ISC Class 12 Biotechnology Board Exam Question Paper 2016 with Solutions

ISC Class 12 Biotechnology Board Exam Question Paper with Solutions 2016

Part-I

Question 1.

(a) Mention any one significant difference between each of the following : [5]
(i) Ligases and Helicases
(ii) Introns and Exons
(iii) Gel electrophoresis and Gel permeation
(iv) Sucrose and Starch
(v) Plasmids and Phages

Answer:
(i) Ligases are the enzymes which help in linking up of Okazaki (DNA) segments produced on the parent strand with 5'-3' direction, whereas Helicases help in unwinding the DNA helix, using ATP hydrolysis as a source of energy.
(ii) Introns are the intervening sequences which do not appear in the mature or processed RNA, whereas Exons are the coding sequences or expressed sequences that form functional and processed RNA.
(iii) Gel Electrophoresis is a technique by which negatively charged DNA fragments are separated by forcing them to move towards the anode under an electric field through a medium/matrix, whereas Gel permeation or filtration involves that molecules of different sizes are separated from each other on the basis of their ability to enter the pores within the beaded gel, followed by passing down a column containing the gel.
(iv) Sucrose is a disaccharide formed of glucose and fructose molecules, whereas starch is a polysaccharide molecule formed of a large number of glucose molecules arranged in the form of chains.
(v) Plasmids are the extra-chromosomal, self-replicating, circular, double-stranded DNA molecules present in bacteria, whereas Phages are viruses which infect bacteria/cells, lyse them, integrate their DNA into them, and replicate with the host chromosome.

Teacher's Note:
a) Focus on the fundamental functional or structural distinction for each pair.
b) Ensure precise biological terminology is used for enzymes and nucleic acids.

(b) Answer the following questions : [5]
(i) Why is the nutrient medium autoclaved before using it for cell culture?
(ii) Name the enzyme that can synthesize DNA at a high temperature.
(iii) Why are restriction enzymes also called as molecular scissors?
(iv) Name the nitrogenous bases present in RNA.
(v) Why is Agrobacterium tumefaciens called as the natural genetic engineer of plants?

Answer:
(i) The nutrient medium is autoclaved to make it sterile, i.e., free from microbes.
(ii) DNA polymerase isolated from the bacterium Thermus aquaticus.
(iii) Restriction enzymes are called molecular scissors because they make cuts at specific positions/recognition sites within both strands of DNA.
(iv) Adenine, guanine, uracil, and cytosine.
(v) Agrobacterium tumefaciens is able to deliver a piece of DNA known as T-DNA to transform normal plant cells into tumor cells. By manipulating its Ti plasmid, it has now been modified into a useful cloning vector for delivering a gene of our interest into a variety of plants.

Teacher's Note:
a) Direct factual recall is essential for these short-answer questions.
b) Note the exact spelling of Thermus aquaticus and the function of Ti plasmid.

(c) Write the full form of each of the following : [5]
(i) YAC
(ii) NCBI
(iii) RAM
(iv) SNP
(v) EMBL

Answer:
(i) YAC = Yeast Artificial Chromosome
(ii) NCBI = National Centre for Biotechnology Information (Note: The official key prints NCBf = National Centre for Bioinformatics Information, but the standard correct form is National Center for Biotechnology Information).
(iii) RAM = Random Access Memory
(iv) SNP = Single Nucleotide Polymorphism (Note: The official key prints Short Nucleotide Polymorphism, but Single Nucleotide Polymorphism is standard).
(v) EMBL = European Molecular Biology Laboratory

Teacher's Note:
a) Full forms must be memorized accurately without spelling errors.
b)

(d) Explain briefly : [5]
(i) Somatic hybridization
(ii) Promoter gene
(iii) Site directed mutagenesis
(iv) DNA probes
(v) Primer

Answer:
(i) Somatic hybrids are the hybrid plants produced through the fusion of protoplasts from two different varieties of plants each having a desirable character. The hybrid protoplasts can be further grown to form a new plant.
(ii) Promoter gene is a gene having a regulatory sequence of DNA that initiates the expression of a gene.
(iii) Site directed mutagenesis involves induction of specified or desired changes in the base sequence at specified sites of genes, most successfully achieved by overlap extension PCR.
(iv) DNA probes are short 15-30 bases long, labelled oligonucleotides (RNA-DNA) used to detect complementary nucleotide sequences after hybridization.
(v) Primer is a short oligonucleotide that hybridizes with the template strand and gives a 3'-OH end at which a DNA polymerase starts synthesis of the DNA chain.

