ISC Class 12 Biotechnology Board Exam Question Paper 2011 with Solutions

ISC Class 12 Biotechnology Board Exam Question Paper with Solutions

Part - I (Compulsory)

Question 1

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

(i) Nucleotide and nucleoside. [1 Mark]

Answer:
A nucleotide is a condensation product of a heterocyclic nitrogen base, a pentose sugar (ribose or deoxyribose), and a phosphate or polyphosphate group, whereas a nucleoside consists only of a pentose sugar and a nitrogen base (purine or pyrimidine) without the phosphate group.

Teacher's Note:
a) Remember that Nucleoside + Phosphate = Nucleotide.
b) Students often confuse the presence of the phosphate group; ensure you mention it explicitly.

(ii) Plasmids and phages. [1 Mark]

Answer:
Plasmids are extra-chromosomal, independent, self-replicating, circular, double-stranded DNA molecules naturally found in bacteria and some fungi, whereas phages (bacteriophages) are viruses that infect bacteria and act as obligate intracellular parasites relying on host machinery to multiply.

Teacher's Note:
a) Plasmids are purely nucleic acid vectors, while phages possess a protein coat encapsulating their viral genome.
b) Mentioning their natural occurrence and mode of existence helps secure full credit.

(iii) Fluorescence spectrometry and mass spectrometry. [1 Mark]

Answer:
Fluorescence spectrometry is a technique that assays the state of a biological system by studying absorption and emission spectra using fluorescent probe molecules, whereas mass spectrometry is an analytical technique that involves the separation of ions based on their mass-to-charge ratio using electric and magnetic fields.

Teacher's Note:
a) Fluorescence spectrometry relies on light absorption and emission properties.
b) Mass spectrometry separates ionized particles based on mass and energy.

(iv) Primer and primases. [1 Mark]

Answer:
A primer is a short strand of RNA (or DNA) that serves as a starting point for DNA synthesis, whereas primase is an enzyme that catalyzes the synthesis of this short RNA segment complementary to a single-stranded DNA template.

Teacher's Note:
a) Distinguish clearly between the molecule (primer) and the catalyst (primase).
b) Note that DNA polymerase requires an existing 3'-OH group provided by the primer.

(v) Introns and exons. [1 Mark]

Answer:
Introns are non-coding DNA base sequences found between exons that are spliced out and do not form part of mature mRNA, whereas exons are coding DNA sequences that are transcribed and eventually translated into amino acids in proteins.

Teacher's Note:
a) Exons are expressed sequences; introns are intervening non-coding sequences.
b) Mentioning post-transcriptional splicing adds precision to the answer.

(b) Answer the following questions : [5]

(i) What are oil eating bacteria? [1 Mark]

Answer:
Bacteria that decompose and use petroleum hydrocarbons as their source of energy are called oil eating bacteria, such as genetically engineered strains of Pseudomonas putida, which can digest a significant portion of hydrocarbons in oil spills.

Teacher's Note:
a) Provide the standard example of Pseudomonas putida to secure full marks.
b) Mention their bioremediation application.

(ii) What are single cell proteins? [1 Mark]

Answer:
Single cell proteins (SCP) refer to the biomass of dry cells of microorganisms such as yeasts, bacteria, filamentous fungi, and algae grown on various carbon sources to be used as protein-rich food or feed supplements.

Teacher's Note:
a) Highlight that SCP refers to microbial biomass, not a purified single protein.
b) Mention source organisms like Spirulina or yeast.

(iii) Who proposed the Operon concept of gene regulation? [1 Mark]

Answer:
François Jacob and Jacques Monod proposed the Operon concept of gene regulation in bacteria.

Teacher's Note:
a) State both scientist names correctly (Jacob and Monod).
b) Mentioning their work on the lac operon is a good supporting detail.

(iv) Explain the term transposons. [1 Mark]

Answer:
Transposons are sequences of DNA that can move around to different positions within the genome of a single cell, commonly referred to as jumping genes or mobile genetic elements.

