[MUSIC] In assignment number seven, we're trying to demonstrate how osmosis occurs in animal cells or animal tissues. In this exercise, we ask a student to purchase shrimps from the market and then divide down into three portions and put them into different treatments. The first one is to immersed the shrimp into a bowl of tap water for 30 minutes. The second one we have the shrimp going into the salty water for 30 minutes. And the third one, what you essentially have nothing done on them, they are simply left there untreated. Now, out of 1,700 students responding to this assignment, 1% of them, they reported that they did not notice any difference among the three portions of shrimps. They taste equally good or equally bad. And, there's no change in terms of the firmness. Now, I'll come back to this observation a little bit later. For the rest of the group, 99% of the students, they reported that they noticed some differences among all free portions. And, when we examined what kind of differences they were reporting? They said that, they found that in Portion A, in terms of the firmness, they score 3.9, which means that they are not very firm, and in our description in the class we called that a bit mushy. Now, for Portion B and C the difference is minor. They score 7.2 and 6.6, and both of them appear to be much firmer than quality of the Portion A. Now, why is that? It is simply because shrimp animals, and they are made of animal cells with a semipermeable membrane. So what happens is that, when you submerge the shrimps into tap water, the minerals present in the cell which have a higher concentration than the level of the minerals in the tap water. As a result, the water would go through this semipermeable membrane in to the cell resulting in swelling and eventually, bursting off the animal tissues and cells. With this breasting, the teacher will start disintegrating and so the net outcome is this portion of treatment will result in a more mushy texture. Now having said that, let's come back to the preparation of the shrimps. We have no really control how the shrimps were prepared ahead of time. Or, how they were frozen before they went into the market or when they were brought home. We know that when we are freezing animal tissue, such as shrimps, some crystals, large and small, would form. And when large crystals are form, they would expand in the size and therefore, results in the bursting of the cells. So it depends on how they were frozen. If they were not done properly, in fact, the tissue will start being broken in terms of the cell membrane as well as some disintegration. So in such a case, no matter when you put it in the salt water or tap water, very little difference would be noticed. So that may explain why some student find that they don't see any difference among different treatments. Now, we also ask our students to provide a reason why such a change of texture occur among different treatments? A small portion of the students reported that they chose answer A, suggesting that, water is drawn out of the animal cells and the cells become flaccid. And so that's why they become mushy. As explained a bit earlier, if these animal tissue, they are alive with in texture cell membrane, the content of the mineral would be high inside the cell but not in the tap water. Therefore, water will not be withdrawn out into the tap water from the animal cell, instead, it's reverse. The tap water will be drawn into the cell from the tap water. So answer A cannot be correct. Answer D, the mineral present in the tap water would flows into the shrimp or their animal cells. That again, cannot be right because we noticed that the mineral in fact is at a lower concentration in the tap water than inside the cell. Now, how about answer C, where we have 19% of our student answering. It says, the solute molecule inside animal cells are being drawn out into the tap water. Now, think about that. If this tissue is intact where the semipermeable membrane is functioning, solute molecules are relatively large, there's no way they can pass through the semipermeable membrane and go into tap water solution. So, therefore, the answer C is also incorrect. With all three answers eliminated, we now see why answer B is the correct one. And in fact, we have over 60% of our students getting it right. In says, the water is drawn into the animal cells from the tap water, and leading to the swelling and bursting of the cells, and eventually the collapse of the tissue. And that's why it gives a mushy mouth feel. Now in fact, this is the same kind of principle that a lot of butcher shop or chef in the restaurants, they would practice in order to make the meat a bit more tender. They usually, they would soak the meat in tap water for a while. Because of this osmosis, drawing in water into the cell leading to bursting, or eventually, osmolysis. That would result in the disintegration of the cells and the tissue. And the net outcome is, they become much tenderer.
