ISC Class 12 Biotechnology Board Exam Question Paper 2019 with Solutions

ISC Class 12 Biotechnology Board Exam Question Paper with Solutions 2019

PART - I (20 Marks)

(Answer all questions)

Question 1.

(a) Mention any one significant difference between each of the following : [5]
(i) Anti codon and codon
(ii) Intrinsic fluorescence and extrinsic fluorescence
(iii) Introns and Exons
(iv) Genomic DNA library and cDNA library
(v) RAM and ROM

Answer:
(i) Codon is a triplet sequence on mRNA that specifies an amino acid, whereas anticodon is the complementary triplet sequence on tRNA that brings the specific amino acid during translation.
(ii) Intrinsic fluorescence is shown naturally by inherent compounds without any additives, whereas extrinsic fluorescence requires coupling the compound with a fluorescent probe or fluor.
(iii) Introns are non-coding DNA base sequences found between exons and are not part of mature mRNA, whereas exons are coding DNA base sequences that are transcribed into mRNA and code for amino acids.
(iv) A genomic DNA library represents the complete genome of an organism including coding and non-coding regions, whereas a cDNA library consists only of complementary DNA clones prepared using mRNA.
(v) RAM is volatile memory that temporarily stores data and programs currently in use, whereas ROM is non-volatile memory that stores permanent instructions like the operating system loader.

Teacher's Note:
a) Ensure clear structural and functional distinction between the terms in each pair.
b) Avoid confusing genomic libraries with cDNA libraries as their template origins differ fundamentally.

(b) Answer the following questions: [5]
(i) Which amino acid is optically inactive and why?
(ii) What is meant by exponential phase?
(iii) What are designer oils?
(iv) What is palindromic sequence?
(v) Which substance is used in diploidization of haploid plants?

Answer:
(i) Glycine is optically inactive because its central carbon (alpha-carbon) is bonded to two identical hydrogen atoms and lacks a chiral center.
(ii) Exponential phase (log phase) is a growth phase in microorganisms where cells divide at their maximum possible rate depending on the growth medium and environmental conditions.
(iii) Designer oils are specially modified plant oils (such as those incorporating phytosterols) designed to reduce LDL blood cholesterol levels and increase energy expenditure in humans.
(iv) A palindromic sequence is a nucleic acid sequence that reads the same forward (5' to 3') on one strand and backward (5' to 3') on the complementary strand from a central axis of symmetry.
(v) Colchicine is the substance commonly used for the diploidization of haploid plants by inhibiting spindle fiber formation during mitosis.

Teacher's Note:
a) Memorize the structural uniqueness of glycine and the definition of biological palindromes for restriction enzyme cleavage sites.
b) Note that colchicine disrupts cell division to double the chromosome number.

(c) Write the full form of each of the following: [5]
(i) NBRI
(ii) NBTB
(iii) BLAST
(iv) PIR
(v) YAC

Answer:
(i) NBRI - National Botanical Research Institute
(ii) NBTB - National Biotechnology Board
(iii) BLAST - Basic Local Alignment Search Tool
(iv) PIR - Protein Information Resource
(v) YAC - Yeast Artificial Chromosome

Teacher's Note:
a) Full forms must be spelled accurately without spelling errors to secure full marks.
b) Bioinformatics acronyms like BLAST and PIR are frequently tested in board examinations.

(d) Explain briefly the following terms : [5]
(i) Callus
(ii) SNPs
(iii) Lyophilisation
(iv) Gene cloning
(v) Cybrids

Answer:
(i) Callus: A mass of meristematic, undifferentiated, and unorganized cells produced in tissue culture.
(ii) SNPs: Single Nucleotide Polymorphisms are variations in a single nucleotide at specific genomic DNA positions among individuals in a population.
(iii) Lyophilisation: A freeze-drying process under vacuum used to preserve microbial suspensions in ampoules at low temperatures for long-term viability.
(iv) Gene cloning: The process of isolating and copying a specific desired gene or DNA segment to produce large quantities.
(v) Cybrids: Cytoplasmically hybrid cells containing organelles from both parental sources and a nucleus derived from only one parent (with the other nucleus denatured).

