Essay about Diffusion : Science

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Jhosias Duran 11/26/11
Class 1H5 Lab Report

Title :
Diffusion through a membrane State Lab .

Question :
How does starch and glucose move through a membrane ?

Hypothesis :
Starch and glucose can move out of the cell

Materials :

Dialysis Tubing
Dental Floss
(Benedict's) Glucose Indicator Solution (Lugol's) Starch Indicator Solution (containing Iodine)
Test Tube Rack
7 Test Tubes
Tap Water
Concentrated Glucose Solution
Starch Solution
Test Tube Holder
Hot Water Bath
Paper Towel

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