Unit 3: The Cell--the Cell Membrane, Diffusion, & Osmosis

Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. This process occurs due to the random motion of particles and does not require any external energy input. It is a fundamental process in various biological and physical systems, such as the exchange of gases in the lungs and the mixing of substances in a solution.

When potato cells are placed in a hypotonic solution, the concentration of solutes outside the cell is lower than inside the cell. This creates a concentration gradient, causing water molecules to move from an area of higher concentration (the solution) to an area of lower concentration (the cell). As a result, water would enter the cells, leading to an increase in their mass.

If the concentration of solute is the same both inside a cell and in the solution it's placed into, then the solution is said to be isotonic. In an isotonic solution, there is no net movement of water across the cell membrane, as the concentration of solute is balanced on both sides. This means that the cell will maintain its shape and size without any swelling or shrinking.

In the diffusion lab, the special tubing represented the plasma membrane. The plasma membrane is a selectively permeable barrier that surrounds the cells and controls the movement of substances in and out of the cell. It allows certain molecules to pass through via diffusion, which is the process of molecules moving from an area of high concentration to an area of low concentration. Therefore, the special tubing in the diffusion lab was used to mimic the function of the plasma membrane in regulating the diffusion of molecules.

When a cell is placed in a solution that has a higher water concentration, water molecules tend to move from an area of higher concentration (the solution) to an area of lower concentration (the cell). This process is called osmosis. In this case, since the cell is 95% water and the solution is 100% water, water will enter the cell through osmosis, causing it to swell.

In the diffusion lab, iodine was placed into a beaker of water and starch was placed inside special semipermeable tubing. This is because starch is a large molecule that cannot pass through the small pores of the tubing, while iodine is a smaller molecule that can diffuse through the tubing. Therefore, when the tubing is placed in the beaker, water molecules will move into the tubing through osmosis, while iodine molecules will move out of the tubing and into the surrounding water. However, the starch molecules will remain trapped inside the tubing, as they are too large to pass through the pores.

Iodine can test for the presence of starch because iodine reacts with starch to form a blue-black color. This is a commonly used test in biology and chemistry laboratories to detect the presence of starch in various substances.

When iodine comes into contact with starch, a chemical reaction occurs. This reaction leads to the formation of a complex between iodine molecules and the starch molecules. This complex has a deep purple or black color, which is why iodine becomes dark purple/black when it comes into contact with starch.

When starch is placed inside a bag and immersed in water, it undergoes the process of diffusion. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. In this case, the starch particles move out of the bag and into the surrounding water. Iodine is used as an indicator for the presence of starch. When iodine comes into contact with starch, it turns purple. Therefore, when the bag of starch is placed in the water, the starch particles diffuse out of the bag and into the water, causing the water in the beaker to turn purple.

When a fish that is accustomed to living in salt water is placed in fresh water, the concentration of solutes inside the fish's cells becomes higher than the concentration in the surrounding water. This creates a concentration gradient that leads to osmosis, the movement of water molecules from an area of lower solute concentration (fresh water) to an area of higher solute concentration (inside the fish's cells). As a result, water enters the fish's cells, causing them to swell and potentially burst, leading to the death of the fish.

The change of color inside the bag indicates that iodine is able to pass through the bag. This is because iodine is a small molecule that can easily diffuse through the pores or openings in the bag, causing a chemical reaction with the substances inside the bag and resulting in a change of color. Starch, on the other hand, is a larger molecule and cannot pass through the bag, so it does not contribute to the change of color. Therefore, the correct answer is that iodine is able to pass through the bag.

Since it's 100% water, it has NO solutes at all.

Hypertonic solution - more solute, less water than the cell. Therefore the cell has a greater concentration of water.

If the left side of the beaker were hypertonic compared to the right side, it means that the concentration of solutes in the left side is higher than in the right side. In this scenario, water would move from an area of lower solute concentration (the right side) to an area of higher solute concentration (the left side) through osmosis. As a result, the level of water on the left side would increase, while the level of water on the right side would decrease.