Looking for classes? Ksquare Career Institute, Bengaluru →
Function of companion cells is
A
Loading of sucrose into sieve elements by passive transport
B
Loading of sucrose into sieve elements
C
Providing energy to sieve elements for active transport
D
Providing water to phloem
Detailed Solution
Sieve tube elements lack a nucleus at maturity, and their functions are controlled by the nucleus of the adjacent companion cells, to which they are connected by pit fields.
According to the pressure flow (mass flow) hypothesis, sucrose made in the mesophyll cells is moved into the companion cells and then into the living sieve tube cells by active transport. This is called phloem loading.
Because loading is active (it uses ATP), it is not a passive process.
Loading makes the phloem hypertonic, so water enters it from the xylem by osmosis; the companion cells do not supply water.
Hence the function of companion cells is loading of sucrose into sieve elements.
According to the pressure flow (mass flow) hypothesis, sucrose made in the mesophyll cells is moved into the companion cells and then into the living sieve tube cells by active transport. This is called phloem loading.
Because loading is active (it uses ATP), it is not a passive process.
Loading makes the phloem hypertonic, so water enters it from the xylem by osmosis; the companion cells do not supply water.
Hence the function of companion cells is loading of sucrose into sieve elements.