Ccea as Biology Coursework: an Investigation to Find the Water Potential of Potato and Carrot Tubers in a Sucrose Solution over a 24 Hour Period

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An investigation to find the water potential of potato and carrot tubers in a sucrose solution, of concentration 0.00 – 0.50Mol, over a 24 hour period

Interpretation

Written Communication
C1

From our graph it can be seen that the concentration of sucrose solution is 0.18 M at 0% change in mass for the potato and 0.355 M at 0% change in mass for the carrot. I will use these values to find the solute potential by using the calibration graph. I will work out the water potential by using the equation, Ψ=Ψs +Ψp (Water Potential = Solute Potential + Pressure Potential). The Ψs of the potato at 0% change in mass is -500 kPa and the Ψs of the carrot at 0% change in mass is -1000 kPa. Through the use of our equation, the water potential of the potato and carrot are -500 kPa and -1000 kPa (respectfully) as in this case the solute potential equals the water potential as there is no pressure potential as the solution is open and it isn’t under a membrane so it is not under pressure. The Water Potential (Ψ) of the solution is equal to the Ψ of the tuber as there is no pressure potential.

C2 and C3

As the concentration of the sucrose solution increases, the average percentage change in mass decreases in the potato tubers and this is the same as in the carrot tubers. At low concentrations of sucrose solutions (0.1 M) the mass of the carrot and potato tubers increases due to water moving into the protoplast of the cell from the sucrose solution by osmosis and at high concentrations of sucrose solutions (0.5 M) the mass of the carrot and potato tubers decreases due to water moving out of the protoplast of the cell to the sucrose solution by osmosis. At certain concentrations (0.18 M of the potato and 0.355 M for the carrot) the potato and carrot tubers don’t change in mass due to the water potential inside the cells equalling the water potential of the sucrose solution. My graph displays a distinct negative correlation; the higher the concentration of sucrose solution, the larger the difference between the mass over the 24 hour period becomes, and the smaller the mass gets. Osmosis is the movement of water from a high water potential to a low water potential across a semi-permeable membrane.

C4 and C5

Osmosis is the net movement of water particles from areas of high water potential to areas of lower water potential across a semi-permeable membrane, such as the cell membrane. This can also be described as moving down a concentration gradient.

The water potential of a substance measures the amount of free energy that is available in an aqueous solution to cause the migration of water molecules during osmosis. The symbol for water potential is Ψ and is measured in kPa (kilo-pascals). The water potential of pure water is zero, as all the particles are free; this means that all particles contain kinetic energy and are under attractive forces, so they in constant random movement.

In relation to my results, at concentration 0.18M for the potato and 0.355M for the carrot, there is an osmotic balance between the potato and carrot cells and sucrose solution – the water potentials are equal. This is also known as an isotonic solution – where equilibrium is reached between the rates of osmosis in and out of a solution. Above this value, the solution becomes hypertonic (having a higher solute concentration than the potato and carrot), while below this value, the sucrose solution becomes hypotonic (having a lower solute concentration than the potato and carrot).

A hypertonic solution has a higher concentration of solutes compared to another solution, while a hypotonic solution has a lower concentration of solutes compared to another solution. An isotonic solution has an identical concentration of solutes as another solution. These can also be described as having a lower, identical, and higher osmotic pressure, respectfully, than another solution.

I noticed that the hypertonic potato and carrot had become soft and...
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