Comparative Table: Endoskeleton and Exoskeleton Functions, Structure & Examples
Support and protection are required for all animals, including vertebrates and invertebrates. Such support and protection can be offered by the skeleton. The endoskeleton provides this support and protection to vertebrates, whereas invertebrates rely on the exoskeleton.
In genetic terms, the skeleton is a protective and supporting framework for an animal's body. Based on its arrangement on the body, the skeleton can be divided into two types, endoskeleton and exoskeleton.
What is an Endoskeleton?
An Endoskeleton is a framework of rigid and hard tissues, also known as bones inside an organism’s body. The Endoskeleton supports the structure and also protects the vulnerable organs and internal tissues. A lot of vertebrates (an animal that possesses a backbone or a spinal column) like mammals, reptiles, amphibians, birds, and fishes have an endoskeleton that is composed of tissues in the form of bones and cartilages.
The endoskeleton is the interior bone and cartilaginous skeleton of vertebrates that provides support and protection. The term "endoskeleton" comes from the Greek words "endon" which means "inner" or "inside," and "skeletons" which means "skeleton." The endoskeleton provides the foundation to the body and it gives physical strength and support to the body of an animal and also protects vital organs such as, lungs, heart, brain, kidney, etc. Endoskeleton is composed of bones and connective tissues including cartilage, ligament and tendons.
Functions of the Endoskeleton
The first and foremost function of the Endoskeleton is to protect and support the body. Without an endoskeleton, the body would have no shape whatsoever, and for e.g., a human would not be able to stand up on its own. The axial skeleton, which is made up of the skull, the rib cage, and the vertebral column, performs the function to protect the fragile organs like the heart, the liver, the kidneys, and the lungs. The appendicular skeleton is made up of the legs and feet, the arm bones, the pelvic girdle, and the shoulder blades, which support the structure and protect the limbs.
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What is an Exoskeleton?
An exoskeleton is a hard surface that covers the exterior of most animals, known as the invertebrates (an animal that lacks a backbone, for e.g., arthropod, mollusk, annelid, coelenterates, etc.). Just like the Endoskeleton in mammals and other animals, the exoskeleton helps the body by supporting and protecting them. The hard and rigid exoskeleton also provides protection from predatory animals. Also, the waterproof feature of an exoskeleton makes sure that the moisture is removed from the surface of the animal, hence protecting it and acting as a barrier.
The word "exoskeleton" comes from the Greek words "exo" which means "outside," and "skeletos," which means "skeleton." An exoskeleton, like an endoskeleton, supports and protects the animal's body. The exoskeleton is a hard protective shell that covers and protects the animal's body. Exoskeletons are seen in invertebrates that lack a backbone. Insects, crustaceans, as well as the shells of some sponges and the numerous families of shelled molluscs, all have exoskeletons. The chief component of the exoskeleton of insects and crustaceans is chitin. The exoskeleton is typically rigid and inflexible, but it may include joints, sections, or breathing holes (spiracles).
Soft interior sections of animals with exoskeletons expand as they mature. Their exoskeletons, on the other hand, do not expand. The exoskeleton splits apart and falls away when an animal's soft body becomes too large for it. This is referred to as "molting." The body of the animal then produces a new exoskeleton. During the formation of the new exoskeleton, the animal is exposed to various threats.
Clams, oysters, mussels, and snails, on the other hand, have an exoskeleton that is similar to a shell. Calcium carbonate is the principle construction material of a shell. Shelled animals do not molt their shells. As the animals expand, their shells form around the edges.
Functions of the Exoskeleton
An exoskeleton is made up of tissues, which adds to the strength and rigidness of the exoskeleton. The functions of an exoskeleton are remarkably similar to that of an endoskeleton. It protects the animals from attacks by unseen creatures so that the soft organs inside them do not get damaged. Chitin is the most important component of the exoskeleton in insects, which protects them. Different types of exoskeletons are The Arthropod Cuticle, the shell, and the molting.
Difference Between Endoskeleton and Exoskeleton in Humans
The Endoskeleton of an animal is present inside the body, which is also known as the internal skeleton. Meanwhile, the exoskeleton of an animal is present outside the body, which is also known as the external skeleton.
The exoskeleton is made up of hard bones and malleable cartilage. Meanwhile, the exoskeleton is made up of scales, cuticles, and shells formed by the chitin tissue.
The Endoskeleton is mainly found inside of vertebrates, which are mammals, birds, fishes, amphibians, and reptiles, whereas the exoskeleton is found inside of invertebrates like insects, spiders, crabs, centipedes, and millipedes.
