Edexcel GCSE Biology · 1BI0
Specification 6.8 · Paper 2
Revise: Xylem and PhloemEach is supported by a neighbouring companion cell. Companion cells release energy by respiration and help load sucrose into the phloem.
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GCSE Biology · key term
A living cell alongside a phloem sieve-tube cell that supplies energy for transporting sucrose.
Used by Edexcel and OCR
Specification 6.8 · Paper 2
Revise: Xylem and PhloemEach is supported by a neighbouring companion cell. Companion cells release energy by respiration and help load sucrose into the phloem.
Specification B2.2h · Paper 1 (Foundation), Paper 3 (Higher)
A living cell next to a sieve tube element that provides it with metabolic support.
Do not say that xylem vessels are living cells. Their conducting cells are dead when mature, whereas phloem sieve tube elements and companion cells are living.
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At maturity they lack a nucleus and much of the internal machinery of an ordinary cell. This leaves more space for substances to move, but it also means that each sieve tube element depends on a nearby companion cell.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A living cell beside a phloem sieve tube that supplies energy for processes including the loading of sugars.
Revise: Xylem and PhloemCompanion cells beside the sieve tubes supply energy needed to load sugars into the phloem. This is an important contrast with the dead, hollow vessels of xylem: phloem relies on living cells for its transport function.