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.

Answer 1

Sieve-tube elements in phloem rely on companion cells for metabolic support and energy, even though they do not produce energy themselves.

Step-by-step explanation:

Sieve-tube elements in phloem do not produce energy directly, but they still need to be alive because they rely on companion cells for metabolic support and energy. The sieve-tube elements are responsible for transporting organic substances like sugars and amino acids through the phloem. The companion cells, which are adjacent to the sieve-tube elements, have more ribosomes and mitochondria, allowing them to produce energy and provide metabolic support to the sieve-tube elements.