HORTICULTURE

Detailed explanation-1: -This active transport of sugar into the companion cells occurs via a proton-sucrose symporter; the companion cells use an ATP-powered proton pump to create an electrochemical gradient outside of the cell.

Detailed explanation-2: -During phloem transportation sugar is moved in form of sucrose in to the companion cells and them into the living phloem sieve tube cells by-

Detailed explanation-3: -Sucrose is loaded (moved into companion cells) by active transport, against the concentration gradient. However, the protein carrier involved in the loading, has two sites, one for sucrose and one for a hydrogen ion.

Detailed explanation-4: -Sucrose is synthesized in the cytoplasm and may move cell to cell through plasmodesmata or may cross membranes to be compartmentalized or exported to the apoplasm for uptake into adjacent cells. As a relatively large polar compound, sucrose requires proteins to facilitate efficient membrane transport.

Detailed explanation-5: -Sucrose transport is favorable for the following reasons: (i) 1 mol sucrose contains more energy than 1 mol of a monosaccharide such as glucose or fructose, thus using the disaccharide is more energy efficient for transport and storage.