Lesson 2

Question 1

What is casparian strip made of?

Answer 1

Waxy substance called Suberin which is impermeable to water and ions such as

Question 2

Describe how water and ions move up to the xylem

Answer 2

• Casparian strip blocks apoplast pathway
• Water and ions forced into symplast
• Active transport moves ions into cytoplasm of endodermal cells
• Ions diffuse into pericycle and then xylem
• Water follows ions as where im the ions go, water potential will decrease so water will move there via osmosis

Question 3

Explain root pressure

Answer 3

When water moves into xylem, hydrostatic pressure is generated and forces water a small distance up the xylem

Question 4

What is transpiration?

Answer 4

Evaporation of water from inside the leaves, through stomata into atmosphere so water potential lowered across plant, forcing water up plant toward stomata in leaf

Question 5

Describe cohesion-tension theory

Answer 5

• Water replaces molecules lost when diffused from lead
• Due to cohesion between hydrogen bonds and adhesion between molecules and xylem vessel walls
• Creates tension on xylem vessel walls so water moves up in unbroken stream

Question 6

What is capillarity?

Answer 6

Adhesion and cohesion allow water molecules to move up narrow tubes a small distanxe

Question 7

Name factors affecting rate of transpiration

Answer 7

Temperature, air movement, humidity, light intensity

Question 8

Describe how to set up potometer to measure rate of transpiration

Answer 8

• Cut a leafy shoot underwater to prevent air bubbles from going in xylem because air will break hydrogen bonds which affects cohesion
• Fit leafy shoot onto apparatus underwater and seal all joints with Vaseline so apparatus is airtight
• Pat leaves dry or water potential gradient will be reduced
• Introduce air bubble
• Measure distance air bubble moves in given amount of time