10 questions🇬🇧English
🌿 Xylem, Phloem & Transpiration – A-level
Biology · A-level — water transport, cohesion-tension theory, potometers and translocation by mass flow
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Questions
Which phloem cells have sieve plates, no nucleus and only a thin layer of cytoplasm?
Tracheids
Sieve tube elements
Companion cells
Xylem vessel elements
20s
Which substance thickens and waterproofs the walls of xylem vessels?
Suberin
Cellulose
Callose
Lignin
20s
Which change would increase the rate of transpiration from a leafy shoot?
A decrease in light intensity
A decrease in temperature
An increase in wind speed
An increase in humidity
20s
In the cohesion-tension theory, what holds water molecules together as a column in the xylem?
Ionic bonds between water molecules
Hydrophobic interactions between molecules
Covalent bonds between water molecules
Hydrogen bonds between water molecules
30s
A leaf is given ¹⁴CO₂. In which stem tissue is the radioactive carbon mainly detected soon after?
Cortex
Pith
Xylem
Phloem
30s
Why does a potometer measure water uptake rather than the exact rate of transpiration?
The air bubble slows down as it moves along
Xylem vessels store most of the water absorbed
Some water is used in photosynthesis and for turgor
Water evaporates from the open capillary tube
30s
A ring of bark containing the phloem is removed from a tree trunk. Why does the bark just above the ring swell?
Sugars build up above the ring and water enters
Water builds up because the xylem is removed
Cells above the ring divide faster to repair it
Sugars move upwards from the roots to the ring
30s
A potometer bubble moves 30 mm in 5 minutes. Capillary radius = 0.5 mm; use π = 3.14. What is the rate of water uptake?
4.7 mm³ min⁻¹
23.6 mm³ min⁻¹
18.8 mm³ min⁻¹
9.4 mm³ min⁻¹
60s
According to the mass flow hypothesis, why does water enter sieve tubes at a source?
Water is actively pumped into the sieve tubes
Loaded sucrose lowers the water potential there
Root pressure forces water into the sieve tubes
Loaded sucrose raises the water potential there
30s
Which observation is evidence against the mass flow hypothesis?
Bark swells above a ring of removed phloem
Different solutes move at different speeds
Pressure is higher near sources than near sinks
Sap is exuded under pressure from aphid stylets
30s