Cytology pdf

The leucoplasts are colorless plastids which have no pigments. They are numerous in storage organs such as roots, seeds and young leaves where there they store food. A stack of flattened membrane bounded sacks called cisternae, consists of a tubular parallel smooth membrane with membrane vesicles at their tips called golgi vesicles.

At one end of stack, new cisternae are constantly being formed by vesicles from the smooth E. A simple spherical sac bounded by a single membrane and contains a mixture of digestive enzymes such as protease, nuclease and lipase which break down proteins, nucleic acids and lipids respectively. The enzymes contained within lysosomes are synthesized on rough E. R and transported to the golgi apparatus.

Golgi vesicles containing the processed enzymes later bud off to form the lysosomes. In plant cells the large central vacuoles may act as lysosome although bodies similar to the lysosome of animal cells sometimes seen in the cytoplasm of plant cell.

Autolysis is the self digestion of a cell by releasing the contents of lysosome within the cell. Autophagy is the process by which unwanted structures within the cell are engulfed and digested within lysosome.

Endocytosis occurs by an infolding or extension of the cell surface membrane to form vesicles or vacuoles. It is of two types, these are:. Material taken up is in solid form. Material taken up is in liquid form. Exocytosis is the process in which waste materials may be removed from cells.

It is the reverse of endocytosis. Are rod shaped or cylindrical organelles surrounded by an envelope of two membranes. The outer membrane is a smooth membrane and the inner membrane folded to form cristae. The cristae provide large surface area for biochemical activities.

It enclose a matrix mixture of protein, lipid and nucleic acid with few ribosomes, a circular DNA molecule and phosphate granules. An aqeous substance containing a variety of cell organelles and other structures such as insoluble wastes and storage products. Some of these are ions and small molecules in true solution, others are large molecules such as proteins which form colloidal solutions.

A vacuole is fluid filled sac bounded by a single membrane. Animal cells contain relatively small vacuoles, such as phagocytic vacuoles, food vacuoles, autophagic vacuoles and contractile vacuoles. Typically plant cells have one or two large vacuoles filled with fluid known as cell sap and surrounded by a membrane called tonoplast.

The cell sap is a watery fluid containing water, sugar, organic acids, mineral salts, pigments and toxic substances. They are responsible for colors in flowers, fruits, buds and leaves. They are important in attracting insects, birds and other animals for pollination and seed dispersal. Both plant cells, prokaryotic and fungi are surrounded by a relatively rigid wall which is secreted by living cell the protoplast within. The plant cell wall differ in chemical composition from those of the prokaryotes and fungi The wall formed during cell division of plants is called the primary wall which is later thickened to become a secondary wall.

The primary wall consists of cellulose fibrils running through a matrix of other polysaccharides. The matrix consists of pectins and hermicellulose.

Pectins are acidic and have a relatively a solubility. The middle lamella that hold neighboring cell walls together is composed of sticky gel-like magnesium and calcium salts of pectins. Hermicellulose are mixed groups of alkali soluble pollysacharides which form less organized, shorter and more branched chain like molecules. In centrosome poorly defined structure which initiates the development of microtubules , the two centrioles lie right angle to each other.

Before an animal cell divides, the centrioles replicate, then each pair becomes part of a separate centrisome. During cell division the centrosomes move apart so that each new cell has its own centrosome. Plant cells have the equivalent of a centrosome but it does not contain centrioles. The functions of the centriole as microtubule organizing centre is to control separation of chromatids or chromosomes by a sliding motion.

The cytoskeleton is a network of interconnected filaments and tubules that extends from the nucleus to the plasma membrane in eukaryotic cells. Actin filaments or microfilaments are long extremely tin fibres that occur in bundles meshlike network. It contains two chains of globular actin monomers twisted about one another in a helical manner. It plays a structural role and involved in the movement of the cell and its organelles. They are rope like assembly of fibrous polypeptides but specific types varies according to the tissue.

They are intermediate in size between the actin filaments and microtubules. Intermediate filament supports the nuclear envelope and plasma membrane and take part in the formation of cell to cell junction.

In the skin, the intermediate filament is made up of protein keratin which gives mechanical strength to the skin cells. Microtubules are straight un-branched hollow cylinders which are usually short in length. They occur I most plant and animal cells.

Microtubules are involved in the movement of cytoplasmic components within the cell. They also occur in centrioles, in the spindle, in cilia and flagella and in the basal bodies. Microtubules are made up of proteins. They help to maintain the shape of the cell and act as routes along which organelles can move.

