Structural Organisation in Animals MCQs for NEET — Zoology Questions with Answers

Page 103, XI NCERT

Page 102, XI NCERT

A gap junction may nexus or macula communicans. These are specialised intercellular connection between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells.

Areolar tissue is a loose connective tissue, and provide flexibility and cushioning. Adipose tissue is also loose connective tissue while, the tendon is a dense connective tissue, which connect the muscles with the bone. Cartilage is composed of specialsed connective tissue called chondrocytes that produce a large amount of extracellular matrix composed of collagen fibre.

Simple squamous eepithelium consists of only one layer of flat, scale like cells usually polygonal cells, which are closely fitted together like the tiles of a mosaic. It is also known as pavement epithelium. It forms lining of blood vessels, lymph vessels, heart, peritoneum, pleura, Bowman's capsule etc.

Ciliated columnar epithelium lines respiratory tract (lower end of bronchi), fallopian tubes, ventricles of brain (ependyma) central anal of spinal cord, etc.

Cuboidal epithelium occurs in certian parts of nephrons of the kidneys.

Glandular epithelium are specialized for secretory activites, eg., unicellular, multicellular, exocrine, endocrine, heterocrine glands, etc.

Squamous epithelium forms lining of blood vessels, lymph vessel, heart, peritoneum, pleura, Bowman's capsule, etc.

In epithelial tissue, at place the adjacent cells form ion-rich gap or cell junctions for intercellualr communication and chemical exchange. These junctions probably do not provide physical support.

Specialized cell junctions occur at many points of cell-cell and cell matrix contact in all tissues, but they are particularly important and plentiful in epithelium.

Desmosomes are intercellualr cell junctions that are often narrow gaps between adjacent cells in animal tissues. In these regions, circular patches of cell membrane are held together by interaction of proteins that exten thorugh each mebrane into the space between the cells. The cell membrane has on the inner side a dense plate of protein and bears fine filaments called tonofibrils, radiating into the cell. Desmosomes act as "sport welds" and keep the cells firmly together. They occur between epithelial cells. 

The tadpole excretes ammonia, but the adult frog shifts to urea excretion. Amphibians actively transport ions in through the skin. Tadpole liver usually does not have high levels of the urea cycle enzymes and the levels do not increase until metamorphosis.