Biology Internal Assessment – Osmosis
BIOLOGY INTERNAL ASSESSMENT
STANDARD LEVEL
OSMOSIS
OSMOSIS IN POTATO STRIPS
- Aim
To investigate the change in the mass of potato strips as a result of the process of osmosis in potato strips over varying periods of time.
- Research Question
How does time affect the mass of potato strips (measured in grams) when immersed in distilled water (H20) over a period of five hours at one hour intervals: 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours?
- Introduction
Osmosis is the passive movement of water molecules from a region of high water concentration to a region of lower water concentration (lower solute concentration to higher solute concentration), across a partially permeable membrane. The plasma membrane is selectively permeable, and it controls the movement of substances in and out of cells, but water is able to move freely in and out of the cell, allowing osmosis to occur. Potato cells have selectively permeable membranes and therefore can be used to show the process of osmosis.
As plant cells generally have a higher solute concentration than their surroundings (lower water concentration), when immersed in H20, the potato strips will be surrounded by a region of high water concentration since water has a solute concentration of 0. This would mean that the distilled water is hypotonic whereby it has a higher concentration of water than the potato cells, causing water to flow from the area of higher water concentration (water solution) to the area of lower water concentration (potato cell).
However, as the duration given for osmosis to occur increases, the volume of fluid in the cell will increase as water continually enters the cell, increasing its turgidity (when pressure inside the cell increases as the volume of its contents increases). Eventually, the cell wall will be stretched to the maximum, achieving full turgor, which will then force water back out of the cell due to the high pressure within the cell. Thus, it is likely that over a long period of time, the water solution will become isotonic: where the water concentration within the cell increases until it is the same as the surrounding solution and water particles move both in and out of the cell, causing the cell to remain the same size.
- Variables
Formula used to measure dependent variable:

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**** An excellent investigation into the effect of osmosis on the potato chips. The introduction gave a good scientific foundation for the investigation and was well laid out with relevant information. The method was very thorough and gave enough detail for the investigation to be repeated. One limitation to the experiment was the independent variable. By choosing time it left the scientific analysis a little basic as osmosis continuing to happen over time is rather obvious. The analysis of the data was excellent. The graphs clearly shown the general trend of the results.