osmosis practical Flashcards
(14 cards)
detailed method
-label six boiling tubes at 0, 0.2, 0.4, 0.6, 0.8 and 1.0 dm-3 sucrose
-use the 1.0dm-3 sucrose solution and water to make up 20cm3 of sucrose solution of each of the following concentrations: 0.2moldm-3 0.4moldm-3 etc
-stand the boiling tubes containing the sucrose solutions in a water bath set at 30 degrees. use a thermometer to check the temperature in all tubes reach 30 degrees
-using a chipper, cut six chips from your potato tuber, remove any peel from the potato, use a ruler, scalpel and tile to cut all chips to same length
-blot the potato chips dry with a paper towel, do not squeeze
-place them on paper towels numbered the same way as the boiling tubes
-weigh each potato chip, record initial masses in suitable table
-place potato chip in its correct boiling tube
-after around 20 minutes, remove the chips from the boiling tubes
-blot the chips dry then reweigh them
-record final masses
-calculate change in mass and percentage change
-plot a graph of processed data and use this to determine the concentration of sucrose which has the same water potential as the potato tuber cells
what can be used to cut the potato
cork borer
why are they cut the same length
so they have the same surface area for osmosis
what should be the same about the solutions we are testing
volume of solution
what is the solute and solvent
solute is sucrose
solvent is water
what are the control variables
time in solution, volume of solution and surface area of potato
what potato do we expect to increase and decrease in mass the most
the one with the lowest sucrose concentration will increase in mass the most
opposite for one w highest sucrose conc
why is measuring the mass of a chip more effective than the length
length only shows one dimension
chips may increase in thickness not length
in tube one with no sucrose solution, why does the mass increase dramatically
water potential of solution is larger than inside the potato
water enters cells by osmosis
increasing mass
in tube 6 with only sucrose solution, why does the mass decrease dramatically
water potential of solution lower than inside potato
water leaves cells by osmosis
decreasing mass
why is it important the chips were from the same potato
cells that are genetically identical have similar water potential in the same environments
how would the potato skin have affected osmosis
it is different tissue which is impermeable to water and has different water potential so would not demonstrate osmosis
why is it necessary to calculate a percentage change in mass
standardized comparison in mass, even if initial masses were different. easy to compare and contrast
