CBSE Question Paper 2018 Class 12 Biotechnology

Time allowed: 3 hours

Maximum Marks: 70

General Instructions:

1. All questions are compulsory.
2. There is no overall choice. However, an internal choice has been provided in one question of 3 marks and one question of 5 marks. You have to attempt only one of the choices in such questions.
3. Questions No. 1 to 6 are very short answer questions, carrying 1 mark each.
4. Questions No. 7 to 14 are short answer questions, carrying 2 marks each.
5. Questions No. 15 to 25 are also short answer questions, carrying 3 marks each.
6. Questions No. 26 to 28 are long answer questions, carrying 5 marks each.
7. Use of calculators is not permitted. However, you may use log tables, if necessary
8. Cancer cells lose 'contact inhibition', an important feature of normal cells. What is 'Contact Inhibition'?

Ans. Cell growth inhibited when in contact with other cells/wall of the container.

1. Van der Waals forces are weak attractions, but are important in proteins. Why? Ans. Van der Waals forces are important in macromolecules such as proteins because the large surface areas involved can result in reasonably large total forces/Several Van der Waals forces together give rise to stronger force.

1. Write the principle used in measuring bacterial cell growth by spectrophotometer. Ans. Bacterial cells scatter light in proportion to their concentration giving rise to high turbidity/absorbance/optical density.
2. To construct a c-DNA library, reverse transcriptase enzyme is needed. Why? Ans. Reverse transcriptase is required to convert unstable m RNA to stable c DNA.
3. For short-term storage of germplasm using explant culture, abscisic acid is added to the medium. What is the purpose of doing so?

Ans. Growth retardant 1/7

1. Name a technique that can help researchers to observe interactions among thousands of genes simultaneously. Ans. Microarray using DNA chip.
2. A biotechnologist wants to develop a variety of rice, which can survive in high salinity. How can he do so?

Ans.

• Create transgenic plants by introducing genes which over express stress related osmolytes/osmoprotectants

<math>\blacktriangle</math> Examples such as sugars (trehalose), sugar alcohol(mannitol), amino acids (proline), betaines (glycine betaine),etc.

1. Both PCR and M-13 bacteriophage can amplify DNA with respect to the DNA fragment obtained. What is the basic difference between the two? Ans. PCR produces double stranded DNA and M-13 produces single stranded DNA.

1. Differentiate between finite and continuous cell lines. Ans. Finite cell line - Limited life span, slow growth rate, show contact inhibition, monolayer form etc.. (Any two) Continuous cell line - No contact inhibition, no anchorage dependence, monolayer or suspension form, rapid growth rate etc.

1. Analysis of m-RNA in a given cell doesn't provide a direct reflection of its protein content. Give two reasons to support the statement. Ans. Several proteins can be obtained from a single m-RNA; processes such as polyadenylation; alternative splicing; m-RNA editing can cause this/post translational modifications.(Any two)

1. Downstream processing becomes difficult and costly, if eukaryotic proteins are produced in prokaryotes. Give two reasons. Ans. Several additional steps are required which may use enzymes and hence add on to the cost. Difficulty arises due to various post-transcriptional and posttranslational modifications. (Any two)

1. How is the blue-white selection method used to screen transformed host cells? Ans. Insertional inactivation of Lac Z gene present in vector. Transformed host cells appear white and non-transformed host cells appear blue on X-Gal substrate
2. Differentiate between primary and secondary metabolites in plants. Ans. Primary metabolites are required for basic metabolic processes e.g. amino acids,

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