6.2 Skeletons (ESG82)

The skeleton is the supporting structure of one organism. There are three different types of skeletons: hydrostatic skeletons, endoskeletons and also exoskeletons.

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Hydrostatic skeleton: Water exerts push on muscular walls, because that example, in jellyfish.Exoskeleton: The steady chitinous or mineralised external shell of one organism, because that example, the covering of a grasshopper or prawn.Endoskeleton: A cartilaginous or mineralized support structure inside the body, for example, in humans and also other vertebrates.

In this chapter we will certainly be spring at assistance systems in animals and also investigating the human skeletal system in some depth.

As girlfriend will find out in the chapter History the Life ~ above Earth, numerous of these structural adaptations permitted animals to relocate from water ~ above land.

The evolutionary development of the skeleton (ESG83)

Learners do have to know detail from this ar on the advancement of skeletons. Rather, it is necessary that they understand how type has adapted to function over time. This section have to be provided to reinforce the learner"s previous expertise of evolution, covered in earlier grades, and also should lay a foundation for the later on chapter on the "History the Life on Earth".

Body support listed by water

The earliest creates of life developed in the oceans. The reality that this is one aquatic environment is key. Water is about \(\text1 000\) time denser than air. The high density of water permits organisms come float, because of a physical, upward force inherent in liquids well-known as buoyancy. Buoyancy allowed organisms come grow and reach large sizes due to the fact that the buoyancy pressure supported the body weight of these animals. However, the thickness of water additionally provides resistance come movement, and animals had to it is adapted to ensure the they were able to move properly through water.

An beforehand adaptation by organisms was the capability to adjust the hydrostatic push within various chambers of your bodies to permit quick movement. This resulted in the development of hydrostatic skeletons. Pets with this kind of skeleton incorporate jellyfish, octopus and also sea anemones. The an altering shape the the pet reduces both friction and drag.


Figure 6.1: The animal over is a jellyfish. It offers its muscle to contract against the hydrostatic skeleton come bring about movement.

Over time, in order to filter movement and improve protection from predators, part organisms arisen a difficult chitinous exoskeleton. Exoskeletons first developed in the aquatic setting in ancient arthropods. Pets with this type of skeleton incorporate crustaceans prefer crabs and lobsters.


Figure 6.2: Crustaceans, such as this crab, emerged a protective exoskeleton.

Eventually, there to be some animals that arisen a skeleton structure interior to the body, i m sorry would come to be the vertebrate team of animals. These pets have one endoskeleton. Initially, all endoskeletons to be made that cartilage, which is a dense rubbery type of tissue. Later, endoskeletons the bone evolved.


Figure 6.3: The an initial vertebrates developed in the oceans. This fish has an internal endoskeleton that renders it streamlined and enables it to move rapidly with water.

The adaptation of the skeleton to a terrestrial environment

The two significant requirements for survive on land space the development of a suitable support system and an air breath mechanism. Among the biggest problems encountered by pets moving indigenous water come land to be the loss of the effect of buoyancy. In order to respond to this, pets needed to develop strong limbs and had to it is adapted the skeleton to assistance their body weight on land. Moving efficiently on land is essential, particularly if one demands to protect against predators, capture prey, or it is adapted to a particular habitat. Various skeleton species have solved these difficulties in various ways.

Animals through exoskeletons like arthropods (a class of animals including insects, crustaceans and arachnids) transitioned native sea come land long prior to the vertebrates (organisms v endoskeletons). A major factor in their success to be the exoskeleton which provides attachment for muscles managing locomotion (movement that appendages). Exoskeletons also listed some protection from dessication (water loss).


Figure 6.4: This beetle is an instance of a insect. Insects have a protective exoskeleton that made it feasible for them to colonise land numerous years ago.

Amphibians with endoskeletons , like frogs and newts, live both on the land and in the water. Your skeletons have adjusted to give advantages in both conditions. They have calcified skeleton to assistance their body weight under the force of gravity. Their skull is light and flattened, for both motility on land and a systematized shape for moving quickly in water. Their pectoral girdle is adjusted to give support for the forelimbs, i m sorry absorb the body weight as soon as landing ~ a jump.


Figure 6.5: Amphibians were the an initial vertebrates to colonise land. They start their life-cycle in water, and also emerge top top land as adults.

Depending top top their means of locomotion, terrestrial pets needed to adapt their shapes and skeletons to conquer the impacts of gravity. Limbless animals, such as snakes, had to overcome drag and friction. Flying animals such together birds and also bats need light skeletons and also very solid sternums for wing muscle attachment. Pets that assistance their bodies clean of the ground essential an power efficient means of preserving balance. Because that this reason, the leg bones of most animals are held straight underneath the body. In this position they act as props or struts and also it is the bones quite than the muscles that take most of the stress, overload of the body"s weight.


Figure 6.6: floor vertebrates frequently have foot placed straight beneath the body. The legs acts together struts, and also are the most energy-efficient method to save the human body suspended above the ground.

Hydrostatic skeleton (ESG84)

A hydrostatic skeleton is a structure found in numerous cold-blooded and also soft-bodied organisms. It consists of a fluid-filled cavity, i beg your pardon is surrounded by muscles. The cavity is referred to as a coelom and also in some animals this cavity is filled v a blood-like substance referred to as haemocoel. The fluid presses versus the muscles, which consequently contract versus the pressure of the fluid. The liquid is incompressible and thus maintains a continuous volume against which the muscles deserve to contract. The hydrostatic skeleton prevents the collapse of the body. The muscle in the body act versus the fluid and also in doing for this reason bring around movement. If the body is segmented, the pressure of the fluid is localised in a couple of segments in ~ a time. Hydrostatic skeletons occur in flatworms, round worms, earthworms, starfish and also slugs.

