7.7 transport of water in the xylem

Question 1

define what transpiration is.

Answer 1

evaporation of water from a plant

Question 2

explain how water moves through the leaf

Answer 2

• mesophyll cells lore water to the air spaces by evaporation due to heat supplied by the sun
• water potential decreased so water enters by osmosis from neighbouring cells
• loss of water from these neighbouring cells lowers their water potential
• they take water from their neighbours by osmosis

Question 3

explain the cohesion- tension theory of water transport

Answer 3

• change in diameter if tree trunks according to the rate of transpiration
• if a xylem vessel is broken and air enters it, the tree can no longer draw up water
• when xylem vessel is broken, water does not leak out

Question 4

cohesion- tension theory

Answer 4

• water evaporates from mesophyll cells by transpiration
• this lowers water potential
• water enters by xylem
• creates tension
• water is cohesive so forms a continuous column
• water is pulled upwards from the roots to the stem