Why is food transported in the …

Transport of food material from leaves to other parts of the plant is called translocation. This food may be stored in fruits, stem or roots. The movement of food can be upward as well as downward depending upon the needs of the plants.
The movement of food in the phloem takes place by utilizing energy. The areas where the nutrients are stored is known as sink (e.g. root) and where they originate as source ( leaf). The movement of food is always from the source to the sink. At source i.e leaves, food is prepared in the form of glucose. Glucose is converted into sucrose. Sucrose enters into the phloem at the expense of energy from ATP. A pressure gradient is set up in the phloem with high pressure at source and low pressure at sink. So the phloem sap with food will move from source to the sink. The phloem transports food according to the need of the plant.