Question

In order to maintain the phloem pressure flow bottom-up in the spring. what happens? Choose all appropriate answersCompanion cells at the source have to continuously upload dissolved sugar from root parenchyma into sieve tube members of rootsCompanion cells at the sink (developing shoots) have to continuously download dissolved sugar from sieve tube members into storage parenchyma or generally growing cell tissuesEnough water needs to be taken up by roots to supply both xylem and phloemSolute concentration at the source (roots) needs to be lower in the phloem than in the xylem so that there is a net flux of water from the xylem into the phloem

Answer 1

In order to maintain the phloem pressure flow bottom-up in the spring, the following things happen:

1. Companion cells at the source have to continuously upload dissolved sugar from root parenchyma into sieve tube members of roots.
2. Companion cells at the sink (developing shoots) have to continuously download dissolved sugar from sieve tube members into storage parenchyma or generally growing cell tissues.
3. Enough water needs to be taken up by roots to supply both xylem and phloem.
4. Solute concentration at the source (roots) needs to be lower in the phloem than in the xylem so that there is a net flux of water from the xylem into the phloem.

All of these processes work together to maintain the phloem pressure flow bottom-up in the spring. This ensures that the plant has enough nutrients and water to support its growth and development during this important time of year.