Teacher's Note:
a) Use the term jumping genes for clarity.
b) Mention that they can cause mutations or alter genome size.

(v) Name one polysaccharide found in the cell wall of bacteria and one polysaccharide found in fungi. [1 Mark]

Answer:
The polysaccharide found in the cell wall of bacteria is peptidoglycan (murein), and the polysaccharide found in fungal cell walls is chitin.

Teacher's Note:
a) Ensure both organisms and their respective correct cell wall polymers are named clearly.
b) Chitin is a homopolymer of N-acetylglucosamine.

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

(i) NCBI [1 Mark]

Answer:
National Center for Biotechnology Information

Teacher's Note:
a) Spell each word correctly according to standard bioinformatics nomenclature.
b) Avoid spelling errors in proper nouns.

(ii) EST [1 Mark]

Answer:
Expressed Sequence Tag

Teacher's Note:
a) ESTs are short sub-sequences of a transcribed cDNA sequence.
b) Commonly used in gene discovery and mapping.

(iii) ROM [1 Mark]

Answer:
Read Only Memory

Teacher's Note:
a) Standard computer science terminology frequently used in bioinformatics databases.
b) Ensure exact spelling.

(iv) PAGE [1 Mark]

Answer:
Polyacrylamide Gel Electrophoresis

Teacher's Note:
a) Crucial laboratory technique for separating proteins and small DNA fragments.
b) Write out the full form without missing any terms.

(v) FMN [1 Mark]

Answer:
Flavin Mononucleotide

Teacher's Note:
a) FMN acts as a prosthetic group for various oxidoreductase enzymes.
b) Derived from riboflavin (Vitamin B2).

(d) Explain briefly: [5]

(i) RNA dependent DNA polymerase [1 Mark]

Answer:
RNA-dependent DNA polymerase (commonly known as reverse transcriptase) is an enzyme that uses an RNA molecule as a template to synthesize a complementary DNA (cDNA) strand, characteristically found in retroviruses like HIV.

Teacher's Note:
a) Mention reverse transcriptase as its common alternate name.
b) Highlight its importance in retroviral replication and cDNA synthesis.

(ii) EMBL [1 Mark]

Answer:
European Molecular Biology Laboratory, which maintains a core bioinformatics database for nucleotide sequence data.

Teacher's Note:
a) Identify EMBL as a major biological database repository.
b) Mention its European origin and global collaboration in data sharing.

(iii) Isoelectric focussing [1 Mark]

Answer:
Isoelectric focusing (IEF) is a zone electrophoresis technique used to separate proteins based on their differing isoelectric points (pI) along a pH gradient in a gel under an electric field.

Teacher's Note:
a) Emphasize the pH gradient and the isoelectric point concept.
b) Proteins stop moving when they reach the pH equal to their pI where net charge is zero.

(iv) Cosmids [1 Mark]

Answer:
Cosmids are hybrid cloning vectors constructed by combining plasmid sequences with the cos sites of bacteriophage lambda, allowing them to package large DNA inserts into viral particles in vitro.

Teacher's Note:
a) Mention both plasmid and phage lambda components.
b) Highlight their capacity to clone large DNA fragments (up to 45 kb).

(v) Vitamins [1 Mark]

Answer:
Vitamins are organic compounds required as essential micronutrients in very small amounts by organisms, often functioning as cofactors or coenzymes in metabolic reactions, and typically cannot be synthesized in sufficient quantities endogenously.

Teacher's Note:
a) State that they act as coenzymes or cofactors.
b) Emphasize that they must be obtained through diet or culture media.

Part - II
(Answer any five questions)

Question 2.

(a) Mention two important chemical properties of each of the following: [4]
(i) Monosaccharides
(ii) Proteins .

