2. Definition of translocation
• Translocation is the movement of sap containing
dissolved products of photosynthesis from leaves to
other tissues throughout the plant via sieve-tube
cells.

3. Sieve-tube cell
• In angiosperms( flowering plants ), sieve-tube cells are the
specialized cells of phloem that function in translocation.
• Sieve-tube members are arranged end-to-end forming long
sieve tubes. Sieve-tube cell
• These cells are very important for translocation.
companion cell
nutrients
sieve tube
sieve tube

4. Sap contents and movement
• Phloem sap contains primarily sucrose*, but also minerals, amino
acids, and hormones.
• Phloem sap movement is not unidirectional( one direction); it moves
through the sieve tubes from source to the sink.
• Source is the organ where sugar is produced by photosynthesis or
by the breakdown of starch (usually leaves)
• The sink is the organ that consumes or stores sugar (growing parts
of plant, fruits, roots, and others).
Leaf( source)
* Commonly known as table sugar
Roots( sink)

5. • The Pressure Flow Hypothesis AKA Source and Sink, also known as
the Mass Flow Hypothesis, is the best-supported theory to explain
the movement of food through the phloem.
• Cells in a sugar source "load" a sieve-tube element by actively
transporting solute molecules like sugar into it. This causes water to
move into the sieve-tube element via osmosis, creating pressure
that pushes the sap down the tube.