ISC Class 12 Biotechnology Sample Paper 2024 with Solutions

SECTION A - 14 MARKS

Question 1

(i) The labelled _____________ are used as probe in Western Blotting technique. [1 Mark]

Answer: antibodies (or radiolabelled / enzyme-linked antibodies)

Teacher's Note:
a) Antibodies specifically bind to the target proteins immobilized on the membrane in Western blotting.
b) Ensure you distinguish between probes used in Southern/Northern blotting (nucleic acids) and Western blotting (antibodies).

(ii) During gel electrophoresis, DNA molecules move towards the __________ electrode. [1 Mark]

Answer: positive (or anode)

Teacher's Note:
a) DNA molecules possess a negative charge due to their sugar-phosphate backbone.
b) Like charges repel and opposite charges attract, hence DNA migrates toward the positive electrode.

(iii) The nitrogenous base that has double rings is: [1 Mark]
(A) Cytosine
(B) Guanine
(C) Thymine
(D) Uracil

Answer: (B) Guanine

Purines (Adenine and Guanine) possess a double-ring structure, whereas pyrimidines (Cytosine, Thymine, and Uracil) have a single ring.

Teacher's Note:
a) Remember the rule that purines are double-ringed nitrogenous bases.
b) Do not confuse pyrimidines with purines while answering structure-based questions.

(iv) A plant geneticist is studying the possibility of combining desirable traits from two different plant species. He is particularly interested in developing a hybrid plant that combines disease resistance from one species with high yield potential from another species. Name the technique that can be used by the plant geneticist to develop the hybrid plant. [1 Mark]

Answer: Somatic hybridization (or Protoplast fusion)

Teacher's Note:
a) Somatic hybridization involves the fusion of isolated protoplasts from two different plant species to form a somatic hybrid.
b) Mention the exact technical term 'Somatic hybridization' to secure full marks.

(v) Give a reason for the following.
(a) A haploid plant obtained by androgenesis produces viable gametes by meiotic division. [1 Mark]

Answer: Although haploid plants have only one set of chromosomes, certain haploid lines undergo chromosome doubling spontaneously or are doubled artificially using colchicine, enabling normal pairing and meiosis during gametogenesis, or through specialized meiotic mechanisms depending on the specific system.

Teacher's Note:
a) Androgenesis yields haploid plants from male gametophytes (anther or microspore culture).
b) Normal meiosis requires homologous pairs; hence doubled haploids are usually fertile.

(b) A co-repressor is required by the repressor to switch off the operator site in a repressible operon. [1 Mark]

Answer: In a repressible operon, the aporepressor protein alone is inactive and cannot bind to the operator site; binding of the co-repressor induces a conformational change activating the repressor to bind to the operator.

Teacher's Note:
a) Co-repressors (like tryptophan in the trp operon) bind to the inactive repressor to make it active.
b) Clearly state the difference between inducible and repressible operon regulatory molecules.

(vi) Define the following:
(a) Genomics [1 Mark]

Answer: Genomics is the comprehensive study of the whole genome of organisms, including sequencing, mapping, and functional analysis of all genes and their interactions.

Teacher's Note:
a) Keywords required are 'mapping', 'sequencing', and 'analysis of entire genome'.
b) Do not confuse genomics with proteomics or transcriptomics.

(b) Single cell protein [1 Mark]

Answer: Single cell protein refers to dried microbial cells or total protein extracted from pure or mixed cultures of algae, yeasts, fungi, or bacteria grown on various carbon sources for use as protein supplements in human food or animal feed.

Teacher's Note:
a) Emphasize that it represents microbial biomass used as a protein source.
b) Mention examples like Spirulina or Methylophilus methylotrophus for completeness.

(vii) Differentiate between the following:
(a) Monocistronic mRNA and Polycistronic mRNA [1 Mark]

Answer:

Teacher's Note:
a) Use a tabular format for clear differentiation.
b) Highlight the occurrence in eukaryotes versus prokaryotes.

(b) Sticky ends and blunt ends [1 Mark]

Answer:

Teacher's Note:
a) Sticky ends facilitate easier ligation due to base complementarity.
b) Blunt ends require specialized blunt-end ligation techniques or linkers.

(viii) Expand the following:
(a) EMBL [1 Mark]

Answer: European Molecular Biology Laboratory

Teacher's Note:
a) Accurate spelling of all words is mandatory.
b) It is one of the major bioinformatics databases for nucleotide sequences.

