Practical 3 - Investigating Water Potential

Question 1

Describe how water potential can be investigated using plant tissue?

Answer 1

1. make a dilution series (of 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol/dm^3) using 1.0 mol/dm^3 of sucrose and distilled water
2. pour 5cm^3 of each concentration of sucrose from a measuing cylinder into a 6 different bioling tubes (labled accoridng to the sucrose concentration)
3. put the boiling tubes in water bath set at 30℃
4. 6 potato chips are cut with cork borer and then cut using a scalple so they are the same length and diameter
5. the chips are then weighed before being put in the boiling tube
6. boiling tubes are put back into the water bath and left for 30 minutes
7. chips are taken out and excess liquid is removed by dabbing them with a paper towel
8. chips are reweighed and the percentage change in mass is calculated

Question 2

how do you find the sucrose concentration initilly inside the potato?

Answer 2

look where the curve meets the x-axis

Question 3

How does adding solutes to water effect the water potential value?

Answer 3

it decreases it’s water potential value

Question 4

What happens to the potato when there is a low concentration of sucrose in the water?

Answer 4

• gradient is established
• there is a higher water potential inside the potato and s lower water potential inside of the potato
• this causes water to move into the potato cells via osmosis
• this causes the cells to become turgid and their mass to increase

Question 5

What happens to the potato when there is a high concentration of sucrose in the water?

Answer 5

• creates a gradient
• there is a lower water potential outside of the potato and a higher water potential inside the potato
• this causes water to move out of the potato cells by osmosis
• this causes the cells to become flaccid and it’s mass to decrease

Question 6

what increases the validity of the results?

Answer 6

• all of the chips comes from the same potato (all the chips have the same water potential initially)
• the chips have the skin removed because the skin is made up of different cells that have a different water potential