DAIS
Osmosis & Potato Strips
Investigating the Effect of Sodium Chloride (NaCl) Solution Concentration on Potato Strips
Assessment Criteria:
Skill C1: Using and organizing techniques, apparatus and materials;
Skill C2: Observing, measuring and recording;
Skill C3: Handling experimental observations and data.
Background Information:
Osmosis is the diffusion of water molecules through a partially permeable membrane from a
region of high water potential to a region of low water potential until the water potential is equal
on both sides of partially permeable membrane (Jones 2010). Osmosis occurs in all plant and
animals cell. It is useful in processes such as: absorption of water along the alimentary canal;
re-absorption of water in the kidney and absorption of water into the root hair cells (Gareth
Williams 2009).
When potato cylinders are put in NaCl solution, cells will either take in water or lose water by
osmosis depending on water potential of the NaCl solution in which they are put in. When
potato cells absorb water by osmosis, they will swell up, become firm, heavier and bigger in size
but they will not burst because the cell membrane is surrounding by a cell wall. The cells will
become turgid (Jackie Clegg 2006). On the other hand, when a potato cells lose water by
osmosis, they shrink and become flaccid i.e. they lose the firmness they had.
Task: In this lab you will be investigating the effect of NaCl solution concentration on the length
of potato cylinders. Based on the results obtained, you can determine which NaCl concentration
is isotonic the cytoplasm of potato cells.
Materials and apparatus:
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1X 5 mm diameter cork borer,
1X 3 large Irish potato,
1X1 scalpel blade,
1X1white tile,
50 ml of: 0.0 mol dm–3; 0.1 mol dm–3; 0.2 mol dm–3; 0.3 mol dm–3 & 0.4 mol dm–3 NaCl
solution.
1X1transparent ruler,
1X 10 paper towels,
1X5 Petri-dishes,
1X10ml measuring cylinder
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DAIS
Osmosis & Potato Strips
Safety: Take care when using a sharp blade to cut the potato cylinders!
Procedure:
1.
You are provided with raw potatoes cylinders of uniform diameter;
2.
Using a scalpel blade accurately cut potato strips of the same lengths. Record this
length;
3.
Take five boiling tubes and label them A, B, C, D and E;
4.
Accurately measure equal volumes of sodium chloride solutions provided into each of
the boiling tubes labelled in (3) above. Record the concentrations of sodium chloride
solutions accordingly;
5.
Place three potato strips into each boiling tube, ensuring that they are completely coved
by sodium chloride solution (Jones 2010). Leave the set-up till the next biology lesson;
6.
Systematically remove the potato strips from the respective solutions, blot them using
the tissue paper prided, measure them and record their length;
7.
Make all necessary qualitative observations and record them;
8.
Process your data as fully as possible, present the processed data using a suitable
method and make your conclusion based on the results obtained.
References:
Gareth Williams, Richard Fosbery and Janet Adams. Biology for Cambridge IGCSE.
Cheltenham: Nelson Thornes Ltd, 2009.
Jackie Clegg, Gareth Price and Mike Smith. Camridge IGCSE Biology. London: Collins, 2006.
Jones, Mary Jones and Geoff. IGCSE Biology Coursebook. Cambridge: Cambridge University
Press, 2010.
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