1. Translocation is a transport process of organic substances and other photosynthetic product from a product source to other parts of plant via phloem
2. The necessity of translocation in plants:

• Transport sucrose,a photosynthetic product from leaves to other parts of plant for metabolism and storage
• Transport other organic substances such as amino acids and other organic acids from shoots to other parts of plant for metabolism and storage

• Pathway of translocation:
• Mesophyll cells
• Companion cell
• Sieve tube
• Leaf phloem
• Stem phloem
• Cells of roots,stem,other shoots,flower and fruit

Mesophyll cells have chloroplast and carry out photosynthesis:

• Photosynthetic products are transported actively into sieve tube by companion cell
• The accumulation organic substances in phloem increases the concentration gradient,then water diffuses from surrounding into phloem
• Hydrostatic pressure generated transports organic substances to other parts
• At other parts of plant such as root,the organic substances in phloem are transported actively into root cell for metabolism and storage.