ISC Class 12 Biotechnology Board Exam Question Paper 2018 with Solutions

ISC Class 12 Biotechnology Board Exam Question Paper with Solutions

PART-I (20 Marks)

Question 1.

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

Answer:
Plasmids are extra-chromosomal, independent, self-replicating, circular double-stranded DNA molecules naturally found in bacteria and some fungi, whereas cosmids are predominantly plasmids containing one or two 'cos' sites derived from bacteriophage lambda, allowing them to package larger DNA fragments.

Teacher's Note:
a) Emphasize that cosmids combine features of both plasmids and phage lambda.
b) Students often confuse cloning capacity limits between the two.

(ii) Nucleotide and Nucleoside [1 Mark]

Answer:
A nucleotide is a condensation product of a heterocyclic nitrogen base, a pentose sugar, and a phosphate 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 the simple equation: Nucleoside + Phosphate group = Nucleotide.
b) Do not miss mentioning the phosphate group when defining a nucleotide.

(iii) Lagging strand and leading strand [1 Mark]

Answer:
The leading strand is synthesized continuously in the 5' to 3' direction towards the replication fork, whereas the lagging strand is synthesized discontinuously in short segments called Okazaki fragments in the direction opposite to the movement of the replication fork.

Teacher's Note:
a) Mention the requirement of DNA ligase specifically for the lagging strand.
b) Clear distinction between continuous and discontinuous synthesis fetches full marks.

(iv) Multipotent cells and unipotent cells [1 Mark]

Answer:
Multipotent cells have the ability to differentiate into many different types of specialized cells within a specific lineage or germ layer (e.g., hematopoietic stem cells), whereas unipotent cells can only differentiate into a single cell type or tissue (e.g., skin cells).

Teacher's Note:
a) Focus on the differentiation potential breadth of the cells.
b) Providing correct examples strengthens the answer.

(v) Microinjection and biolistic [1 Mark]

Answer:
Microinjection involves the direct and forcible introduction of foreign DNA into the nucleus of a cell using a fine glass micropipette, whereas the biolistic method involves bombarding target cells with microscopic gold or tungsten particles coated with the desired DNA using a particle bombardment apparatus.

Teacher's Note:
a) Microinjection is typically used for animal cells/oocytes, while biolistics is widely used for plant transformation.
b) Highlight the physical delivery mechanisms for each technique.

(b) Answer the following questions : [5]
(i) Who coined the term vitamin ? Write the chemical name of vitamin D. [1 Mark]

Answer:
The term vitamin was coined by Casimir Funk. The chemical name of Vitamin D is Cholecalciferol (Vitamin D3) or Ergocalciferol (Vitamin D2).

Teacher's Note:
a) Casimir Funk is credited with the discovery and naming of vitamins.
b) Mentioning either D2 or D3 is acceptable as a chemical name.

(ii) Why is amino acid said to be amphoteric ? [1 Mark]

Answer:
Amino acids are said to be amphoteric because they possess both acidic (carboxyl group, -COOH) and basic (amino group, -NH₂) functional groups, allowing them to donate a proton or accept a proton depending on the pH of the medium.

Teacher's Note:
a) Explain the zwitterionic form in neutral solutions where it acts as a dipolar ion.
b) Clearly state the roles of carboxyl and amino groups.

(iii) What is Bioremediation ? [1 Mark]

Answer:
Bioremediation is the process of using microorganisms or their metabolic processes to degrade, detoxify, or remove environmental pollutants and hazardous waste materials into less toxic or non-toxic forms.

Teacher's Note:
a) Focus on the application of microbial strains for pollution control.
b) Mention the conversion of toxic compounds to harmless end products.

(iv) What is a primer ? [1 Mark]

Answer:
A primer is a short single-stranded sequence of RNA or DNA that serves as a starting point for DNA synthesis, providing a free 3'-OH group to which DNA polymerase can add incoming nucleotides.

Teacher's Note:
a) Emphasize the requirement of a 3'-OH end for DNA polymerase action.
b) Note that RNA primers are naturally used during DNA replication, while DNA primers are used in PCR.

(v) What are cryoprotectants ? [1 Mark]

Answer:
Cryoprotectants are substances added to solutions containing biological cells or tissues to protect them from membrane damage and ice crystal formation during freezing and low-temperature storage. Examples include DMSO and polyethylene glycol.

