Bio. Lab. Report – Membrane Transport Essay
Objectives: To study the effects of hypotonic, hypertonic and isotonic solutions on plant and animal cells. Materials and Apparatus: * Microscope * Electronic balance * Stirring rod * Small knife * Glass slide and cover * 250, 500 ml beakers * Distilled water * Cotton * Test tubes * Spatula * Onion * Ethanol (70%) * Filter paper * Table sugar (sucrose) * Table salt (NaCl) * Potato EXPERIMENT 1 PART 1 Procedure: 1. The epidermal layer of an onion is scaled off carefully and placed on a drop of distilled water on the glass slide; 2. The glass slide is slowly lowered down on the epidermal layer using the needle; .
The onion cells are examined through the microscope; 4. The structure of the onion cells is drawn as observed under the microscope. Results & Observations: In the hypotonic solution the water will move from the solution to the onion cells which will become bigger. PART 2 Procedure: 1. The distilled water is removed using the filter paper; 2. A drop of 5% of sucrose solution is placed at a side of the cover slip and the solution across the epidermal layer is drawn by placing filter paper on the other side of the cover slip; 3.
The onion cells are examined once again through microscope. The structure of the onion cells is drawn as observed under the microscope. Results & Observations: In the isotonic solution, there is no difference in the osmolarity, no change in the cells sizes. PART 3 Procedure: 1. Repeat step (1 – 3 of PART 2) using 30% of sucrose solution. Results & Observations: In the hypertonic solution we can notice the shrinking of the cell membrane due to the loose of water. Discussion & Conclusion:
Water will move in or out of the onion cells according to the concentration of sucrose in and out of the onion cells: in an isotonic solution no change will happen; in a hypertonic solution the cells will shrink due to water moving out in order to balance the inner and outer concentration of sucrose. EXPERIMENT 2 Procedure: 1. The potato is sliced into 4 – 6 cm long sticks and 1 cm in diameter. Their initial weights (g) are recorded in 2 decimals places; 2. 4 vials with different salt solutions are prepared: 10% (w/v) NaCl, 3. 5% (w/v) NaCl, 0. 8% (w/v) NaCl, and distilled water; 3. One or two potato sticks are put into each solution. The weights of the potato sticks are recorded again after 20 min. The change in weight (final weight – initial weight) is calculated; 4. The percentage of the water gain or loss is calculated. Results & Observations: Salt conc. (w/v)| Initial wt. of potato sticks (g)| Final wt. of potato sticks (g)| Change in wt. (g)| Change in wt. (%)| Rank relative Water loss or gain| 10% NaCl| 1. 80| 1. 37| -0. 43| -23. 89%| Loss| 3. 5% NaCl| 1. 78| 1. 61| -0. 17| -9. 5%| Loss| 0. 88% NaCl| 1. 82| 2. 04| 0. 22| 12. 09%| Gain| Distilled water| 1. 79| 2. 12| 0. 33| 18. 44%| Gain| Discussion & Conclusion: When the solution is hypotonic water will diffuse into the potato sticks and so they will gain weight. When we use a hypertonic solution, the water contained in the potato sticks will diffuse out and cause the potato sticks to lose weight as they lose water. With 6 six different strips being out into 6 different solutions of different concentration, it will lead us to find the isotonic solution for the potato slices.
In an isotonic solution, there will not be any change in the potato sticks’ weight. EXPERIMENT 3 Procedure: 1. Test tubes are labelled with A, B, and C; 2. The test tubes are filled with 5 ml of distilled water, 4. 0% (w/v) NaCl and 0. 85% (w/v) NaCl, respectively; 3. A drop of blood is added into each test tube and they are left for 5 min. ; 4. A drop of each solution is examined under the microscope. Results & Observations: Hypotonic solution| Hypertonic solution| Isotonic Solution| Distilled water| 4. % (w/v) NaCl solution| 0. 85% (w/v) NaCl solution| | | | | Discussion: The picture below shows how normal red blood cells look like: The first solution used is distilled water which is a hypotonic solution. In this situation, water will diffuse into the red blood cells causing them to expand and be round (as shown in the above results) and sometimes they may rapture as shown in the picture below: In a hypertonic solution, the red blood cells will shrink and be destroyed, as water diffuse out of them.
Finally, in an isotonic solution there will not be any change in the shape of the red blood cells as there is no net movement of water in or out of the red blood cells. Conclusion: Type of Solution| Description| Examples| Effects on cell. | Isotonic| Has the same concentration of dissolved substances as the fluid in the cell. | 0. 85% salt (normal saline); 5% dextrose (glucose)| None; cell in equilibrium with its environment. | Hypotonic| Has a lower concentration of dissolved substances than the fluid in the cell. | Less than 0. 5% salt or 5% dextrose| Cell takes in water, swells, and may burst; red blood cell undergoes haemolysis. | Hypertonic| Has a higher concentration of dissolved substances than the fluid in the cell| Higher than 0. 9% salt or 5% dextrose| Cell will lose water and shrink; cell undergoes crenation| | | | | References: 1. http://movementofsubstances. blogspot. com/2011/02/32-movement-of-substance-across-plasma. html 2. http://internalandexternalenvironments2012. wikispaces. com/Hypertonic,+hypotonic+and+isotonic+effects+on+plants+and+animal+cells.