Transport of organic substances in the phloem Flashcards
(17 cards)
What is translocation?
Translocation refers to the movement of molecules or particles from on location to another within a cell or across cell membranes
What is the function of companion cells in phloem?
They are associated with sieve tube elements and help with transport by providing ATP and metabolic support
What tissue transports biological molecules in flowering plants?
Phloem
What are sieve tube elements?
Long, thin structures in the phloem arranged end to end, with perforated end walls forming sieve plates
What are the sites of production of sugars in a plant called?
Sources
What are the places where sugars are used or stored in a plant called?
Sinks
In which direction does translocation occur in the phloem?
Both upwards and downwards, depending on the location of sources and sinks
Name two organic molecules transported in the phloem
starts with = (S + Aa)
Sucrose and Amino acids
Name four organic ions transported in the phloem
starts with (K+Cl+P+Mg)
Potassium
Chloride
Phosphate
Magnesium ions
What is the currently accepted theory for translocation in plants?
The mass flow theory
Why can’t diffusion alone explain the transport of materials in the phloem?
The rate of movement is too fast to be explained by diffusion
What are the three main phases of the mass flow theory?
1/ Transfer of sucrose into sieve elements from photosynthesising tissue
2/Mass flow of sucrose through sieve tube elements
3/ Transfer of sucrose from the sieve tube elements into storage or sink cells
Where is sucrose manufactured in a plant?
In cells with chloroplasts using the products of photosynthesis
How does sucrose initially move from photosynthesising cells to companion cells?
By facilitated diffusion down a concentration gradient
How are hydrogen ions involved in the transfer of sucrose into sieve elements?
1/ Hydrogen ions are actively transported from companion cells into cell wall spaces using ATP
2/ Then they diffuse back into sieve tube elements through carrier proteins
What is the process called when sucrose is transported along with hydrogen ions into sieve tube elements?
What are the protein carries involved in co - transport called?
Co - transport
Co - transport proteins
Outline the full process of translocation
“Some Active Wasps Help Mighty Sunflowers Relax”
1/ Sucrose is produced in the source during photosynthesis
2/ Sucrose is then actively transported into sieve tube elements by companion cells, using ATP
3/ This lowers the water potential in the sieve tubes, so water enters by osmosis from the xylem
4/ The entry of water increases hydrostatic pressure in the phloem at the source
5/ Sucrose is transported by mass flow from the high - pressure source to the low - pressure sink
6/ At the sink, sucrose is actively removed from the phloem into surrounding cells
7/ This raises water potential in the phloem, so water leaves by osmosis, reducing pressure and maintaining the flow
