ISC Class 12 Biotechnology Sample Paper 2023 with Solutions

SECTION A - 14 MARKS

Question 1

(i) ___________ is used in dairy industry to make cheese. [1]

Answer: Rennet (or Rennin / Lactic acid bacteria)

Teacher's Note:
a) Rennet is a proteolytic enzyme complex produced in the stomachs of ruminant mammals, containing chymosin.
b) Students must mention the specific enzyme or microbial culture used in dairy processing to secure full marks.

(ii) _____________ are extra chromosomal, circular, self-replicating molecules. [1]

Answer: Plasmids

Teacher's Note:
a) Plasmids are extrachromosomal DNA molecules found naturally in bacteria and some other organisms.
b) Ensure the spelling is correct and avoid writing just 'DNA' as it is incomplete.

(iii) In gel electrophoresis, the gel is composed of _____________. [1]
(a) Nitrocellulose
(b) Agarose
(c) Phospholipids
(d) Sodium nitride

Answer: (b) Agarose

Agarose gel is widely used in electrophoresis to separate nucleic acids.

Teacher's Note:
a) Agarose is a linear polysaccharide derived from seaweed, forming a porous matrix for molecular separation.
b) Do not confuse agarose with nitrocellulose, which is used for blotting techniques.

(iv) When a monochromatic beam passes through a homogenous solution, its intensity decreases as the thickness of solution increases. Which one of the following laws states this?
[1]
(a) Beer's Law
(b) Lambert's Law
(c) Hooke's Law
(d) Beer Lambert Law

Answer: (b) Lambert's Law

Lambert's law states that the rate of decrease in light intensity with the thickness of the medium is proportional to the intensity of light.

Teacher's Note:
a) Lambert's law deals with the thickness of the absorbing medium, whereas Beer's law deals with concentration.
b) Students often mistakenly select Beer-Lambert Law, which combines both concentration and path length.

(v) State whether the following statements are True or False. Give a reason in support of your answer.

(a) In Sanger's DNA sequencing method, all the ddNTPs are labelled with coloured substances. [1]

Answer: False.
Reason: In Sanger's method, each dideoxynucleotide (ddNTP) is typically labelled with a distinct fluorescent dye, or the primers are labelled, rather than all ddNTPs sharing the same coloured substance.

Teacher's Note:
a) Dideoxynucleotides lack the 3'-OH group, terminating DNA chain elongation.
b) Always provide the justification when answering True or False questions.

(b) Helicase enzyme is used for repairing the DNA molecule. [1]

Answer: False.
Reason: Helicase is used to unwind the DNA double helix during replication, whereas DNA ligase and polymerases are involved in repair.

Teacher's Note:
a) Helicases break the hydrogen bonds between nitrogenous bases.
b) Ensure enzyme functions are clearly memorised to avoid confusion between replication and repair enzymes.

(vi) Define the following:

(a) Cosmids [1]

Answer: Cosmids are hybrid vectors derived from plasmids that contain a lambda phage cos sequence, allowing them to package DNA into phage particles for cloning large DNA fragments.

Teacher's Note:
a) Cosmids can carry larger DNA inserts (up to 45 kb) compared to standard plasmid vectors.
b) Mentioning the 'cos site' is critical for getting full credit.

(b) Tissue engineering [1]

Answer: Tissue engineering is an interdisciplinary field that combines engineering and life sciences to develop biological substitutes that restore, maintain, or improve tissue function.

Teacher's Note:
a) It involves the use of cells, scaffolds, and biologically active molecules.
b) Keep definitions concise and scientifically precise.

(vii) Differentiate between the following:

(a) Primer and Primase [1]

Answer:

Teacher's Note:
a) Always present differences in a tabular format for clarity.
b) Clearly distinguish between the molecule (primer) and the enzyme that makes it (primase).

(b) dNTP and ddNTP [1]

Answer:

Teacher's Note:
a) The presence or absence of the 3'-OH group is the key structural and functional difference.
b) Mentioning their role in DNA sequencing vs normal replication adds high value.

(viii) Expand the following:

(a) DDBJ [1]

Answer: DNA Data Bank of Japan

Teacher's Note:
a) DDBJ is an international nucleotide sequence database.
b) Spelling of biological acronyms must be precise.

