Transport of Food in Plants

Food is manufactured in the leaves and green stems of the plant during a process called photosynthesis. The food made by the leaves is in the form of a simple sugar named glucose. Other types of substances are called plant hormones, they are released from the tips of roots and shoots.  The movement of food from leaves to other parts of the plant is called translocation. In plants, the phloem vessel translocates the food and other substances.

Phloem consists of sieve tubes and companion cells. Sieve tubes are living cells which contain cytoplasm but do not have a nucleus. So its function is supported by a companion cell. The phloem vessel in the vascular bundle will transport sucrose and amino acids away from the leaf. As the vascular bundles are connected with similar structures in the roots, each sieve tube is continuous with those in the roots. Sucrose and amino acids enters the phloem by active transport. Later, it is translocated from the sources to the sinks.

Food is prepared in the mesophyll cells of the leaf. The palisade mesophyll cells is just below the upper epidermis layer. It that contains more chloroplats than the spongy mesophyll layer. The spongy mesophyll layer is below the palisade mesophyll layer that have large air sacs. There is a slight separation between the cells to  provide absorption of carbon dioxide, this separation must be very little to support capillary action for water distribution. Food is translocated in the form of sucrose. The movement of water and dissolved minerals in xylem is always upward, from the soil to the leaves. The movement of food can be upward as well as down ward depending upon the needs of the plants.

Acknowledgements:

http://manravbioeducation.blogspot.sg/2007/08/transport-of-materials-in-plants.html

http://en.wikipedia.org/wiki/Leaf#Mesophyll