Biology 9700 · AS & A Level · Structure of transport tissues

Structure of transport tissues — practice question

Which row gives the correct description of the adaptations of companion cells, phloem sieve tube elements and xylem vessel elements for their roles?

  • Acompanion cell: a thin layer of cytoplasm to reduce resistance to flow; phloem sieve tube element: strong, lignified cell walls for supporting the plant; xylem vessel element: many plasmodesmata for communication between cells
  • Bcompanion cell: empty cells allowing water to flow freely; phloem sieve tube element: many plasmodesmata for communication between cells; xylem vessel element: strong, lignified cell walls for supporting the plant
  • Ccompanion cell: many plasmodesmata for communication between cells; phloem sieve tube element: a thin layer of cytoplasm to reduce resistance to flow; xylem vessel element: empty cells allowing water to flow freely
  • Dcompanion cell: strong, lignified cell walls for supporting the plant; phloem sieve tube element: empty cells allowing water to flow freely; xylem vessel element: a thin layer of cytoplasm to reduce resistance to flow

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