Transport of organic substances in the phloem Flashcards
What is the process by which organic molecules and some mineral ions are transported in plants?
Translocation
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 first stage of the mass flow theory, the transference of sucrose into sieve elements from photosynthesising tissue
1/ Sucrose is manufactured from the products of photosynthesis in cells with chloroplasts
2/ The sucrose diffuses down a concentration gradient by facilitated diffusion from the photosynthesising cells into companion cells
3/ Hydrogen ions are actively transported from companion cells into the spaces within cell walls using ATP
4/ These hydrogen ions then diffuse down a concentration gradient through carrier proteins into the sieve tube elements
5/ Sucrose molecules are transported along with hydrogen ions in a process called co - transport
The protein carriers are therefore also known as co - transport proteins
