Investigating transpiration using a potomoter

Question 1

Transpiration stream

Answer 1

• Loss of water from the leaves of a plant causes water to be absorbed by the plant, moved through the xylem vessels, up the leaves
• Upward movement of water through the plant

Question 2

Transpiration

Answer 2

Evaporation of water from the leaves to the atmosphere

Question 3

what is the assumption of rate of transpiration

Answer 3

it is equal to rate of water uptake

Question 4

why isn’t the measurement of transpiration rate not 100% accurate

Answer 4

• a very small volume of water drawn up from the plant is used in physiological processes, e.g photosynthesis
• around 1%

Question 5

Factors affecting transpiration

Answer 5

• temperature
• light
• humidity
• wind
• atmospheric pressure

Question 6

Potometer

Answer 6

measures how much water is taken up

Question 7

Step 1 -

Answer 7

• Immerse potometer fully underwater and assemble to prevent entry of air bubbles
• place cut end of plant stalk underwater and cut last cm of stalk of underwater
• whilst underwater, push stalk inro potometer so stalk fits in tightly
• use rubber seals to prevent no air bubbles getting in
• remove plant and potometer from underwater

Question 8

after we remove the potometer and plant from underwater after assembly, we apply vaseline to the joints - why

Answer 8

• prevents any water leaking out = airtight
• prevents flow of water out of leaves, increasing accuracy
• ensures water only leaves out of stomata by evaporation

Question 9

what do we do after applying vaseline

Answer 9

• dab leaves with paper towels to prevent excess water
• clamp potometer in an upright position with end of capillary tube underwater
• remove capillary tube from underwater and let air bubble form (5/10 secs)
• place end of capillary tube underwater

Question 10

how do we measure rate of transpiration after equipment has been assembled

Answer 10

• when an air bubble reaches 0 on the scale bar
• record how fair the bubble travels in a known time

Question 11

calculate transpiration rate

Answer 11

distance moved by bubble / time taken

Question 12

transpiration rate - units

Answer 12

• mm min-1
• mm3, cm2, min-1

Question 13

when would we want to investigate transpiration rate

Answer 13

• looking at effects of transpiration
• investigating effects on different plants

Question 14

control variables

Answer 14

• surface area of the leaves
• number of leaves

Question 15

explain why apparatus must be set up and plant shoot must be cut underwater

Answer 15

• cohesion tension creates a negative pressure in xylem
• if it was cut in air, it would draw air into xylem tube
• this would break continuous water column and prevent transpiration
• by cutting underwater only water is drawn into the xylem

Question 16

3 precautions -

Answer 16

• do not allow air to enter, cut end / shoot =
• prevent airlock / ensures continuous
  column of water
• keep named abiotic factor constant =
• affects, rate of transpiration / evaporation
  of water
• keep screw clip closed =
• prevents entry of water whilst measuring