(b) NHGRI [1]

Answer: National Human Genome Research Institute

Teacher's Note:
a) NHGRI spearheaded the US involvement in the Human Genome Project.
b) Memorize standard bioinformatics and genomics expansions.

(ix) Assertion: Haploid production by gynogenesis is a difficult task.
Reason: Isolation of unfertilized ovaries and ovules is not easy.
[1]
(a) Assertion and Reason are true and Reason is correct explanation for assertion.
(b) Assertion and Reason are true but Reason is not the correct explanation for assertion.
(c) Assertion is true but Reason is false.
(d) Both Assertion and Reason are false.

Answer: (a) Assertion and Reason are true and Reason is correct explanation for assertion.

Gynogenesis involves culturing unfertilized female gametophytes, and isolating these delicate structures is technically challenging.

Teacher's Note:
a) Gynogenesis is used in plant breeding to obtain doubled haploids.
b) Verify the logical link between technical difficulty and procedural isolation.

(x) Assertion: Membrane filters are used for sterilizing enzymes, hormones and antibiotics during cell culture technique.
Reason: Enzymes, hormones and antibiotics are heat sensitive.
[1]
(a) Assertion and Reason are true and Reason is correct explanation for assertion.
(b) Assertion and Reason are true but Reason is not the correct explanation for assertion.
(c) Assertion is true but Reason is false.
(d) Both Assertion and Reason are false.

Answer: (a) Assertion and Reason are true and Reason is correct explanation for assertion.

Heat sterilization (autoclaving) destroys heat-sensitive biomolecules, making membrane filtration necessary.

Teacher's Note:
a) Membrane filters typically have a pore size of 0.22 micrometers to remove bacteria.
b) Ensure students understand why alternative sterilization methods are needed for biochemicals.

SECTION B - 28 MARKS

Question 2 [4]

Write short notes on the following:
(i) Objectives of HGP
(ii) DNA Microarray

Answer:
(i) Objectives of Human Genome Project (HGP):
1. To identify all the approximately 20,000 to 25,000 genes in human DNA.
2. To determine the sequences of the 3 billion chemical base pairs that make up human DNA.
3. To store this information in public databases and improve tools for data analysis.
4. To address ethical, legal, and social issues (ELSI) that may arise from the project.
(ii) DNA Microarray:
1. It is a collection of microscopic DNA spots attached to a solid surface, used to measure expression levels of large numbers of genes simultaneously.
2. It works on the principle of nucleic acid hybridization using fluorescently labelled cDNA probes.
3. It is widely used in gene expression profiling, disease diagnosis, and pharmacogenomics.

Teacher's Note:
a) Break down answers into bullet points for structured evaluation.
b) For HGP, mention both sequencing and data-sharing objectives; for microarray, emphasize hybridization.

Question 3 [4]

(i) Briefly explain the following:
(a) Western blotting
(b) In vitro pollination

Answer:
(a) Western blotting:
1. It is a laboratory technique used to detect specific proteins in a sample of tissue homogenate or extract.
2. Proteins are separated using gel electrophoresis, transferred to a nitrocellulose or PVDF membrane, and detected using specific antibodies.
(b) In vitro pollination:
1. It is the technique of germinating pollen grains on isolated pistils or artificial nutrient media under aseptic conditions.
2. It is used to overcome self-incompatibility and produce interspecific hybrids.

Teacher's Note:
a) Distinguish Western blotting from Southern (DNA) and Northern (RNA) blotting.
b) In vitro pollination is a valuable tool in plant breeding and reproductive biology.

OR

(ii) Briefly explain the following:
(a) The sterilization of vitamins
(b) The sterilization of transfer area

Answer:
(a) The sterilization of vitamins:
1. Vitamins are heat-sensitive components of plant tissue culture media.
2. They are sterilized using membrane filtration (passing through a 0.22 micrometer filter) rather than autoclaving.
(b) The sterilization of transfer area:
1. It involves cleaning and disinfecting laminar air flow benches or inoculation chambers.
2. Surfaces are wiped with 70 percent ethanol and exposed to UV germicidal lamps before use.

Teacher's Note:
a) Emphasize why heat cannot be used for vitamins.
b) Mention safety and aseptic precautions for transfer areas.

