Find out if different strengths of solutions affect the rate of osmosis and try to and establish the strength of solution inside the potato cells.

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GCSE Biology Investigation

OSMOSIS IN POTATOES

Task: Using your knowledge of osmosis from previous experimental work, find out how different strengths of solutions affect the process of osmosis

Aim: To find out if different strengths of solutions affect the rate of osmosis and try to and establish the strength of solution inside the potato cells.

Predictions:

 

  • Potato placed in distilled water will become turgid, increasing in size and weight as a result of osmosis
  • Potato placed in a concentrated sucrose solution will become flaccid, decreasing in size and weight as a result of osmosis
  • Potato placed in the same strength solution as inside the potato will remain the same size and weight

My predictions are supported by my findings in previous experiments; raisins in a weaker solution swelled and increased in weight, those in the same strength solution stayed the same and those in a stronger solution decreased in size and weight. From this background knowledge and subsequent predictions, I can now put forward a hypothesis and plan a reliable experiment to support my thoughts on osmosis.

Hypothesis: In my experiment, I will use potato cut into cylinders using a cork borer therefore…

  1. The cylinders in water will grow in size, weight and become turgid
  2. Those in a stronger solution will decrease in size and weight and will become flaccid
  3. The cylinders in a same strength solution (relative to that inside the potato) will stay the same size and weight
  4. The cylinders in a weaker solution, as those in water, will grow in size and weight.

Background Knowledge:

Definition of Osmosis:         Osmosis is the movement of water molecules from a weak solution to a strong solution                 through a selectively permeable membrane. (Water molecules placed in a weak         solution will pass through a membrane that allows through small particles to a strong         solution)

  • A weak solution has a high solvent concentration and a low solute concentration
  • A strong solution has a low solvent concentration and a high solute concentration

A selectively permeable membrane is like a sieve, which allows solvent molecules to pass through it, but prevents larger molecules dissolved in the solvent from passing through. If a selectively permeable membrane separates two solutions of different concentrations, then solvent molecules pass through the membrane from the side of lesser concentration to the side of greater concentration. This tends to equalise the concentrations on the each side of the membrane.

Other experiments of osmosis: -

        

Osmosis is of great importance in many processes that occur in animas and plants, examples being the intake of water by the hairs on the plant roots and the production of urine in the kidney. For example, if red blood cells that are normally found in blood plasma are placed in pure water, then the cell walls allow the water to diffuse inwards and the cells swell and eventually burst. The turgidity of plant cells is due to their maintaining a difference in pressure across their cell walls. Water enters their concentrated cell contents and effectively 'inflates' the cell. For an example, raisins can be placed in water for twenty-four hours. At the start the raisins are shrivelled and small but after twenty-four hours, they will be soft, larger in size and turgid, proving that the skin of a raisin is partially permeable and that osmosis has taken place. Therefore, the solution inside the raisin is placed outside of it. However, if the raisin in placed in a stronger solution, such as a sucrose solution, water molecules from inside the raisin pass through the partially permeable membrane to the solution outside, leaving the raisin smaller than originally. When the raisin is placed in water it becomes turgid and when its placed in sucrose solution, it becomes flaccid. This similarly happened with potato. From this knowledge I can predict the following.

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Diagram:

        

Apparatus:

  • Distilled water.
  • Sugar solution in these strengths (measured in molar concentrations) 0.1, 0.2, 0.3, 0.4, 0.5
  • Potato and a cork borer
  • 6 plastic Petri dishes
  • Ruler
  • Tile and Knife
  • Clingfilm (to prevent evaporation)
  • Sticky Labels

Preliminary method: 

When doing this experiment, I intend to…

  1. Take a potato and using the cork borer, cut out twelve potato cylinders
  2. Then cut these cylinders into the same size of preferably 4cm in length on a tile using a knife
  3. Take two cylinders and allocate them to each plastic dish and ...

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