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Difficulty: MediumSupport Structures and Locomotion

During a prolonged drought, a non-woody plant wilts due to a loss of turgor pressure in its soft tissues. Which of the following supporting tissues provides permanent mechanical strength to mature plant organs independent of water availability?

  1. Sclerenchyma tissue with dead, heavily lignified cell wallsAnswer
  2. B
    Collenchyma tissue with thin, unlignified primary cell walls
  3. C
    Parenchyma tissue with high central vacuolar water content
  4. D
    Phloem sieve tube elements with active cytoplasmic streaming

Answer

Sclerenchyma tissue with dead, heavily lignified cell walls provides permanent mechanical support independent of water availability.
Sclerenchyma cells develop thick secondary cell walls heavily impregnated with lignin and lose their living protoplasts at maturity. Because their mechanical strength stems from rigid chemical wall deposition rather than internal fluid pressure, they maintain structural integrity even during severe water stress.

Step-by-Step Solution

1
Differentiate between hydrostatic support and structural wall support in plants.
Hydrostatic support relies on osmotic turgor pressure inside living parenchyma cells, which fails during drought.
Loss of water reduces internal pressure against cell walls, leading to wilting.
2
Identify the tissue composed of thick, lignified, non-living cell walls at maturity.
Sclerenchyma tissue consists of fibers and sclereids with thick secondary walls impregnated with lignin.
Lignin provides high tensile and compressive strength that remains intact regardless of hydration state.

Key Concept

Plant Mechanical Support Tissues
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Topics

Support Structures and Locomotion

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