ISC Class 12 Biotechnology Board Exam Question Paper 2013 with Solutions

ISC Class 12 Biotechnology Board Exam Question Paper with Solutions

Part 1

Question 1.

(a) Mention any one significant difference between each of the following: [5]

(i) Gene and Genome [1 Mark]

Answer:
Gene is a sequence of DNA that occupies a specific position on a chromosome and determines a particular characteristic, whereas genome is the total genetic information or all the genes contained in a haploid set of chromosomes in eukaryotes, a single chromosome in bacteria, or in the DNA or RNA of viruses.

Teacher's Note:
a) Remember that a gene codes for a specific trait while the genome represents the entire genetic complement.
b) Students often confuse a single gene locus with the entire genomic pool of an organism.

(ii) Multi potent cell and Uni potent cell [1 Mark]

Answer:
Multipotent cells have the ability to differentiate into many of the various types of specialized cell types within a particular group or germ layer, whereas unipotent cells can only differentiate into a single type of cell or tissue.

Teacher's Note:
a) Multipotent stem cells have broader differentiation potential than unipotent cells.
b) Give examples like umbilical cord stem cells for multipotent and skin cells for unipotent.

(iii) Galactose and Glycine [1 Mark]

Answer:
Galactose is a monosaccharide sugar found in milk as part of lactose, whereas glycine is a neutral amino acid and one of the building blocks of proteins.

Teacher's Note:
a) Galactose is a carbohydrate molecule, while glycine is a nitrogenous amino acid containing an amino and a carboxyl group.
b) Ensure clarity in chemical classification when comparing biomolecules.

(iv) Batch culture and Continuous culture [1 Mark]

Answer:
In a batch culture, nutrients are fed initially or added without removing growth products continuously, whereas a continuous culture is an open system where nutrients are supplied continuously along with the removal of products in the same volume.

Teacher's Note:
a) Batch culture operates in a closed system, whereas continuous culture operates in an open system maintaining steady state.
b) Emphasize the continuous inflow and outflow in continuous culture.

(v) Coding region and Non-coding region [1 Mark]

Answer:
The coding region (exon) is the part of DNA that codes for a protein, whereas the non-coding region (intron) is the part of DNA that does not directly code for a protein.

Teacher's Note:
a) Exons are expressed sequences, while introns are interspersed non-coding sequences.
b) Mention that introns are spliced out during post-transcriptional processing in eukaryotes.

(b) Answer the following questions : [5]

(i) Name the enzyme used in PCR. What is the source of this enzyme? [1 Mark]

Answer:
The enzyme used in PCR is Taq DNA polymerase, and its source is the thermophilic bacterium Thermus aquaticus.

Teacher's Note:
a) Taq polymerase is heat-stable, allowing it to withstand high denaturation temperatures during PCR cycles.
b) Students must spell Thermus aquaticus correctly with proper binomial nomenclature.

(ii) Why is Bt-cotton resistant to boll worm? [1 Mark]

Answer:
Bt-cotton contains a cry gene derived from the bacterium Bacillus thuringiensis, which produces an insecticidal crystal protein that kills the bollworm.

Teacher's Note:
a) The protoxin is activated in the alkaline gut of the insect, causing pore formation and lysis of midgut epithelial cells.
b) Highlight the role of the cry gene and the source bacterium.

(iii) Mention any two methods of ex-situ conservation of germplasm. [1 Mark]

Answer:
Two methods of ex-situ conservation of germplasm are seed banks and botanical gardens (or cryopreservation and zoological parks).

Answer:
Proteomics is the large-scale study of the entire complement of proteins, particularly their structures, modifications, and functions.

Teacher's Note:
a) The term proteome was coined by Marc Wilkins and proteomics complements genomics.
b) Note that the proteome is dynamic and changes constantly in response to cellular environments.

