D2.3 - measuring the impact of osmosis (3j)

Question 1

how can you investigate changes due to water movement in plant tissue bathed in hypotonic and those bathed in hypertonic solutions?

Answer 1

1. using a white tile and sharp knife, trim 30 potato chips, of equal diameter, to the same length
2. pour six different concentrations of sugar into five small beakers each, and label the beakers
3. measure the initial mass of each potato chip using a balance, and record this
4. place the potato chips into the beakers containing the corresponding solution, cover the beakers and leave for 60 minutes
5. remove the potato chips from the solutions and place on a paper towel to remove the excess solution
6. measure the final mass of each potato chip

Question 2

how can you analyse the data to deduce isotonic solute?

Answer 2

1. calculate percentage mass change for each chip, to account for the different initial masses
2. calculate the mean percentage change in potato mass at each concentration
3. plot a graph of sugar concentration against mean percentage mass change of potato
   - depending on the range of concentrations chosen, the line of best fit may be straight or curved
4. use (a) standard deviation and (b) standard error to compare the reliability of the measurements; the larger the values the more variation in the data and so the less reliable the measurements

• the isotonic solution is where the concentration meets the x-axis

Question 3

how can percentage mass be used to determine osmolarity of a solution?

Answer 3

percentage mass change allows for the determination of relative osmolarity

• there will be no percentage mass change when the tissue is placed in an isotonic solution
• there will be a positive percentage mass change when the tissue is placed in an hypotonic solution, as water moves into cells
• there will be a negative percentage mass change when the tissue is placed in an hypertonic solution, as water moves out of cells