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Zorluk: ZorGrowth, Development, and Metamorphosis

A student monitored the growth of a cockroach nymph over a six-week period by measuring its linear body length at regular intervals. The resulting plot showed a distinct staircase (step-like) growth curve with flat horizontal plateaus interrupted by vertical increases, rather than a continuous smooth curve. Which of the following biological processes accounts for the rapid increase in body length between the horizontal plateaus?

  1. A
    Rapid mitotic division and elongation of jointed leg appendages occurring beneath an unbroken, flexible cuticle
  2. Periodic shedding of the rigid chitinous exoskeleton during ecdysis, allowing tissue expansion before the new cuticle hardensCevap
  3. C
    Continuous accumulation of dry biomass during intermoult periods causing gradual mechanical stretching of body segments
  4. D
    Secretion of high concentrations of juvenile hormone causing immediate fusion of abdominal segments

Cevap

Periodic shedding of the rigid chitinous exoskeleton during ecdysis, allowing tissue expansion before the new cuticle hardens
Arthropods possess an inelastic chitinous exoskeleton that prevents continuous expansion in linear dimensions. During the intermoult period (represented by the horizontal plateaus), tissue mass increases internally. However, visible increases in length occur abruptly during ecdysis (molting), when the old cuticle is shed and the soft, new cuticle expands rapidly prior to sclerotization (hardening).

Adım Adım Çözüm

1
Analyze the nature of growth curves in arthropods versus non-arthropod organisms.
Identify that arthropods exhibit discontinuous (step-like) linear growth curves due to their non-expandable chitinous exoskeleton.
The rigid cuticle restricts continuous increase in external dimensions such as body length.
2
Evaluate the physiological events occurring during the horizontal plateau phase.
Recognize that cell division and accumulation of dry mass occur during intermoult (instar) periods without changes in external linear measurements.
Internal tissue growth compresses within the fixed exoskeleton.
3
Identify the cause of the rapid vertical jump in the staircase curve.
Conclude that ecdysis (molting) allows rapid intake of air or water to expand body volume before the new cuticle hardens.
Linear growth occurs in short bursts immediately following the shedding of the old exoskeleton.

Anahtar Kavram

Discontinuous growth and ecdysis in arthropods
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Konular

Growth, Development, and Metamorphosis

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