(v) Glucose and fructose have the same chemical formula (C₆H₁₂O₆), yet they differ in chemical properties. Why ? [1 Mark]

Answer:
They differ because of the different arrangement of atoms within their molecules; glucose is an aldose sugar with an aldehyde group (-CHO) at position 1, whereas fructose is a ketose sugar with a keto group (-C=O) at position 2.

Teacher's Note:
a) This is an example of functional group isomerism.
b) Mention the specific presence of the aldehyde versus ketone functional groups.

(c) Write the MI form of the following : [5]

(i) GDB [1 Mark]

Answer:
Genome Data Base

Teacher's Note:
a) GDB stands for Genome Data Base, an important bioinformatics repository.
b) Ensure exact expansion without spelling errors.

(ii) PIR [1 Mark]

Answer:
Protein Information Resource

Teacher's Note:
a) PIR is a comprehensive protein database supporting genomic and proteomic research.
b) Memorize standard biological database abbreviations.

(iii) YAC [1 Mark]

Answer:
Yeast Artificial Chromosome

Teacher's Note:
a) YACs are vector systems used to clone large DNA fragments in yeast.
b) Distinguish YAC from BAC and plasmid vectors.

(iv) NCBI [1 Mark]

Answer:
National Center for Biotechnology Information

Teacher's Note:
a) NCBI is a primary hub for molecular biology information and databases like GenBank.
b) Watch out for spelling of Biotechnology.

(v) ddNTP [1 Mark]

Answer:
Dideoxynucleoside triphosphate

Teacher's Note:
a) ddNTPs lack the 3'-OH group and are used as chain terminators in DNA sequencing.
b) Emphasize the absence of the hydroxyl group at the 3' carbon position.

(d) Explain briefly : [5]

(i) Bacterial Artificial Chromosome [1 Mark]

Answer:
A Bacterial Artificial Chromosome (BAC) is a cloning vector construct based on the F-plasmid of Escherichia coli, used for transforming and cloning large DNA inserts ranging from 300 to 350 kbp.

Teacher's Note:
a) BACs contain an ori gene, selectable markers, and cloning sites.
b) Mention their high stability and utility in genomic mapping projects.

(ii) Vascular differentiation [1 Mark]

Answer:
Vascular differentiation is the developmental process by which precursor cells give rise to specialized vascular tissues (xylem and phloem) that differ in structure and function.

Teacher's Note:
a) It involves cell specialization and structural modification in plants.
b) Relate it to complex plant tissue development.

(iii) Phenylketonuria [1 Mark]

Answer:
Phenylketonuria is a recessive genetic disorder caused by a gene mutation leading to the absence of the enzyme phenylalanine hydroxylase, which converts phenylalanine into tyrosine.

Answer:
Quaternary proteins are multimeric proteins formed by the association of two or more polypeptide chains linked together into a functional 3D structure, such as haemoglobin.

Teacher's Note:
a) This level of protein structure involves non-covalent interactions between multiple subunits.
b) Haemoglobin is the classic textbook example.

(v) Designer oils [1 Mark]

Answer:
Designer oils are genetically modified or specially formulated oils designed to provide health benefits, such as reducing LDL blood cholesterol levels and increasing energy expenditure.

Teacher's Note:
a) They often incorporate functional food ingredients like phytosterols.
b) Mention their role in functional foods and cardiovascular health.

Part II

Question 2.

(a) Give a comparative account of DNA and RNA on the basis of their following characteristics: [4]
(i) Chemical composition and structure
(ii) Location and function

Answer:
(i) Chemical composition and structure:
- DNA contains 2-deoxyribose sugar, purines (adenine and guanine), and pyrimidines (cytosine and thymine), and exists as a double-stranded helical structure.
- RNA contains ribose sugar, purines (adenine and guanine), and pyrimidines (cytosine and uracil), and exists primarily as a single-stranded helix.
(ii) Location and function:
- DNA is located in the nucleus, chloroplasts, and mitochondria, and controls the transmission of hereditary characters.
- RNA is located in the cytoplasm (and nucleus), and controls the synthesis of proteins.

