I am studying high school biology and I got these two pieces of information in khan academy and wikipedia:
- Sieve elements in phloem are living cells because the translocation includes active transport which uses energy that is only produced in living cells. (Starting from 10:36 https://www.khanacademy.org/science/in-in-class-10-biology/in-in-life-processes/in-in-transportation-in-plants/v/phloem-translocation-life-processes-biology-khan-academy)
- All of the cellular functions of a sieve-tube element are carried out by the (much smaller) companion cell. (https://en.wikipedia.org/wiki/Phloem)
So this is my question: if the sieve elements do not actually produce the energy, why do they need to be alive? The argument that the required energy is only produced in the living cells is no longer relevant since the energy does not come from sieve elements themselves, but instead companion cells.
If being alive does not serve a specific function, then being dead cells like those that make xylem should cost less energy. However, this reasoning does not match with the fact that sieve elements do have organelles.
I am not sure about statement 1 since it is not from a formal wiki and I may be just getting an oversimplification of the functions of sieve elements.
