3.1.3 Plant Transport – Translocation Flashcards
(10 cards)
What is the function of translocation in a plant?
Translocation is the transport of assimilates throughout the plant in the phloem, from source to sink.
What are assimilates?
Assimilates = sucrose, amino acids
Define ‘source’ and ‘sink’ and give examples of each.
Source – the site where assimilates are loaded into the phloem e.g. leaf
Sink – the site where assimilates are removed from the phloem e.g. root tip
State the 2 cells of phloem that are involved in active transport.
Companion cell
Sieve tube element
Describe the active process that loads sucrose into the phloem at the source.
- Hydrogen ions are actively transported out of the companion cell.
- A hydrogen ion concentration gradient is created.
- Hydrogen ions diffuse back into the companion cell through facilitated diffusion using a cotransporter.
- Sucrose or an amino acid diffuse with the hydrogen ion into the companion cell using the cotransporter.
Why do companion cells have many mitochondria?
To produce ATP to allow the active transport of hydrogen ions to occur.
Which structure do the assimilates pass through to get into the sieve tube element from the companion cell?
Plasmodesmata
How is a low hydrostatic pressure produced in the phloem at the sink?
- The assimilates/sucrose are unloaded from the phloem through facilitated transport.
- This increases the water potential in the sieve tube of the phloem at the sink.
- Water moves out of the sieve tube into the xylem by osmosis.
How is a high hydrostatic pressure produced in the phloem at the source?
- The assimilates/sucrose enter the sieve tube of the phloem and lower the water potential.
- Water moves in from the xylem by osmosis increasing the hydrostatic pressure.
What do the differences in hydrostatic pressure in the phloem at the source and sink cause to happen?
The assimilates/sucrose move from the area of high hydrostatic pressure (at the source) to an area of low hydrostatic pressure (at the sink) by mass flow.
