(EXTRACTED FROM “THE SCIENCE COORDINATION GROUP”-“REVISION GUIDE FOR GCSE DOUBLE SCIENCE-BIOLOGY” AND “WORLD BOOK 1999”)
VARIABLES
Factors, which can be altered:
- Temperature of the water
- Volume of water in beaker
- Type of potato
- Size of potato
- Whether I am going to use a sugar or salt based solution
MEASUREMENTS AND OBSERVATIONS
Points I could record:
- The amount of water in beaker
- The time it takes for sugar solution to fully with potato cells.
- Concentration of sugar
- Size and weight of potato before and after diluting it in the solution
- Area of potato
FAIR TESTING
I am going to use the same potato borer each time-number 6 so the diameter of the potato is kept the same each time.
The length is also going to be kept the same; I am going to keep it at 4-cm/40 mm each time.
SAFETY
To make my experiment safe I will have to put away my bag under the table so I don’t trip over whilst working, I will also be careful whilst using the scalpel as they can be quite sharp and dangerous.
MY PREDICTION
I predict that the higher the concentration of the sugar in the sugar liquid, the lighter the potato will be. The size of the potato will decrease. I think this will happen because in pure water-with no added sugar the potato tubes will gain more water because their sugar levels be high, so more water will be required to level out the sugar and water in the potato and water cell. However in a rich sugar solution the potato tubes get smaller because the concentration of the sugar solution is high on the outside so the water leaves their cells, this is due to osmosis.
This diagram shows us a part of the potato cell, and how osmosis occurs. There are more sugar particles on the outside so the water has to mix with it so there is an equal amount of sugar and water on both sides of the cell-in the solution and in the potato cell. However, if there were more sugar particles on the inside the water would have to go into the cell for osmosis to occur. The weight of the potato segments will differ at the start and at the end. This will be because the potato will either gain or lose water, according to the amount of sugar in the potato cells.
EQUIPMENT
- Potato(s)
- Potato Borer
- Scalpel
- Pure water
- Sugar solutions- 5%, 10%, 15%, 20% and 25% sugar in 100 ml of water
- Beaker(s)
- Ruler to measure length of potato
METHOD
- Using the potato borer-no. 6, cut through a potato to create 30 equal length- 4 mm potato fragments. Weigh all five pieces together and work out average.
- Pour each of the five 100 ml of sugar solution into separate beakers.
- Place five pieces of potato's into the beakers
- Leave for 30 mins before taking out each piece carefully out of the solution and gently patting it dry.
- Measure length and weigh all pieces together-again work out an average.
TABLE OF RESULTS
From the table I can see that as the concentration of the sugar in the beaker increases the average lengths of the potato pieces left in that solution for 30 mins decreases but as the concentration decreases the length increases. I can also see that between 10g and 15g at 13g the result could be 0, this would be because the sugar levels in both the potato and the solution would be the same, therefore there would be no movement of particles. I did 5 tests so I could work out a reliable average.