Teacher's Note:
a) Present the comparison clearly under headings or bullet points.
b) Emphasize the structural differences in pentose sugar and pyrimidine bases (thymine vs. uracil).

(b) Mention the uses of the following in genetic engineering techniques : [4]
(i) Shuttle vectors and Expression vectors
(ii) Restriction endonucleases

Answer:
(i) Shuttle vectors and Expression vectors:
- Shuttle vectors have two origins of replication allowing them to replicate in two different species (such as prokaryotes and eukaryotes), facilitating DNA transfer between them.
- Expression vectors contain a promoter upstream of the cloning site to allow direct transcription and expression of cloned genes into proteins in host cells.
(ii) Restriction endonucleases:
- Used to cleave DNA molecules at specific, predictable nucleotide recognition sequences (such as GAATTC for EcoRI) to generate DNA fragments with sticky or blunt ends for recombinant DNA technology.

Teacher's Note:
a) Clearly distinguish between the dual-host ability of shuttle vectors and the transcriptional control of expression vectors.
b) Highlight the molecular scissors role of restriction enzymes.

(c) What is electroporation ? [2 Marks]

Answer:
Electroporation is a mechanical or physical method used to introduce polar molecules like DNA into host cells by applying a brief, high-voltage electric pulse that temporarily disturbs and permeabilizes the cell membrane's phospholipid bilayer.

Teacher's Note:
a) It creates transient pores in the cell membrane for gene transfer.
b) Mention that it is widely used for both plant protoplasts and animal cells.

Question 3.

(a) What is gene cloning ? Mention the steps involved in this process [4]

Answer:
Gene cloning is the technique of recombinant DNA technology in which a desired gene of interest is inserted into a self-replicating vector to produce multiple identical copies.
Steps involved in gene cloning:
1. Isolate the DNA segment containing the gene of interest from the source organism.
2. Cleave the gene and the plasmid vector using the same restriction enzyme to produce complementary sticky ends.
3. Use DNA ligase to join the gene of interest into the plasmid vector, forming recombinant DNA.
4. Introduce the recombinant plasmid into a host cell (transformation) and plate on selective agar media to identify and isolate colonies containing the cloned gene.

Teacher's Note:
a) Sequential order of steps is crucial for full credit.
b) Emphasize isolation, restriction digestion, ligation, transformation, and screening.

(b) Explain the following : [4]
(i) Acidic and basic amino acids
(ii) Phospholipids and glycolipids

Answer:
(i) Acidic and basic amino acids:
- Acidic amino acids (such as aspartic acid and glutamic acid) have side chains with carboxylic acid groups that can lose protons at neutral pH, becoming negatively charged.
- Basic amino acids (such as lysine, arginine, and histidine) have side chains containing nitrogen groups that bind protons, gaining a positive charge at neutral pH.
(ii) Phospholipids and glycolipids:
- Phospholipids are lipid derivatives where one fatty acid is replaced by a phosphorylated group via phosphorylation.
- Glycolipids are lipid derivatives where a sugar residue (such as galactose) is attached via glycosylation.
Both form essential components of cell membranes.

Teacher's Note:
a) Explain based on the ionization state of their side chains at neutral pH.
b) Note that both phospholipids and glycolipids are amphipathic membrane constituents.

(c) State any four objectives of germplasm conservation. [2 Marks]

Answer:
Four objectives of germplasm conservation are:
1. Conservation of rare germplasm arising through somatic hybridization.
2. Storage of pollen to enhance longevity.
3. Maintenance of recalcitrant seeds.
4. Development of genes for adaptation to varying biotic and abiotic stresses, and breeding high-yielding varieties.

Teacher's Note:
a) Any four valid objectives from the standard list are accepted.
b) Emphasize preservation of genetic diversity and stress-resistance traits.

Question 4.