Flagella and cilia are organelles that project from the surface of cells but are connected to a basal body just below the plasma membrane. Flagella occur singly or in small number where as cilia occur in large number on large cells and are typically shorter that flagella. Simultaneously, flagella and cilia are almost identical and both are able to move. Flagella and cilia are enclosed to plasma membrane and internally they consist of microtubules arranged in an outer ring of nine pairs surrounding one central pair.

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Home About download notes Provide Support. Is the study of cells structures and their functions A cell is an organized independent mass of protoplasm nucleus and cytoplasm which makes the basic primary structure of an organism.

The cell theory embraces four ideas, these are: Living organisms are made up of smallest sufficient unit of living matter called cell. The new cell is derived from pre-existing ones by cell division. Each cell is independent with others but function as integral part of the whole organism. The cell contains the hereditary material which is passed from generation to generation. Share Facebook Twitter Email Print. Like this: Like Loading Leave a Reply Cancel reply Enter your comment here Fill in your details below or click an icon to log in:.

Email required Address never made public. Name required. Follow Following. Advance Level Notes Join 87 other followers. Sign me up. They have an acidic pH- 5 They have a group of enzymes called Hydrolases. The enzyme content varies in different tissues according to the requirement of tissues or the metabolic activity of the tissue. Lysosomal membrane is impermeable and specific translocators are required.

Vesicles containing external material fuses with lysosomes, form primary vesicles and then secondary vesicles or digestive vacoules. Lysosomes are also involved in autophagy. Products of lysosomal digestion are released and reutilised.

Indigestible material accumulates in the vesicles called residual bodies and their material is removed by exocytosis. Some residual bodies in non-dividing cells contain a high amount of a pigmented substance called Lipofuscin. Also called age pigment or wear —tear pigment. In some genetic disease individual lysosomal enzymes are missing and this lead to the accumulation of that particular substance.

Such lysosomes gets enlarged and they interfere the normal function of the cell. Such diseases are called lysosomal storage diseases Most impt is I-cell disease.

Called Peroxisomes because of their ability to produce or utilize H2O2. They are small, oval or spherical in shape. They have a fine network of tubules in their matrix. About 50 enzymes have been identified. The number of enzymes fluctuates according to the function of the cells. Xenobiotics leads to the proliferation of Peroxisomes in the liver. Have an important role in the breakdown of lipids, particularly long chain fatty acids. Synthesis of glycerolipids.

Synthesis of glycerol ether lipids. Synthesis of isoprenoids. Synthesis of bile. Oxidation of D- amino acids. Oxidation of Uric acid to allantoin animals Oxidation of Hydroxy acids which leads to the formation of H2O2. Contain catalase enzyme, which causes the breakdown of H2O2. In electron micrographs of cells, mitochondria appears as — rods, spheres or filamentous bodies. Size: 0. Mitochondria has got an inner membrane and an outer membrane. The space between these two is called intermembranous space.

Inner membrane convolutes into cristae and this increases its surface area. Both the membranes have different appearance and biochemical functions: Biomedical importance Inner membrane: It surrounds the matrix. It contains components of electron transport system. For the transport special carriers are present e.

Complex II i. Succinate dehydrogenase. Complex V i. ATP synthase complex. Outer membrane: It is permeable to most ions and molecules which can move from the cytosol to intermembranous space. Matrix: It is enclosed by the inner mitochondrial membrane.

Contains enzymes of citric acid cycle. Enzymes of amino acids oxidation. Some enzymes of urea and heme synthesis. Mitochondrial DNA. Mitochondrial cytochrome P system- it causes: a. Hydroxylation of cholesterol to steroid hormones placenta, adrenal cortex, ovaries and testes b. Bile acid synthesis liver c. Vitamin D formation kidney. Mitochondria plays a key role in aging- Cytochrome c component of ETC plays a main role in cell death and apoptosis.

Cytoplasm of eukaryotic cells contain a network of interconnecting membranes. This extensive structure is called endoplasmic reticulum. It consists of membranes with smooth appearance in some areas and rough appearance in some areas- Smooth endoplasmic reticulum and rough endoplasmic reticulum.

Rough Endoplasmic Reticulum These membranes enclose a lumen. In this lumen newly synthesized proteins are modified.

Rough appearance is due to the presence of ribosomes attached on its cytosolic side outer side. These ribosomes are involved in the biosynthesis of proteins.