Phloem - Transport of minerals and nutrients

The nutrient storage and transportation

The leaves of plants carryout photosynthesis and synthesize sugar. The sugars that are synthesized in the leaves are utilized for the plant metabolism. Sugars are stored in the form of starch and they are used in the synthesis of proteins and lipids. The plant parts which are not photosynthetic like roots also need energy to survive. The food is sent to those parts from the photosynthetic region through a tissue called as phloem.

Phloem and food transport

The phloem consists of cell types like sieve tube cells, phloem parenchyma cells and companion cells. The sieve cells have end walls known as sieve plates. The sieve cells will not have their nuclei and still they can survive. The sieve cells at maturity will become empty with the plasma membrane functioning effectively. The sugars are sent into the sieve elements through the companion cells. The sieve cells are connected with each other to form sieve tubes. The fluids move in the phloem and the sap trans locates from one part of the plant to another.

The source is the plant part, where the sugars are synthesized. The sink is the plant part where the sugars are used up for survival or sugars are stored. The food material travels through the phloem with the help of a method called pressure flow mechanism. The osmotic pressure is the instrument by which the movement of sugars from the source to the sink takes place. The source is the leaf and the sink being roots.

The movement of sap or food through the sieve element allows the entry of water into the sieve elements. The presence of water and sugar increases the cell pressure. The high pressure at the source region makes the food to move to the sink tissues where the pressure in the cells is very less. The sugars that reach the sink tissues will be removed from the tissues through an active mechanism. The sugars are also converted into starch or they will be metabolized at the sink tissues.