Question

Osmotic pressure at sink decreases in phloem transport because

• A. Sugar is transported through phloem as sucrose
• B. Loading of phloem at source sets up a water potential gradient
• C. Sugar removed from phloem sap at sink is either utilised to release energy or converted into starch or cellulose
• D. Water passes out from phloem sap to the xylem vessel at sink

Answer 1

The correct option is C Sugar removed from phloem sap at sink is either utilised to release energy or converted into starch or cellulose

Osmotic pressure is the pressure which is applied when the molecules of solvent flow from higher to lower concentration through the semipermeable membrane. This is explained in the 'Pressure flow hypothesis' given by Munch in 1927. According to this hypothesis, all the organic substances move from higher to lower concentration maintaining pressure. Due to the active transport of sugars will move out of the phloem and transported to another part of the cells and convert them into energy. Since all the sugars are moved from the phloem and the osmotic pressure gets decreased and the water moves out of the phloem and towards the cell.

So, the correct option is 'Sugar removed from phloem sap at sink is either utilised to release energy or converted into starch or cellulose'