Class 1H5 Lab Report
Diffusion through a membrane State Lab .
How does starch and glucose move through a membrane ?
Starch and glucose can move out of the cell
(Benedict's) Glucose Indicator Solution (Lugol's) Starch Indicator Solution (containing Iodine)
Test Tube Rack
7 Test Tubes
Concentrated Glucose Solution
Test Tube Holder
Hot Water Bath
Introduction : The "Diffusion Through A Membrane" Lab covered many topics
dealing with diffusion, cells, and molecules. Diffusion is the movement of molecules
from an area of greater concentration (where there is more of the molecule) to an area of
lesser concentration (where there is less of that molecule). They will continue to do so,
until the molecules have reached a state of equilibrium, meaning that both areas are
balanced with the same amount of molecules. (1) Diffusion of molecules in cells occurs
through a membrane, which is a layer between the cell wall and the contents of the cell
containing pores. Cell membranes are selectively permeable, meaning that it allows some
materials/molecules to pass through it, and others are not. (2) Whether molecules are able
to pass through the membrane depends on the size of the molecules (smaller ones can,
and larger ones cannot). Part 1 of the lab focused on this type of diffusion, and required
us to create our own model cells(pouring starch and glucose in tied dialysis tubing) , so
we could test which substances would diffuse through a membrane(the ones with smaller
molecules) and which ones couldn't(and therefore, the larger molecules.) We tested
which molecules diffused with starch indicator solution (called Lugol's Iodine) and
Glucose Indicator Strips. When starch indicator solution comes into contact with starch, it
turns black, and when Glucose Strips turn green, it shows the liquid contains glucose.
These tests would help us to figure out what had diffused where. For this investigation, I
hypothesized that the cell would become amber colored, because the iodine solution
would diffuse into it (I did not yet know that when Starch Indicator solution mixes with starch the product turns black). I also predicted that the water outside the cell would get
cloudy from some starch diffusing through (This was an incorrect prediction.. .see results
for actual outcome). Osmosis, which was the main focus of the second part of the lab, is
defamed as "division of water across a membrane." It has to do with cells maintaining
balance in the amount of water that is inside them, in order for them to properly function.
In cells, water and solutes (which are dissolved substances that extract water from a cell)
diffuse in and out of the cell to make sure there is an equal amount of water and solute on
each side, so the cell will remain healthy. (3) A cell needs enough water so it doesn't
dehydrate, but at the same time, it needs solutes as well so it doesn't swell and explode.
In this part, we saw the effect of salt (a solute) on the cell and the amount of water in the
cell, by looking at onion skin cells with distilled (pure) water and then salt solution water.
Another part of this lab was chemical testing, which was discovering how indicator
solutions work. This was done by a series of mixing tests in test tubes. We used indicator
solutions to prove that when a substance mixes with its indicator solution, a reaction
happens and will show a (color) change, alerting you of the presence of the tested
substance. When an