Final answer:
Arthropods developed an exoskeleton for adaptation to terrestrial life, but face challenges with growth due to its non-expanding nature. They overcome this by molting to accommodate growth. The exoskeleton is fortified with materials like calcium carbonate and has apodemes for muscle attachment, while jointed limbs support mobility.
Step-by-step explanation:
Restraints of the Arthropod Exoskeleton and How Arthropods Have Overcome These Restraints
Arthropods evolved a protective exoskeleton as a way to adapt to life on land. One of the main restraints of this exoskeleton is that it does not grow with the organism. To overcome this, arthropods must shed or molt their exoskeletons in a process called molting. When an arthropod grows, it has to synthesize a new, larger exoskeleton underneath the existing one, and then molt to allow for further growth.
Due to the fixed size of the exoskeleton, it can lead to limited growth. The exoskeleton's thickness must be increased to accommodate any gain in weight which presents another challenge. An arthropod's body weight can increase by a factor of eight with a doubling of body size, which necessitates a significantly thicker exoskeleton. This need for a thicker chitin-based exoskeleton usually limits arthropods to a relatively small size.
Additionally, the exoskeleton must be both strong to provide protection and support, and flexible to allow for movement. The exoskeleton is reinforced by materials such as calcium carbonate, which is fused to the animal’s epidermis. Muscles are attached to ingrowths called apodemes which function similarly to tendons. Overcoming the rigid nature of exoskeletons, arthropods developed jointed limbs that facilitate movement and support a wide range of activities, contributing to their evolutionary success.
To address respiration issues, terrestrial arthropods have adapted by evolving structures such as book lungs or trachea for breathing air. These adaptations, along with the development of the exoskeleton, were crucial to allowing arthropods to thrive on land after making the transition from aquatic environments.