Osmosis

To define osmosis.
To explain the importance of osmosis in plant and animal cells and describe the effects of water gain or loss.
To understand how to measure osmosis using plant tissue and interpret results, including calculating percentage mass change.

Osmosis is a special type of diffusion that involves the movement of water molecules across a partially permeable membrane.
During osmosis:
- Water moves from an area of dilute solution (where there is a higher concentration of water molecules) to an area of concentrated solution (where there is a lower concentration of water molecules).
- This process continues until the concentration on both sides of the membrane is balanced.

Osmosis.

Plant Cells:
- Plants rely on osmosis to absorb water from the soil and to maintain cell turgidity.
- Turgid cells are swollen with water, which helps the plant stay upright and supported.
- If plant cells lose water, they become flaccid (soft) and the plant may wilt.
Animal Cells:
- Animal cells also use osmosis to balance water levels.
- Unlike plant cells, animal cells lack a cell wall. This means that if an animal cell absorbs too much water, it can swell and eventually burst (lysis) due to the pressure inside the cell.
- If too much water leaves the cell, it will shrink and may become dehydrated.

To study osmosis, we often use plant tissues, like potato slices, in different concentrations of sugar or salt solutions. Students are expected to:
1. Measure the Rate of Water Uptake: By observing how much water is taken up by plant tissue in a given time, we can study the rate of osmosis.
2. Calculate Percentage Gain or Loss of Mass:
  - Place the plant tissue in a solution and weigh it before and after the experiment.
  - Calculate the percentage change in mass using: :

(End mass - start mass) / start mass x 100

1. - A gain in mass indicates water has moved into the tissue by osmosis, while a loss in mass shows water has left the tissue.
2. Graphical Interpretation: A typical osmosis graph might show how different solution concentrations affect the water movement in and out of plant cells.

Osmosis: The diffusion of water molecules across a partially permeable membrane from a dilute solution to a concentrated solution.
Partially permeable membrane: A membrane that allows some molecules (like water) to pass through but not others (like larger solute molecules).
Dilute solution: A solution with a high concentration of water molecules (low solute concentration).
Concentrated solution: A solution with a low concentration of water molecules (high solute concentration).
Turgid: A plant cell swollen with water due to osmosis, providing support to the plant.
Flaccid: A plant cell that has lost water by osmosis, causing it to become soft and the plant to wilt.
Lysis: The bursting of an animal cell due to excessive water uptake by osmosis.
Solution concentration: The amount of solute dissolved in a given volume of solvent, affecting the direction of osmosis.

Osmosis in Action (Egg Experiment): Carefully remove the shell from an egg by soaking it in vinegar, leaving the membrane intact. Place the de-shelled egg in different solutions (e.g., pure water, sugar solution) and observe the changes in size over time due to osmosis.
Graph Analysis Practice: Find example graphs online showing the percentage change in mass of plant tissue placed in solutions of varying concentrations. Practice describing the trends shown and explaining them in terms of osmosis.