AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Phloem is composed of tubes of elongated cells. Cell sap can move from one…
Full specification wording
Plant organ system: Phloem is composed of tubes of elongated cells. Cell sap can move from one phloem cell to the next through pores in the end walls.
Phloem tissue forms tubes made of elongated living cells joined end to end.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 13 of 13
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Phloem tissue forms tubes made of elongated living cells joined end to end. The end walls between neighbouring phloem cells contain pores, so cell sap can pass from one cell to the next along the tube. This continuous pathway allows dissolved food molecules to be translocated from sources to sinks. The cells remain alive, which is essential because loading and unloading of sugars depends on energy from respiration. A useful method is to imagine a line of elongated cells with perforated end walls: sap enters at a source, flows through the pores, and leaves at a sink. Comparing this with xylem, whose cells are dead and hollow, helps clarify why phloem is described as living transport tissue.
What earns the marks
- Phloem is made of tubes of elongated cells arranged end to end.
- The end walls of phloem cells contain pores that allow cell sap to pass between cells.
- Cell sap moves from one phloem cell to the next along the tube rather than leaking randomly through side walls.
- Phloem cells are living, which supports the energy-dependent processes of translocation.
- The porous end walls create a continuous pathway from source to sink.
- A labelled diagram should show elongated cells, end walls with pores and the direction of sap movement.
Common mistakes and how to put them right
Describing phloem as dead hollow tubes.
Put it right: Phloem cells are living, whereas mature xylem vessels are dead.
Placing the pores in the side walls instead of the end walls.
Put it right: The pores are in the end walls between adjacent cells.
Confusing cell sap with cytoplasm alone.
Put it right: Cell sap is the fluid containing dissolved food molecules that moves through the pores.
Exam tips
- When drawing phloem, label elongated cells, end walls, pores and the direction of cell sap movement.
- Use the phrase 'through pores in the end walls' rather than vague wording such as 'through gaps'.
- Link structure to function by stating that the pores allow a continuous flow of cell sap along the tube.
Try the lesson
The start of the Plant organ system: Phloem is composed of tubes of elongated cells. Cell sap can move from one phloem cell to the next through pores in the end walls. lesson, made from checked teaching notes for this specification point.
Have a go first
In a plant stem, cell sap moves from one phloem cell to the next. Which structure allows this movement to occur?
Listen
Phloem tissue forms tubes made of elongated living cells joined end to end. The end walls between neighbouring phloem cells contain pores, so cell sap can pass from one cell to the next along the tube. This continuous pathway allows dissolved food molecules to be translocated from sources to sinks. The cells remain alive, which is essential because loading and unloading of sugars depends on energy from respiration. A useful method is to imagine a line of elongated cells with perforated end walls: sap enters at a source, flows through the pores, and leaves at a sink. Comparing this with xylem, whose cells are dead and hollow, helps clarify why phloem is described as living transport tissue. A strong answer earns marks for these points. Phloem is made of tubes of elongated cells arranged end to end. The end walls of phloem cells contain pores that allow cell sap to pass between cells. Cell sap moves from one phloem cell to the next along the tube rather than leaking randomly through side walls. Phloem cells are living, which supports the energy-dependent processes of translocation. Exam tip: When drawing phloem, label elongated cells, end walls, pores and the direction of cell sap movement.
Key words
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Structure and function of phloem
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Continuous transport pathways
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Living transport tissue
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See every definition
- Structure and function of phloem
- Phloem is composed of tubes of elongated cells, and cell sap can move from one phloem cell to the next through pores in the end walls.
- Continuous transport pathways
- The pores in the end walls create a continuous pathway along the tube, so cell sap can pass from one phloem cell to the next.
- Living transport tissue
- Phloem cells are living, which supports the energy-dependent processes of translocation.
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