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Questions and Answers
Which of the following characteristics is present in companion cells but absent in sieve tube elements?
Which of the following characteristics is present in companion cells but absent in sieve tube elements?
- Cell walls containing lignin
- Perforated end walls
- Nucleus (correct)
- Living cytoplasm
What structural feature facilitates the transport of substances between adjacent sieve tube elements?
What structural feature facilitates the transport of substances between adjacent sieve tube elements?
- Cytoplasmic strands
- Thick cell walls containing lignin
- Sieve plates with small holes (correct)
- Companion cells with nuclei
How do companion cells support the function of sieve tube elements, which lack a nucleus?
How do companion cells support the function of sieve tube elements, which lack a nucleus?
- By directly transporting water through xylem tissue
- By controlling both cells' activities through their nucleus (correct)
- By providing structural support with thick lignin walls
- By producing sieve plates for efficient substance transport
In xylem tissue, what is the main function of the gaps formed where the end walls of two cells have been lost?
In xylem tissue, what is the main function of the gaps formed where the end walls of two cells have been lost?
What distinguishes the cell walls of xylem from those of phloem?
What distinguishes the cell walls of xylem from those of phloem?
What cellular component is present in xylem tissue to help in the transfer of water?
What cellular component is present in xylem tissue to help in the transfer of water?
What is the direct function of the sieve plate?
What is the direct function of the sieve plate?
How does the absence of lignin in the cell walls of sieve tube elements relate to their function?
How does the absence of lignin in the cell walls of sieve tube elements relate to their function?
If a plant cell lacks a nucleus, which nearby cell provides the function of controlling the cell?
If a plant cell lacks a nucleus, which nearby cell provides the function of controlling the cell?
If a plant has a transverse section that lacks lignin, which of these is the plant section?
If a plant has a transverse section that lacks lignin, which of these is the plant section?
Flashcards
Phloem Tubes
Phloem Tubes
Phloem tubes consist of cells connected end to end, with perforated end walls.
Sieve Plates
Sieve Plates
Perforated end walls in phloem tubes that allow substances to pass through.
Sieve Tube Element
Sieve Tube Element
A cell in phloem tubes containing living cytoplasm but no nucleus.
Companion Cell
Companion Cell
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Xylem Tissue
Xylem Tissue
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Lignin
Lignin
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Study Notes
Structure of Phloem Tubes
- Phloem tubes are composed of cells joined end to end.
- The end walls of phloem tubes do not completely break down, instead they become perforated with small holes.
- These perforated end walls are called sieve plates.
- Each cell in the phloem tube is called a sieve tube element.
- Sieve tube elements contain living cytoplasm but lack a nucleus.
- The cell walls of sieve tube elements do not contain lignin.
- Each sieve tube element has a companion cell next to it.
- The companion cell has a nucleus that probably controls both cells.
Xylem Tissue Sections
- Transverse section shows the cells in cross-section.
- Longitudinal section shows the cells lengthwise.
- Xylem tissue contains thick cell walls containing lignin.
- The gap between the end walls of two cells shows where the end walls have been lost.
- The space in the xylem cell has no cytoplasm to allow water to pass through.
Sieve Tube Element Sections
- The end walls of the two cells do not completely break down; this is a sieve plate, which has small holes.
- A companion cell containing a nucleus and cytoplasm is found next to a sieve tube element.
- Cytoplasm can be seen as strands.
- Cell walls do not contain lignin.
- Transverse section of the cells.
- Companion cells are seen when the section runs through the sieve plate.
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