Test: Structural Organisation in Animals - Assertion and Reasoning - NEET MCQ

Specialization of cells into tissue, organ and organ systems is advantageous for the organisms. It increases the operational efficiency through division of labour which avoids duplication of work.

Squamous epithelium is a single layer of flattened cells in contact with basal lamina of the epithelium. This type of epithelium is often permeable and occurs where small molecules need to pass quickly through membranes.

Urinary bladder is not lined by squamous epithelium but by transitional epithelium which is a stretchable compound epithelium. It has a single layer of cuboidal cells at the base, 2-3 middle layers of large polygonal cells and a superficial layer of large, broad rectangular cells. Stretching considerably flattens and broadens the cells of superficial and middle layers, hence causing expansion of the urinary bladder.

Columnar epithelium is a type of simple epithelium characterised by the presence of tall column like cells. Its major function is absorption or secretion. It covers the inner surface of the intestine, stomach and gall bladder. In the intestine, it appears to have a brush like appearance on the free surface, which is due to the presence of large number of microvilli. Function of microvilli is to enhance absorption. Due to the presence of microvilli, the epithelium is also called as brush bordered columnar epithelium.

Surface of skin is impervious to water because it is covered by stratified keratinised squamous epithelium. This epithelium has many superficial layers of horny, scale like remains of dead squamous cells and several deeper layer of living polygonal cells. Heavy deposits of the insoluble protein keratin are present in the dead superficial layers which makes this epithelium impervious to water. Stratified cuboidal epithelium, on the other hand, lines the inner surface of sweat gland, larger salivary and pancreatic ducts.

The columnar epithelium is composed of a single layer of tall and slender cells. Their nuclei are located at the base. Free surface may have microvilli. They are found in the lining of stomach and intestine and help in secretion and absorption.

All cells in epithelium are held together with little intercellular material. In nearly all animal tissues, specialized junctions provide both structural and functional links between its individual cells. Three types of cell junctions are found in the epithelium and other tissues. These are called as tight, adhering and gap junctions. Adhering junctions perform cementing function to keep neighbouring cells together.

Simple epithelium does not cover surfaces exposed to mechanical or chemical abrasions because it is made up of a single layer of cells, hence it is not effective in protecting the underlying tissue. Simple epithelium occurs mainly on secretory and absorptive surfaces. There is another types of epithelial tissue called compound epithelium which being multilayered is effective in providing protection to underlying tissues, therefore, covers the surfaces exposed to mechanical and chemical abrasions.

Compound epithelium performs the function of providing protection against chemical and mechanical stress. Thus, it has limited role in absorption, secretion and excretion. This epithelium is found in the moist surface of buccal cavity, pharynx, inner lining of duct of salivary gland but not in stomach lining.

Cartilage comprises of mucopolysaccharide called chondroitin sulphate. Bone is a hard connective tissue while blood is a fluid connective tissue.

Connective tissue is the most abundant and widely distributed tissue of the body. It connects different tissues or organs and provides support to various structures of animal body. The connective tissue consists of living cells and extra-cellular matrix. It includes soft connective tissues and specialised tissues like cartilage, bone, adipose and blood.

Tendon is made up of white fibrous tissue. Tendon connects a skeletal muscle to bone. It is tough and inelastic. Ligament is strong and elastic and made up of yellow elastic tissue with some collagen fibres. Ligament connects a bone to another bone.

All cells of connective tissue except blood secrete fibres. Fibroblasts are the main cells of connective tissue, which secrete various types of fibres. There are three types of fibres secreted by connective tissue cells and each type is formed by proteins. These are collagen fibres (made up of collagen protein), elastic fibres (formed of elastin) and reticular fibres (made up of reticulin). All provide strength, elasticity and flexibility to the connective tissue.

Ordinary connective tissue is absent inside the central nervous system. i.e. brain and spinal cord and has no function in the conduction of nerve impulse. The neurons of nerve tissue inside the brain and spinal cord are held together by supporting cells called neuroglia cells. Neuroglia cells resemble neurons and have long radiating processes but no nissl granules.

It is not tendon but another type of connective tissue called ligament which is present in most of the bone joints and connect the bones together. Ligament also helps in holding the bones in position. Tendon, on the the other hand, is a dense, strong, fibrous connective tissue which forms strong inextensible attachment of a skeletal muscle to a bone.

The cell secretes fibres of structural protein in all the connective tissues called collagen. Neuroglea is made up of more than one half the volume of neural tissue in human body

Skeletal muscles action are voluntary i.e., they can be removed according to our will, walls of the blood vessels contain epithelial tissue not skeletal muscles

In wounds, germs are removed by WBCs accumulation at wound site by diapedesis. It is squeezing of leucocytes out from endothelium of capillaries to fight external agent.

The symptoms of an allergic reaction develop in response to histamine. Mast cells release a large amount of histamine into the blood stream and it also act as initiator of the inflammatory response which aids the arrival of leucocytes at a site of infection. Histamine stimulates capillary dilation, increased capillary permeability, closure of bronchial tubes, mucus secretion, pain and swelling.

Mast cells are large irregular cells with granular cytoplasm, present in the areolar connective tissue. These cells store inflammation producing substances such as histamine in dense granules. Mast cells defend themselves which in turn helps in body defence by attracting phagocytes to the injured tissue.