers are appropriate.