CBSE Questions for Class 11 Medical Biology Cell The Unit Of Life Quiz 17 - MCQExams.com

The mechanism used for the translocation of sugars from source to sink is called the pressure flow hypothesis. As glucose is prepared at the source, it is converted to sucrose. This is moved into the companion cells and then into the living phloem sieve tube cells by active transport. Again active transport is necessary to move the sucrose out of the phloem sap and into the cells which will use the sugar converting it into energy. 

Recognition proteins have active sites shaped to fit specific signal molecules, such as hormones. Once the protein is activated by the substance, it sets off a series of changes in the cell, such as increased metabolic rate or cell division.