2.2.1 skeletons  (Page 2/4)

Endoskeleton

• This skeleton is found inside the body and can consist of bone (vertebrates) or cartilage (sharks).

Advantages:

• Endoskeletons consist of living tissue - so it is able to grow steadily within the animal enabling some to reach a large size.
• It can support the weight of a large animal
• the skeleton is jointed which allows for flexible movement and support
• muscles attach directly to the skeletal bones to allow for movement and support
• vital organs are protected by bone cavities like the ribcage and the pelvic girdle
• lends itself to adaptation to the environment Vertebrates move in differet ways ( e.g. running, jumping, swimming, flying.)

Disadvantages:

• Lack of mineral elements like calcium and phosphates will cause brittle bones and affect movement and support
• Lack of vitamin D in the diet results in a condition/disease caused rickets. A disease characterised by bowed legs.

Developmental progression and why skeletons are needed for terrestrial life

Problems that animals moving from water to land had to overcome

• Loss of body support provided by water

Water is about 1000 times denser than air and is a much more resistant medium to move through, its high density buoys up the body providing support.. One of themajor problems by animals moving from water to land was the increase in the force of gravity. In order to counter this, animals needed to develop stronglimbs and to adapt the skeleton to support their body weight on land.

• Locomotion

Moving effectively on land is essential particularly if one needs to avoid predator, catch prey or adapt to a particular habitat.

• Desiccation

Exposure to air results in evaporation of water from breathing organs and body surface. If this problem is not overcome animals will be confined to damphabitats

Constancy of temperature

Natural bodies of water do not show much temperature fluctuation, whereas on land, the range and fluctuation in temperatures can be large. This can causehuge problems for animals which have no temperature control mechanisms.

• Gaseous exchange

Gills depend on water flow or movement through water to operate. To survive on land a completely new mechanism of breathing needed to evolve.

• Opportunities for breeding on land

The provision of safe shelter for the protection of vulnerable eggs and young is far easier on land than in water habitats.. The main problem here was to findmethods of reproduction which did not require fertilization in water

• Variety of habitats

On land there are a tremendous variety of habitats e.g. tropical, coniferous and temperate forests, grasslands, deserts, mountains, oceanic islands and polarregions. Aquatic habitats, despite being far less diverse contain the greatest number and variety of living organisms on earth. Each habitat will havedifferent requirements with regard to access to food,, shelter, protection from enemies etc.

The exoskeleton in terrestrial arthropods

Arthropods moved onto the land long before the vertebrates emerged and a major factor in their success was the exoskeleton.

• Highly protective without sacrificing mobility
• Provides attachment for muscles which control movement of appendages
• In insects and spiders it is impregnated with waxes forming a waterproof barrier which prevents drying out.