Thirsty leaves, busy pipes

Science · Organisms & Life Processes · ages 15-16

Name ______________________ Date ____________

What does phloem carry?
- Dissolved sugar to where it is used or stored
- Water up from the roots
- Sunlight into leaves
What does xylem carry, and in which direction?
- Sugar down to the roots
- Water and minerals up to the leaves
- Air into the soil
Closing the stomata saves water and boosts photosynthesis.
Circle one: True False
What do guard cells do in a drought?
- Gape wide for more carbon dioxide
- Swell the stomata shut to ration water
- Grow longer roots
Which day gives the fastest transpiration?
- Hot, windy and dry
- Humid, still and cool
- Cold, still and damp
What pulls more water up behind the water leaves lose?
- Root pushing alone
- Evaporation tugging the whole column upward
- Rain pressing down
Sam says xylem carries sugar down to the roots. What is wrong?
- Nothing, Sam is right
- Sugar down is phloem's job; xylem lifts water up
- Roots need no sugar
On a humid still day a plant opens its stomata wide. Why is that a safe deal?
- Sugar travels faster in humidity
- Roots rest on humid days
- Water loss is slow, so carbon dioxide comes cheap

Answer key

For grown-ups. Fold this page away before handing over the rest.

Dissolved sugar to where it is used or stored · Sugar made in leaves travels by phloem to roots and fruits.
Water and minerals up to the leaves · Xylem is the upward water pipe from roots to leaves.
False · Closed pores save water but shut out carbon dioxide too.
Swell the stomata shut to ration water · Shutting the pores rations water at the cost of food.
Hot, windy and dry · Heat, wind and dry air all pull vapour off the leaf faster.
Evaporation tugging the whole column upward · Losing water on top tugs the whole column higher.
Sugar down is phloem's job; xylem lifts water up · Two pipes, opposite flows: xylem lifts water, phloem delivers sugar.
Water loss is slow, so carbon dioxide comes cheap · Slow loss means the plant can afford wide-open food shopping.