Translocation of sucrose Flashcards
What is translocation?
movement of organic compounds from where they are made at their source, to where they are required at their sink.
What type of process if translocation?
It is an active process which can be used to transport phloem up or down the plant.
What is the source
Where an organic compound is made (where all the energy is created)
what is the sink?
Where an organic compound is required and used. (where it is neede)
what is a Assimilate
the stuff that flows through the pholem
What are some examples of sources
Green leaves and stems
Storage organs such as tubers when unloading stores during a growth period
What are some examples of sinks
-Roots that are absorbing mineral ions via active transport.
-Meristems
Any part of the plant creating food stores such as tubers.
What is pholem loading
Movement of soluble product into the phloem.
How does assimilates move into the pholem
They move into the phloem by diffusion.
What is the role of assilimiates in the phloem (apoplast)
Assimilates move through the spaces in the loose cellulose fibres of the cell wall, known as the apoplast.
What is phloem unloading
-Sucrose is offloaded to cells which need it by diffusing down a concentration gradient.
Loss of solutes from phloem causes water to osmose to surrounding cells. Some of the water enter the transpiration stream in xylem
What are the evidence for transloaction?
-If mitochondria are poisoned, translocation stops, suggesting it is an active process which requires ATP.
Why might the mass flow hypothesis not be true?
The rate of translocation of different organic substances was measured and the results showed that amino acids appeared to travel more slowly than sucrose
-The mass flow hypothesis states should be flowing at the same rate
Some scientists have conducted experiments that detected different substances (within the same sieve element) moving in opposite directions
-The mass flow hypothesis states everything should be flowing in one direction
What does the mass flow hypothesis state
Dissolved sucrose moves in pholem by means of a pressure graident between sources (cells in the leaves to roots)
A high concentration of sucrose reduces mesophyll and sieve cell water potential so water is drawn, creating a HP
This forces the MF of the pholem sap towards the sink where HP is lower due to the use of sucrose or its storage
Phloem vessels are made up of two types of cell what are they?
sieve tube elements and companion cells.
How are sieve tubes formed
sieve tube elements are living cells and are joined end-to-end
What are sieve plates?
They are plates formed at the end of sieve tube elements
What is the role of sieve plate? (S&F)
contains lots of holes to allow solutes to move from one cell to the next.
What adapation does the sieve tube have?
contain no organelles and very little cytoplasm to create more space for solutes to be transported.
What is each sieve tube element assoicated with (S&F)
Companion cell
What does the companion cell contain? (S&F)
which contains a nucleus and is packed full of mitochondria.
What is the role of mitochondria in the companion cell? (S&F)
The mitochondria provide lots of energy for the active loading of sucrose into the sieve tube element
How are the sieve tube element and companion cell connected? (S&F)
connected through plasmodesmata (channels in the cell wall) which allows the two cells to communicate.
How are the sieve tubes adapted to its function?
Sieve tubes
Companion cells
what is + of sieve tube elements having thin cytoplasm?
Reduces friction to facilitate the movement of assimilates
What is the positive of sieve tube elements have cellulose cells walls
strengths the wall to withstand the hydro-static pressure that moves assimilates
what is mass flow hypothesis
`how solutes are transported from source cells into sinks through the phloem
