lecture 14

Question 1

what keeps water in a tree trunk?

Answer 1

• cohesion between water molecules keeps the water column from breaking apart
• adhesion of water molecules to the xylem cell walls helps overcome gravitational force

Question 2

what is transpiration?

Answer 2

the evaporative loss of water from aerial parts of the plant

Question 3

how is negative pressure exerted in water movement?

Answer 3

evaporation of water in stomata exerts negative pressure (tension) on the water columns in the xylem - pulling the water up the stem

Question 4

how are high concentrations of water vapour in leaf air spaces generated?

Answer 4

water evaporates from the apoplast of the leaf parenchyma

Question 5

how is humidity and water concentration lowered inside a plant?

Answer 5

concentrated evaporated water diffuses through the stomatal pores to the environment

Question 6

how is water potential of the xylem lowered?

Answer 6

tension is transmitted through the xylem to the root, which draws water into the xylem from the endodermis

Question 7

how is water transported in the phloem?

Answer 7

water moves from source tissues (source of solutes) to sink tissues (where solutes are consumed). this is caused by pressure flow which requires energy

Question 8

where does the water come from in phloem transport?

Answer 8

drawn into the cells from the apoplast

Question 9

what happens to the sucrose in phloem transport?

Answer 9

• oxidized to produce energy (mitochondrial respiration)
• stored as starch or other storage compounds