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Difficulty: MediumExcretion and Excretory Organs

Match each plant excretory structure or product on the left with its corresponding physiological mechanism or mode of elimination on the right.

  • Stomata and lenticelsRelease of gaseous metabolic by-products via simple diffusion
  • HydathodesExudation of liquid water containing dissolved salts through guttation
  • Old bark and heartwoodDeposition and long-term storage of tannins, resins, and gums in non-functional tissues
  • Calcium oxalate crystals (raphides)Insoluble waste precipitation within vacuoles to prevent cellular toxicity

Answer

Stomata and lenticels match with the release of gaseous metabolic by-products via simple diffusion; Hydathodes match with exudation of liquid water containing dissolved salts through guttation; Old bark and heartwood match with deposition and long-term storage of tannins, resins, and gums in non-functional tissues; Calcium oxalate crystals (raphides) match with insoluble waste precipitation within vacuoles to prevent cellular toxicity.
Each plant excretory structure is correctly paired with its specific mechanism: stomata and lenticels eliminate gaseous by-products by diffusion; hydathodes eliminate liquid water droplets containing dissolved minerals through guttation; old bark and heartwood store secondary organic metabolites like tannins and gums; calcium oxalate crystals safely isolate metabolic oxalic acid in an insoluble crystalline form inside vacuoles.

Step-by-Step Solution

1
Identify the primary excretory pathway for plant gases.
Stomata (in epidermal tissues of leaves) and lenticels (in bark of woody stems) serve as diffusion channels for CO2CO_2 from respiration and O2O_2 from photosynthesis.
Gaseous waste elimination relies on direct kinetic movement of gas molecules down concentration gradients.
2
Determine the mechanism associated with hydathodes.
Hydathodes exude drops of liquid water and dissolved minerals during guttation when transpiration rates are low and root pressure is elevated.
Hydathodes are permanently open pores at leaf margins distinct from stomatal guard cells.
3
Analyze how plants store organic secondary metabolites.
Non-utilizable organic substances such as resins, gums, and tannins are stored in non-functional secondary xylem (heartwood) or bark prior to organ shedding.
Plants lack complex excretory organs and frequently use tissue sequestration followed by abscission.
4
Evaluate the role of calcium oxalate crystal formation.
Toxic oxalic acid is neutralized by binding with calcium ions to yield insoluble raphide crystals stored inertly inside vacuoles.
Precipitating waste as insoluble salt crystals prevents osmotic imbalance and cytoplasmic chemical toxicity.

Key Concept

Plant Excretory Mechanisms and Waste Storage
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Topics

Excretion and Excretory Organs

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