Teacher's Note:
a) Mention the mechanism of preventing ice crystal damage.
b) Give standard examples like Dimethyl Sulfoxide (DMSO).

(c) Write the full form of each of the following : [5]
(i) NBPGR [1 Mark]

Answer:
National Bureau of Plant Genetic Resources

Teacher's Note:
a) Ensure exact spelling of all terms.
b) Do not make abbreviation errors in institutional names.

(ii) ARS [1 Mark]

Answer:
Agricultural Research Service

Teacher's Note:
a) Standard scientific terminology abbreviation.
b) Accurate recall is essential for full marks.

(iii) RFLP [1 Mark]

Answer:
Restriction Fragment Length Polymorphism

Teacher's Note:
a) Commonly used molecular marker technique.
b) Spell out restriction and polymorphism correctly.

(iv) HEPA [1 Mark]

Answer:
High Efficiency Particulate Air Filter

Teacher's Note:
a) Essential component in laminar air flow benches and biotechnology labs.
b) Accurate expansion ensures full marks.

(v) SCP [1 Mark]

Answer:
Single Cell Protein

Teacher's Note:
a) Refers to protein derived from cultured microbial cells.
b) Frequently asked abbreviation in biotechnology papers.

(d) Explain briefly : [5]
(i) Gene splicing [1 Mark]

Answer:
Gene splicing is a post-transcriptional modification process of primary transcript (hnRNA) in eukaryotes where non-coding introns are removed and coding exons are joined together to form mature mRNA.

Teacher's Note:
a) Mention both introns and exons clearly.
b) Specify that it occurs in eukaryotic transcript processing.

(ii) Supramolecular assembly [1 Mark]

Answer:
Supramolecular assembly is a complex system of molecules held together by non-covalent interactions (such as hydrogen bonds, hydrophobic interactions, and van der Waals forces) that can dynamically dissemble and reassemble.

Teacher's Note:
a) Highlight the reliance on non-covalent bonds rather than covalent bonds.
b) Mention its importance in biological structural organization.

(iii) Interferon [1 Mark]

Answer:
Interferons are natural anti-viral glycoproteins belonging to the cytokine family produced by vertebrate cells in response to viral infections, parasites, or tumor cells to inhibit viral replication.

Teacher's Note:
a) Classify them as host defense proteins against pathogens.
b) Note their clinical relevance, such as in Hepatitis-C treatment.

(iv) Gene scan [1 Mark]

Answer:
Gene scan is an ab initio computational gene prediction algorithm used in bioinformatics to identify protein-coding genes and analyze sequence alignments.

Teacher's Note:
a) Relate it to computational tools in genomics.
b) Mention its role in identifying gene structures.

(v) Saponification [1 Mark]

Answer:
Saponification is the alkaline hydrolysis of triglycerides (fats or oils) in the presence of a strong base like sodium hydroxide to yield glycerol and soap (fatty acid salts).

Teacher's Note:
a) Mention the reactants (triglycerides and alkali) and products (soap and glycerol).
b) Standard biochemical term often tested in biomolecules.

PART-II (50 Marks)

Question 2.
(a) Explain in detail, how Dolly, the sheep was created. [4 Marks]

Answer:
1. Dolly was the first mammal to be cloned from an adult somatic cell by Ian Wilmut and his colleagues at the Roslin Institute in Scotland using somatic cell nuclear transfer.
2. An udder cell was isolated from an adult Finn Dorset ewe, and its nucleus containing the complete genetic material was extracted.
3. An unfertilized oocyte was collected from a Scottish Blackface ewe, and its haploid nucleus was surgically removed to create an enucleated egg cell.
4. The donor somatic nucleus was inserted into the enucleated egg cell, and the hybrid cell was stimulated with a mild electric shock to trigger fusion and subsequent embryonic cleavage into a blastocyst, which was then implanted into a surrogate mother.

Teacher's Note:
a) Ensure the sequential steps of somatic cell nuclear transfer are clearly outlined.
b) Mention the specific breeds involved or state donor and recipient roles clearly.

