AP BIOLOGY

Detailed explanation-1: -1: Translocation to the sink: Sucrose is actively transported from source cells into companion cells and then into the sieve-tube elements. This reduces the water potential, which causes water to enter the phloem from the xylem.

Detailed explanation-2: -Once sugar is unloaded at the sink cells, the s increases, causing water to diffuse by osmosis from the phloem back into the xylem. This movement of water out of the phloem causes p to decrease, reducing the turgor pressure in the phloem at the sink and maintaining the direction of bulk flow from source to sink.

Detailed explanation-3: -The addition of sucrose into the sieve tubes increases the concentration of this solute, causing water to flow into the sieve tubes by osmosis. With the entry of water, the sieve tube pressure near the source cells increases and forces the solution to move to regions of lower pressure.

Detailed explanation-4: -Phloem sap is an aqueous solution that contains up to 30 percent sugar, minerals, amino acids, and plant growth regulators. The high percentage of sugar decreases s, which decreases the total water potential, causing water to move by osmosis from the adjacent xylem into the phloem tubes.

Detailed explanation-5: -Water from surrounding tissues, enters the sieve tube members by osmosis following a concentration gradient.. The water absorbed into the sieve tube creates hydrostatic pressure that forces the phloem sap to flow (bulk flow) towards the sink.