The Endoskeleton is made up of the endoderm (the innermost layer of cells of an embryo during the early development stage) and is a living structure. Meanwhile, the exoskeleton is made up of the ectoderm (the outermost layer of cells of an embryo during the early development stage) and is a non living structure.
The Endoskeleton of animals grows with the body throughout their lives, and it does not molt. Whereas the exoskeleton does not grow with the body, it remains the same but goes through a shedding phase, known as molting.
Similarities of endoskeleton and exoskeleton
The major purpose of an animal's endoskeleton and the exoskeleton is to provide structural support.
Both the endoskeleton and the exoskeleton let animals move about and protect their internal organs.
FAQs on Endoskeleton vs Exoskeleton: Main Differences
1. What is the main difference between an endoskeleton and an exoskeleton?
The primary difference lies in their location. An endoskeleton is an internal structural framework found inside an organism's body, such as the bony skeleton in humans. In contrast, an exoskeleton is a hard, external covering on the outside of an organism's body, like the shell of an insect or crab. The endoskeleton grows with the body, while the exoskeleton must be shed periodically.
2. What are some examples of animals with an endoskeleton and an exoskeleton?
Animals with different types of skeletons provide clear examples of this biological distinction:
Animals with an endoskeleton: This group includes all vertebrates like humans, fish, birds, reptiles, and amphibians. Their skeletons are made of bone and cartilage.
Animals with an exoskeleton: This group primarily includes arthropods such as insects (grasshoppers, beetles), arachnids (spiders), and crustaceans (crabs, lobsters). Their skeletons are made of chitin.
3. How does an endoskeleton facilitate movement in vertebrates?
An endoskeleton facilitates movement by acting as a system of levers. Muscles are attached to the bones via tendons. When a muscle contracts, it pulls on a bone, causing it to move at a joint. The different types of joints, such as hinge joints (in the elbow) and ball-and-socket joints (in the hip), allow for a wide range of specific movements, from simple bending to full rotation.
4. What are the typical materials that make up endoskeletons and exoskeletons?
The composition of these skeletons is fundamentally different. Endoskeletons in vertebrates are primarily composed of living tissues like bone (which is a matrix of collagen and calcium phosphate) and cartilage. In contrast, exoskeletons are non-living and are mainly composed of a tough, structural polysaccharide called chitin, which may be further hardened with minerals like calcium carbonate.
5. How does having an exoskeleton affect an animal's growth?
An exoskeleton is a rigid, non-living structure that cannot grow with the animal. To increase in size, an animal with an exoskeleton must undergo a process called moulting or ecdysis. During this process, it sheds its old, smaller exoskeleton and forms a new, larger one. This period of moulting is a significant disadvantage as it leaves the animal soft-bodied and extremely vulnerable to predators until the new skeleton hardens.
6. What are the key functions of the human endoskeleton besides providing structure?
Beyond providing a structural framework and shape, the human endoskeleton performs several other vital functions:
Protection: It shields vital internal organs, such as the skull protecting the brain and the rib cage protecting the heart and lungs.
Movement: It acts as an attachment point for muscles, enabling locomotion.
Mineral Storage: It serves as a reservoir for minerals, especially calcium and phosphorus, playing a key role in homeostasis.
Blood Cell Production: The bone marrow within bones is the site of haematopoiesis, the process of producing red and white blood cells.
7. Is a snail's shell considered an exoskeleton? How does it differ from an insect's exoskeleton?
While a snail's shell is an external protective structure, it differs from a true exoskeleton found in arthropods (like insects). The main difference is function and structure. A snail's shell, made of calcium carbonate, is primarily for defence and preventing dehydration; it is not jointed and does not have muscle attachment points for locomotion. An insect's chitinous exoskeleton is a complete body covering with flexible joints and internal muscle attachments that are essential for movement.
8. What are the main advantages and disadvantages of an endoskeleton compared to an exoskeleton?
Both skeletal types have distinct evolutionary trade-offs:
Endoskeleton Advantages: Allows for continuous growth without moulting, supports a much larger body size and weight, and offers greater flexibility and range of motion.
Endoskeleton Disadvantages: Provides less external protection from predators and physical damage.
Exoskeleton Advantages: Offers excellent protection against predators and the environment, prevents water loss, and provides a robust structure for muscle attachment.
Exoskeleton Disadvantages: Restricts growth, requires the vulnerable process of moulting, and limits the maximum size an organism can attain.