(b) Mention any two chemical properties of each of the following: [4 Marks]
(i) Proteins
(ii) Carbohydrates

Answer:
(i) Chemical properties of proteins:
1. Acid hydrolysis: Proteins yield constituent amino acids in the form of hydrochlorides when hydrolyzed with concentrated hydrochloric acid.
2. Xanthoproteic test: Proteins react with concentrated nitric acid upon heating to develop a yellow color due to the presence of aromatic amino acids containing a benzene ring.
(ii) Chemical properties of carbohydrates:
1. Reducing property: Carbohydrates with free hemiacetal or hemiketal groups (reducing sugars like glucose and fructose) can reduce alkaline solutions of copper salts (Fehling's or Benedict's solution) to give a red or yellow precipitate of cuprous oxide.
2. Osazone formation: Reducing sugars react with excess phenylhydrazine upon heating to form characteristic yellow crystalline derivatives known as osazones.

Teacher's Note:
a) Clearly separate protein tests from carbohydrate tests.
b) Mention specific chemical reagents and resulting color changes.

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

Answer:
Okazaki fragments are short, newly synthesized DNA fragments formed discontinuously on the lagging template strand during DNA replication. They are joined together into a continuous strand by the enzyme DNA ligase, which catalyzes the formation of a phosphodiester bond between adjacent fragments.

Teacher's Note:
a) Identify the lagging strand as the site of Okazaki fragment formation.
b) Name DNA ligase explicitly as the joining enzyme.

Question 3.
(a) Describe the effect of each of the following factors on enzyme activity. [4 Marks]
(i) pH
(ii) Temperature
(iii) Enzyme concentration
(iv) Concentration of products

Answer:
(i) pH: Every enzyme exhibits maximum catalytic activity at an optimum pH. A deviation from this optimum pH alters the ionization state of amino acid residues at the active site, reducing enzyme activity or causing denaturation.
(ii) Temperature: An increase in temperature initially increases the reaction rate due to higher kinetic energy and collision frequency between substrate and enzyme molecules. However, excessively high temperatures cause thermal denaturation of the protein structure, leading to a sharp decline in activity.
(iii) Enzyme concentration: The rate of an enzyme-catalyzed reaction increases linearly with an increase in enzyme concentration when substrate is in excess, as more active sites become available. Eventually, the rate plateaus when all substrate molecules are bound.
(iv) Concentration of products: High accumulation of reaction products generally decreases enzyme velocity. Products may bind reversibly to the active site or form loose complexes, acting as inhibitors and slowing down the forward reaction.

Teacher's Note:
a) Explain the bell-shaped response curves typically seen for temperature and pH.
b) Differentiate between substrate saturation effects and product inhibition.

(b) With reference to suspension culture, explain the following : [4 Marks]
(i) A chemostat
(ii) A turbidostat

Answer:
(i) A chemostat is a continuous culture system in which the growth rate of cells is controlled by maintaining a limiting nutrient at a constant, growth-limiting concentration while fresh medium is continuously added and an equal volume of culture is withdrawn.
(ii) A turbidostat is a continuous culture system in which the cell density or turbidity of the culture is maintained at a constant level by automatically regulating the flow rate of fresh nutrient medium.

Teacher's Note:
a) Clearly distinguish between nutrient-limiting control (chemostat) and turbidity-based control (turbidostat).
b) Mention that both are continuous cultivation methods used in biotechnology.

(c) What is genomics ? What are its different types ? [2 Marks]

Answer:
Genomics is a branch of molecular biology and genetics that deals with the comprehensive sequencing, mapping, and structural/functional analysis of an organism's entire genome. It is broadly divided into two types: structural genomics (focusing on genome mapping and physical structure) and functional genomics (focusing on gene expression, transcriptome, and proteome analysis).

Teacher's Note:
a) Define genomics as the study of the entire genome rather than single genes.
b) List both structural and functional genomics accurately.

Question 4.
(a) What are the basic facilities that should be available for tissue culture in a biotechnology laboratory ? [4 Marks]

Answer:
1. Washing area: Equipped with sinks, distilled water supplies, and cleaning agents for washing glassware and instruments.
2. Media preparation and sterilization area: Equipped with balances, pH meters, hot plates, chemical storage, and an autoclave for sterilizing media and equipment.
3. Aseptic transfer area: Equipped with laminar air flow benches or sterile hoods to inoculate and transfer plant tissues without microbial contamination.
4. Incubation or culture room: Environmentally controlled growth rooms with regulated light, humidity, and temperature for maintaining cultured plant tissues.