Answer:
(i) Chemical properties of monosaccharides:
1. Mutarotation: When alpha and beta isomeric forms of D-glucose are dissolved in water, their optical rotation changes with time and reaches a final constant equilibrium value of +53 degrees due to interconversion via the open-chain form.
2. Formation of glycosides and acetals/ketals: Monosaccharides react with alcohols in the presence of acid catalysts to form acetals (glycosides) through their hemiacetal or hemiketal groups.
(ii) Chemical properties of proteins:
1. Acid hydrolysis: Proteins when hydrolyzed by concentrated acids (such as HCl) yield constituent amino acids in the form of their hydrochlorides.
2. Colorimetric characteristic reactions: Proteins undergo specific color reactions such as the Xanthoproteic test (yellow color with concentrated nitric acid due to benzene rings) and Sanger's reaction (reaction with FDNB).

Teacher's Note:
a) Clearly separate monosaccharides and protein properties into distinct points.
b) Mentioning specific tests like Xanthoproteic test awards full marks for protein chemistry.

(b) What are restriction enzymes ? How do they act ? Give any two examples of restriction enzymes. [4]

Answer:
Restriction enzymes are specialized endonuclease enzymes found in bacteria that cut DNA molecules at specific palindromic nucleotide sequences, earning them the nickname 'molecular scissors'. They act by recognizing a specific target sequence in double-stranded DNA and cleaving phosphodiester bonds on both strands, producing either sticky or blunt ends. Examples include EcoRI, HindIII, and BamHI.

Teacher's Note:
a) Define restriction enzymes as restriction endonucleases.
b) Provide correct and well-known examples such as EcoRI and HindIII.

(c) What are derived lipids ? Give an example. [2]

Answer:
Derived lipids are lipid-like substances or hydrolysis derivatives of simple and compound lipids, such as sterols, terpenes, and prostaglandins.
Example: Cholesterol or Prostaglandins.

Teacher's Note:
a) Explain their origin through the hydrolysis of simple or compound lipids.
b) Give a clear, unambiguous example like cholesterol.

Question 3.

(a) Give an account of various enzymes that play a role in the process of DNA replication. [4]

Answer:
1. Helicase: Unwinds the double-helical DNA structure by breaking hydrogen bonds between bases.
2. Topoisomerase (Gyrase): Relieves torsional strain and supercoiling ahead of the replication fork by causing single or double strand breaks and religation.
3. RNA Primase: Synthesizes short RNA primers required to initiate DNA synthesis.
4. DNA Polymerase: Synthesizes the new DNA strand by adding nucleotides in the 5'-to-3' direction, with specific forms like DNA polymerase delta and epsilon handling leading and lagging strands.
5. DNA Ligase: Seals the nicks in the sugar-phosphate backbone by joining Okazaki fragments on the lagging strand.

Teacher's Note:
a) List at least four major enzymes with their precise biological functions.
b) Mention DNA ligase and helicase as essential core components.

(b) Write short notes on : [4]
(i) Secondary structure of proteins
(ii) Designer oils.

Answer:
(i) Secondary structure of proteins: Refers to the local folding of polypeptide chains into regular structures stabilized by intramolecular hydrogen bonds between imide (-NH-) and carbonyl (-CO-) groups. The two main types are the alpha-helix (spiral conformation) and beta-pleated sheets (extended sheet-like conformation).
(ii) Designer oils: Vegetable or seed oils modified through genetic engineering or processing (such as incorporating phytosterols) to improve nutritional profiles, reduce LDL cholesterol levels, and increase oxidative stability.

Teacher's Note:
a) Define hydrogen bonding as the stabilizing force for protein secondary structures.
b) For designer oils, mention their health benefits like cholesterol reduction.

(c) What is meant by synchronization of cell culture. [2]

Answer:
Cell culture synchronization is the manipulation of growth conditions in an asynchronous cell culture so that the majority of cells proceed through each phase of the cell cycle (G1, S, G2, and M) simultaneously. It can be achieved using physical methods (such as size separation) or chemical methods (such as starvation or biochemical inhibitors).

Teacher's Note:
a) Define synchronous vs. asynchronous cultures clearly.
b) Mention at least one method (physical or chemical) used to achieve synchronization.

Question 4.