Question 4 [4]

State any two differences between the following:
(i) mRNA and tRNA
(ii) Genomic library and cDNA library

Answer:
(i) Differences between mRNA and tRNA:

(ii) Differences between Genomic library and cDNA library:

Teacher's Note:
a) Tabular comparisons ensure clarity and help students cover distinct parameters.
b) Ensure structural and functional differences are highlighted correctly.

Question 5 [4]

(i) Discuss the process of gel electrophoresis.

Answer:
1. Gel electrophoresis is a technique used to separate DNA, RNA, or proteins based on size and charge.
2. A gel matrix (agarose or polyacrylamide) is cast with wells and placed in an electrophoresis chamber containing a buffer solution.
3. Samples are loaded into the wells, and an electric field is applied.
4. Negatively charged nucleic acids migrate toward the positive electrode (anode).
5. Smaller molecules move faster and farther through the pores of the gel than larger molecules, resulting in separation by size.
6. Bands are visualized using stains like ethidium bromide under UV light.

Teacher's Note:
a) Mention the principle of charge and pore-size sieving.
b) Step-by-step description fetches full marks.

OR

(ii) Discuss the process of DNA isolation from animal cell.

Answer:
1. Cell lysis: Animal cells lack a cell wall; hence, detergents like SDS are added to disrupt the cell membrane and nuclear envelope.
2. Deproteinization: Protease enzymes (like proteinase K) are added to digest proteins associated with DNA.
3. Removal of RNA: Ribonuclease (RNase) is added to degrade RNA contaminants.
4. Precipitation: Chilled absolute ethanol or isopropanol is added to precipitate the purified DNA out of solution.
5. Spooling or Centrifugation: The precipitated DNA is recovered as white threads by spooling or centrifugation.

Teacher's Note:
a) Emphasize the difference between plant and animal DNA isolation (absence of cell wall lysis step like cellulase).
b) List the specific enzymes used in each step.

Question 6 [4]

Give reasons for the following:
(i) hnRNA is called Cindrella RNA.
(ii) Agrobacterium is called natural genetic engineer.

Answer:
(i) hnRNA is called Cinderella RNA because it undergoes extensive processing (splicing, capping, and tailing) in the nucleus before transforming into functional mRNA, much like Cinderella transforming into a princess.
(ii) Agrobacterium is called a natural genetic engineer because it naturally transfers a specific segment of its DNA (T-DNA) into the host plant genome, causing crown gall tumors, a mechanism harnessed in recombinant DNA technology.

Teacher's Note:
a) Scientific analogies must be explained with proper biological reasoning.
b) Mention T-DNA transfer for Agrobacterium to secure complete credit.

Question 7 [4]

How are Flavor Savor tomatoes produced? Explain.

Answer:
1. Flavor Savor tomatoes are genetically modified tomatoes engineered to have a longer shelf life.
2. The gene responsible for producing the enzyme polygalacturonase (PG), which degrades pectin and softens the fruit, was identified.
3. An antisense gene corresponding to the PG gene was introduced into the tomato plant.
4. The antisense RNA binds to the normal mRNA of the PG gene, blocking its translation.
5. This significantly reduces polygalacturonase activity, delaying fruit softening and rotting while allowing the tomato to ripen naturally on the vine.

Teacher's Note:
a) Clearly mention the target enzyme (polygalacturonase) and the antisense RNA technology used.
b) Explain how delayed ripening benefits commercial distribution.

Question 8 [4]

Explain the process of micropropagation.

Answer:
1. Selection of explant: A small piece of plant tissue (shoot apex or meristem) is selected and sterilized.
2. Initiation culture: The explant is placed on a nutrient medium containing minerals, vitamins, and hormones (auxins and cytokinins) to induce callus formation.
3. Multiplication: The callus or multiple shoots are subcultured onto a fresh medium to rapidly multiply shoot numbers.
4. Rooting: Shoots are transferred to a rooting medium supplemented with auxins to induce root development.
5. Hardening: The resulting plantlets are acclimatized gradually to external environmental conditions before field transfer.

Teacher's Note:
a) Micropropagation is a technique of rapid vegetative propagation in vitro.
b) Mentioning hormone roles (auxins and cytokinins) adds precision.