Teacher's Note:
a) Emphasize the importance of aseptic conditions in plant tissue culture facilities.
b) List at least four distinct infrastructural zones of a standard laboratory.

(b) Explain the experiment which proves the semi-conservative mode of replication. [4 Marks]

Answer:
1. Meselson and Stahl (1958) grew Escherichia coli in a medium containing heavy nitrogen isotope (¹⁵N) for several generations until all cellular DNA became uniformly heavy.
2. These bacteria were then transferred to a medium containing normal light nitrogen isotope (¹⁴N) and allowed to replicate for successive generations corresponding to the cell division time of 30 minutes.
3. DNA extracted after each generation was subjected to cesium chloride (CsCl) density gradient centrifugation to determine its density.
4. The DNA extracted after the first generation formed a single hybrid density band (intermediate between heavy and light), and after the second generation, it formed two distinct bands (one hybrid and one light), which conclusively proved the semi-conservative mode of DNA replication.

Teacher's Note:
a) Mention the contribution of Meselson and Stahl clearly with the isotopes used.
b) Explain the centrifugation results for generation 1 and generation 2.

(c) What is cDNA ? [2 Marks]

Answer:
Complementary DNA (cDNA) is a double-stranded DNA molecule synthesized in vitro from a mature messenger RNA (mRNA) template using the enzyme reverse transcriptase. It lacks non-coding introns and represents the expressed genes of the genome.

Teacher's Note:
a) Highlight the role of reverse transcriptase and mRNA template.
b) Mention that cDNA contains only exons (expressed sequences).

Question 5.
(a) Explain any four methods employed to induce haploid production. [4 Marks]

Answer:
1. Anther and pollen culture (Androgenesis): Culturing excised anthers or isolated microspores on artificial nutrient media to develop haploid plants directly from pollen grains.
2. Ovule and ovary culture (Gynogenesis): In vitro culture of unpollinated female gametophytes or ovaries to induce the development of haploid embryos.
3. Interspecific hybridization and chromosome elimination: Crossing two different species where chromosomes of one parent are selectively eliminated during early embryonic divisions, resulting in haploid progeny.
4. Chemical or physical treatment: Applying chemical agents like colchicine, chloramphenicol, or physical treatments such as ionizing radiation or temperature shocks to induce chromosome elimination or parthenogenesis.

Teacher's Note:
a) Describe both in vitro and in vivo approaches for haploid induction.
b) Emphasize the significance of haploids in crop breeding programs.

(b) Describe the automated method of DNA sequencing. [4 Marks]

Answer:
1. Automated DNA sequencing is an advanced refinement of the Sanger dideoxy method utilizing fluorescent dye-labeled dideoxynucleotides (ddNTPs).
2. Each of the four ddNTPs is tagged with a distinct fluorescent dye that emits a specific wavelength of light when excited by a laser beam.
3. The reaction mixture containing the DNA fragments is separated according to size by high-resolution capillary electrophoresis in a single tube.
4. As the fragments pass through the detector, a laser excites the fluorescent dyes, and an optical detector records the emitted light signals, which are automatically processed by a computer to generate an electropherogram and determine the nucleotide sequence.

Teacher's Note:
a) Explain the role of fluorescent labeling and capillary electrophoresis.
b) Mention how computerized detection reads the sequence data.

(c) What is the difference between gel electrophoresis and gel permeation? [2 Marks]

Answer:
Gel electrophoresis separates charged macromolecules (such as DNA or proteins) based on their size and charge under the influence of an applied electric field through a gel matrix, whereas gel permeation (size-exclusion chromatography) separates molecules based solely on their molecular size as they pass through a porous gel filtration column without an electric field.

Teacher's Note:
a) Mention the dependence on electric field in electrophoresis versus molecular sieving through porous beads in gel permeation.
b) State their typical applications (DNA separation vs. protein purification).

