Cell Biology - Osmosis
What is osmosis?
The net movement of water molecules from a dilute solution to a more concentrated solution through a semi-permeable membrane
What type of process is osmosis?
A passive process as it does not require energy
Water moving in/out of cells via osmosis depends on what?
The difference in concentration of the cytoplasm compared to the solution outside of the cell
What factors affect the rate of osmosis?
-Higher temperature = increased rate
-Higher surface area = increased rate
-Higher concentration gradient = increased rate
What happens when cells are in a dilute solution?
Water moves into cells via osmosis
-Animal cells can swell and can burst
-Plant cells swell but don't burst due to cell wall (Turgid)
What happens when cells are in a solution of the same concentration as their cytoplasm?
There is no net movement of water in/out of cells (no osmosis)
What happens when cells are in a concentrated solution?
What moves out of cells via osmosis
-Animal cells can shrink and shrivel up
-In plant cells the vacuole shrinks and cytoplasm can pull away from the cell wall (Plasmolyzed)
Osmosis Practicle Method
1-Prepare potato cylinders:
-Use a borer to cut out 6 cylinders,ensuring same length and diameter;weigh and record enitial mass
2-Prepare solutions:
-Prepare 6 boiling tubes, each containing different concentrations of sugar of salt solution;include a boiling tube with water as a control
3-Soak the cylinders:
-Place one cylinder into each boiling tube while keeping track of which cylinder goes in which solution;allow cylinders to soak for a specific time e.g. 40 mins
4-Measure the changes:
-Carefully remove each cylinder from its solution and blot dry with a paper towel, and measure again;calculate the percentage change in mass for each cylinder
Repeat experiment multiple times for each solution to ensure accuracy and ignore ang anomalous results
5-Analyse the results:
-Plot a graph of percentage change in mass again concentration of solution