On page 74, Shubin tell us about animals with exoskeletons and animals like us with the skeleton on the inside of our body. Using our previous knowledge, what are the two different skeletons made of and what are the benefits to having this skeletal plan? Why do some animals have an exoskeleton and some have an endoskeleton?
Benny Jeong
bennyjeong218@gmail.com
While human and fish contain teeth and inner skeletons made of hydroxyapatite, a crystal molecule that makes teeth/bones "hard" and resistant to breakdown and deterioration, exoskeletons found in clams and lobsters are typically made out of other materials such as calcium carbonate and chitin to cover the body in a protective shell. Some benefits to an exoskeleton include having a rigid support system that muscles can pull and contract against, more protection for soft inner tissues, and an outer covering that has more flexible joints for mobility than that of a simple mollusk or cnidarian shell. Thus, the hard, jointed composition of an exoskeletal structure is directly related to its functions for protection and mobility. Moreover, organisms with exoskeletons have proven benefits to survival since arthropods are generally considered the most successful and one of the most plentiful phylums. On the other hand, some advantages to endoskeletons are that they can easily support the large weight and size of organisms like humans without becoming too heavy, can metabolize certain minerals with the included hydroxyapatite molecules, and are not vulnerable to outside attack or weakness that exoskeletal organisms face when they molt (the periodical shedding and growing of new exoskeletons).
ReplyDeleteAnimals develop either an exoskeleton or endoskeleton due to environmental changes over time and evolution, because certain qualities or lifestyles that demand one skeletal structure or the other will give exoskeletal organisms physical advantages in one environment through natural selection, and vice versa. Since continual molting and shedding of shells prevents exoskeletal animals from developing the large size that endoskeletal animals may have, smaller marine organisms and insects are more likely to develop exoskeletons. Likewise, a larger terrestrial mammal that requires teeth and bones to support itself and masticate food will find that having an endoskeleton gives them a selective advantage in their environment.
Sources:
1.http://faculty.fmcc.suny.edu/mcdarby/animals&plantsbook/animals/07-Arthropods.htm#Skeletons
Christine Lin
choco_cat11@comcast.net
Exoskeleton is where the support structures of animals such as insects, crabs, shrimps, and lobsters are located on the outer surface of the body. It is mostly composed of chitin which are linked units of amino sugar called N-acetyl-glucosamine (Lale). Chitin produces a material called chitosan which is used “as a flocculating agent, a wound healing agent, a sizing and strengthening agent for paper, and a delivery vehicle for pharmaceuticals and genes.” (Lale) One of the major functions of this structure is that the animal has the capacity to “cause differences in support muscle/organ development” (Compare).
ReplyDeleteThere are many advantages of having an exoskeleton. One of them is that they are capable of handling natural damage and the organs are well protected. The skeleton outside absorbs as much of the damage as possible so not as much is left when it comes to the organs.
There are more disadvantages in having an exoskeleton. First of all, they are heavier and the muscles are the main tissues to keep the exoskeleton in position and act as a supporting agent. Also, once the chitin is breached, there are no bones to absorb the damage therefore leaving the delicate organs to take on. No matter how hard the bones become, they are at a high risk of shattering because some of these invertebrates use their back to move things around from place to place. The more they are used, the more the bones will wear out and weaken. The biggest disadvantage is that an exoskeleton prevents efficient motility for a lot of creatures such as a turtle. Even though the shell provides a strong support and a shelter for the delicate animal, it does not allow the turtle to move as fast (Compare). The exoskeleton will not be able for function properly in terms of protection and allowing motility if the structure is heavier or the same weight as the body itself.
Endoskeleton is made of bone, cartilage and mineralized tissue. Cartilage is the soft form a bone and it hardens as one matures and gets older.
One of the advantages of having an endoskeleton is that it functions as a support system for the body structure and it often serves as “an attachment site for muscle and a mechanism for transmitting muscular forces” (Endoskeleton). This skeleton structure is mostly found in animals of classes such as Chordata, Echinodermata, Porifera, and Coleoidea (Endoskeleton). It also gives a true shape to the body, helps protect the internal organs, and promotes mobility. Endoskeleton protects the internal organs more than an exoskeleton because the bone and mineralized tissue is stronger and thus is less prone to fracture and get damaged easily.
One major disadvantage is that the endoskeleton does not protect every organ as a whole. For example, in humans, there are no skeleton structures found in the abdomen area. This soft tissue area with muscular structures are at great risk for injury while the lungs and the heart are not because of the strong rib cage. Also, since the skeleton is located deep into the tissues and muscles, it does not protect the skin and the muscles that surround the bone.
Chandrika D.
(shiningstar0393@gmail.com)
“Compare and Contrast Advantage or Disadvantages of an Exoskeleton?”. Retrieved on
April 1, 2011, from
http://answers.yahoo.com/question/index?qid=1006032310650
“Endoskeleton”. Wikipedia. Retrieved on April 10, 2011 from
http://en.wikipedia.org/wiki/Endoskeleton
Lale, R. and Mis, Z. 2005. Retrieved on April 1, 2011, from http://www.euchis.org/
Although I agree with Christine and Chandrika on some of the advantages of exoskeletons, I think they overlooked two key benefits of exoskeletons.
ReplyDeleteThe first important feature of exoskeletons is their role in water conservation. The transition from water-based life to land-based life was made difficult largely by the lack of moisture and water on land. Plants and animals had to adapt to their new, dry environment in order to avoid desiccation. Somewhat like how plants evolved C4 and CAM systems to conserve water, exoskeletons help animals on land conserve their moisture because they have a water-impermeable layering of chitin and lipids that greatly reduces evaporative water loss (Campbell 201; http://livingwithinsects.wordpress.com/2011/03/17/a-polymer-for-the-ages/). This allows organisms like arthropods to remain in land environments that are not moist but still conserve their moisture to survive more efficiently.
The second feature is the role of exoskeletons in innate immunity. Since arthropods, which have exoskeletons, only have innate immunity (as opposed to vertebrates, that also have acquired immunity), their barrier defenses are even more important in preventing infection. Whereas organisms with an endoskeleton have somewhat porous skin and moreover digestive tracts, arthropods and other organisms with exoskeletons have chitinous barriers inside and out that further protect them from pathogens (Campbell 932). The barrier provided by chitinous exoskeletons reduces the amount of pathogens that can get inside the organism’s body, much more so than fleshy endoskeletons, which decreases infection and is another advantage of exoskeletons.
- Vincent Fiorentini
(vincent@panatechcomputer.com)