Teacher's Note:
a) Keep definitions concise yet scientifically complete, covering origin and application where relevant.
b) Differentiate clearly between hybrids and cybrids based on nuclear contribution.

PART - II (50 Marks)

(Answer any five questions)

Question 2.

(a) With reference to composition of culture medium, answer the following : [4]
(i) Cytokinins
(ii) Auxin's

Answer:
(i) Cytokinins: These are plant growth hormones added to the culture medium that stimulate cell division and promote shoot morphogenesis along with auxins.
(ii) Auxins: These plant hormones promote callus formation, cell elongation, and vascular tissue (xylem) development while inhibiting lateral bud growth.

Teacher's Note:
a) Highlight the synergistic role of auxins and cytokinins in plant tissue culture differentiation.
b) Specify physiological effects clearly.

(b) Explain the induced fit hypothesis of enzyme action with the help of suitable illustrations. [4]

[Figure: Diagram showing enzyme and substrate with flexible active site undergoing conformational change upon binding, matching the hand-in-glove model.]

Answer:
1. The induced-fit theory modifies the rigid lock-and-key hypothesis by proposing that the active site of an enzyme is not fully preformed to exact rigidity.
2. When the substrate approaches and binds to the enzyme, it induces a conformational change in the enzyme's active site structure, much like a hand putting on a glove.
3. This conformational shift ensures precise alignment of catalytic groups on the enzyme surface with the substrate for effective catalysis.
4. It also explains phenomena like non-competitive inhibition where an inhibitor binds to an allosteric site and distorts the active site shape.

Teacher's Note:
a) Clearly contrast the induced-fit model with the older lock-and-key model.
b) Mention the hand-in-glove analogy as it is standard in board grading schemes.

(c) Write a note on Quaternary structure of proteins. [2]

Answer:
1. The quaternary structure represents the highest level of protein organization found in oligomeric proteins consisting of two or more polypeptide chains (subunits or protomers).
2. These subunits are held together by non-covalent interactions such as hydrogen bonds, ionic bonds, and hydrophobic interactions.
3. Subunits can be identical (homogeneous quaternary structure, e.g., phosphorylase) or different (heterogeneous quaternary structure, e.g., hemoglobin containing two alpha and two beta chains).

Teacher's Note:
a) Emphasize that quaternary structure applies only to multi-subunit proteins.
b) Provide hemoglobin as a classic example.

Question 3.

(a) Explain the important postulates of central dogma. [4]

Answer:
1. The central dogma of molecular biology outlines the directional flow of genetic information within a biological system.
2. Information stored in DNA is replicated to make new DNA molecules (DNA replication).
3. DNA is transcribed into messenger RNA molecules (transcription), carrying genetic instructions out of the nucleus.
4. mRNA is translated at the ribosomes into functional proteins composed of amino acids (translation).
5. An exception includes reverse transcription, where genetic information flows from RNA to DNA in retroviruses like HIV.

Teacher's Note:
a) List the three core steps clearly: replication, transcription, and translation.
b) Include reverse transcription to reflect modern updates to Francis Crick's original model.

(b) Name and explain the method used to sterilize the following : [4]
(i) Vitamins
(ii) Forceps and Scalpels
(iii) Nutrient Media
(iv) Explant

Answer:
(i) Vitamins: Filter sterilization (using membrane filters) followed by aseptic addition to pre-sterilized cooled media, as heat destroys vitamins.
(ii) Forceps and Scalpels: Flaming or dry heat sterilization (incineration), often by dipping in 25 percent ethanol and flaming.
(iii) Nutrient Media: Autoclaving (steam sterilization) at 15 psi pressure and 121 degrees Celsius for 15 to 30 minutes.
(iv) Explant: Surface sterilization using chemical disinfectants like sodium hypochlorite or mercuric chloride, followed by repeated washing with sterile distilled water.

Teacher's Note:
a) Match the sterilization method precisely to the physical and chemical nature of each item.
b) Explain why heat-labile components like vitamins cannot be autoclaved.

(c) What is the Chargaff's rule of equivalence ? [2]

Answer:
1. Chargaff's rule states that in double-stranded DNA, the total amount of purines (adenine and guanine) equals the total amount of pyrimidines (thymine and cytosine).
2. Specifically, the concentration of adenine equals thymine ([A] = [T]), and the concentration of guanine equals cytosine ([G] = [C]).

