You need to know a couple of things like:
Humidity decreases transpiration rate as there is more water vapour in the air than in the plant.
-Temperature increases the transpiration rate as the molecules gain more kinetic energy which help them escape.
- Light increases the rate also as the guard cells in the stoma are activated by light. So no light no water escaping..
Water and salts travel up the xylem
Amino acids and sugars travel from the leaf to all the parts of the plants using the phloem.
The mechanism of water uptake is simple..
The water travels from the root to the shoot due to the continues chain of water molecules being attracted by the hydrogen ions (H+).
Then all you need to know is the adaptation and functions of the cactus and of the water plant.. which is simple i'll explain it too if u want..
hope u understood something