(a) Why are enzymes temperature sensitive ? Briefly explain the mode of action of enzymes on their substrate. [4]

Answer:
Enzymes are temperature sensitive because they are proteins with a specific tertiary structure maintained by weak bonds that break at high temperatures, causing denaturation and loss of catalytic activity due to altered active sites.
Mode of enzyme action (Lock and Key Mechanism proposed by Emil Fischer, 1898):
The substrate fits into the active site of the enzyme like a key in a lock, forming an unstable enzyme-substrate complex. This complex immediately breaks down to release the end products and regenerate the free enzyme.

Teacher's Note:
a) Explain both thermal denaturation and the lock-and-key hypothesis clearly.
b) Mention that enzymes lower the activation energy of biochemical reactions.

(b) How is the hormone insulin synthesized, using genetic engineering technique ? State two ways in which this technique is better than the techniques used earlier. [4]

Answer:
Synthesis of human insulin (Humulin):
1. The gene responsible for producing human insulin is isolated from human DNA.
2. A plasmid is extracted from a bacterial cell and cut open using restriction enzymes.
3. The human insulin gene is inserted into the plasmid ring and sealed with DNA ligase to form recombinant DNA.
4. The recombinant plasmid is introduced into a host bacterium, which multiplies and expresses the insulin gene during fermentation.
Two advantages over earlier techniques (extraction from animal pancreas):
1. Recombinant human insulin is pure and causes no allergic reactions.
2. It is much cheaper and can be produced quickly in limitless quantities compared to animal-extracted insulin.

Teacher's Note:
a) Outline the r-DNA steps clearly from gene isolation to bacterial expression.
b) Highlight the absence of immunological rejection as the major clinical advantage.

(c) What is a supra-molecular assembly ? [2 Marks]

Answer:
A supra-molecular assembly (or super molecule) is a well-defined complex of molecules held together by non-covalent bonds, combining into spherical or rod-like structures through molecular self-assembly, with dimensions ranging from nanometers to micrometers.

Teacher's Note:
a) Emphasize the role of non-covalent interactions in self-assembly.
b) Mention the typical nanoscale dimensions.

Question 5.

(a) What is plant tissue culture ? Discuss the organization of a tissue culture laboratory under the following headings: [4]
(i) Media preparation
(ii) Culture room.

Answer:
Plant tissue culture is the technique of in vitro maintenance and growth of plant cells, tissues, and organs under aseptic conditions on a suitable artificial nutrient medium under controlled environmental conditions.
(i) Media preparation room: An area equipped with bench space for chemicals, labware, culture vessels, balances, pH meters, hot plates, and autoclaves required for preparing and sterilizing nutrient media.
(ii) Culture room: A controlled-environment room maintained at $25\pm2^{\circ}\text{C}$ and 20-98% relative humidity with regulated illumination (typically 12 hours of light and 12 hours of darkness) for incubating cultures.

Teacher's Note:
a) Provide exact laboratory specifications for both rooms.
b) Emphasize the maintenance of aseptic conditions.

(b) Explain any two methods used for the identification of recombinant host cells from the non-recombinant host cells. [4]

Answer:
1. Antibiotic sensitivity (selectable markers): Recombinant plasmids carry antibiotic resistance genes. Host cells transformed with the recombinant plasmid survive on media supplemented with the specific antibiotic, whereas non-transformants die.
2. Insertional inactivation: The insertion of foreign DNA into the coding sequence of an enzyme gene (such as beta-galactosidase) inactivates the enzyme. Colonies with recombinant plasmids fail to produce colour (e.g., remain white), whereas non-recombinants produce blue colonies on screening media.

Teacher's Note:
a) Explain antibiotic resistance selection clearly.
b) Describe the blue-white screening principle of insertional inactivation.

