Osmosis Internal Assessment (Biology)
BIOLOGY INTERNAL ASSESSMENT STANDARD LEVEL OSMOSIS OSMOSIS IN POTATO STRIPS i. 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. ii. 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? iii. 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.1 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.2 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 0.3 This would mean that the distilled water is hypotonic whereby it has a higher concentration of water than the potato cells,
Investigating the relationship between cell size and rate of diffusion
Investigating the relationship between cell size and rate of diffusion Aim: To plan and carry out an investigation to show the relationship between volume, surface area, and diffusion; and to demonstrate, using diffusion, why the size of cells is limited. Hypothesis: In this experiment, I expect to find that when the surface area to volume of a cell reaches a certain level, diffusion alone won't be able to supply the cell materials needed, and as single-celled organisms take in and release substances by means of diffusion across the cell membrane, this process limits cell size. I predict that as the rate of diffusion will be too slow to deliver materials to the center of the cell in the larger cells, it could result in cell malfunction. Variables: In this investigation, the variable I am manipulating, the independent variable are the dimensions of surface area to volume ratio of the agar cube. The variable I am observing/recording, the dependent variable, is the rate of diffusion (NaOH turns the agar cube pink as it disperses into it). The controlled variables will be keeping the concentrations of the Sodium Hydroxide constant, to use agar jelly from the same batch (so the type of agar jelly is exactly the same), and to keep the time even for all cubes so the NaOH has the same amount of time to disperse into the cube. Apparatus: 3 agar cubes containing pH indicator
