Potato cylinders

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Potato cylinders

The variable I am going to change is the sugar concentration.

Prediction

I think that the potato cylinder will get shorter if the sugar concentration is increased.

This will happen because of osmosis, osmosis is the movement of a liquid through a cell membrane from a lower to a higher concentration.

The water in the potato is a lower density than the sugar solution, therefore when the water exits the potato through the membranes the potato will gradually shrink.

A diagram to show osmosis

Water =

Sugar =

The water molecules can pass through the gaps but the sugar particles cannot fit through. The water molecules are passing through to the left-hand side to balance the quantities.

Further information on potato plant cells:

Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what makes the green parts of the plant "stand up" into the sunlight.

When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid." This is the exact opposite of "turgid". The contents of the potato cells shrinks and pulls away from the cell wall. These cells are said to be plasmolysed.

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When plant cells are placed in a solution, which has exactly the same osmotic strength as the cells, they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. "Incipient" means, "about to be".

Variables:

  • To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed. I have chosen to vary the concentration of the sugar solution. This will give me a vary varied set of results from which I hope to make a decent conclusion. If any of the non-variables below ...

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***This is a nicely presented piece of work but it needed to be organized more carefully to enable the reader to follow the experimental plan. The recording of results was confused and the data analysis was weak. There was no evaluation or background research to help inform the plan. To improve: Planning: The candidate decided for themselves factors such as the range, interval and number of repeat readings that they should take, and the variables that needed to be controlled, but key statements such as the name of the sugar to be used were omitted in some sections. The candidate should ensure that all details are recorded so that someone else could carry out their plan without asking for further information. The candidate should independently research their experiment and include background references to help inform the plan and carry out a more thorough risk assessment. Carrying out: The student appears to have collected some sensible data but needs to ensure that all data in tables has the correct heading and units. There were several other data tables included with no indication as to what they refer to. Analysis and Evaluation: The candidate did link their results to the prediction but did not explain them fully using relevant background theory. The analysis was confused by references to other results of unknown source. The candidate referred to using percentage change in length to analyse the data which is a good idea but these calculations or graphs using these figures were not in evidence. They need to evaluate the method of collection and the quality of the resulting data and analyse further secondary data drawn from the same topic area as their investigation.