Lysosome – Ultrasturucture and Polymorphism

Christian de Duve first observed these organelles in animal cells in 1949, by cell fractionation studies and Novikoff (1960) suggested that they are derived from pinocytic vesicles. These are single membrane bound small vesicular structures of 0.2 – 0.5 mm in diameter or larger, rich in hydrolyzing enzymes (acid hydrolases) and you can find lysosomes … Read more

Vesicular transport processes or transcytosis

Many substances are transported across the cell membrane by endocytosis and exocytosis. Endocytosis It involves intake of materials in the form of carrier vesicles formed by invagination of small regions of plasma membrane. Endocytosis It is of three types : (i) phagocytosis (ii) pinocytosis and (iii) receptor-mediated endocytosis. (i) Phagocytosis : It is the process … Read more

Plasma Membrane


It is the outer limiting membrane of both prokaryotic and eukaryotic cells. It is an ultra thin, elastic, living membrane. Plasma membrane is a dynamic and selective transport barrier. Since the plasma membrane is ultra thin, it could be observed only under electron microscope. Structure of the membrane is studied by isolating the same from … Read more

Cytological Techniques

Cells are transparent and optically homogeneous organisations. They can be observed either directly or after preservation. For direct observation, the specimen needs sufficient contrast. Direct observation is possible by using vital stains. Vital stains :- Vital dyes or stains are taken up by living cells without killing them. They selectively stain intracellular structures without affecting … Read more


The cells are very minute and complex organisations. The small dimensions and transparent nature of cell and its organelles pose problems to cell biologists trying to understand its organisation and functioning. Various instruments and techniques have been developed to study cell structure, molecular organization and function. The diameters of majority of cells range from 5-500 … Read more

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