Teacher's Note:
a) Definitions should be concise and cover the core mechanism or biological role.
b) Mentioning structural features like the 3'-OH end for primers fetches full marks.

Part-II

Question 2.

(a) With reference to amino acids, explain :
(i) Any one physical and any one chemical property of amino acids.
(ii) Essential and non-essential amino acids. [4]

Answer:
Amino acids are the building blocks of molecular proteins.
(i) Physical Property: They generally exist as dipolar ions (zwitterions) at physiological pH, conferring high melting points and solubility in water.
Chemical Property: Amino acids contain both an amino group (-NH₂) and a carboxylic group (-COOH), allowing them to condense to produce a peptide (-NHCO-) bond.
(ii) Essential amino acids are essential for our body but they are not synthesised inside our body, e.g., valine, isoleucine, lysine, etc. They must be supplemented through diet. Non-essential amino acids are those which are synthesised through transformation and transamination inside our body, e.g., serine, alanine, etc.

Teacher's Note:
a) Clearly distinguish between physical behavior (like zwitterion formation) and chemical bonding (peptide bond formation).
b) Provide appropriate examples for essential and non-essential amino acids.

(b) Briefly outline the various steps involved in the gene cloning technique [4]

Answer:
The various steps involved in gene cloning technique are:
1. Identification and isolation of desired DNA.
2. Amplification of gene of interest using PCR.
3. Fragmentation/cutting of desired DNA and vector DNA by restriction enzymes.
4. Ligation/joining of desired DNA fragment into vector using ligase enzyme.
5. Transferring the recombinant DNA into host cell/organism by transformation, transfection, electroporation, microinjection, biolistics, or Agrobacterium/retrovirus-mediated gene transfer.
6. Culturing the host cell for obtaining the foreign gene product/recombinant protein.
7. Extraction of desired products or downstream processing.

Teacher's Note:
a) Sequence of steps is crucial in recombinant DNA technology questions.
b) Mentioning both vector-mediated and vectorless gene transfer methods is recommended.

(c) List any four characteristics of genetic code. [2]

Answer:
The characteristics of genetic codes are:
1. Codes are universal.
2. Codes are unambiguous and specific.
3. Code is degenerate, i.e., some amino acids are coded by more than one codon.
4. Codons are read in a continuous fashion, i.e., there are no commas or punctuations.

Teacher's Note:
a) List standard features clearly as bullet points.
b) Avoid writing contradictory statements regarding degeneracy.

Question 3.

(a) Describe the three dimensional structure of DNA as proposed by Watson, Crick and Wilkins. Name a biochemical technique that was used by them to confirm the structure of DNA. [4]

[Figure: Coiling in double helix or duplex of DNA showing major and minor grooves, pitch of 3.4 nm, and interchain distance of 20 A]

Answer:
Salient features of double helix structure of DNA include:
1. Double helix made of two polynucleotide chains where sugar and phosphate form the backbone and nitrogen bases project inside.
2. The two chains are antiparallel with one chain having the polarity of 5' to 3' and the other 3' to 5'.
3. Presence of double hydrogen bonds between A=T, and triple bonds between G=C. Purines always pair opposite to pyrimidines to create a uniform distance.
4. The two chains are coiled in a right-handed fashion with a pitch (one turn) of 3.4 nm containing 10 base pairs (0.34 nm gap between adjacent base pairs).
5. The two chains of DNA are 20 A far apart, and the plane of one base pair stacks over the other to confer stability.
Rosalind Franklin confirmed this structure of DNA through X-Ray crystallography.

Teacher's Note:
a) Accurate dimensions (pitch, diameter, base pairs per turn) must be specified.
b) Mentioning Rosalind Franklin and X-Ray crystallography completes the answer.

(b) Explain the role of the following enzymes during the process of protein synthesis : [4]
(i) RNA polymerases and amino acyl tRNA synthetase.
(ii) Start codons and end codons.

Answer:
(i) RNA polymerases associate transiently with the initiation sigma factor to bind to the promoter site and catalyze the synthesis of RNA in the 5' to 3' direction on the DNA template without requiring a primer. Amino acyl tRNA synthetases couple each amino acid to its appropriate set of tRNA molecules (there are 20 synthetases for the 20 natural amino acids).
(ii) Start codons (such as AUG in prokaryotes) act as the initiation site for translation and code for methionine. End codons (UAA, UAG, UGA) function as stop codons, do not code for any amino acid, and terminate protein synthesis.

Teacher's Note:
a) Differentiate clearly between transcription enzymes and translation termination signals.
b) Note that the official key contains a minor typo 'UAQ' which stands for UAG; use standard biological abbreviations.

