First, we poured mL of distilled water into a cup and added about 4 mL of IKI solution to the water and mixed well. We also modified one item into a question about human cells, rather than plant cells, so it would be more appropriate for our human physiology courses, where students might not have strong preparation in plant biology and cell structure.
Pure water has a water potential of 1 atmosphere. However, there were possible factors for error in this experiment. Cell membranes act as a barrier for the cell. During the experiment conducted in Lab 1A, the results and data collected make it possible to conclude that glucose and Iodine Potassium Iodide can pass through a selectively permeable membrane and will if the concentrations on either side are not equal.
The membrane is semipermeable, meaning only specific molecule may enter the cell. This may have occurred in part because the onion itself was already dried out and dehydrated, or while the onion was being looked at through the microscope, the heat from it may have caused the cells to loose water.
We tied one end of the dialysis tubing to create a bag. Glucose was initially in the dialysis bag and is predicted to flow in and out of the dialysis bag and exist in both the cup and dialysis bag. This shows how the onion cells had high water potential and moved to the area outside the cell with lower water potential.
The word osmosis refers to the diffusion of water across a selectively permeable membrane in order to evenly distribute concentration levels on both sides of the membrane.
In addition, we wanted to reduce the length of the instrument to encourage more faculty, even those teaching large college classes, to use it to inform their teaching, and to encourage students to pay close attention and read all items carefully and reflect on their answers. In a plant cell, it is ideal to have an isotonic solution.
A simple rule to remember is: If the molecules are headed toward an open pore in the cell membrane, it may pass through the pore or rebound depending on its size to the pore.
This is why it is dangerous to drink sea water - its a myth that drinking sea water will cause you to go insane, but people marooned at sea will speed up dehydration and death by drinking sea water.
The diffusion of water molecules across the cell membrane is called osmosis. We then cut a hole into the bag large enough for a glucose test strip to enter. Is there any influence of solute concentration to the net movement of water molecules across the cell membrane?
This is also why "salting fields" was a common tactic during war, it would kill the crops in the field, thus causing food shortages. Lab 1D — In this part of the lab, only calculations were made, so no human error probably occurred during this time.
Lab 1C — There was some discrepancy in this experiment in the 1. In this lab, we have used specific materials and methods to present this process. Sometimes, large molecules cannot cross the plasma membrane, and are "helped" across by carrier proteins - this process is called facilitated diffusion.
During Lab 1D calculations were made and questions were answered to help give a better understanding of water and solute potential. In plant cells, the central vacuole loses water and the cells shrink, causing wilting.
Using a procedure involving osmosis occurring between the unknown substances and a solution of known concentration, we were able to calculate the percent composition of starch in solutions A and B. In animal cells, the cells also shrink.
After we were finished, we discarded the used glucose test strip. Cell membranes dispose of waste products from the cell and lets important molecules, like water and oxygen, into the cell.
Hypertonic solutions are solutions with higher amounts of solutes and hypotonic solutions are solutions with a lower amount of solutes. Then, after adding water back to the cells, water would have moved back into the cells increasing turgor pressure.
Osmosis occurred—there was a change in mass of both the dialysis tubing filled with a solution of unknown concentration and the beaker of sucrose and water, for both solutions A and B.
Water potential was a key element in each part of the experiment. In Lab 1B, it can be concluded that sucrose cannot pass over a selectively permeable membrane, but instead water molecules will move across the membrane to the area of lower water potential to reach dynamic equilibrium.
The data decreases consistently until the 1. In plant and animal cells, loss or gain of water can have different effects. We then waited 30 minutes and worked on an activity relating to Figure 2. When water enters the plant cell, the membrane is pressed up against the cell wall and creates turgor pressure.
As the results demonstrate, we determined that A originally had a percent composition by mass of 1. The tubing may not have been submerged in the beaker for long enough to reach equilibrium.
This indicates that solution A had a lower concentration of starch than that of the solution in the beaker—however, this was not supported by our calculations.
How does diffusion across the cell membrane work?Lab One- Diffusion and Osmosis- Write Up of Analysis Q’s. Frances Coronel- AP BIO- Bells 5/6 Part 1A: Analysis Questions 1.
Which substance(s) are entering the bag and which are leaving the bag?5/5(4). Biology student mastery regarding the mechanisms of diffusion and osmosis is difficult to achieve. To monitor comprehension of these processes among students at a large public university, we developed and validated an item Osmosis and Diffusion Conceptual Assessment (ODCA).
Part A: Diffusion and Osmosis From table in this part of the lab, it is seen that IKI is flowing into the bag and glucose is flowing out of the bag. That is because of diffusion and osmosis.
Diffusion and osmosis occur because the concentrations should somewhat equal out (Sheppard 1). The main difference is that osmosis is the diffusion of water. Water molecules often diffuse across cell membranes, so the process is important.
Osmosis is the result of diffusion across a semipermeable membrane. If two solutions of different concentration are separated by a semipermeable membrane, then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution.
Osmosis is the diffusion of water molecules across a semipermeable membrane. When the concentration levels of two solutions on either sides of the membrane are equal and no movement is detected, the solutions are isotonic.Download