Which of the following statements about excretion in plants and animals is correct?

Question

Which of the following statements about excretion in plants and animals is correct?

1. A. Plants lack specialized excretory organs, so all metabolic wastes are removed exclusively through stomata by diffusion.
2. B. Plants assimilate ammonia into amino acids and can store waste in leaves, bark, and vacuoles. (Correct answer)
3. C. In mammals, the primary nitrogenous waste is uric acid, which requires minimal water for excretion compared to ammonia.
4. D. Animals and plants both rely mainly on transpiration as their primary mechanism of excretion.

Correct Answer

Option B — Plants assimilate ammonia into amino acids and can store waste in leaves, bark, and vacuoles.

Detailed Solution & Explanation

The correct answer is Plants assimilate ammonia into amino acids and can store waste in leaves, bark, and vacuoles.

Key Points

• Plants have no specialised excretory organs. They deal with waste by:
  • Assimilating ammonia into amino acids and other nitrogenous compounds rather than excreting it.
  • Storing wastes as resins, gums, tannins, latex and crystals in old leaves, bark, and cell vacuoles, then shedding those leaves or bark.
  • Releasing gaseous wastes through stomata and lenticels, and passing some solutes into the surrounding soil.

Additional Information

• Why the other statements are wrong:
  • Option A — plants do lack excretory organs, but wastes are not removed exclusively through stomata; storage in vacuoles and bark, and shedding of leaves, are equally important routes.
  • Option C — in mammals the chief nitrogenous waste is urea, not uric acid. Mammals are ureotelic. Uric acid is the waste of birds, reptiles and insects, which are uricotelic and conserve water by excreting it as a paste.
  • Option D — transpiration is a water-loss and transport mechanism, not an excretory mechanism, and animals do not transpire at all.
• The three excretory patterns:

• Useful plant products that are technically wastes: rubber (latex), gum arabic, resin, opium and quinine — all commercially valuable secondary metabolites.