SECTION C - 28 MARKS

Question 9

(i) Explain 3 - D model of DNA with the help of diagram. [4]

Answer:
1. Proposed by Watson and Crick in 1953, DNA consists of two polynucleotide chains wound around a common axis in a double helix.
2. The two strands are antiparallel, meaning one runs in the 5' to 3' direction and the other in the 3' to 5' direction.
3. The backbone is composed of alternating sugar and phosphate groups, while the nitrogenous bases project inward.
4. Bases pair specifically through hydrogen bonds: Adenine (A) pairs with Thymine (T) via two hydrogen bonds, and Guanine (G) pairs with Cytosine (C) via three hydrogen bonds (Chargaff's rule).
5. The helix has a diameter of 2 nm, and each complete turn has a length of 3.4 nm containing approximately 10 base pairs.

[Figure: Diagram of DNA double helix showing antiparallel strands, major and minor grooves, sugar-phosphate backbone, and base pairing A-T and G-C]

Teacher's Note:
a) Dimensions (2 nm diameter, 3.4 nm pitch) are vital structural parameters.
b) Students must draw a neat, labelled diagram showing antiparallel polarity.

(ii) Mention any three differences between DNA and RNA. [3]

Answer:

Teacher's Note:
a) Tabular format helps score full marks easily.
b) Ensure all three parameters (sugar, bases, structure) are clearly stated.

OR

(i) How is rDNA molecule constructed? [4]

Answer:
1. Isolation of genetic material: Target DNA containing the gene of interest and vector DNA (plasmid) are isolated.
2. Fragmentation of DNA: Restriction endonucleases are used to cut both the target DNA and the vector at specific recognition sites, producing sticky or blunt ends.
3. Ligation of DNA: The gene of interest is inserted into the cut vector using the enzyme DNA ligase, which joins the sugar-phosphate backbones.
4. Introduction of rDNA into host: The recombinant DNA (rDNA) is introduced into a host organism (like E. coli) via transformation, electroporation, or microinjection for replication and expression.

Teacher's Note:
a) Mention the key enzymes: restriction endonucleases (molecular scissors) and DNA ligase (molecular glue).
b) Step-wise explanation ensures clarity in recombinant technology processes.

(ii) Write short notes on NCBI and EMBL. [3]

Answer:
(a) NCBI (National Center for Biotechnology Information):
1. Established in 1988, it is a part of the United States National Library of Medicine.
2. It hosts public databases such as GenBank for DNA sequences and PubMed for biomedical literature, providing critical computational tools for biological research.
(b) EMBL (European Molecular Biology Laboratory):
1. It is a European research organization funded by member states, focusing on molecular biology research.
2. It maintains the European Nucleotide Archive (ENA), one of the world's primary nucleotide sequence databases.

Teacher's Note:
a) Highlight the primary databases associated with each organization (GenBank for NCBI, ENA for EMBL).
b) Keep descriptions concise and informative.

Question 10

(i) Discuss triploid production. Mention its application. [4]

Answer:
1. Triploid production: Triploids (3n) are organisms having three sets of chromosomes.
2. They are typically produced by crossing a tetraploid (4n) parent with a diploid (2n) parent, resulting in triploid (3n) progeny.
3. Alternatively, they can be produced by the fusion of an unreduced diploid gamete (2n) with a normal haploid gamete (n).
4. Application: Triploids are widely used in agriculture and horticulture to produce seedless fruits such as seedless watermelons and bananas, as meiotic pairing fails, preventing seed formation.

Teacher's Note:
a) Explain the genetic cross (4n x 2n = 3n) clearly.
b) Connect triploidy directly to seedlessness in commercial fruits.

(ii) Explain the process of somatic hybridization. [3]

Answer:
1. Isolation of protoplasts: Plant cells are treated with cell wall-degrading enzymes (cellulase and pectinase) to isolate naked protoplasts.
2. Protoplast fusion: Protoplasts from two different plant species are brought together and fused using fusogenic agents like Polyethylene Glycol (PEG) or electrical stimulation.
3. Selection and culture: Somatic hybrid cells (cybrids or somatic hybrids) are isolated and cultured on nutrient media to regenerate cell walls, divide into calli, and eventually develop into hybrid plantlets.