(a) Write the steps in the process of activation of amino acids during the process of translation. [4]

Answer:
1. Recognition and charging: Specific amino acids are coupled to their corresponding tRNA molecules by enzymes called aminoacyl-tRNA synthetases.
2. Step 1 of reaction: Amino acid reacts with ATP in the presence of an enzyme and Mg2+ to form aminoacyl-adenylate (AA-AMP) and release pyrophosphate (PPi).
3. Step 2 of reaction: The activated amino acid is transferred from aminoacyl-adenylate to the specific tRNA molecule to form charged aminoacyl-tRNA and release AMP.
4. High-energy bond formation: The resulting amino acid-tRNA bond is a high-energy linkage that subsequently drives peptide bond formation during translation.

Teacher's Note:
a) Detail the two-step enzymatic reaction involving ATP and aminoacyl-tRNA synthetase.
b) Emphasize that this charging step precedes actual ribosomal translation.

(b) What is the significance of genetic code in protein synthesis ? Mention four important characteristics of the genetic code. [4]

Answer:
Significance: The genetic code provides the transcript dictionary through which triplet nucleotide sequences on mRNA are translated into specific amino acid sequences to construct functional polypeptides.
Four characteristics:
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 nearly all living organisms.
3. Non-ambiguous code: Each specific codon specifies only one single amino acid.
4. Degenerate code: Most amino acids are specified by more than one codon.

Teacher's Note:
a) Clearly state both the biological significance and any four key features.
b) Use accurate genetic code terminologies like universal, triplet, and non-ambiguous.

(c) Name the important steps in a single cycle of polymerase chain reaction. [2]

Answer:
The three main steps in a single PCR cycle are:
1. Denaturation (high-temperature melting of double-stranded DNA templates)
2. Primer Annealing (binding of oligonucleotide primers to single-stranded templates at lower temperature)
3. Extension / Polymerization (synthesis of new DNA strands by Taq polymerase at optimal temperature)

Teacher's Note:
a) List the three thermal cycle steps in correct chronological order.
b) Keep descriptions concise for a 2-mark question.

Question 5.

(a) Write notes on : [4]
(i) Proteomics.
(ii) De-differentiation and Re-differentiation.

Answer:
(i) Proteomics: Proteomics is the large-scale identification, analysis, and characterization of the proteome (the entire set of proteins expressed by a cell, tissue, or organism under defined conditions), aimed at understanding protein functions, structures, and post-translational modifications.
(ii) De-differentiation and Re-differentiation: De-differentiation is the cellular process by which mature, specialized cells revert to an unspecialized, meristematic state capable of dividing, whereas re-differentiation is the subsequent process where these de-differentiated cells specialize again to form specific tissues.

Teacher's Note:
a) Define proteomics as protein complement analysis.
b) Explain de-differentiation and re-differentiation as complementary plant tissue culture phenomena.

(b) Mention the objectives of germplasm conservation using the cell culture technique. What are the limitations of conservation of germplasm using conventional methods? [4]

Answer:
Objectives of germplasm conservation using cell culture:
1. To preserve endangered, rare, or genetically modified plant species safely.
2. To maintain disease-free plant material and clonal lines in compact storage space.
Limitations of conventional seed or field storage methods:
1. Seeds of many tropical and recalcitrant crop species lose viability quickly at ambient temperatures.
2. Clonal crops and vegetatively propagated species are prone to genetic heterogeneity, pest susceptibility, and require vast field space.

Teacher's Note:
a) Highlight the advantages of in vitro conservation over traditional seed banks.
b) Mention recalcitrant seeds as a primary limitation of conventional methods.

(c) The base sequence of one strand of DNA is 3' CATGAC 5'. What will be the base sequence of its : [2]
(i) Complementary DNA strand.
(ii) Complementary RNA strand.

Answer:
(i) Complementary DNA strand: 5' GTACTG 3'
(ii) Complementary RNA strand: 5' GUACUG 3'

Teacher's Note:
a) Pay close attention to 5' and 3' polarity directions in nucleic acid sequences.
b) Remember that RNA contains Uracil (U) in place of Thymine (T).

