Date | November 2019 | Marks available | 1 | Reference code | 19N.3.HL.TZ0.3 |
Level | Higher level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
Command term | Estimate | Question number | 3 | Adapted from | N/A |
Question
An experiment was carried out to study osmosis in plant cells. Small cylinders of zucchini (Cucurbita pepo) were cut and placed in different sucrose solutions at 25 °C. The figure shows the percentage changes in mass after 24 hours.
Estimate the solute concentration of the zucchini cells.
If a zucchini is allowed to dry in the open air, predict how the osmolarity of the zucchini cells would change.
Explain one reason for calculating the percentage changes in mass.
Predict what would happen to a red blood cell placed in distilled water.
Markscheme
0.36 mol dm-3/M ✔
Units required
Allow a range of 0.35–0.37 mol dm-3/M.
osmolarity will increase «because the cells become dehydrated»
OR
the cells become hypertonic ✔
Accept water potential of the tissue decreases.
Do not accept "change" instead of "increase".
a. the change in mass indicates whether the tissue has gained/lost water ✔
b. the pieces of tissue will not all be the same mass «at the beginning of the experiment» ✔
c. to compare the relative changes in mass ✔
a. water would move into the red blood cells ✔
b. it would lyse
OR
swell
OR
burst ✔