Structural Organisation in Animals Biology NEET Quiz Online

Nissl granules are present in the cyton and even extend into the dendrite but absent in axon and rest of the neuron.

Nissl granules are in fact composed of free ribosomes and RER. They are responsible for protein synthesis.

Smooth muscles are involuntary, fusiform, nonstriated muscles.

• Columnar epithelium is present in the lining of stomach.
• Tendon is dense connective tissue and connects muscle to bone.
• Tip of nose consists of elastic cartilage.

Gap junctions are communicating junctions in animals which facilitates communication between two adjoining cells by protein bridges for rapid transfer of ions, small molecules and large molecules.

Yellow elastic cartilage is present in pinna, ear canal, eustachian tube, tip of nose and some laryngeal components.

The epithelium consist of columnar cells that possess cilia over their free surface. Ciliated columnar epithelium occurs in respiratory tract (except terminal bronchioles and alveoli), fallopian tube, parts of uterus and cervix and efferent tubules of testes.

Blood vessels contain a central lumen lined with single layer of flattened epithelial cells-squamous epithelial cells. The smooth surface of squamous epithelium minimizes resistance to flow of blood.

External ears and pinna is made of yellow elastic cartilage.

In nerve cells power of division and regeneration are absent.

Spleen eliminates worn out or damaged red blood cells so spleen is often called graveyard of RBCs.

Endocytosis is a process by which material move into cell. Pinocytosis is mechanism by which cells ingest extracellular fluid and its contents; it involves formation of invagination by cell membrane and which closes and breaks off from to form fluid-filled vacuoles in cytoplasm.

Pinocytosis and phagocytosis are both types of endocytosis. Pinocytosis is cellular drinking and phagocytosis is cellular eating.

NCERT Class 11th Page No.101

Desmosomes are intercellular junctions, these are plaque like areas which provides strong attachment between two adjacent cells with the help of adhesion molecules and filaments. Desmosomes serve anchoring function.

Stratum germinativum or stratum basale is a layer of columnar epithelium cells that actively divide and are responsible for regenerating epidermis.

Basement membrane is delicate non cellular layer made of extracellular material that lies below epithelium in contact with its basal surface. Basement membrane is made of two parts outer basal lamina and inner reticular lamina. Basement membrane provides elestic support and also anchors epithelial tissues to underlying connective tissue for obtaining nutrients. Basal lamina : Secreted by epithelial cells and formed by glyco-protein and mucopolysaccharides. Reticular lamina : Inner thick layer composed of collagen or reticular fibers of underlying connective tissue.

Cyton or cell body of neurons contain characteristic deeply stained particles called Nissl’s granules. Nissl’s granules are large and irregular masses of ribosomes and rough endoplasmic reticulum.

The ground substance or matrix of cartilage is called chondrin. Chondrin is a bluish-green gelatin-like substance, made of protoglycans consisting of glycoproteins and glucosaminoglycans.

Tendons are made of white fibrous dense regular connective tissue and contain abundant fasicles of white collagen fibers. Tendons are inelastic in nature and connect muscle to bones.

Ligaments are yellow elastic fibrous (dense regular) connective tissue. Ligaments are elastic in nature where matrix is pervaded by bundles of elastic fibres and collagen fibres.

Due to reduction in blood supply, hair follicle does not receive proper nutrition. Due to poor nutrition hair fall occurs in old age.

When bone is kept dipped in dilute acid for long hours, then calcium, magnesium and potassium of inorganic part of matrix get dissolved but organic part remain intact. Bones become flexible if immersed in acid as calcium salts are removed from bone.

Simple or unilaminal epithelium is a tissue that is made of single layer of compactly arranged cells all of which rest over a non cellular basement membrane.

Myelinated neurons possess axons enveloped with lipid rich sheath called myelin sheath. Myelin sheath is present as spiral wrapping around axons of each neurons. Myelin sheath in neuron is not a continuous sheath. Certain gaps/intervals are present between adjacent sheaths of single axon. These gaps which are present between two adjacent myelin sheath are called node of ranvier.

• Connective tissue is most abundant and widely distributed tissue in body of animals. Connective tissue consist of living cell embedded in abundant non-living intercellular matrix which connects different tissues or organs. Areolar tissue loose connective tissue and most widely distributed connective tissue in animal body.
• Stratified epithelial tissue consist of variously shaped cells closely arranged in one or more layers. There is little intercellular material between epithelial cells.
• Striated muscles are made up of many long, cylindrical, fiber like-cells, arranged in the form of sheet or bundles. The muscle fibers have no intercellular substances.
• Myelinated nerve fibers does not possess intercellular substances or extracellular material.

Cyton or cell body of neurons contain characteristic deeply stained particles, called Nissl’s granules. Nissl’s granules are large and irregular masses of ribosomes and rough endoplasmic reticulum.

Mast cells contain cytoplasmic granules of heparin and histamine. Heparin prevents blood clotting. Histamine produces inflammation, increases permeability of blood vessels and causes contraction of smooth mucles.

Epithelial cells are held together by intercellular junctions which serve as structural and functional links between them.