What holds the xylem water column together under tension?

• Hydrogen bonds between water molecules
• Lignin pumps inside the vessels
• Air bubbles spacing the molecules out

Where does the force that lifts xylem water act from?

• The roots pushing from below
• The stem squeezing in the middle
• The leaves pulling from above

Root pressure alone is strong enough to lift water to the top of a tall tree.

Circle one:   True   False

Which day gives the fastest water uptake at the roots?

• A cold, still, humid night
• A hot, dry, windy day
• A mild day with closed stomata

The stomata close on a dry afternoon. What happens to xylem flow?

• Flow speeds up as pressure builds
• Flow slows or stops as the pull vanishes
• Flow reverses back down to the roots

What part does adhesion play in water movement?

• It narrows the leaves to cut evaporation
• It sticks water to xylem walls, steadying the column
• It pumps ions into the roots at night

A trunk narrows slightly on a hot day. How does the theory explain it?

• Tension in the water column tugs the walls inward
• Roots swell and crush the stem from below
• Leaves push excess water back down

A student says water rises because xylem vessels pump it upward. What is wrong?

• Xylem vessels are dead tubes with no pumping parts
• The pull comes from leaf evaporation, not vessel pumping
• Water never moves through xylem at all