Teacher's Note:
a) State the exact molar equivalence ratios clearly.
b) Mention base pairing rules (A pairs with T, G pairs with C) as the structural basis for this equivalence.

Question 4.

(a) Differentiate between oils and fats. Discuss hydrolysis, rancidity and hardening shown by lipids. [4]

Answer:
1. Difference: Fats are solid at room temperature, mostly saturated, and primarily derived from animal sources, whereas oils are liquid at room temperature, unsaturated, and mostly derived from plants.
2. Hydrolysis: The breakdown of triglycerides into glycerol and free fatty acids by the addition of water, often catalyzed by lipase enzymes.
3. Rancidity: The chemical decomposition or oxidation of fats and oils resulting in unpleasant odors and unpalatable tastes.
4. Hardening: The catalytic hydrogenation of unsaturated fatty acids in plant oils to convert them into saturated fats with higher melting points.

Teacher's Note:
a) Present the comparison between fats and oils clearly with state, saturation, and origin.
b) Define lipid reactions precisely.

(b) Using tissue culture method one can produce disease free plants. Discuss the method used to produce virus free plants. [4]

Answer:
1. Meristem-tip culture is the most effective and widely used method for producing virus-free plants.
2. The apical meristem of plants is generally free from viruses because viral transport relies on vascular tissues, which are absent in the rapidly dividing meristematic dome.
3. An excised shoot apical meristem (tip of about 0.1 to 1 millimeter size) is aseptically cultured on a nutrient medium supplemented with appropriate growth regulators.
4. Thermotherapy (heat treatment of the mother plant at 35 to 40 degrees Celsius) can also be combined prior to excision to eliminate viruses more effectively.

Teacher's Note:
a) Explain the physiological reason why apical meristems lack viral particles (absence of vascular connections).
b) Mention the exact size range of the meristem tip used for culture.

(c) Write the main objectives of HGP. [2]

Answer:
1. To determine the complete sequence of all 3 billion base pairs in the human genome with high accuracy.
2. To identify all estimated human genes and develop faster sequencing technologies along with addressing ethical, legal, and social implications.

Teacher's Note:
a) Keep objectives concise, focusing on sequencing and gene identification.
b) Mention ELSI (Ethical, Legal, and Social Issues) as a key objective.

Question 5.

(a) Discuss the mechanism of the lac operon model of regulation of gene expression. [4]

Answer:
1. The lac operon is an inducible operon in bacteria responsible for lactose metabolism, consisting of a promoter, operator, and structural genes (lacZ, lacY, lacA).
2. In the absence of lactose, a repressor protein synthesized by the regulator gene binds to the operator region, blocking RNA polymerase from transcribing the structural genes (repressed state).
3. When lactose is introduced, allolactose acts as an inducer that binds to the repressor protein, causing a conformational change that inactivates it.
4. The inactive repressor detaches from the operator, allowing RNA polymerase to transcribe the structural genes into enzymes required for lactose utilization (induced state).

Teacher's Note:
a) Clearly distinguish between the repressed state and the induced state.
b) Name the inducer (allolactose) and structural genes (lacZ, lacY, lacA) correctly.

(b) Give four points of difference between southern blotting technique and northern blotting technique. [4]

Answer:
1. Target molecule: Southern blotting is used for detecting specific DNA sequences, whereas Northern blotting is used for detecting specific RNA sequences.
2. Gel electrophoresis: DNA fragments are separated using agarose gel electrophoresis in Southern blotting, whereas RNA molecules are separated using formaldehyde-agarose gels in Northern blotting.
3. Transfer membrane: DNA is transferred to a nitrocellulose membrane in Southern blotting, whereas RNA is typically transferred to a nylon membrane in Northern blotting.
4. Denaturation: DNA requires alkaline denaturation (using NaOH) to form single strands, whereas RNA secondary structures are denatured using chemical agents like formaldehyde.

Teacher's Note:
a) Contrast targets (DNA vs RNA) as the primary distinguishing factor.
b) Note the difference in transfer membranes commonly employed for each technique.

