what is the dependent and independt variable for this prac? biology*

Question

Osmosis & Diffusion Lab – Dialysis Tubing

 

Introduction

The movement of molecules through a cell membrane is termed osmosis or diffusion. Such movement is principally possible because nutritive molecules are smaller than membrane micro pores. If the molecules are too large, no molecular transfer, or diffusion occurs.

Thus, some membranes may transmit selectively and are termed semi-permeable membranes. In the following experiment, cellophane dialysis tubing serves as an excellent representation of the cell membrane. The enclosed tube may, for the purpose of this experiment, be considered a single living cell in greatly enlarged form.

Materials

1. Glucose Solution,
2. Starch Solution,
3. Iodine Solution,
4. Glucose Test Strips,
5. Dialysis Tubing,
6. String,
7. 400 ml Beaker,
8. 10 mL Graduated Cylinder,
9. Scissors,
10. Ruler

 

Method

1.                 Measure and cut 20 cm of dialysis tubing.

2.                 Place this tubing in a beaker and cover it with water. Allow it to soak for about five minutes.

3.                 Remove the tubing from the water and rub one of the ends between your thumb and pointer finger to open. Once open, submerge it in water again for about thirty seconds.

4.                 Tie one end of the tubing in an overhand knot

5.                 Measure 5 ml of starch solution using the 10 ml graduated cylinder and pour it into the tube.

6.                 Thoroughly rinse the graduated cylinder, shake dry, and measure 5 ml of glucose solution. Pour this into the tubing as well.

7.                 Tie the second end of the tubing in an overhand knot and rinse it under the tap. Set your “cell” on a clean surface.

8.                 Fill the 400 ml beaker ¾ full with tap water. Add 10 drops of Iodine solution and stir well.  (Iodine will turn blue-black in the presence of starch).

9.                 Test the solution in the beaker for the presence of glucose by dipping a glucose test strip into it. After 30 seconds, compare the color on the strip to the color chart on the side of the bottle. Complete the Initial Status information on your data table.

10.             Place the artificial cell (the sealed tubing with solutions) into the beaker of solution and allow it to remain undisturbed for 15-20 minutes.

11.             Remove the tubing from the beaker and record your observations in the data table for final status of the solution and the bag.

12.             Retest the solution in the beaker and in the bag with a new glucose test strip and record this data

Answer 1

A good way to look at is to ask yourself: is the study asking if X depends on Y, or if Y depends on X?

In this way of laying it out, the variable on the left of "depends" is the dependent, and the one on the right is the independent. In this case, that would look like:

A) The study is asking if the membrane micro pore size depends on molecule osmosis ability

or

B) The study is asking if molecule osmosis ability depends on membrane micro pore size

When you lay it out like that, it can become much clearer to see which is the independent and which is the dependent variable- often when you say it one way it doesn't biologically make sense, or just doesn't make sense in general!

Give it a shot- which one do you think it is having seen it from this perspective?

If you guess B), yep! Molecule osmosis ability is the dependent variable, and membrane micro pore size is the independent.