BIOL 304 EXAM 1 | QUESTIONS AND
ANSWERS | 2026 UPDATE | WITH
COMPLETE SOLUTIONS
What materials move in the xylem and in the phloem? - ANSWER>Water and ions are transported in the xylem,
whereas the phloem contains water and carbohydrates (sugars)
What source of energy drives movement in the xylem? - ANSWER>driven by sunlight/dry atmosphere as water
needs to evaporate through stomata and create a hydraulic rope to pull water upwards, all the way from its roots.
What features of phloem structure are important for its function? - ANSWER>made up of sieve-tube elements and
companion cells, alive at maturity, lack secondary walls (parenchyma). at the end of a sieve tube = sieve plate with
large pored for phloem sap to flow through
Consider a plant 20 cm tall growing in well watered soil. In a dark and humid greenhouse, in the middle of the
night, you measure the turgor pressure of a living leaf cell of this plant using a probe inserted in the cell. You find
that the turgor pressure is 1.9 MPa. Given the current conditions, what is your prediction of the osmotic potential
of this cell? - ANSWER>-At night and in the dark-> soil and root and leaf solute potentials at equilibrium, well
watered, can ignore solute potential.
, -only forces contributing to water potential are pressure potential and osmotic potential, since plant is only 20 cm
- PSIw= PSIs + PSIp + PSIg + PSIm
- 0 = 0 + 1.9 MPa + 0 - 1.9 Mpa
*osmotic potential needs to be -1.9 Mpa to be at equilibrium
If you were to study a similar cell (from question 1), under similar environmental conditions (night, saturating
humidity, turgor pressure = 1.9 MPa), found at the top of a redwood tree on a misty night in California. How would
your prediction of the osmotic potential change if you knew that the cell was located at the top of a 100 m tall
tree? Explain the reason for the change in your prediction using the water potential equation. - ANSWER>At the
top of a 100 m tree, gravitational potential is now relevent, as it increases 0.1 MPa for every 10m -> 1 MPa
Osmotic potential must decrease to be 2.9 for the system to still be at equilibrium since turgor pressure remains
the same:
PSIw = PSIs + PSIg + PSIm + PSIp
0 = 0 + 1 MPa - 2.9 Mpa + 1.9 MPa
ANSWERS | 2026 UPDATE | WITH
COMPLETE SOLUTIONS
What materials move in the xylem and in the phloem? - ANSWER>Water and ions are transported in the xylem,
whereas the phloem contains water and carbohydrates (sugars)
What source of energy drives movement in the xylem? - ANSWER>driven by sunlight/dry atmosphere as water
needs to evaporate through stomata and create a hydraulic rope to pull water upwards, all the way from its roots.
What features of phloem structure are important for its function? - ANSWER>made up of sieve-tube elements and
companion cells, alive at maturity, lack secondary walls (parenchyma). at the end of a sieve tube = sieve plate with
large pored for phloem sap to flow through
Consider a plant 20 cm tall growing in well watered soil. In a dark and humid greenhouse, in the middle of the
night, you measure the turgor pressure of a living leaf cell of this plant using a probe inserted in the cell. You find
that the turgor pressure is 1.9 MPa. Given the current conditions, what is your prediction of the osmotic potential
of this cell? - ANSWER>-At night and in the dark-> soil and root and leaf solute potentials at equilibrium, well
watered, can ignore solute potential.
, -only forces contributing to water potential are pressure potential and osmotic potential, since plant is only 20 cm
- PSIw= PSIs + PSIp + PSIg + PSIm
- 0 = 0 + 1.9 MPa + 0 - 1.9 Mpa
*osmotic potential needs to be -1.9 Mpa to be at equilibrium
If you were to study a similar cell (from question 1), under similar environmental conditions (night, saturating
humidity, turgor pressure = 1.9 MPa), found at the top of a redwood tree on a misty night in California. How would
your prediction of the osmotic potential change if you knew that the cell was located at the top of a 100 m tall
tree? Explain the reason for the change in your prediction using the water potential equation. - ANSWER>At the
top of a 100 m tree, gravitational potential is now relevent, as it increases 0.1 MPa for every 10m -> 1 MPa
Osmotic potential must decrease to be 2.9 for the system to still be at equilibrium since turgor pressure remains
the same:
PSIw = PSIs + PSIg + PSIm + PSIp
0 = 0 + 1 MPa - 2.9 Mpa + 1.9 MPa
