Water Highways
What process in the leaf creates the pulling force that moves water upward?
Evaporation from the leaf (transpiration)
Which mesophyll layer is tightly packed and absorbs light?
Palisade mesophyll.
Which gas escapes the leaf most easily?
Water vapor.
What enzyme accidentally grabs O₂ instead of CO₂?
Rubisco.
What enzyme do C4 plants use to grab CO₂?
PEP carboxylase.
What property of water keeps the xylem column from breaking?
Cohesion between water molecules
Which mesophyll layer has air spaces for gas movement?
Spongy mesophyll.
Why does water vapor escape faster than CO₂ enters?
Stronger concentration gradient.
What causes O₂ to build up inside the leaf?
Stomata closing
Why is PEP carboxylase helpful?
It never grabs O₂ by mistake.
What additional property helps water stick to xylem walls?
Adhesion
Why does the spongy mesophyll have large air pockets?
To allow CO₂ to diffuse quickly through the leaf.
When stomata open, what is the plant trying to get?
CO₂ for photosynthesis.
What happens to CO₂ levels when stomata close?
CO₂ drops
Where is Rubisco located in C4 plants?
Bundle‑sheath cells.
Why doesn’t the plant need ATP to move water up the xylem?
The pull is created passively by evaporation.
Why are palisade cells shaped like columns?
To maximize light absorption.
What is the trade‑off of opening stomata?
Water loss.
What is wasted during photorespiration?
Energy
What do C4 plants transport to bundle‑sheath cells?
A 4‑carbon acid containing CO₂.
What is the name of the continuous column of water inside the xylem?
The transpiration stream.
What structure controls gas exchange on the leaf surface?
Stomata.
What term describes movement from high concentration to low concentration?
Diffusion
Why is photorespiration harmful to the plant?
It releases CO₂ instead of making sugar
What problem does the C4 pathway solve?
Photorespiration in hot, sunny environments.