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ISC Class XII Board Exam 2020 : Biotechnology Paper 2 (Practical)

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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 time.) ------------------------------------------------------------------------------------------------------------------------Answer all questions. The intended marks for questions or parts of questions are given in brackets [ ]. ------------------------------------------------------------------------------------------------------------------------Question 1 (a) Take a 2'' piece of a ripe banana in a 100 ml beaker. Mash it properly. To this, add 30 ml of extraction fluid (labelled EF) provided to you. Incubate the beaker at 60oC for 15 minutes. Stir the contents of the beaker gently with a glass rod and filter the content. Allow the filtrate to cool. Take 5 ml of filtrate in a test tube and label the test tube as D. Gently add 5 ml of ice-cold 90% ethanol to test tube D. Allow the test tube to stand for 10 minutes. Show the test tube to the Visiting Examiner. Answer the following questions: (b) (i) Name the substance obtained in the test tube after the completion of the experiment. [1] (ii) State the method that will be used to extract the isolated substance from the test tube. [1] (iii) Name the two contaminants present in test tube D, along with the isolated substance. [1] You are provided with vegetable oil (coconut oil), common salt (NaCl) and 20% sodium hydroxide (NaOH) solution. Take 25 ml of vegetable oil in a measuring cylinder and pour it into a 250 ml glass beaker. Measure 30 ml of 20% NaOH solution in another measuring cylinder. Pour it into the beaker containing vegetable oil. Stir the mixture using a glass rod. Place the beaker on a wire gauze placed over a tripod stand. Heat the beaker on a Bunsen burner till the mixture turns into whitish paste. ---------------------------------------------------------------------------------------------------------------------------This paper consists of 3 printed pages and 1 blank page. 1220-878B Turn over Copyright reserved. Remove the beaker from the flame and allow it to cool. Check the acidic or basic nature of the mixture by using Litmus paper. Add 10 gm of NaCl to the above mixture and stir it with a glass rod. On adding NaCl, the soap gets precipitated. Isolate the soap by using filter paper and a funnel. Show the precipitate on the filter paper to the Visiting Examiner. Answer the following: (i) Name the process by which soap is obtained in this experiment. [1] (ii) What is the use of common salt in the experiment? [1] (iii) Based on the litmus paper test, state the nature of the mixture. [1] Question 2 You are provided with a solution labelled S and a solution labelled E. Follow the steps given below: Take three test tubes and label them as S1, S2 and S3. (a) Pour 2 ml of solution S in each of these three test tubes. (b) Next, take two test tubes and label them as E1 and E2. Pour 2 ml of solution E into both the test tubes. Place test tubes E1 and S1 in a water bath set at 90oC and test tubes E2 and S2 in a water bath set at 37oC for about 15 minutes. (c) Next, add 2 3 drops of Iodine solution into test tube S3. Mix well and note the colour change. (d) Remove test tubes E1, S1, E2 and S2 from the water baths. (e) Pour the solution in test tube E1 into test tube S1 and the solution in test tube E2 into test tube S2. Mix well and allow the test tubes S1 and S2 to stand for 10 minutes. (f) Add 2 - 3 drops of iodine solution to each of the two test tubes, S1 and S2. Observe the colour change. Answer the following questions: (i) Report your observations and inference for the test tubes S1 and S2, in a tabular form as shown below: Test tube Observation [2] Inference S1 S2 (ii) What is the colour change in test tube S3? Give the reason for the colour change. [1] (iii) Identify solution S and solution E, based on the above tests. [1] (iv) Mention the reason for colour change in test tubes S1 and S2. [1] ---------------------------------------------------------------------------------------------------------------------------2 1220-878B Question 3 You are provided with 1 gm peptone, 0 5 gm yeast extract, 0 5 gm NaCl and 1 5 gm agar. Using these substances, prepare a 100 ml culture medium in a 250 ml flask, following the steps given below: Put the given substances in a 250 ml beaker and mix them well, using a glass rod. Mark the final volume to 100 ml by adding distilled water. Note the pH by using a pH paper. Adjust the pH to 7 by adding either dil. NaOH or dil. HCl, as required. Transfer the content to a 250 ml flask. Put a cotton plug at the mouth of the flask. Sterilise the flask in an autoclave. After sterilisation, allow the content to cool. Pour 2 ml of the culture medium in a petri plate and 5 ml in a test tube to make a slant. Show the petri plate and the slant to the Visiting Examiner. Answer the following: (a) How was the slant prepared in the test tube? [1] (b) What is the importance of preparing a slant? [1] (c) What causes solidification of culture medium? [1] (d) What is the importance of sterilising the culture medium in an autoclave? [1] Question 4 Show the following to the Visiting Examiner for assessment: (a) Project (b) Biotechnology Practical File [10] ---------------------------------------------------------------------------------------------------------------------3 1220-878B [5]

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