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

Answer:
1. Triplet code: A codon consists of three adjacent nitrogen bases specifying one amino acid.
2. Universal code: The genetic code is nearly universal across almost all living organisms.
3. Non-ambiguous: A specific codon always codes for the same single amino acid.
4. Degenerate: Most amino acids are specified by more than one codon.

Teacher's Note:
a) List four distinct, standard characteristics of the genetic code.
b) Avoid overlapping points to secure full credit.

Question 6.

(a) With reference to vector less methods of gene transfer explain each of the following : [4]
(i) Liposome mediated gene transfer
(ii) Electroporation
(iii) Transfection
(iv) Transformation

Answer:
(i) Liposome-mediated gene transfer: Artificial lipid vesicles encapsulating DNA fuse with cell membranes to deliver genetic material into protoplasts.
(ii) Electroporation: Application of high-voltage electrical pulses to transiently create microscopic pores in cell membranes for DNA uptake.
(iii) Transfection: The process of deliberately introducing naked DNA or RNA into eukaryotic host cells using non-viral methods.
(iv) Transformation: The uptake and incorporation of exogenous naked plasmid DNA by competent bacterial cells (such as E. coli) often aided by calcium chloride and heat shock.

Teacher's Note:
a) Define each direct gene transfer method clearly based on its physical or chemical mechanism.
b) Highlight the role of chemical treatment or electrical pulses where applicable.

(b) With reference to application of tissue culture techniques, explain the following : [4]
(i) Haploid production
(ii) Triploid production

Answer:
(i) Haploid production: Anther or microspore culture is used to produce haploid plants, which can be doubled using colchicine to obtain pure homozygous doubled haploid lines in a single generation.
(ii) Triploid production: Endosperm culture or hybridization generates triploid plants which exhibit the gigas effect (larger leaves, flowers, and fruits) and are sterile, making them useful for producing seedless fruits.

Teacher's Note:
a) Mention anther culture for haploids and endosperm culture for triploids.
b) Emphasize applications such as rapid homozygosity and seedless fruit production.

(c) What is meant by DNA probe ? [2]

Answer:
1. A DNA probe is a single-stranded sequence of DNA labeled with a radioactive isotope or fluorescent tag that is complementary to a target gene or sequence.
2. It is used to detect and identify complementary nucleic acid sequences via hybridization.

Teacher's Note:
a) Mention both single-stranded nature and labeling (radioactive/fluorescent).
b) State hybridization as its primary working principle.

Question 7.

(a) Explain how biotechnology helps in developing following traits in crops : [4]
(i) Biodegradable plastic
(ii) Pest resistance
(iii) Drought resistance
(iv) Salinity resistance

Answer:
(i) Biodegradable plastic: Genes encoding polyhydroxybutyrate (PHB) production from bacteria are introduced into plants like Arabidopsis so plants accumulate plastic granules in chloroplasts.
(ii) Pest resistance: Insertion of insecticidal crystal protein genes (cry genes) from Bacillus thuringiensis (Bt) into crops protects them against specific insect pests.
(iii) Drought resistance: Transferring drought-tolerance genes (DR genes) helps plants minimize water loss and maintain cellular turgor under water-stress conditions.
(iv) Salinity resistance: Introducing genes that encode proteins to compartmentalize excess sodium ions into vacuoles prevents salt toxicity in plant cells.

Teacher's Note:
a) Link each agronomic trait to its specific transgenic modification technique.
b) Cite standard examples like Bt crops and PHB-producing plants.

(b) Write the principle and applications of the following techniques : [4]
(i) Hydrophobic interaction
(ii) Colorimetry

Answer:
(i) Hydrophobic interaction (Chromatography): Principle is based on the interaction between hydrophobic patches on proteins and hydrophobic ligands on the chromatography matrix, used for purifying proteins.
(ii) Colorimetry: Principle is based on Beer-Lambert law where light absorption by a colored solution is proportional to the concentration of the solute, used for quantitative estimation of biomolecules.

Teacher's Note:
a) State the underlying physical or chemical principle for each technique.
b) List reliable biological applications for both.

(c) What are start and stop codons ? [2]

Answer:
1. Start codon: The triplet codon (AUG) that signals the initiation of protein translation and codes for methionine.
2. Stop codons: Triplet codons (UAA, UAG, UGA) that do not code for any amino acid and signal the termination of polypeptide synthesis.

