3.3.7 Transpiration in Plants

Question 1

Apoplastic Pathway

Answer 1

• Spaces running through cellulose walls and xylem
• Diffusion
• Move from cell wall to cell wall or through intercellular spaces
• More rapid than symplastic
• When water reaches suberin (casparian strip), apoplastic pathway is blocked
• Water then takes the symplastic pathway

Question 2

Symplastic Pathway

Answer 2

• Cytoplasm and plasmodesmata or vacuolar
• Osmosis into cells
• Slower

Question 3

What is the cohesion tension theory

Answer 3

• Movement of water through plants is because of evaporation of water at leaves
• Low water potential at leaves, high at roots
• Water moves down gradient
• Transpiration pull puts xylem under tension because of the cohesive nature of water and hydrogen bonding
• So a continuous stream of water is pulled up xylem

Question 4

Transpiration Pull Cohesion Tension

Answer 4

Question 5

Role of Stomata

Answer 5

• Made of guard cells
• Guard become turgid, opening stomata
• When flaccid, stomata is closed
• When open, greater rate of transpiration
• usually open during day, as exchange of CO2 and O2 occurs at stomata as well, which happens mainly during the day when the plant needs CO2 for photosynthesis