Biological World

  Diversity of Thallus Structure in Fungi The thallus is the vegetative body of a fungus. It may consist of a single cell, a network of delicate filaments, or a compact tissue-like mass of hyphae. Fungi show remarkable diversity in thallus organization, and this diversity reflects differences in their mode of nutrition, habitat, growth, and reproduction. The organization of the thallus is also an important character used in the study and classification of fungi. 1. Unicellular thallus In the simplest fungi, the thallus consists of a single cell rather than a system of hyphae. Such fungi are generally microscopic and may reproduce by budding or fission. Yeasts are the best-known examples of unicellular fungi. A common example is Saccharomyces cerevisiae , the baker’s and brewer’s yeast. Each individual is usually a single oval or spherical cell, although daughter cells produced by budding may temporarily remain attached. Thus, Saccharomyces represents a typical unicellular fu...

 Practical: Study of Nostoc Nostoc is a filamentous, photosynthetic cyanobacterium. It commonly occurs in freshwater, moist soil, wet rocks and other damp habitats. Colonies are usually gelatinous because numerous filaments remain embedded in a mucilaginous matrix. Materials Required Fresh or preserved Nostoc material, clean glass slide, cover slip, dropper, dissecting needle, water, blotting paper and compound microscope. Procedure Take a small quantity of Nostoc colony with the help of a dissecting needle and place it on a clean glass slide. Add one or two drops of water and gently tease the material so that the filaments become separated. Place a cover slip carefully over the material without trapping air bubbles. Remove excess water with blotting paper. First observe the preparation under low power and then under high power of the compound microscope. Observations The plant body of Nostoc is thalloid and usually forms a soft, jelly-like colony. A colony contains numerous ...

  Anatomical Features of Tinospora cordifolia Observations The transverse section of the stem of Tinospora cordifolia shows a more or less circular outline. The internal tissues are differentiated into cork, cortex, pericycle, vascular tissues, medullary rays and a large central pith. 1. Cork or Periderm The outermost region of an older Tinospora stem consists of several layers of cork cells. These cells are compactly arranged and provide protection to the internal tissues. The cork becomes well developed as the stem undergoes secondary growth.  The outer bark of an old stem therefore appears rough and fissured. 2. Cortex Below the cork lies the cortical region. The cortex is comparatively broad and is mainly composed of parenchymatous cells. These cells may contain reserve food materials  In younger portions of the stem, the outer cortical region may contain chlorenchymatous cells containing chloroplasts. The cortical tissues gradually merge into the inner region. 3. P...

Phytochemistry in Taxonomy Phytochemistry is the study of the chemical substances produced by plants. These substances include primary metabolites, such as carbohydrates, proteins and lipids, and a very large number of secondary metabolites, such as alkaloids, flavonoids, terpenoids, phenolics, glucosinolates, cyanogenic glycosides and essential oils. When information about these plant chemicals is used to identify, compare or classify plants, the approach is called chemotaxonomy or chemical taxonomy. Chemotaxonomy is especially useful because many biosynthetic pathways are genetically controlled and therefore certain compounds or groups of compounds tend to occur repeatedly within particular taxa. Traditional plant taxonomy is based mainly on morphological characters such as habit, leaves, flowers, fruits and seeds. However, different species may sometimes look very similar, while unrelated plants may independently develop similar external features because they live under similar envi...

                                                                          DNA Double Helix Deoxyribonucleic acid (DNA) is the hereditary material of almost all cellular organisms and contains the information required for the growth, development, functioning and reproduction of living systems. The accepted structural model of DNA was proposed by James Watson and Francis Crick in 1953, based on chemical information about nucleotides, Chargaff's base-composition rules and X-ray diffraction evidence obtained from DNA fibres. Their model showed that DNA is not a simple linear chain but a highly organized double-stranded molecule in which two polynucleotide chains wind around a common axis to form a double helix. General Organization of the Double Helix The DNA double helix is formed ...

  Introduction DNA is a flexible double-helical molecule that can adopt more than one three-dimensional conformation. The best-known forms are A-DNA, B-DNA and Z-DNA. These conformations differ in helical direction, diameter, number of base pairs per turn, pitch, sugar pucker, groove geometry and the orientation of the bases relative to the helix axis. The particular form adopted by DNA depends on nucleotide sequence, hydration, ionic conditions, supercoiling and interactions with proteins or other molecules. B-DNA is the predominant form under normal physiological conditions, whereas A-DNA and Z-DNA become favored under particular environmental or structural conditions. Understanding these three forms is important because DNA structure is not merely a static framework for genetic information. Changes in helix geometry can influence protein binding, transcription, chromatin organization, DNA recognition and the response of nucleic acids to changes in the cellular environment. The f...