(c) Why are auxins and cytokinins used in plant tissue culture ? [2]

Answer:
Auxins are used because they help in the formation of callus, development of xylem, promotion of cambial activity, and cell elongation. Cytokinins are used because they stimulate cell division and help in the morphogenesis of plant cells along with auxins.

Teacher's Note:
a) Mention the synergistic role of auxins and cytokinins in organogenesis.
b) Keep the explanation concise and focused on tissue culture applications.

Question 4.

(a) Explain how DNA technology has been used to create the following : [4]
(i) Dolly
(ii) Hepatitis B vaccine

Answer:
(i) Dolly: Created using nuclear transfer technology in 1996 by Ian Wilmut and his research group. The nucleus of an udder cell from a 6-year-old sheep was fused with an enucleated unfertilized egg cell from another sheep using a mild electric shock. The resulting hybrid cell was cultured and implanted into a surrogate mother, resulting in the birth of Dolly.
(ii) Hepatitis B vaccine: A recombinant Hepatitis B vaccine was produced by cloning the synthetic gene for the surface antigen of the virus into yeast cells. The gene expressed well in yeast cells and produced 22 nm particles of hepatitis B virus surface antigen with high immunogenicity, providing safe and effective protection against HBV infection.

Teacher's Note:
a) Highlight the key technological breakthrough for both cloning (nuclear transfer) and recombinant vaccines (surface antigen expression in yeast).
b) Ensure proper terminology like enucleated egg and surrogate mother are included.

(b) Write short notes on : [4]
(i) Batch culture and continuous culture.
(ii) Salinity resistance in crops.

Answer:
(i) Batch culture: A closed culture system where the same medium and all cells are retained in the vessel, exhibiting a sigmoid growth curve (lag, log, and stationary phases) ending due to nutrient depletion and waste accumulation. Continuous culture: An open or closed system where the cell population is maintained in a steady state by regularly replacing a portion of used medium with fresh medium.
(ii) Salinity resistance in crops: Plants can be genetically engineered to tolerate high salinity by introducing genes that secrete stress-related osmolytes such as sugars, sugar alcohols (mannitol), and amino acids (betaine, proline). For example, introducing the E. coli betA gene via Ti plasmid into tobacco increased its salt tolerance significantly.

Teacher's Note:
a) Clearly contrast batch culture (closed system with phases) with continuous culture (steady state).
b) Mention specific osmolytes like betaine when explaining salinity resistance.

(c) Name any two chemicals used to prepare the gel for gel electrophoresis. [2]

Answer:
1. Agarose
2. Polyacrylamide

Teacher's Note:
a) Direct and straightforward chemical/polymer naming.
b) Both agarose and polyacrylamide are standard gel matrices.

Question 5.

(a) Give the step wise procedure of the Southern Blotting technique. Mention any two differences between Southern Blotting technique and Northern Blotting technique. [4]

[Figure: Southern blotting technique diagram showing genomic DNA digestion, agarose gel electrophoresis, transfer to nitrocellulose membrane via capillary action, and hybridization with radioactive DNA probe]

Answer:
Step-wise procedure of Southern Blotting:
1. Genomic DNA is isolated and digested with restriction enzymes.
2. DNA fragments are separated by agarose gel electrophoresis according to size.
3. DNA on the gel is denatured using NaOH and transferred to a nylon or nitrocellulose membrane by blotting (capillary action).
4. The transferred DNA is fixed to the membrane by UV radiation or baking.
5. The membrane is incubated with a radio-labeled DNA probe which hybridizes with complementary sequences.
6. After washing and drying, the membrane is exposed to a photographic film to detect the bands.
Differences: Southern Blotting is used for the separation and identification of specific DNA fragments, whereas Northern Blotting is used for the analysis of RNA.

Teacher's Note:
a) Sequence of steps (digestion, electrophoresis, blotting, probing, autoradiography) must be accurate.
b) Clearly state the nucleic acid type targeted in Southern versus Northern blotting.

(b) Explain the principle and any two applications of each of the following biochemical techniques:
(i) Ion Exchange Chromatography
(ii) Colorimetry [4]

Answer:
(i) Ion Exchange Chromatography Principle: Based on the reversible exchange of ions in solution with ions electrostatically bound to an insoluble support medium, separating molecules based on differences in their charges and charge densities.
Applications: 1. Separating two proteins differing by only one charged amino acid. 2. Separating species with very minor differences in properties.
(ii) Colorimetry Principle: Based on the interaction of light energy with coloured solutions; the amount of light absorbed at specific wavelengths is proportional to the concentration of the compound (Beer-Lambert law).
Applications: 1. Quantitative estimation of concentration in solution. 2. Detection and identification of biomolecules.