Question 6.
(a) What is in vitro pollination ? Why is it done ? Write the steps involved in this process. [4 Marks]

Answer:
In vitro pollination is the technique of artificially placing pollen grains directly onto cultured ovules or stigmas on an artificial nutrient medium in a test tube or culture vessel to achieve fertilization and seed formation. It is performed to overcome self-incompatibility barriers, produce homozygous lines, and rescue hybrid embryos in endangered plant species. The process involves isolating mature pistils and viable pollen, sterilizing them, placing pollen onto the receptive stigma or directly onto exposed ovules under aseptic conditions, and incubating them for fertilization and seed development.

Teacher's Note:
a) Define in vitro pollination clearly in the context of plant biotechnology.
b) Outline both the objectives and procedural steps.

(b) Why is Agrobacterium called a natural genetic engineer ? How does it help in creating transgenic plants ? [4 Marks]

Answer:
Agrobacterium tumefaciens is called a natural genetic engineer because it naturally infects plant cells and transfers a specific segment of its plasmid DNA (T-DNA) into the host plant genome, causing tumor formation (crown gall disease) without human intervention. In plant biotechnology, this bacterium is utilized by replacing the pathogenic tumor-inducing genes with desired foreign genes of interest within the T-DNA region. When the modified Agrobacterium infects plant tissues, it stably inserts the foreign gene into the plant's chromosomal DNA, thereby generating transgenic plants with desirable traits.

Teacher's Note:
a) Explain the natural role of the Ti plasmid and T-DNA transfer mechanism.
b) Describe how scientists disarm the Ti plasmid for safe genetic transformation.

(c) Write a short note on site directed mutagenesis. [2 Marks]

Answer:
Site-directed mutagenesis is a molecular biology technique used to introduce targeted, specific mutations (such as single nucleotide changes or deletions) at a predetermined site within a DNA molecule. It is widely used to study protein structure-function relationships and alter enzyme activities.

Teacher's Note:
a) Differentiate site-directed mutagenesis from random spontaneous mutations.
b) Mention its primary requirement: prior knowledge of the target DNA sequence.

Question 7.
(a) What is HGP ? Name any two scientists involved in this. Write any two achievements of HGP. [4 Marks]

Answer:
HGP stands for the Human Genome Project, an international scientific research project initiated to determine the complete sequence of chemical base pairs making up human DNA and identify all human genes. Two prominent scientists involved in leadership roles were James Watson and Francis Collins. Two major achievements of HGP include mapping and sequencing the entire human genome (identifying approximately 25,000 genes) and providing foundational data for understanding, diagnosing, and treating hereditary genetic diseases.

Teacher's Note:
a) Expand HGP correctly and mention its primary goal.
b) List key scientific leaders and clear medical/scientific achievements.

(b) List the functions of the following in Bioinformatics : [4 Marks]
(i) ENTREZ
(ii) PDB
(iii) FASTA
(iv) MGD

Answer:
(i) ENTREZ: An integrated database retrieval system of NCBI used to access scientific literature, nucleotide sequences, protein sequences, and 3D structural data.
(ii) PDB (Protein Data Bank): A global repository containing experimentally determined 3D structures of proteins and nucleic acids.
(iii) FASTA: A software package and algorithm used for nucleotide and protein sequence alignment and similarity searches.
(iv) MGD (Mouse Genome Database): An integrated information resource providing comprehensive genetic, genomic, and phenotypic data on the laboratory mouse.

Teacher's Note:
a) Provide precise functions for each bioinformatics tool.
b) Mention their primary databases or search purposes.

(c) Mention two differences between the organisation of prokaryotic and eukaryotic genomes. [2 Marks]

Answer:
1. Prokaryotic genomes are much smaller, simpler, and lack a nuclear membrane (nucleoid), whereas eukaryotic genomes are larger, complex, and enclosed within a distinct nuclear membrane.
2. Prokaryotic DNA is naked and not associated with histone proteins, whereas eukaryotic DNA is tightly bound to histone proteins to form nucleosomes and chromatin.

Teacher's Note:
a) Contrast nuclear membrane presence and histone association.
b) Keep the points concise and scientifically precise.

