Osmosis required practical

percentage change in mass = ((mass at end - mass at start ) ÷ mass at start ) x 100 this allows the data to be COMPARATIVE as they all have different starting masses EXPLANATION: -Percentage change is used because the potato pieces start with different masses, so it allows a fair comparison between samples. Why not just use mass change (final − start)? Because potato pieces don’t all start the same size/mass. Example: Potato A: starts at 2 g, gains 0.2 g Potato B: starts at 10 g, gains 0.2 g Using mass change: Both changed by +0.2 g, so they look the same. But actually: A gained 10% of its mass B gained only 2% So the effect of osmosis was much bigger in A, but you wouldn’t see that with just grams.

when the outside solution was more dilute than the inside of the potato -water moved into the potato by osmosis (In exam answer include which has higher / lower water concentration) I would say: The potato chip gained mass when when it was placed in a less concentrated solution than the cell contents . This is because the water moved from the the higher water potential in the surrounding solution to a lower water potential inside the potato ( the cell took up water by osmosis)

when the outside solution was more concentrated than the inside of the potato -water moved out of the potato by osmosis (In exam answer include which has higher / lower water concentration) I would say: The potato chip lost mass when when it was placed in a more concentrated solution than the cell contents . This is because the water moved from the the higher water potential in the potato to a lower water potential in the surrounding solution ( the cell lost water by osmosis)

when the outside of the potato had the same water concentration as inside the potato -no NET movement of water I would say : when the surrounding solution had the same water potential as the inside of the potato , this meant there was no net movement of water . The mass remained the same

• covers at least 50 % -labelled y -axis with units -labelled x- axis with units -correct line of best fit (2 either side)

in case the movement of water through the skin is at a different rate than through freshly cut potato

-in the dilute solutions the potato chips are drawing water in by osmosis as their cells contents are more concentrated than the outside solution (increase in mass) -in more concentrated (less water) solutions ,the potato chips lose water by osmosis as their cell contents are less concentrated than the outside solution (decrease in mass) -at one concentration the cell contents are in equilibrium with the outside solution and so there will be no change in mass of the potato chip / at one concentration the concentration of the solution and inside the potato will be in equilibrium, there will be no NET movement of water so there will be no change in mass (NOTE : in exams refer to water potential ) e.g. When the potato chip is placed in a more dilute / less concentrated solution , the surrounding solution has a higher water potential than the inside of the potato , the potato CELL takes up water by osmosis and there is an increase in mass of the potato chip

so that we are sure that we are measuring change in mass of the potato chips (and it isn’t heavier due to excess liquid)

it is the same as (the concentration of ) the solution with NO change in mass me: (the concentration of the cell contents of the potato is the same as the concentration of the solution in which there was no change in mass)