Potometer Flashcards
(14 cards)
What is a potometer?
A piece of equipment used to investigate the rate of transpiration of a plant
Does the potometer actually measure rate of transpiration?
No, measures water uptake
However these values are very similar: as a very small amount of water from water uptake by plant is taken into cells, as the rest is evaporated in transpiration
Why do we cut the stem of the plant we are measuring the rate of transpiration of under water?
To prevent air from entering xylem
Potometer apparatus
Capillary tube with scale
Into a beaker of water
Attached to a reservoir of water with a tap
Attached to place with stem
Filled with water underwater
Why do we assemble the plant into the potometer underwater?
To ensure no air bubbles enter
Cut underwater to ensure no air bubble enters xylem and breaks continuous water column and prevent transpiration
Because of cohesion tension in the xylum that draws up air inside
What does the reservoir and tap do?
Supplies more water to restart the measurement: pushes air bubble back
What is important to let plant do?
Equilibrate to these new conditions to measure true rate of transpiration under the new manipulated conditions by drying leaves
How do we use the potometer to measure rate of transpiration?
Introduce an air bubble into the tube by lifting capillary tube from water beaker
Recording the distance it travelled/ area of tube it travelled within the tub per given time
How to find volume of water air bubble moved?
By calculating the area of the capillary tube it travelled as if it were a cylinder
Why do we cut the stem of the plant at a slant?
to increase the surface area for water uptake
Why is water uptake not completely the same as rate of transpiration?
Because not all water taken into plant by xylem is lost
Some water is used in photosynthesis
Some water is used to make cells turgid
Water is made by respiration
What are all joints covered wit?
Petroleum jelly
Why cover joins with petroleum jelly?
To ensure apparatus is airtight and sealed to prevent airbubbles entering = prevents flow of water
Prevents leak of water = accurate measure of water movement into plant stem
Control varaibles using different species of plant
Surface area (number and size of leaves)