(c) Name any four in vivo techniques employed in haploid production. [2 Marks]

Answer:
Four in vivo techniques employed in haploid production are:
1. Gynogenesis
2. Ovule and rogenesis (androgenesis)
3. Genome elimination by distant hybridization
4. Chemical treatment or semigamy

Teacher's Note:
a) List standard botanical haploid production methods.
b) Ensure accurate terminology like gynogenesis and distant hybridization.

Question 6.

(a) Write the principle and any two applications of each of the following biochemical techniques : [4]
(i) Ion - exchange chromatography
(ii) Gel - permeation

Answer:
(i) Ion - exchange chromatography:
- Principle: Based on the reversible exchange of ions in solution with ions electrostatically bound to an insoluble matrix, separating molecules according to differences in their net surface charge.
- Applications: Separation of amino acids, small peptides, nucleotides, and proteins.
(ii) Gel - permeation chromatography:
- Principle: Uses molecular sieves (cross-linked gels) with specific pore sizes to separate macromolecules based on molecular size, where smaller molecules enter the pores and are delayed while larger molecules elute first.
- Applications: Separation of polysaccharides, enzymes, and antibodies, and analysis of molecular-weight distributions of polymers.

Teacher's Note:
a) Clearly state the separation basis (charge for ion-exchange, size for gel-permeation).
b) List correct biological applications for each.

(b) What is a genetic code ? Enlist three important properties of genetic code. [4]

Answer:
The genetic code is the sequence of triplet codons on mRNA that specifies the sequence of amino acids in a polypeptide chain.
Three important properties:
1. Triplet code: Three adjacent nitrogen bases form a codon specifying one amino acid.
2. Universal code: The same codon specifies the same amino acid across almost all living organisms.
3. Non-ambiguous code: Each codon specifies only one single amino acid and no other.

Teacher's Note:
a) Define triplet nature clearly.
b) Mention other valid properties like degeneracy, start, and stop signals if required.

(c) What are DNA probes ? [2 Marks]

Answer:
A DNA probe is a single-stranded sequence of radioactive or fluorescently labeled DNA or oligonucleotides used to detect and identify complementary DNA sequences via hybridization reactions.

Teacher's Note:
a) Mention that probes rely on specific base-pairing complementarity.
b) Highlight their diagnostic utility in molecular biology.

Question 7.

(a) How can the following plants be obtained, using genetic transformation techniques : [4]
(i) Drought and salinity tolerant plants
(ii) Somatic hybrids

Answer:
(i) Drought and salinity tolerant plants:
Obtained by isolating stress-tolerance genes from naturally tolerant plants (such as Xerophyta viscosa or genes controlling compatible solutes like glycine betaine) and introducing them into crops using genetic transformation.
(ii) Somatic hybrids:
Obtained by the fusion of isolated somatic protoplasts from different plant species under in vitro conditions (somatic hybridization), followed by culture and regeneration of the resulting heterokaryon into a hybrid plant.

Teacher's Note:
a) Explain gene transfer for stress tolerance.
b) Explain protoplast fusion for somatic hybridization.

(b) Explain the process involved in the transcription of DNA to mRNA. Also, mention any two post transcriptional changes that occur in the mRNA formed. [4]

Answer:
Process of transcription:
- Initiation: RNA polymerase binds to the promoter region on DNA and unwinds the double helix.
- Elongation: RNA polymerase moves along the template strand (3' to 5' direction) synthesizing mRNA in the 5' to 3' direction using complementary ribonucleotides (A pairs with U, T with A, G with C, C with G).
- Termination: Transcription stops when a termination signal is reached, and the mRNA transcript is released.
Two post-transcriptional modifications in eukaryotes:
1. 5' capping: Addition of 7-methylguanosine ($m^{7}G$) to the 5' end.
2. 3' polyadenylation: Cleavage at the 3' end followed by the addition of a poly(A) tail.

Teacher's Note:
a) Detail the three phases of transcription.
b) Specify capping and polyadenylation as essential eukaryotic mRNA processing steps.

