Biology Classes by Jagmohan Sir(M.Sc. NET)

   MEANS OF TRANSPORT Diffusion • Passive movement and may be from one part of the cell to the other, or from cell to cell, or over short  distances, say, from the intercellular spaces of the leaf to the outside.  • No energy expenditure takes place.  • Molecules move in a random fashion, the net result being substances moving from regions of higher  concentration to regions of lower concentration.  • Diffusion is a slow process and is not dependent on a 'living system'.  • Diffusion is obvious in gases and liquids, but diffusion in solids rather than of solids is more likely.  • Diffusion is very important to plants since it the only means for gaseous movement within the plant body.  • Diffusion rates are affected by the gradient of concentration, the permeability of the membrane separating them, size of the substances, temperature and pressure. Facilitated Diffusion  :  • The diffusion of any substance across a membrane also depends on its solubility in lipids, the major  con

   Late blight of potato : Phytopthora infestans Symptom : It affects leaves, stems and  tubers. Water soaked spots appear on  leaves, increase in size, turn purple  brown& finally black colour White  growth develops on under surface of  leaves. This spreads to petioles, rachis&  stems. It frequently develops at nodes.  Stem breaks at these points and the plant topples over. In tubers, purplish brown spots  and spread to the entire surface on cutting, the affected tuber show rusty brown necrosis spreading from surface to the center.  Pathogen The mycelium is endophytic, coenocytic and hyaline which are inter cellular with  double club shaped haustoria type. Sporangiophores are hyaline, branched intermediate  and thick walled. Sporangia are thin walled, hyaline, oval or pear shaped with a definite  papilla at the apex. The sporangium may act as a conidium and germinate directly to form  a germ tube. Zoospores are biflagellate possess fine hairs while the other does not. Mode of

  RED ROT OF SUGARCANE: This is one of the most severe of the known diseases of sugarcane. Causal Organism : Colletotrichum falcatum Symptom : The 3rd and 4th leaves (from the top) of the infected plants display yellowing and drying. At a later stage, show discoloured lesion on the rind. Fungal spores develop on rind and nodes. 3. If the diseased stalk split open, reddened internal tissues with intermingled white spots may be seen. The internal colour becomes brown, pith cavity become larger, greyish hyphae inside pith become visible. A sour and alcoholic smell emanates from the infected tissues. At a later stage, stalks become discoloured and hollow. Acervuli (black fruiting bodies) develop on rind and nodes. After splitting open the diseased stalk, a sour smell emanates. The internal tissues are reddened with intermingled transverse white spots. In advanced stage of the disease, the colour becomes earthy brown with pith cavity in the centre showing white cottony hyphae and sometimes

   Polymerase chain reaction , or  PCR , is a technique to make many copies of a specific DNA region  in vitro  (in a test tube rather than an organism). PCR relies on a thermostable DNA polymerase,  Taq  polymerase , and requires DNA  primers  designed specifically for the DNA region of interest. In PCR, the reaction is repeatedly cycled through a series of temperature changes, which allow many copies of the target region to be produced. PCR has many research and practical applications. It is routinely used in DNA cloning, medical diagnostics, and forensic analysis of DNA. What is PCR? Polymerase chain reaction  ( PCR ) is a common laboratory technique used to make many copies (millions or billions!) of a particular region of DNA. This DNA region can be anything the experimenter is interested in. For example, it might be a gene whose function a researcher wants to understand, or a genetic marker used by forensic scientists to match crime scene DNA with suspects. Typically, the goal of