Teacher's Note:
a) Emphasize the basis of separation (charge for ion exchange, light absorption for colorimetry).
b) List valid biochemical applications for each technique.

(c) What is the cause of inborn metabolic disorders? Give any two examples of these disorders. [2]

Answer:
Inborn metabolic disorders are caused by a change or mutation in the gene controlling the synthesis of a specific enzyme (often inherited as autosomal recessive traits), leading to enzyme deficiency and metabolic block.
Examples: 1. Albinism 2. Alkaptonuria (Other accepted examples: Phenylketonuria, Sickle-cell anaemia, Cystic fibrosis).

Teacher's Note:
a) State gene mutation and enzyme deficiency as the primary cause.
b) Provide clear and common examples such as Albinism or Phenylketonuria.

Question 6.

(a) Discuss the significance of each of the following techniques used in cell culture technology: [4]
(i) Androgenesis and gynogenesis
(ii) In-vitro pollination

Answer:
(i) Androgenesis and gynogenesis: Both techniques are used for the production of haploid plants. Androgenesis involves the development of a plant from an egg cell containing only the male nucleus (after female nucleus elimination), while gynogenesis involves development from unfertilized egg cells (often stimulated by irradiated pollen) and is useful in breeding programs and generating homozygous lines.
(ii) In-vitro pollination: A laboratory procedure where pollination and fertilization occur under in vitro conditions to overcome interspecific and intergeneric incompatibility barriers that prevent crossing by conventional plant breeding.

Teacher's Note:
a) Define haploid production for androgenesis and gynogenesis.
b) Explain how in-vitro pollination solves breeding incompatibility.

(b) Enumerate any two post transcriptional changes in the mRNA to produce a completely mature mRNA. [4]

Answer:
The post-transcriptional modifications in primary transcript (hnRNA) include:
1. Capping: Addition of an extra methyl-guanosine triphosphate residue at the 5' end to protect mRNA from exonucleases and aid in translation.
2. Tailing (Polyadenylation): Addition of a string of adenosine residues (poly-A tail) at the 3' end.
3. Splicing: Removal of non-coding introns and joining of coding exons together.

Teacher's Note:
a) Detail at least two major modifications (capping, tailing, or splicing) clearly.
b) Mention the functional significance of each modification.

(c) State any four achievements of the Human Genome Project. [2]

Answer:
1. Sequenced the 3 billion base pairs of the human genome and identified repeated sequences.
2. Sparked the development of bioinformatics to store and analyze biological data.
3. Enabled a new approach to biological research and understanding biological systems.
4. Identified genes associated with common human disorders like cardiovascular diseases, diabetes, and Alzheimer's disease to aid in drug design.

Teacher's Note:
a) Keep the points concise and directly linked to HGP outcomes.
b) Mentioning bioinformatics and disease gene identification is crucial.

Question 7.

(a) Explain the method used for the construction of a genomic DNA library. Also state how a genomic DNA library differs from a cDNA library. [4]

Answer:
Construction of Genomic Library:
1. High molecular weight genomic DNA is isolated and digested with compatible restriction enzymes.
2. The resulting fragments are separated by agarose gel electrophoresis to obtain desired sizes.
3. Fragments are dephosphorylated using alkaline phosphatase and ligated into a vector (plasmid, phage, or cosmid).
4. The recombinant vectors are introduced into a host by electroporation and amplified.
Difference: A genomic library contains all DNA sequences (genes and non-coding regions) of an organism's genome, whereas a cDNA library contains only expressed genes (derived from mRNA) and lacks introns.

Teacher's Note:
a) Outline the step-by-step creation from restriction digestion to host transformation.
b) Clearly distinguish genomic libraries from cDNA libraries based on intron presence and coding content.

(b) Discuss any four vector-less methods of transfer of foreign DNA into the host cells. [4]

Answer:
1. Transfection: Chemical-mediated transfer using cationic liposomes or calcium phosphate to facilitate DNA uptake by host cells.
2. Electroporation: Application of a high-voltage electric current to create temporary microscopic pores in the cell membrane for DNA entry.
3. Microinjection: Direct and forcible micro-needle injection of foreign DNA into the nucleus of animal or plant cells.
4. Particle Bombardment (Biolistics): High-velocity bombardment of microscopic gold or tungsten particles coated with desired DNA into target cells using a particle gun.

