REQUIRED PRACTICAL 3 - WATER POTENTIAL

Question 1

what is the aim of this practical

Answer 1

to produce a dilution series of a solute, to produce a calibration curve with which to identify the WP of plant tissue

Question 2

what is a calibration curve and what is its purpose

Answer 2

• they are graphs used to determine an unknown concentration of a sample by comparing the unknown to a set of standard samples with known concentrations
• a dilution series can be used to create a set of samples with known concentrations
• it can be used to determine an unknown water potential in a potato sample

Question 3

what is water potential

Answer 3

• the tendency of water to diffuse from one area to another

Question 4

how does water move

Answer 4

• osmosis
• where water molecules move from areas of a high WP to areas of a low WP via osmosis

Question 5

what is WP determined by

Answer 5

the concentration of solutes

Question 6

the movement of water in and out of cells is related to what

Answer 6

the relative concentration of solutes on either side of the cell membrane

Question 7

what is the equipment list for this practical

Answer 7

• potato tuber
• cork borer
• scalpel
• ruler
• distilled water
• sucrose solution (1M)
• boiling tubes
• boiling tube rack
• timer
• digital balance
• paper towels

Question 8

describe the method of this practical

Answer 8

• make a series of dilutions of the 1M sucrose solution, the dilutions should be 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 M
• dilution can be done through distilled water
• measure 5cm3 of each dilution into separate test tubes
• use a cork borer to cut out 6 potato chips and cut down the sections into IDENTICALLY sized chips
• dry each chip so it doesn’t contain excess water, but dont squeeze
• weigh each chip before the start of the experiment
• place a potato chip in each test tube, one chip per sucrose concentration, and leave it there for 20 mins
• remove each potato chip, dry gently using a paper towel and weight them in turn
• calculate the % change in mass for each sucrose solution

Question 9

what are potential hazards for this practical

Answer 9

• scalpel
• broken glass

Question 10

what is the risk for the use of the scalpel

Answer 10

cuts from a sharp object

Question 11

what is the safety precaution for the use of the scalpel

Answer 11

• cut away from fingers
• use forceps to hold the sample whilst cutting
• keep away from the edge of the desk

Question 12

what is the risk for broken glass

Answer 12

cuts from a sharp object

Question 13

what is the safety precaution for the broken glass

Answer 13

• take care when handling glass objects
• keep away from the edge of the desk

Question 14

what are the conclusions for this practical

Answer 14

• potato chips in a LOWER conc of sucrose solution will INCREASE in mass, whilst those in a HIGHER conc of sucrose solution will DECREASE in mass
• in the DILUTE sucrose solutions there is a HIGHER WP than the potato, so water PASSIVELY moves via OSMOSIS to the area of LOWER WP -> causing the potato to INCREASE in mass
• in the CONCENTRATED sucrose solution, water will move OUT of the potato -> potato will DECREASE in mass