Question 8.
(a) Briefly describe the steps involved in the Southern blotting technique. [4 Marks]

Answer:
1. Restriction digestion: DNA samples are cleaved into smaller fragments using restriction endonucleases.
2. Gel electrophoresis: The DNA fragments are separated by size on an agarose gel and denatured into single strands using an alkaline solution.
3. Blotting: The separated single-stranded DNA fragments are transferred from the gel onto a nitrocellulose or nylon membrane by capillary action, retaining their exact spatial pattern.
4. Hybridization and detection: The membrane is incubated with a labeled single-stranded DNA or RNA probe that binds to its complementary target sequence, and the location of the probe is detected using autoradiography or enzymatic color development.

Teacher's Note:
a) Outline the four key stages: digestion, electrophoresis, transfer, and hybridization.
b) Name the inventor (Edwin Southern) and membrane types (nitrocellulose/nylon) for extra clarity.

(b) What is the need of germplasm conservation ? Give an account of the in-situ and ex-situ conservation of germplasm. [4 Marks]

Answer:
Germplasm conservation is essential to preserve the total genetic diversity of crop plants and their wild relatives to prevent genetic erosion and provide diverse genetic traits for future plant breeding programs. In-situ conservation involves protecting endangered plant species and wild relatives within their natural habitats (such as national parks and biosphere reserves), whereas ex-situ conservation involves preserving genetic resources outside their natural habitats in gene banks, botanical gardens, seed banks, or through tissue culture methods.

Teacher's Note:
a) Emphasize the threat of genetic erosion due to modern high-yielding mono-cropping.
b) Clearly define and differentiate in-situ versus ex-situ conservation approaches.

(c) What is peptidoglycan ? Where is it found ? [2 Marks]

Answer:
Peptidoglycan (murein) is a rigid polymer composed of sugars (N-acetylglucosamine and N-acetylmuramic acid) and amino acids that form a crystal lattice meshwork. It is found exclusively in the cell walls of most bacteria, providing structural strength and shape.

Teacher's Note:
a) Define its biochemical composition (sugars and peptides).
b) State its precise location in bacterial cell walls.

Question 9.
(a) How are biomolecules separated by the following techniques : [4 Marks]
(i) Ion exchange chromatography
(ii) Partition chromatography

Answer:
(i) Ion exchange chromatography: Biomolecules are separated based on their net surface charge through reversible electrostatic interactions between charged molecules in solution and oppositely charged ions bound to an insoluble stationary support matrix.
(ii) Partition chromatography: Biomolecules are separated based on differences in their partition coefficients as they distribute themselves continuously between two liquid phases (a stationary liquid phase and a mobile liquid phase) flowing through a chromatography column.

Teacher's Note:
a) Highlight electrostatic charge differences as the basis for ion exchange.
b) Highlight partition coefficient differences between two liquid phases for partition chromatography.

(b) What is the cause and the symptoms of the following diseases : [4 Marks]
(i) Sickle cell anaemia
(ii) Alkaptonuria

Answer:
(i) Sickle cell anaemia: Caused by an autosomal recessive point mutation in the beta-globin gene of hemoglobin, resulting in the substitution of glutamic acid by valine at the 6th position. Symptoms include severe fatigue, vaso-occlusive painful crises, breathlessness, spleen damage, and abnormal crescent-shaped red blood cells under low oxygen tension.
(ii) Alkaptonuria: Caused by a genetic deficiency of the enzyme homogentisic acid oxidase, leading to the accumulation and excretion of homogentisic acid. Symptoms include urine turning dark or black upon standing in air, ochronosis (pigmentation of connective tissues), and arthritis in joints and cartilage.

Teacher's Note:
a) Specify genetic causes and amino acid substitutions for sickle cell anemia.
b) Specify enzyme deficiency and characteristic urine oxidation symptom for alkaptonuria.

(c) What is the difference between peptide bond and phosphodiester bond ? [2 Marks]

Answer:
A peptide bond is a covalent amide bond formed between the carboxyl group of one amino acid and the amino group of another, linking amino acids in proteins. A phosphodiester bond is a covalent ester bond formed between phosphoric acid and two hydroxyl groups of adjacent pentose sugars, linking nucleotides together in nucleic acid backbones.

Teacher's Note:
a) Contrast protein linkages (peptide) with nucleic acid linkages (phosphodiester).
b) Mention the reacting functional groups for each bond type.