Note the starfish and other Echinoderms have actually an external skeleton that calcareous (chalky) ossicles (little bones) or spicules which room like tiny spines because that protection. This external skeleton encloses a water vascular system with tube feet the are relocated by fluid pressure alters (it serves together a hydrostatic skeleton which controls movement).


Figure 6.7: The animal over is a jellyfish. It provides its muscle to contract versus the hydrostatic skeleton come bring around movement.


Figure 6.8: The animal depicted over is one Echinoderm - a starfish - which offers its pipe feet because that movement.

Advantages that a hydrostatic skeleton

Fluid shape: This allows organisms through hydrostatic skeletons come fit v oddly shame passages, i beg your pardon is valuable for burrowing or swimming.Strength: Creatures v hydrostatic skeletons have the right to squeeze in between spaces and also expand, making a "prying open" movement which allows them to pressure their way into miscellaneous regions of rock and soil surfaces.Healing: healing takes place faster in organisms through hydrostatic skeletons 보다 in organisms through bone structures. This is due to the fact that the haemocoel included within the hydrostatic skeleton is made up mostly of water, and thus, can be refilled quickly. This allows many organisms through hydrostatic skeletons such together earthworms to grow ago their body mass after damage. Lightweight: The hydrostatic skeleton permits the animal to move in a much more flexible manner together it needs very small muscle mass for movement. Circulation: The fluid cavity enables circulation of nutrients and also waste. Protection: The hydrostatic skeletons cushions the inner organs the the animal from shock. Suited to environment: Hydrostatic skeletons are suited for life in moist or aquatic environments, relying on the animal"s adaptations.

Disadvantages that a hydrostatic skeleton

Structure and surface because that attachment: The hydrostatic skeleton lacks a structure and does not have surfaces because that the attachment of muscle or limbs. absence of protection: over there is very tiny protection because that the internal organs. Dessication: A moist or water habitat is necessary for survive of these animals in bespeak to prevent dessication (drying out). minimal strength: Terrestrial pets with hydrostatic skeletons cannot boost their body dimension as they would collapse under their own body weight.

Exoskeleton (ESG85)

An exoskeleton is an outside skeleton that supports and also protects one animal"s body. The skeleton is non-living and consists the a cuticle strengthened through chitin, a substance secreted through the epidermis (skin). Crustaceans such as crabs have their exoskeleton additional strengthened by calcium carbonate. There space muscles attached come the within of the exoskeleton which provides the resistance required for muscle action.

The exoskeleton is limit to animals such as insects, spiders, scorpions, crabs etc., all of which belong to the Phylum Arthropoda (jointed-legged and jointed-bodied animals). The exoskeleton acts together a difficult outer covering, and is made up of a series of plates or tubes. We often call huge exoskeletons `shells". Exoskeletons very first appeared in the fossil record throughout the time of the Cambrian explosion and also comprises a substantial section of our fossil document (as you will find out in thing 10).


Figure 6.9: picture of a spider, a type of arthropod.

Advantages the the exoskeleton

Muscle attachment: The exoskeleton develops the suggest of attachments of internal muscles required for locomotion thereby providing much better leverage for muscle action.Protection: The exoskeleton protects the soft internal tissues and organs.Support: The exoskeleton provides structural support and also shape.Prevents Dessication: The exoskeleton avoids desiccation (drying out) on land.Light-weight: The exoskeleton the insects has a low density and also is thus lightweight, to enable for flight.Diversity: The mouth-parts can be modified for biting, sucking, piercing grasping thus providing for a diversity diet for organisms own an exoskeleton compared to those that do not.

Disadvantages the the exoskeleton

Size restriction: The final body dimension is limited because as the body size increases, the surface ar area to volume ratio decreases. The bigger the animal, the heavier the exoskeleton, make movement much more difficult.Non-living skeleton walk not grow with animal: The overall growth the the animal is limited due to periodic moulting. Since the exoskeleton restricts growth, moulting is forced to accommodate for boosts in the size of the animal.Vulnerability throughout moulting: The pet is breakable when that is in the moulting process, because the new skeleton is very soft until the new exoskeleton has actually dried and hardened.Sites of structure weakness: Exoskeletons are weaker at the joints.

Endoskeleton (ESG86)


This skeleton is uncovered inside the body and also can covers bone (all vertebrates other than sharks) or cartilage (sharks) and some endoskeletons consist of both.

Advantages that the endoskeleton

Living: Endoskeletons consist of living tissue, so that is may be to thrive steadily within the animal allowing some to with a huge size.Structure and support: The endoskeleton offers shape and also structural support.Structural diversity and also adaptation: The bones have the right to vary in size and also shape to support the animal"s mass.Flexible: The endoskeleton is jointed which permits for versatile movement and support.Muscle attachment: The muscles connect directly to the skeletal skeletal to allow for movement and also support.Protection: The endoskeleton protects the an important organs such together the heart and also lungs i m sorry are protected by the ribcage. Diversified locomotion: The breakthrough of one endoskeleton has enabled for pets to come to be successfully adapted to locomotion in the setting in which lock live. Vertebrates (organisms with a vertebral column and also an endoskeleton) have become adapted to move in a number of different settings of locomotion, e.g. Running, jumping, swimming, and also flying.

Disadvantages of the endoskeleton

Vulnerable to external environment: The endoskeleton walk not market the animal any protection from the exterior, it is in it a physical attack or transforms in environmental conditions. The animal is therefore really vulnerable.

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Susceptible to disease: The skeleton consists of living tissue so is at risk to infections and also disease.