ANSWER:
By having their stomata open merely enough to enable photosynthesis
Step-by-step explanation:
Homeostasis. Angiosperms or flowering plants sustain homeostasis by maintaining their stomata (opening in the underneath of a leaf that provides carbon dioxide to disperse inside and outside of the leaf) open merely sufficient to permit photosynthesis to take place but not so much that they dissipate an unnecessary amount of water.