Exoskeletons have a role in defense from pests and predators, support and in providing an attachment framework for musculature. Exoskeletons contain chitin; the addition of calcium carbonate makes them harder and stronger. Ingrowths of the arthropod exoskeleton known as apodemes serve as attachment sites for muscles.

Exoskeleton is mainly responsible for the diversification of insects on land.

Explanation:
- Insects are the most diverse group of animals on Earth, with over a million described species. They have successfully colonized almost every terrestrial habitat, including deserts, forests, grasslands, and even the Arctic.
- One of the main reasons for their success and diversification is their exoskeleton, a rigid external covering that provides several advantages.
- The exoskeleton is made of a tough and flexible material called chitin, which provides support and protection to the insect's body. It acts as a suit of armor, shielding the insect from physical injuries, predators, and desiccation.
- The exoskeleton also serves as an attachment site for muscles, providing the insect with strength and mobility. It allows for efficient movement and the ability to resist external forces, such as wind or water currents.
- Another important feature of the exoskeleton is its ability to grow with the insect. Insects undergo a process called molting, where they shed their old exoskeleton and replace it with a larger one. This allows them to grow and adapt to their environment throughout their life cycle.
- The exoskeleton also plays a crucial role in insect flight. Insects have developed specialized wings that are attached to their exoskeleton. The rigid structure of the exoskeleton provides support for the wings, allowing insects to fly efficiently.
- Furthermore, the exoskeleton provides a barrier against microbial infections and parasites. It forms a physical barrier that prevents the entry of pathogens into the insect's body.
- The exoskeleton also helps in reducing water loss through the insect's body. Insects are highly susceptible to desiccation, and the exoskeleton acts as a waterproof layer, preventing excessive water loss and maintaining the insect's internal moisture balance.
- Overall, the exoskeleton is a key adaptation that has allowed insects to thrive and diversify on land. It provides protection, support, mobility, flight capabilities, and resistance to environmental challenges, making insects one of the most successful groups of organisms on Earth.