Prequiz Chap 7a

In the pressure flow model of phloem translocation, what is the direct consequence of sucrose being actively loaded into sieve tube elements at the source?

• Decrease in turgor pressure at the source

• Increase in water potential (Ψw) in the phloem

• Osmotic uptake of water, leading to high hydrostatic pressure

• Blockage of sieve plate pores by callose

A farmer observes that removing mature leaves from a tomato plant reduces fruit growth. Which of the following best explains this observation?

• A) Mature leaves act as sinks, competing with fruits for sugars.

• B) Mature leaves are sources of photosynthates required for fruit development.

• C) Immature leaves compensate by increasing their photosynthetic rate.

• D) Roots stop absorbing water, disrupting xylem transport.

Which type of companion cell is specialized for transferring solutes from the apoplast into the phloem by increasing plasma membrane surface area?

• Ordinary companion cells

• Intermediary cells

• Transfer cells

• Albuminous cells

During phloem loading, sucrose is transported against its concentration gradient into sieve elements. Which mechanism directly enables this process?

• Passive diffusion through plasmodesmata

• Proton-sucrose symport driven by a H+-ATPase pump

• Callose deposition in sieve plate pores

• Bulk flow driven by transpiration

If a plant’s phloem is damaged, how do P-proteins contribute to short-term repair?

• By synthesizing callose to seal sieve plates permanently

• By forming plugs to prevent sap loss from damaged sieve elements

• By actively transporting sugars to undamaged regions

• By converting sucrose into starch for storage