Q52 - Phloem Transport Under Water Stress
In conditions of drought, photosynthesis slows down while translocation of assimilates can continue as long as phloem turgor is maintained. The figures show the relationship between leaf water potential and (1) photosynthesis and translocation rates, and (2) the allocation of assimilates to different sinks under increasing water stress.
True or false?
Q52.1. Phloem transport of assimilates from source leaves is consistent with the Munch pressure flow theory.
Q52.2. The decreased consumption of assimilates in expanding sink leaves may increase translocation rate.
Q52.3. At a leaf water potential of -2.7 MPa, photosynthesis rate was approximately equal to translocation rate.
Q52.4. At a leaf water potential of -2.0 MPa, translocation had not significantly changed while photosynthesis had already decreased.
Q52.5. Preferential translocation to growing root tips in moist soil is a significant survival mechanism.
Question reproduced from IBO 2023, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF