AP BIOLOGY

Detailed explanation-1: -As the phloem sap moves down from the leaves, the sugar is absorbed by the stem and roots of the plants thus, removing the sugar from the phloem. When the sugar is removed at the sink, the osmotic pressure of the phloem decreases.

Detailed explanation-2: -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.

Detailed explanation-3: -Answer. Translocation is the process by which assimilates from photosynthesis are moved around the plant, from where they are made to where they are needed. The place where these assimilates are produced is called the source, and the place they are moved to is called the sink.

Detailed explanation-4: -Material like sucrose is transferred in phloem tissue using ATP. This increases the osmotic pressure of tissue causing water to move into it. This pressure moves the material in the phloem to tissue which have less pressure. This allows the phloem to move materials according to the need of plant.

Detailed explanation-5: -At the sink, assimilates exit the sieve elements and move into recipient sink cells where they are used for growth or storage. Movement from sieve elements to recipient sink cells is called phloem unloading.