Transport through the phloem(2)

What is the role of ATP in a companion cell when sucrose is loaded into a sieve tube element?

• moving sucrose into the sieve tube element
• removing protons out of the cytoplasm of the companion cell into the surrounding
• removing protons from the sieve tube element
• taking up sucrose into the cytoplasm of the companion cell

How are co-transport proteins invovled in transport of assimilates through the phloem

• transport of sucrose together with protons out of the companion cells
• transport of sucrose together with protons into the companion cells
• trasnport of sucrose together with protons into the mesophyl cells
• transport of sucrose together with protons out of the sieve tube elements

How is proton pump involved in the transport of assimilates through the phloem

• active transport of protons out of the sieve tube elements
• active transport of protons out of the mesophyl cells
• active transport of protons out of the companion cells
• active transport of protons out of the xylem vessel elements

which feature of companion cell does not enhance loading?

• presence of plasmodesmata connecting them to sieve tube element
• presence of cotransport proteins on their cell surface membranes
• presence of proton pumps on their cell surface membrane
• presence of golgi apparatus for packaging and modifying assimilates

What is the sequence of events in the translocation of sucrose?

• active loading of sucrose into sieve elements at the source, increased hydrostatic pressure, mass flow, unloading at the sink
• hydrolysis of storage compounds in sinks, lowered water potential, unloading of sucrose from sieve elements, mass flow from the source
• lowered pressure in sieve elements at the source, movement of sucrose down the pressure gradient, mass flow down a diffusion gradient to the sink
• mass flow of dissolved sucrose into the sieve elements at the source, lowered hydrostatic pressure, diffusion of sucrose to sink, active unloading

With reference to the table, which changes to the water potential and volume of liquid in the phloem occur when amino acids are taken out of a sink in a phloem sieve tube?

• A

• B

• C

• D

What is the most accurate description of translocation in the phloem of plants?

• transport of water from down hydrostatic pressure gradient
• transport of sucrose down hydrostatic pressure gradient
• transport of various assimilates down hydrostatic pressure gradient
• transport of dissolved ions down hydrostatic pressure gradients

Which statement supports the theory of active loading of sucrose into companion cells?

• The pH decreases in the cell wall of the companion cells compared to the cytoplasm
• the pH decreases in the cytoplasm of the companion cells compared to the cell wall
• the pH decreases in the plasmodesmata between companion cells and sieve tube elements
• the pH decreases in the sieve tube elements comapred to the companion cells

Which statement about the transport of sucrose is correct?

• ATP is synthesised by mitochondria of companion cells provides the energy to move sucrose from phloem sieve tube elements in leaves to sink

• Sucrose moves through plasmodesmata by passive diffusion from mesophyl cells through companion cells in phloem sieve tube elements

• The water potential in phloem sieve tube elements becomes more negative following the entry of sucrose

• Water enters companion cells and hydrostatic pressure builds up to push sucrose into phloem sieve tube elements by mass flow

ATP is used in companion cells to provide the energy for loading a sieve tube element with sucrose. How does the co-transporter mechanism use this energy?

• to pump protons into the sieve tube elements
• to pump protons out of the companion cells
• to pump sucrose into the sieve tube elements
• to pump sucrose out of the companion cells