Core Practical 8

Question 1

Safety

Answer 1

careful not to break capillary tubing when push in shoot

Question 2

Using this method

Answer 2

assuming the plant takes up an equal volume of water that is lost by transpiration

Question 3

Structure of potometer

Answer 3

can be a simple length of capillary tubing or may have a reservoir to allow it to be refilled easily (look at images so familiar with different structures)

Question 4

How to test different factors

Answer 4

Light intensity :use a lamp at different distances and use a light meter
Air movement:use a fan at different distances of speed settings
Temperature:use an incubator and set at different temperatures
Humidity:increase humidity by covering the shoot with a clear plastic bag

Question 5

Quick how to set up potometer

Answer 5

1. Lay capillary tube +rubber connector under water and fill
2. Select a leafy shoot which has a stem close in diameter to the rubber connector .keep end of shoot under water always
3. Quickly insert tube into rubber connector under water
4. Clamp keep bottom of capillary tube under water
5. Make air tight by smearing petroleum jelly around joints for an airtight seal .Dry leaves by blotting them with paper towels
6. Give time for water to be drawn up the capillary tube if no air bubble present remove end quickly from water and place paper towel at the end

Question 6

How to work out leaf area of shoot

Answer 6

Using squared graph paper

Question 7

How to convert distance moved per second into millimetres cubed per metre squared per hour

Answer 7

measure radius of hole in capillary tubing then use v=pi r2 h to calculate volume h is distance moved by the bubble then divide volume by time taken (rate of water uptake).divide by leaf area

Question 8

how to measure water loss directly

Answer 8

measure mass loss

Question 9

when using sources

Answer 9

date them when use accessed them

Question 10

how to control variables

Answer 10

Temperature -same plant same room
Light Intensity-shut blinds and placed lamp at same distance
Humidity -same plant same room
stomatal density and leaf area-same plant
air movement -minimal indoors

Question 11

tips for setting up

Answer 11

do not get any water on the leaves
make airtight underwater
do not move plant anymore than necessary

Question 12

why is an airtight seal required

Answer 12

so water can be drawn up the capillary tube due to the suction created allowing the air bubble to move

Question 13

Possible uncontrolled variables

Answer 13

temp could vary and if not completely air tight bubble movement may be slowed

Question 14

how to control

Answer 14

monitor temperature using a thermometer several layers of tape