Question 6.

(a) Why are enzymes called biocatalysts ? Briefly discuss the mode of enzyme action. [4]

Answer:
Enzymes are called biocatalysts because they are biological macromolecules (proteins) that accelerate biochemical reaction rates without themselves being consumed or permanently altered in the process. Mode of enzyme action involves binding of substrate molecules to the enzyme's active site to form an enzyme-substrate complex, lowering the activation energy barrier, and converting substrates into products through models such as the Lock-and-Key hypothesis or Induced-Fit model.

Teacher's Note:
a) Explain why they are termed biological catalysts (proteinaceous nature and unconsumed status).
b) Mention the active site and activation energy reduction.

(b) Explain the principle and applications of each of the following biochemical techniques: [4]
(i) Gel permeation.
(ii) Colorimetry.

Answer:
(i) Gel permeation chromatography (Size exclusion):
Principle: Separates molecules based on their molecular size using porous gel beads where smaller molecules enter the pores and are delayed, while larger molecules elute faster.
Application: Used for purifying proteins, separating polymers, and determining molecular weights.
(ii) Colorimetry:
Principle: Based on Beer-Lambert law, measuring the absorption of light of a specific wavelength by a colored solution, where absorption is proportional to solute concentration.
Application: Used extensively to determine concentrations of unknown chemical and biochemical substances in solutions.

Teacher's Note:
a) Clearly separate principle and application headings for both techniques.
b) State Beer-Lambert law for colorimetry.

(c) How are the diseases cystic fibrosis and albinism caused? [2]

Answer:
Cystic fibrosis is caused by mutations in the gene encoding the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) transport protein, leading to defective salt and fluid secretion and thick mucus accumulation. Albinism is caused by autosomal recessive gene mutations that result in the failure or deficiency of enzymes (like tyrosinase) required to convert tyrosine into melanin pigment.

Teacher's Note:
a) Mention CFTR protein defect for cystic fibrosis.
b) Mention tyrosinase/melanin deficiency for albinism.

Question 7.

(a) Explain how 'Dolly' was created. What is its importance in the field of biotechnology? [4]

Answer:
Dolly the sheep was created using the technique of somatic cell nuclear transfer (SCNT). The nucleus from an adult somatic mammary gland cell was extracted and fused with an enucleated unfertilized sheep egg cell using an electric pulse. The resulting hybrid embryo was stimulated to divide in vitro and then implanted into a surrogate mother sheep. Importance: It proved that differentiated adult somatic cells retain all genetic information needed to form an entire organism, revolutionizing cloning technology and regenerative medicine.

Teacher's Note:
a) Clearly describe somatic cell nuclear transfer steps.
b) Emphasize that Dolly was the first mammal cloned from an adult somatic cell.

(b) Differentiate between: [4]
(i) PCR and Gene Cloning.
(ii) Batch Culture and Continuous Culture.

Answer:
(i) PCR and Gene Cloning:
- PCR is an in vitro enzymatic amplification method that rapidly produces millions of DNA copies without host cells.
- Gene cloning is an in vivo method where target DNA is inserted into a vector and introduced into host cells for replication.
(ii) Batch Culture and Continuous Culture:
- Batch culture is a closed system where nutrients are added initially and medium is not replenished, resulting in a standard sigmoid growth curve.
- Continuous culture is an open system where nutrient medium is continuously added and spent medium with cells is withdrawn to maintain cells in a steady log phase.

Teacher's Note:
a) Use clear comparative points for both sub-parts.
b) Highlight in vitro vs in vivo for PCR vs gene cloning.

(c) What are polysaccharides? How are they formed? [2]

Answer:
Polysaccharides are complex polymeric carbohydrate molecules composed of numerous monosaccharide monomer units joined together by glycosidic bonds. They are formed through enzyme-catalyzed condensation (dehydration synthesis) reactions linking multiple sugar units, such as in starch and glycogen.

Teacher's Note:
a) Define them as complex carbohydrates with glycosidic linkages.
b) Mention condensation/dehydration reaction as the mode of formation.