Teacher's Note:
a) List four distinct physical or chemical vectorless delivery methods.
b) Briefly explain the mechanism for each method.

(c) Define glycosidic bond and peptide bond. [2]

Answer:
Glycosidic bond (-O-) is the covalent bond formed between the -OH group attached to the anomeric carbon of a monosaccharide and the -OH group of another monosaccharide, leading to the formation of a disaccharide. Peptide bond (-NHCO-) is the amide bond formed between the carboxylic group (-COOH) of one amino acid and the amino group (-NH₂) of another amino acid with the elimination of a water molecule.

Teacher's Note:
a) Give chemical bond formulas and interacting functional groups for both bonds.
b) Mention dehydration/water elimination clearly.

Question 8.

(a) Explain the secondary and the quaternary structure of proteins. Mention any two important functions of proteins. [4]

[Figure: alpha-helix, beta-pleated sheet, and collagen helix protein structures]

Answer:
Secondary Structure: Involves folding or coiling of the polypeptide chain stabilized by hydrogen bonds, forming structures such as the alpha-helix, beta-pleated sheet, and collagen helix.
Quaternary Structure: Found in multimeric proteins composed of two or more polypeptide subunits (protomers) held together by non-covalent interactions (e.g., hemoglobin with two alpha and two beta chains).
Functions of proteins: 1. Act as enzymes/biocatalysts. 2. Serve structural roles (e.g., hair keratins, collagen).

Teacher's Note:
a) Describe alpha-helices and beta-sheets for secondary structure, and subunit assembly for quaternary structure.
b) List fundamental biological functions like catalysis and structural support.

(b) Discuss the method used for DNA sequencing by Automated DNA sequencing technique. [4]

[Figure: Autoradiogram of electrophoresed DNA sequencing gel showing lanes for ddATP, ddGTP, ddTTP, and ddCTP]

Answer:
In Automated DNA Sequencing, each of the four dideoxynucleotides (ddNTPs) is tagged with a distinct fluorescent dye that emits light of a specific wavelength. All labelled ddNTPs and DNA fragments are separated by size using capillary gel electrophoresis. As fragments pass through a laser beam, the fluorescent dyes are excited, and the emitted light is recorded by a detector and fed directly into a computer to generate an electrogram chromatogram, rapidly determining the nucleotide sequence.

Teacher's Note:
a) Emphasize the use of fluorescently labelled ddNTPs and laser detection.
b) Mention capillary electrophoresis as the core separation mechanism.

(c) Give any one example each of in-situ and ex-situ conservation. [2]

Answer:
In-situ conservation example: National Park (or Wildlife Sanctuary, Biosphere Reserve).
Ex-situ conservation example: Botanical Garden (or Zoological Park, Gene Bank).

Teacher's Note:
a) Differentiate clearly between on-site (in-situ) and off-site (ex-situ) conservation.
b) Standard examples like National Parks and Botanical Gardens are universally accepted.

Question 9.

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

Answer:
Genomics is the scientific discipline of mapping, sequencing, and analyzing the entire genome (complete set of genes) of an organism. Structural genomics deals with DNA sequencing, sequence assembly, and construction of high-resolution genetic and physical maps, whereas Functional genomics deals with interpreting genome sequences to determine gene functions, expression patterns, and protein interactions.

Teacher's Note:
a) Define genomics as the study of complete genomes.
b) Contrast structural mapping/sequencing with functional gene characterization.

(b) How do the following databases contribute towards managing biological data : [4]
(i) GDB and MGD
(ii) PDB and PIR

Answer:
(i) GDB (Genome Database): Acts as the official central repository for genome mapping data created by the Human Genome Project. MGD (Mouse Genome Database): Provides comprehensive information on mouse genetic markers, phenotypes, and comparative mapping data.
(ii) PDB (Protein Data Bank): Stores 3-D structural data of proteins and nucleic acids determined by crystallography or NMR spectroscopy. PIR (Protein Information Resource): An integrated public bioinformatics resource supporting genomic, proteomic, and systems biology research.

Teacher's Note:
a) Identify each database by its specific domain (genome mapping, mouse genetics, protein structures, protein information).
b) Accuracy in database acronym expansions and roles is valued by examiners.

(c) Name any two organisms whose genomes have been completely sequenced. [2]

Answer:
1. Escherichia coli (E. coli)
2. Saccharomyces cerevisiae (Yeast)
(Other accepted answers: HIV, Phage lambda, Drosophila melanogaster).

Teacher's Note:
a) Provide standard model organisms whose sequencing milestones are well-documented.
b) Naming any two valid sequenced organisms is sufficient for full marks.