(c) What are Okazaki fragments ? How are they joined ? [2 Marks]

Answer:
Okazaki fragments are short, newly synthesized DNA fragments produced discontinuously on the lagging template strand during DNA replication. They are joined together by the enzyme DNA ligase.

Teacher's Note:
a) Associate Okazaki fragments specifically with lagging strand synthesis.
b) Highlight the sealing action of DNA ligase.

Question 8.

(a) What is meant by the term genomics ? Write the differences between structural genomics and functional genomics. [4]

Answer:
Genomics is the study of an organism's entire genome, involving mapping, sequencing, and analyzing genomic information to understand gene structure and function.
Differences:
- Structural genomics deals with DNA sequencing, sequence assembly, physical mapping, and determining the 3D structures of proteins.
- Functional genomics uses the data from structural genomics to determine the biological functions and interactions of genes and proteins on a genome-wide scale.

Teacher's Note:
a) Define genomics as whole-genome analysis.
b) Differentiate between mapping/sequencing (structural) and gene function discovery (functional).

(b) Name and explain any four methods of synchronization of cells. [4]

Answer:
Four methods of cell synchronization:
1. Physical selection by volume: Separating cells based on cell aggregate size.
2. Chemical starvation: Depriving suspension cultures of essential growth compounds to arrest cell cycles.
3. Chemical inhibition: Temporarily blocking cell cycle progression using biochemical inhibitors and subsequently releasing the block.
4. Stationary phase accumulation: Allowing cultures to reach stationary phase where cells naturally accumulate at a specific cell cycle checkpoint before dilution into fresh medium.

Teacher's Note:
a) Categorize methods into physical and chemical approaches.
b) Explain how synchronization helps study uniform cell cycle phases.

(c) What is meant by Expressed sequence tags ? [2 Marks]

Answer:
An Expressed Sequence Tag (EST) is a short sub-sequence of a transcribed cDNA sequence representing a partial gene, used to identify gene transcripts and aid in gene discovery and micro-arrays.

Teacher's Note:
a) Define ESTs as partial cDNA sequences.
b) Mention their applications in gene mapping and discovery.

Question 9.

(a) What is Human Genome Project ? Mention its objectives and significant achievements. [4]

Answer:
The Human Genome Project (HGP) was an international scientific research project with the primary goal of determining the sequence of chemical base pairs making up human DNA and identifying all human genes.
Objectives and achievements include mapping human genes, sequencing genomes of model organisms, developing fast sequencing technologies, and providing biomedical databases that facilitate advances in diagnosing and treating genetic diseases like cancer and cystic fibrosis.

Teacher's Note:
a) Describe HGP as a landmark international genome sequencing initiative.
b) Highlight both medical and scientific milestones achieved.

(b) Write short notes on : [4]
(i) Locus - link
(ii) Microprocessor
(iii) EMBL
(iv) Taxonomy Browser

Answer:
(i) Locus-Link: An NCBI online resource designed to link related information on genetic loci and gene products from multiple sources.
(ii) Microprocessor: The central processing unit (brain) of a computer that performs computational tasks, classified based on instruction set, bandwidth, and clock speed.
(iii) EMBL (European Molecular Biology Laboratory): An organization that collects, organizes, and distributes nucleotide sequence data through its primary nucleotide sequence database (EMBL-Bank).
(iv) Taxonomy Browser: An NCBI search tool that provides taxonomic information and scientific names for organisms with available sequence data, linking genetic data to biological classification.

Teacher's Note:
a) Provide concise, accurate definitions for each bioinformatics tool and database.
b) Ensure proper acronym expansions for EMBL and NCBI-linked resources.

(c) What is site-directed mutagenesis ? [2 Marks]

Answer:
Site-directed mutagenesis is a molecular biology technique used to make targeted and specific mutations at a pre-determined site within a DNA molecule.

Teacher's Note:
a) Contrast site-directed mutagenesis with random mutagenesis.
b) Mention its use in studying protein structure and function.