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Question

Difficulty: MediumGrowth, Development, and Metamorphosis

During an investigation into seedling growth, a student recorded a significant increase in the fresh weight of plants following heavy irrigation, but observed no change in their dry mass. Which of the following best explains why dry mass is considered a more reliable parameter for measuring biological growth than fresh weight?

  1. Dry mass measures the irreversible accumulation of synthesized organic material and cellular structures, excluding temporary water fluctuations.Answer
  2. B
    Fresh weight reflects growth caused by auxins migrating toward and accumulating on the illuminated side of growing shoots.
  3. C
    Dry mass allows for non-destructive, repeated measurements of the exact same living seedling throughout its development.
  4. D
    Fresh weight translocates organic nutrients bidirectionally while dry mass translocates water and mineral salts unidirectionally.

Answer

Dry mass measures the irreversible accumulation of synthesized organic material and cellular structures, excluding temporary water fluctuations.
Growth is defined as a permanent and irreversible increase in size and dry mass resulting from cell division and the synthesis of new organic cellular material. Fresh weight varies considerably depending on water uptake, humidity, and transpiration rates, whereas dry mass measures the actual organic content synthesized by the plant.

Step-by-Step Solution

1
Define biological growth in living organisms
Biological growth is defined as an irreversible, permanent increase in size, dry mass, and cell number.
Temporary changes in shape or volume due to water uptake do not constitute true biological growth.
2
Compare fresh weight and dry mass parameters
Fresh weight includes total plant mass, composed largely of water subject to transpiration and absorption changes. Dry mass measures constant organic matter after water evaporation.
Water content varies rapidly with humidity, irrigation, and physiological state, making fresh weight an unreliable indicator of true cellular synthesis.
3
Identify the correct explanation
The option stating that dry mass measures the irreversible accumulation of synthesized organic material excluding water fluctuations is correct.
It accurately highlights why dry mass reflects true organic matter synthesis.

Key Concept

Measurement of growth (dry mass versus fresh weight)
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Topics

Growth, Development, and Metamorphosis

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