To investigate the effects of using different concentration of Sucrose solutions in Osmosis with a cucumber

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*Planning*

Introduction

Throughout this experiment I shall be investigating how different solution concentrations can affect osmosis. For this I have chosen to use sucrose solution, and cucumbers.

Diffusion is the movement of a substance through a fluid (i.e. liquid or gas). In a solution, diffusion happens when there is a higher concentration of a substance in one part of the solution than in another. It spreads until the concentration is the same  throughout the solution.  

Osmosis is the diffusion of water from an area of low concentration (i.e. high concentration of water) to an area of high concentration through a selectively permeable membrane.

In both plant and animal cells water can pass through but in the latter there is no cell wall to keep the cell from bursting. So if the water concentration is higher outside the cell, then water will pass until the cell bursts. (Unless a stable point is reached before). However in plant cells, the cell wall, which is entirely permeable and very strong, can keep the cell from bursting.

Turgor and plasmolysis. These are the two different “states” in which a cell can be left if it’s concentration within is not the same as outside. (Note, animal cells can go flaccid but not turgid, they burst instead). Flaccid means “floppy” and turgid means “hard” or “stiff”.

Diagram

Plan

        

Apparatus

  • Petri dishes (x10)
  • Cucumber slicer
  • Cucumber
  • Sucrose solution (1M)
  • Water
  • Balance
  • Filter paper
  • Measuring cylinder

Method

The Petri dishes will be lined up on the table in two rows of five. The second row is the one in which the repeats shall be done. Then the 1M sucrose solution shall be diluted into 0.75, 0.5  and 0.25 M. 20cm3 of the solutions shall be placed in the appropriate dish (as shown in  the diagram).

Then the cucumber shall be cut up using the slicer into ten equal pieces. These shall then have their mass recorded, one by one, and keeping track of which slice is which placed in the Petri dishes and left there for 20 minutes. This will ensure that the test is fair.

After the twenty minutes the pieces shall be quickly removed, and dabbed on the filter paper to remove the water on the surface, then re-massed and weight recorded.

Variables

Time ………………………. Controlled Variable

Concentration …………. Independent Variable

Mass of slice …………… Controlled Variable

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Volume of solution…… Controlled Variable

Surface area of the slice and volume ratio ……..(see evaluation)

Safety

There are no major safety issues regarding this experiment except that the teacher will be making the cucumber slices to avoid accidents.

Diagram

*Distilled Water.

Hypotheses and predictions

From the evidence shown in my introduction it was seen that:

  • Water will move across the semi permeable membrane leaving it’s solute behind to find a balance in concentration, and
  • Bigger molecules such as ...

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