Question 8.

(a) Briefly explain the concept and application of: [4]
(i) In vitro pollination.
(ii) Protoplast fusion.

Answer:
(i) In vitro pollination: The technique of placing pollen grains directly onto exposed ovules, placentas, or cut styles in a sterile nutrient medium to overcome pre-zygotic interspecific hybridization barriers.
Application: Overcoming self-incompatibility and producing hybrid embryos.
(ii) Protoplast fusion: The enzymatic removal of plant cell walls followed by the fusion of isolated protoplasts from different species using fusogens like PEG or high pH/Ca2+ treatment to create somatic hybrids.
Application: Somatic hybridization and developing disease-resistant crop strains.

Teacher's Note:
a) Define both techniques and specify their utility in plant breeding.
b) Mention PEG as a common fusogen for protoplast fusion.

(b) Mention the significance of plants obtained by each of the following types of plant tissue culture techniques : [4]
(i) Endosperm culture.
(ii) Anther culture.

Answer:
(i) Endosperm culture: Used to obtain triploid plants which are often seedless and sterile, making them commercially desirable for cultivating seedless fruits (such as bananas and grapes) and high-quality pulpwood.
(ii) Anther culture: Used to produce haploid plants in vitro from microspores, which allows for the rapid generation of homozygous pure lines and immediate expression of recessive mutations.

Teacher's Note:
a) Highlight triploidy and seedlessness for endosperm culture.
b) Highlight haploidy and pure-line production for anther culture.

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

Answer:
1. Sequencing the complete sequence of approximately 30,000 to 35,000 human genes and mapping their chromosomal locations.
2. Advancing molecular medicine, enabling better understanding, diagnosis, and potential gene therapy treatments for hereditary genetic disorders and cancers.

Teacher's Note:
a) Mention mapping and sequencing of human genes.
b) Mention applications in disease diagnosis and gene therapy.

Question 9.

(a) What type of information is obtained from each of the following database. [4]
(i) Taxonomy Browser
(ii) PDB.
(iii) GENSCAN
(iv) PIR.

Answer:
(i) Taxonomy Browser: Provides taxonomic information, scientific names, and phylogenetic lineage data for organisms available in NCBI databases.
(ii) PDB (Protein Data Bank): Contains 3D structural data and coordinates of proteins and nucleic acids resolved by X-ray crystallography or NMR.
(iii) GENSCAN: An eukaryotic ab initio gene finder algorithm used for predicting gene structures and identifying exons/introns in genomic sequences.
(iv) PIR (Protein Information Resource): A comprehensive annotated protein sequence database providing analytical tools and functional protein information.

Teacher's Note:
a) Accurately match each database name with its specific type of biological data.
b) Emphasize PDB for 3D structures and PIR for protein sequences.

(b) Explain the method of DNA sequencing using automated DNA sequencing technique. [4]

Answer:
Automated DNA sequencing is an advanced version of the Sanger dideoxy method utilizing fluorescently labeled dideoxynucleotides (ddNTPs), each tagged with a distinct fluorescent dye. DNA fragments generated in a single reaction tube are separated by size using capillary electrophoresis. As fragments pass a laser detector, the fluorescent dyes emit light of characteristic wavelengths. A computer records these light signals as an electrogram chromatogram, automatically converting the fluorescence peaks into nucleotide sequences.

Teacher's Note:
a) Mention fluorescent labeling of ddNTPs and capillary electrophoresis.
b) Explain laser detection and computer-generated chromatogram analysis.

(c) Write any two examples of each of the following plant hormones commonly used in media preparation: [2]
(i) Auxins.
(ii) Cytokinins.

Answer:
(i) Auxins: Indole-3-Acetic Acid (IAA) and 2,4-Dichlorophenoxyacetic acid (2,4-D).
(ii) Cytokinins: Kinetin and 6-Benzylaminopurine (BAP).

Teacher's Note:
a) Provide standard, recognized hormone abbreviations and chemical names.
b) Ensure both examples for auxins and cytokinins are correct.