Support And Movement In Animals

Support And Movement In Animals.

The tough and rigid framework of the body of animals which provides protection shape and support to the body organs is called skeleton. It is composed of inorganic or organic substance or both. It is secreted by cell in protozoa. It is composed of specialized cells in multicellular organism. There are three types of skeleton in animals i. e. hydroskeleton, exoskeleton and endoskeleton.

1. Hydroskeleton:

The skeleton of the body which is produced due to fluid filled within the gastrovascular or coelomic cavity is called hydroskeleton. It is present in the animals in which hard skeleton is absent like earthworm. Hydrostatic skeleton provides support and resistance to contraction of muscles. It results in movement of the body. It is found in cnidarians, annelids and soft bodied invertebrates. The sea anemone has hydrostatic skeleton. Its cavity is filled with sea water. This cavity extends into body and tentacles. The muscles of sea anemone are arranged in a circle around its body. It closes its mouth and constricts its muscle fibers. This contraction put pressure on the fluid within the body cavity.

This pressure forces the body to maintain upright stature.

2. Exoskeleton:

A hard skeleton present at the outer surface to which internal muscles are attached is called exoskeleton. The exoskeleton is inert and non-living. It is secreted by the ectoderm in animals cells. It is composed of two layers:

➤ Epicuticle:

The outer layer is called epicuticle. It is made up of waxy lipoproteins. It is impermeable to water. So it acts as water barrier for the microorganisms and insects.

➤ Procuticle:

It is bulb (base) of exoskeleton. It is present below the epicuticle. The procúticle is composed of chitin. Chitin is a tough and leathery substance. It is made up of polysaccharide and several kinds of proteins. Chitin is further hardened by sclerotization (deposition of calcium). It is, sometimes, further impregnated by calcium carbonate.

(a) Exoskeleton in Mollusks:

The simplest example of the exoskeleton is the shell of mollusk. This shell generally consists of one of two pieces. The shell of some marine bivalve (shell with two pieces).and snail are composed of crystal of calcium carbonate. The shells of land snails generally lack hard minerals. So these shells are lighter in weight. The shells of mollusks grow with the growth of animals. Thus growth rings are apparent on the shell. The soft parts of the body of mollusks also contain hydroskeleton.

(b) Exoskeleton in Arthropods:

The arthropods have most complex exoskeleton. They have different adaptations to live 

grow within exoskeleton. These are:

1. The invagination of exoskeleton forms firm ridges and bars for the attachment of muscle.

2. The exoskeleton of arthropods forms joints. The skeleton is thin, soft and flexible at joint. Thus joints move very easily.

3. The skeleton has sensory receptor called sensilla.  The sensilla are in form of bristles and lenses.

4. There are modifications in exoskeleton for the exchange of gases.

The exoskeleton of arthropods protects the animals against their enemies and rough environment. It also protects them from drying.

3. Endoskeleton:

The skeleton present inside the muscles is called endoskeleton. The

endoskeleton is primarily is made up of two types of tissues: bones and cartilage.

These bone and cartilage are types of rigid connective tissues. Bones and cartilage consist of living cell embedded in the matrix of protein called collagen.

Bone:

The most rigid form of connective tissues is called bone. The deposition of calcium carbonate hardened the collagen fibers of bone. The bones have two parts:

(i) Compact bone:

It forms the outer shell of the bone. It is dense and strong. It provides site for the attachment of muscle.

(ii) Spongy bone:

It is present in the interior of the bone. It is light, rich in blood capillaries and highly porous. The cavities of the spongy bone contain bone marrows. Blood cells are formed in these bone marrow.