Teacher's Note:
a) Mention the enzymes used for wall digestion (cellulase and pectinase) and the fusing agent (PEG).
b) Somatic hybridization allows crossing across sexual barriers.

Question 11

(i) Figure 1 shows an important process. Study the figure given below and answer the questions that follow: [4]

[Figure: Diagram of DNA replication showing a replication fork, enzyme E at the fork, leading and lagging strands, template strand A with 5' to 3' polarity, and directional arrows]

(a) Identify the process shown in Figure 1.
(b) What is the strand A known as?
(c) Which factor helps the enzyme E to begin the process shown in the figure? Write the name of enzyme E involved in the process?
(d) If the sequence of strand A is 5' - A T G C A C T A G C T A C G - 3', then what should be sequence on the newly formed strand?

Answer:
(a) DNA replication.
(b) Template strand (or parent strand).
(c) Primer (RNA primer); Enzyme E is DNA Polymerase.
(d) 3' - T A C G T G A T C G A T G C - 5' (or 5' - G C A T C G A T C A C G T A - 3' depending on antiparallel alignment; complementary strand synthesized 5' to 3' is 3' - T A C G T G A T C G A T G C - 5').

Teacher's Note:
a) Verify base-pairing rules (A=T, G=C) carefully when answering sequence questions.
b) Ensure polarity (5' to 3') is correctly stated in sequence answers.

(ii) Figure 2 shows an important process. Study the figure given below and answer the questions that follow: [3]

[Figure: Centrifuge tubes showing DNA bands in Meselson and Stahl's experiment: Generation Zero with heavy 15N band at bottom, Generation One with midweight 14N-15N band in middle, Generation Two with light 14N band and midweight band]

(a) What is represented by heavy band in generation zero of Figure 2.
(b) Which method was used to determine the density of DNA?
(c) What is the result for generation 1?

Answer:
(a) DNA containing heavy isotope of nitrogen (¹⁵N).
(b) CsCl (Cesium chloride) density gradient centrifugation.
(c) All DNA molecules were hybrid (midweight), containing one ¹⁵N strand and one ¹⁴N strand.

Teacher's Note:
a) This illustrates Meselson and Stahl's experiment proving semi-conservative DNA replication.
b) Mentioning cesium chloride gradient centrifugation is essential for part (b).

Question 12

Read the following passage and answer the questions that follow:

At a crime spot, the police discovered that the victim had few hairs in his closed fist. They suspected them as the hair of the criminal and sent these to the forensic laboratory for testing. However, the sample collected was considered insufficient by the forensic team.

(i) Name the technique that is used at the beginning of the process for testing. Explain the technique. [3]

Answer:
1. Technique: DNA Fingerprinting (or DNA Profiling / STR analysis).
2. Explanation: It is a technique used to identify individuals based on variations in their DNA sequences, specifically looking at VNTRs (Variable Number of Tandem Repeats) or STRs (Short Tandem Repeats).
3. It involves DNA isolation, restriction digestion, electrophoresis, Southern blotting, and autoradiography or hybridization with DNA probes.

Teacher's Note:
a) Connect forensic testing directly to DNA fingerprinting.
b) Briefly outlining the steps ensures full marks.

(ii) '...the sample collected was considered insufficient.' Name the technique used to increase the amount of sample collected for testing. [1]

Answer:
Polymerase Chain Reaction (PCR).

Teacher's Note:
a) PCR is used for DNA amplification.
b) Keep one-word answers direct and precise.

(iii) Explain the technique used for increasing the amount of sample for testing. [3]

Answer:
1. Denaturation: The double-stranded DNA template is heated to about 94°C to 95°C to separate into single strands.
2. Annealing: The mixture is cooled to allow short DNA primers to bind to complementary sequences on the single strands.
3. Extension: Taq polymerase extends the primers using dNTPs at around 72°C to synthesize new DNA strands.
4. This thermal cycle is repeated multiple times to exponentially amplify the target DNA sequence.

Teacher's Note:
a) Mention the three distinct temperature steps: denaturation, annealing, and extension.
b) Highlight the role of thermostable Taq polymerase.