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_An experiment on the effect of surface area to volume ratio on the rate of osmosis of Solanum tuberosum L._
A cell needs to perform diffusion in order to survive. Substances, including water, ions, and molecules that are required for cellular activities, can enter and leave cells by a passive process such as diffusion. Diffusion is random movement of molecules in a net direction from a region of higher concentration to a region of lower concentration order to reach equilibrium. Diffusion does not require any energy input. Diffusion is needed for basic cell functions - for example, in humans, cells obtain oxygen via diffusion from the alveoli of the lungs into the blood and in plants water is obtained through the root hairs via osmosis.[1: http://www.tiem.utk.edu/~gross/bioed/webmodules/diffusion.htm]
Osmosis is a special kind of diffusion that involves water molecules passing through a partially permeable membrane, in this case, the plasma membrane of cells. Cell membranes have tiny holes that allow small molecules to pass through but not larger ones. The rate of osmosis is dependent on many factors - temperature, pressure and surface area to volume ratio, which is being explored in this experiment.
The aim of this biology laboratory experiment is to explore the effect of surface area to volume ratio on the rate of osmosis of tap water of Solanum tuberosum L.
Solanum tuberosum L., also known as potato, was the selected plant to be tested because it was easy to measure the percentage change in mass due to the osmosis of water into the tissue.
How does the surface area to volume ratio of potato tissue (Solanum tuberosum L.) affect the rate of osmosis of tap water?
The smallest cube of potato (1x1x1), having a higher surface area to volume ratio, will have the fastest rate of osmosis. The smallest cube will have a higher rate of osmosis because it has a proportionally larger amount of surface area (cm2) compared to its volume (cm3).
15 raw potatoes (Solanum tuberosum L.)
2.5 liters of tap water
5 x 500ml graduated beakers
Electronic weighing scale
Skin the potatoes using a potato peeler
Using a ruler to measure the length of the sides, cut the potatoes into cubes (5 cubes x 1/1.5/2/2.5/3cm)
Weigh each cube of potato to obtain its mass
Fill each of the 5 beakers with 500ml of tap water
Place 5 cubes of the same side length into a beaker, for every beaker
Start the stopwatch and leave the cubes in water for 20mins
Take the cubes out of the beakers and individually weigh their Mass After
Calculate their percentage increases and find the average
Draw up a table of results
Fig. 1.1 - Step 2 Fig. 1.2 - Step 5
Surface Area to Volume ratio
1 cm sides x 5 cubes
1.5 cm sides x 5 cubes
2 cm sides x 5 cubes
2.5 cm sides x 5 cubes
3 cm sides x 5 cubes
Rate of osmosis
The same volume of water was used per beaker (500ml)
The water used came from the same source
The potato cubes were dropped in the beakers at the same time
The amount of time the potato cubes were left in water (20mins)
Same concentration of minerals/impurities in the tap water
Same concentration of water in the potato tissue
Same batch of potatoes grown from the same farm
The experiment was carried out over twenty minutes instead of a few hours to avoid the concentration of water in the potato tissue and in the surrounding water from reaching its equilibrium, defeating the purpose of finding how the surface area to volume ratio (the manipulated variable) affects the rate of diffusion, and thus the change in mass (the measured variable). It is assumed that the tap water used...
Bibliography: Walpole, Brenda. _Biology for the IB Diploma Second Edition._ United Kingdom: Cambridge University Press, 2014. Print.
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