HardBiologyHigh School (11–12)Tissues and Organs › Anatomy of Flowering PlantsTissues and Organs › Plant TissuesConceptualA-LevelIB
A mature sieve tube element has no nucleus, yet it stays alive for a long time…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A mature sieve tube element has no nucleus, yet it stays alive for a long time.
- Which cell lies beside it and controls its work?
- Name one other job of that cell.
- Is the xylem vessel living in the same way? Explain.
Need a reminder? The key ideaShow
Xylem carries water and minerals: tracheids, vessels, xylem fibres (dead) and xylem parenchyma (living). Phloem carries food: sieve tube elements, companion cells, phloem parenchyma (living) and phloem fibres (dead). In a stem the protoxylem lies towards the centre (endarch); in a root it lies towards the outside (exarch).
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The companion cell. It has the nucleus that controls both cells.
Step 2. (b) It helps to keep up the pressure gradient in the sieve tube, which moves the food.
Step 3. (c) No. A vessel member is dead at maturity and has no cytoplasm, so nothing controls it. It is only an empty tube.
Answer: (a) the companion cell; (b) it helps keep up the pressure in the tube; (c) no, a vessel is dead.
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