required practical 3:production of a dilution series

Question 1

what does the y-intercept of a graph plotted sucrose conc. against change in mass (%) indicate?

Answer 1

• the point of no osmosis (on x-axis after drawing a line of best fit)
• cross over x-axis could also indicate the water potential (use another resource to find water potential)

Question 2

why is % change in mass calculated?

Answer 2

to compare the results because they vary in starting mass

Question 3

why are repeats important?

Answer 3

obtain a more reliable mean so helps to identify anomalies

Question 4

why are the same species of plant tissue used?

Answer 4

because they will have similar alleles so have genetic similarities

Question 5

why are the skins of the potato removed?

Answer 5

they have a different water potential so ensures same amount of water on outside

Question 6

why are cylinders cut to the same length?

Answer 6

same surface area=same rate of osmosis

Question 7

why are the cylinders left for 45 minutes?

Answer 7

to ensure a measurable change in mass as hopefully it would be the maximum change

Question 8

why did the potato gain mass in the weak solution?

Answer 8

higher water potential in the surrounding solution so water enters by osmosis

Question 9

A plant cell was observed with an optical microscope describe how the length of the cell could be estimated

Answer 9

• measure using eyepiece graticule
• then use a stage micrometer
• then calculate the calibration(curve?)

Question 10

explain the C1V1=C2V2 calculation

Answer 10

C1=conc. of solution you’re provided with
V1=how much of this to use? (when finding water volume do V2-V1
C2=conc. that you want to make up
V2=volume that you want to make up

Question 11

why would the data in a table be described as processed results?

Answer 11

calculated from raw data

Question 12

what is the name of the method used to produce sucrose solutions usually?

Answer 12

dilution series

Question 13

how should you cut cylinders using a cork borer to ensure it was a fair test and reliable?

Answer 13

• cut lengthways/down the root

- through one tissue only

Question 14

why would the bungs be placed in the tube?

Answer 14

to prevent water from evaporating which could change the water potential/concentration of that solution as a result

Question 15

why could the % loss in mass for one of the values be recorded as not applicable?