Question

refer to the u - tube pictures above when answering the questions below.

1. why did the number of water molecules on each side of the membrane change, whereas the number of sugar molecules stayed the same?
2. how does the plasma membrane of a cell compare with the membrane in the u - shaped tube?
3. explain the behavior of water molecules in the isotonic solution.
4. does osmosis occur if a cell is placed in an isotonic solution?
5. why does water enter a cell that is placed in a hypotonic solution?
6. what happens to the pressure inside a cell that is placed in a hypertonic solution?
7. what can happen to animal cells when placed in a hypotonic solution? explain.
8. what causes a plant to wilt?

Explanation:

1. The membrane is selectively - permeable. Water can pass through, but sugar molecules are too large to cross, so water moves to equalize the concentration gradient (osmosis), changing the number of water molecules on each side while sugar molecule numbers remain the same.
2. Both are selectively - permeable membranes. The plasma membrane of a cell and the U - tube membrane allow certain substances (like water) to pass through while restricting others (like large sugar molecules).
3. In an isotonic solution, water molecules move into and out of the cell at the same rate, resulting in no net movement of water. There is an equal concentration of solutes inside and outside the cell.
4. Osmosis does not result in a net movement of water in an isotonic solution. Although water molecules are moving across the membrane in both directions, the rates are equal, so there is no overall change in the amount of water in the cell.
5. In a hypotonic solution, there is a lower solute concentration outside the cell compared to inside. Water moves from an area of lower solute concentration (outside the cell) to an area of higher solute concentration (inside the cell) to equalize the concentration gradient.
6. In a hypertonic solution, water leaves the cell. As water exits, the pressure inside the cell (turgor pressure in plant cells or hydrostatic pressure in animal cells) decreases.
7. Animal cells placed in a hypotonic solution will take in water by osmosis. Since animal cells lack a cell wall, they may swell and potentially burst (lyse) due to the influx of water.
8. A plant wilts when there is a loss of turgor pressure. This occurs when plant cells lose water, often due to being in a hypertonic environment (e.g., soil with high salt concentration) or when water uptake is insufficient.

Answer:

1. The membrane is selectively - permeable; water can cross but sugar molecules cannot.
2. Both are selectively - permeable, allowing water but restricting large molecules.
3. Water moves in and out at the same rate with no net movement.
4. There is no net osmosis as water movement rates are equal.
5. Water moves from lower solute (outside) to higher solute (inside) concentration.
6. The pressure inside the cell decreases as water leaves.
7. They may swell and burst as they take in water due to osmosis.
8. Loss of turgor pressure from water loss in plant cells.