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ISC Class XII Board Specimen 2020 : Biotechnology Paper 2

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ISC 12th
Indian School Certificate Examination (ISC), New Delhi
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BIOTECHNOLOGY PAPER 2 (PRACTICAL) (Maximum Marks: 30) (Time allowed: Three hours) (Candidates are allowed additional 15 minutes for only reading the paper. They must NOT start writing during this period.) Answer all questions. The intended marks for questions or parts of questions are given in brackets [ ]. Question 1 (a) Prepare a 100 ml culture medium in 250 ml flask using the composition as given below: Peptone 1 gm Yeast extract 0.5 gm NaCl 0.5 gm Agar 1.5 gm Take 50 ml of distilled water in a 250 ml beaker. Note the pH by using pH paper. Stir continuously; make the volume to 100 ml by adding distilled water. Note the pH by using pH paper. Adjust the pH of the mixture to 7 by adding drops of dil. NaOH or HCl. Transfer the content to the 250 ml flask and put a cotton plug at its mouth. Sterilize the medium in an autoclave. After sterilization allow the content to cool down. Pour 20 ml of the culture medium in a Petri plate and 4 ml in a test tube to make a slant. Show the slant to the Visiting Examiner. Answer the following: (b) (i) Write the pH of culture medium when the volume is 50 ml and 100 ml respectively. [1] (ii) Note the time taken to solidify in the Petri plate. What causes the solidification of the medium? [1] (iii) What is the importance of the pH and slant in culture process? [1] A milk sample for the isolation of protein has been provided to you. Take 25 ml of sample in a beaker and proceed as follows: First warm the sample in water bath set at 35oC. Note the pH of milk sample using a pH meter or a pH meter. Next, add 0.4 N HCl into beaker drop wise until the protein starts coagulating. Show the coagulated protein to the Visiting Examiner. Note the pH at which maximum separation of protein takes place. Filter the solution through thin muslin cloth to separate out the protein. (i) Report the: [1] (1) Initial pH of the milk sample. (2) Final pH of the milk sample when the protein is isolated. ------------------------------------------------------------------------------------------------------------------------------------------------ 1 ISC SPECIMEN QUESTION PAPER - 2020

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