Salt and Water Balance Experiment

Introduction

Salt and water balance is essential for the survival of any cell. The cell membrane helps maintain this balance through a process called diffusion. Diffusion is defined as: “The passive movement of molecules or particles along a concentration gradient, or from regions of higher to regions of lower concentration.” (Biology Online, 2008) The cell membrane is semi-permeable, allowing certain materials to pass through easily and others not at all. There are two types of transport that occurs in cells: Passive Transport and Active Transport. Passive transport moves molecules with the concentration gradient; however Active transport moves molecules against the gradient, using energy to achieve this. (Active and Passive Transport, 2014) Molecules have thermal energy due to their constant motion, which can be a result of diffusion. The main aim for molecules is to be at equilibrium. Factors that affect this include temperature, pressure and concentration of the internal and external environments. (Reece et al. 2012)

Objectives

This experiment will be conducted to investigate and analyse the regulation of water and solute balance in cell like structures. The process of diffusion will be investigated thoroughly.

Materials

Part A

• Dialysis tubing
• Beakers
• Distilled Water
• 0.5M NaCl
• 1.0M Glucose
• 0.5M Lactose
• 1.0M Lactose
• Starch Suspension
• Scales
• Ruler
• Funnel
• Paper Towels
• Silver Nitrate
• Benedict’s solution
• Potassium Iodide-Iodine
• Stop watch
• Test Tubes

Part B

• Razor Blade
• An Onion
• Distilled Water
• Slide
• Coverslip
• Microscope
• 1.0M Mannitol

Method

Part A

Full details are given in Dearnaley and Kennedy (2014).

1. The materials were collected.
2. A piece of dialysis tube was obtained, and one end was tied tightly.
3. A funnel was inserted into the open end, and 15mL of the selected solution of either: Distilled Water (Control), 0.5M NaCl, 1.0M Glucose, 0.5M Lactose, 1.0M Lactose or Starch Suspension, was poured in.
4. The tube was tied off leaving as little air as possible inside.
5. The knots were adjusted so the length between both knots was approximately 15cm. This was measured using a ruler.
6. The tube was rinsed with distilled water.
7. The tube was dried with a paper towel and checked for leaks.
8. The tube was weighed and the weight was recorded.
9. 250 ml of distilled water was placed in a tray.
10. The tube was placed in the tray and a stop watch was started.
11. At the times of 5, 10, 15, 30 and 60 minutes, the tube was removed from the tray, dried, and then weighed. This was repeated for every said solution and the results were documented.
12. The cumulative change, which is the difference between the starting weight and the weight at a particular interval, was calculated.
13. The remaining fluid in the tray as well as the original solute was tested with the following tests:

1. Chloride Test

1. Two drops of Silver Nitrate was added to the test tubes.
2. A white-grey precipitate would indicate the presence of Chloride.

1. Glucose and Lactose test

1. 1mL of Benedict’s reagent was added to the test tubes.
2. The tubes were placed in a boiling water bath for 30 seconds.
3. A colour change from blue to yellow, greenish-yellow or orange would indicate the presence of Glucose or Lactose.

1. Starch Test

1. Several drops of potassium iodide-iodine solution was added to the test tubes.
2. A blue-black colour would indicate the presence of starch.

1. The experiment could be re-conducted if any unexpected results presented themselves.

Part B

1. The materials were collected.
2. A razor blade was used to peel off a thin layer of the onion.
3. The thin layer of onion was placed on a slide, along with a drop of distilled water.
4. Using the microscope, a small section of the onion cells were drawn.
5. The slide was flooded with the 1.0M Mannitol solution.
6. After waiting 5 to 10 minutes, the slide was observed under the microscope again and if possible the same area was drawn again.
7. The slide was then flooded with distilled water.
8. After waiting 5 to 10 minutes, the slide was again observed under the microscope and the same area was drawn.

Bibliography

1. Reece J.B., Meyers N., Urry L.A., Cain M.L, Wasserman S.A., Minorsky P.V., Jackson R.B., Cooke B.N. (2012). Cambell Biology. 9th edition, Australian version, Pearson Publishing Australia.
2. Dearnaley, J.D.W. and Kennedy U. (2014) Biology 1. Practical notes and Excercises. University of Southern Queensland.
3. Biology Online, (2008), ‘Diffusion’, http://www.biology-online.org/dictionary/Diffusion (15/04/14)
4. Active and Passive Transport,  (2012), http://www.diffen.com/difference/Active_Transport_vs_Passive_Transport (16/04/2014)

Appendix

Raw Table 1.1: Raw data of diffusion experiment