Teacher's Note:
a) Provide the exact sequences for start (AUG) and stop (UAA, UAG, UGA) codons.
b) Mention their functional roles in translation.

Question 8.

(a) List any four responsibilities carried out by NCBI. [4]

Answer:
1. Creating and maintaining public biomedical and genomic databases such as GenBank and PubMed.
2. Developing computational tools and software for analyzing genomic sequences (e.g., BLAST).
3. Supporting research on fundamental molecular biology and bioinformatics problems.
4. Promoting international scientific communication and data standardization in biological nomenclature.

Teacher's Note:
a) Keep points focused on database maintenance, tool development, and research support.
b) Mention GenBank or BLAST as key NCBI contributions.

(b) Give a comparative account of cell differentiation, dedifferentiation, redifferentiation and vascular differentiation. [4]

Answer:
1. Differentiation: The process by which newly formed cells from meristems undergo permanent structural and functional changes to mature (e.g., tracheary elements).
2. Dedifferentiation: The phenomenon where mature, living differentiated cells regain the capacity to divide mitotically and form meristematic tissue (e.g., cork cambium).
3. Redifferentiation: The process where dedifferentiated cells lose their division capacity again and mature to perform specific specialized functions.
4. Vascular differentiation: The specific differentiation of meristematic cells into vascular tissues (xylem and phloem) regulated by auxin and cytokinin hormones.

Teacher's Note:
a) Clearly define the cyclical progression from differentiation to dedifferentiation and redifferentiation.
b) Mention hormonal control in vascular differentiation.

(c) What is the difference between dNTP and ddNTP ? [2]

Answer:
1. Deoxynucleoside triphosphates (dNTPs) have a hydroxyl group at both the 2' and 3' positions of the ribose sugar and allow continuous chain elongation.
2. Dideoxynucleoside triphosphates (ddNTPs) lack a hydroxyl group at the 3' carbon position, which terminates further DNA chain elongation when incorporated.

Teacher's Note:
a) Emphasize the absence of the 3'-OH group in ddNTPs.
b) Explain its significance in Sanger's chain-termination DNA sequencing method.

Question 9.

(a) Proteins have many important functions in an organism. Justify the statement giving its various roles with an example of each. [4]

Answer:
1. Structural support: Proteins provide mechanical strength to tissues (e.g., collagen in connective tissues and keratin in hair).
2. Catalysis: Enzymes accelerate biochemical reactions within cells (e.g., trypsin aids protein digestion).
3. Transport: Carrier proteins transport molecules across biological fluids and membranes (e.g., hemoglobin transports oxygen in red blood cells).
4. Regulation and Defense: Hormones regulate physiological processes (e.g., insulin regulates blood glucose), and immunoglobulins provide immune defense.

Teacher's Note:
a) Categorize protein functions clearly into structural, enzymatic, transport, and regulatory roles.
b) Provide accurate biological examples for each category.

(b) With reference to screening strategies, explain the following : [4]
(i) Insertional Inactivation method
(ii) Blue - White method

Answer:
(i) Insertional inactivation: A method where foreign DNA is inserted into a marker gene (such as the tetracycline resistance gene in pBR322), inactivating it so recombinants can be identified by loss of that specific antibiotic resistance.
(ii) Blue-white screening: A molecular technique utilizing the lacZ gene encoding beta-galactosidase; recombinant colonies remain white because insertional inactivation disrupts the gene, whereas non-recombinant colonies turn blue in the presence of X-gal.

Teacher's Note:
a) Explain how gene disruption serves as a marker for successful cloning.
b) Distinguish clearly between blue (non-recombinant) and white (recombinant) colonies in screening.

(c) How was insulin obtained before the advent of rDNA technology ? [2]

Answer:
1. Before recombinant DNA technology, insulin was commercially extracted and purified from the pancreases of slaughtered domestic animals such as cattle and pigs.
2. Although animal insulin is chemically similar to human insulin, it occasionally caused allergic immune reactions in some diabetic patients.

Teacher's Note:
a) Mention animal pancreas extraction (pigs and cattle) as the historical source.
b) Briefly note the clinical limitations, such as immunogenicity, which drove the shift to recombinant human insulin.