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UNIT TEST CLASS XII UNIT TEST CLASS XI

NUTRITION IN ORGANISMS

Frederick Griffith: Bacterial transformation In 1928, British bacteriologist Frederick Griffith conducted a series of experiments using  Streptococcus pneumoniae  bacteria and mice. Griffith wasn't trying to identify the genetic material, but rather, trying to develop a vaccine against pneumonia. In his experiments, Griffith used two related strains of bacteria, known as R and S. R strain.  When grown in a petri dish, the R bacteria formed colonies, or clumps of related bacteria, that had well-defined edges and a rough appearance (hence the abbreviation "R"). The R bacteria were nonvirulent, meaning that they did not cause sickness when injected into a mouse. S strain.  S bacteria formed colonies that were rounded and smooth (hence the abbreviation "S"). The smooth appearance was due to a polysaccharide, or sugar-based, coat produced by the bacteria. This coat protected the S bacteria from the mouse immune system, making them virulent (capable of ...

SAMPLE PAPER BIOLOGY CLASS XII

HUMAN GENOME PROJECT The Human Genome Project (HGP) was the international, collaborative research program whose goal was the complete mapping and understanding of all the genes of human beings. All our genes together are known as our "genome." Human Genome Project (HGP) was called a mega project. Goals of HGP Identify all the approximately 20,000-25,000 genes in human DNA. Determine the sequences of the 3 billion chemical base pairs that make up human DNA. Store this information in databases; Improve tools for data analysis; Transfer related technologies to other sectors, such as industries; Address the ethical, legal, and social issues (ELSI) that may arise from the project QUIZ HUMAN GENOME PROJECT

Meselson and Stahl’s Experiment Meselson and Stahl’s Experiment was an experimental proof for semiconservative DNA replication. In 1958, Matthew Meselson and Franklin Stahl conducted an experiment on  E.coli  which divides in 20 minutes, to study the replication of DNA. Experiment 15 N (heavy) and  14 N (normal) are two isotopes of nitrogen which can be distinguished based on their densities by centrifugation in cesium chloride (CsCl). Meselson and Stahl cultured E.coli in a medium constituting  15 NH 4 Cl over many generations. As a result,  15 N was integrated into the bacterial DNA. Later, they revised the  15 NH 4 Cl medium to normal  14 NH 4 Cl. At a regular interval of time, they took the sample and checked for the density of DNA. MESELSON AND STAHL INTERACTIVE MESELSON AND STHAL EXPERIMENT