IMO Practice Test — Transport in Plants
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
If a cell's water potential is more negative than its surroundings, water will:
Enter the cell
Leave the cell
Not move
Freeze
Explanation: Water moves from higher (less negative) to lower (more negative) potential — so it enters the cell.
Question 2 of 6
Wilting of a plant on a hot day happens because the rate of transpiration:
Exceeds the rate of water absorption
Is less than absorption
Is zero
Equals photosynthesis
Explanation: When water loss outpaces uptake, cells lose turgor and the plant wilts.
Question 3 of 6
A continuous, unbroken water column in the xylem is maintained by:
Cohesion between water molecules
Active transport
Gravity
Phloem loading
Explanation: Hydrogen-bond cohesion keeps the water column unbroken as it is pulled up.
Question 4 of 6
A storage root that is filling with sugar acts as a ____, but when it sprouts it acts as a ____.
Sink; source
Source; sink
Sink; sink
Source; source
Explanation: While storing sugar it is a sink; when sprouting it exports sugar, becoming a source.
Question 5 of 6
Translocation in the phloem is an active process mainly because:
Loading sugar at the source requires energy
Water moves down a gradient
It uses transpiration pull
It needs no membranes
Explanation: Active loading of sugar at the source uses ATP, making translocation energy-dependent.
Question 6 of 6
Ringing (removing a ring of bark including phloem) causes the bark above the ring to swell because:
Sugars accumulate above the cut as downward transport is blocked
Water stops rising
The xylem is removed
Stomata close
Explanation: Removing phloem blocks downward food transport, so sugars build up and the bark swells above the ring.