(b) NCBI [1 Mark]

Answer: National Center for Biotechnology Information

Teacher's Note:
a) Memorize standard biological acronyms accurately.
b) NCBI hosts essential databases like GenBank and PubMed.

(ix) Assertion: Lac operon is an inducible operon.
Reason: Lactose inhibits the process of transcription in Lac operon. [1 Mark]
(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: (C) Assertion is true but Reason is false.

Lactose acts as an inducer that inactivates the repressor, thereby promoting transcription, not inhibiting it.

Teacher's Note:
a) Lactose binds to the repressor protein, causing it to fall off the operator, thus turning transcription ON.
b) Read the reason carefully as it states the opposite physiological effect.

(x) Assertion: In Sanger's DNA sequencing method, radio labelled ddNTPs are used to terminate the chain.
Reason: ddNTPs have the radiolabelled nitrogenous bases which are identified by autoradiography. [1 Mark]
(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.

Chain-terminating dideoxynucleotides (ddNTPs) are radiolabelled or fluorophore-labelled to enable detection of the synthesized fragments.

Teacher's Note:
a) Dideoxynucleotides lack the 3' hydroxyl group, halting further chain elongation.
b) Radiolabelling or fluorescent tagging allows visualization on gels or capillary sequencers.

SECTION B - 28 MARKS

Question 2 [4 Marks]
Write short notes on the following:
(i) Identification of recombinant host by Blue - white selection method [2 Marks]

Answer:
1. The blue-white selection method is based on the insertional inactivation of the lacZ gene, which encodes the enzyme beta-galactosidase.
2. Recombinant colonies appear white because the foreign DNA insert disrupts the lacZ gene, preventing the conversion of X-gal into a blue-coloured product, whereas non-recombinant colonies retain enzyme activity and appear blue.

Teacher's Note:
a) Emphasize the role of the lacZ gene and beta-galactosidase enzyme.
b) Clearly differentiate why transformants with inserts stay white while self-ligated vectors turn blue.

(ii) Reverse transcription [2 Marks]

Answer:
1. Reverse transcription is the process of synthesizing complementary DNA (cDNA) from a single-stranded RNA template, catalyzed by the enzyme reverse transcriptase.
2. This mechanism is widely used by retroviruses and in molecular biology laboratories to generate cDNA libraries from mRNA molecules.

Teacher's Note:
a) Mention the enzyme reverse transcriptase and the direction of synthesis (RNA to DNA).
b) Highlight its importance in cloning eukaryotic genes without introns.

Question 3 [4 Marks]
(i) Briefly explain the following:
(a) Edible vaccines [2 Marks]

Answer:
1. Edible vaccines are transgenic plants expressing specific antigenic proteins from pathogens, which, when ingested, stimulate mucosal and systemic immunity against that pathogen.
2. They offer advantages such as easy administration, needle-free delivery, and elimination of cold-chain storage requirements.

Teacher's Note:
a) Define edible vaccines clearly as plant-derived antigen delivery systems.
b) State at least two major practical advantages over conventional injectable vaccines.

(b) Growth regulators in plant cultures [2 Marks]

Answer:
1. Plant growth regulators (PGRs) such as auxins and cytokinins are synthetic or natural hormones added to culture media to control cell division, differentiation, and morphogenesis.
2. The ratio of auxins to cytokinins determines whether callus tissue forms roots (high auxin to cytokinin ratio) or shoots (high cytokinin to auxin ratio).

Teacher's Note:
a) Give examples of primary classes of PGRs used in tissue culture.
b) Explain the critical role of the auxin-cytokinin balance in organogenesis.

OR

(ii) Briefly explain the following:
(a) Colorimetry [2 Marks]

Answer:
1. Colorimetry is an analytical technique used to measure the absorbance or transmittance of light of a specific wavelength by a coloured chemical solution.
2. According to Beer-Lambert law, the concentration of the solute in the solution is directly proportional to its absorbance, enabling quantitative estimation of biochemical substances.

Teacher's Note:
a) State the underlying principle based on the Beer-Lambert law.
b) Mention its application in quantifying proteins, nucleic acids, or microbial growth turbidity.

(b) Biolistic [2 Marks]

Answer:
1. Biolistics (gene gun method) is a physical method of gene transfer where micro-particles of gold or tungsten coated with foreign DNA are shot at high velocity into target plant or animal cells.
2. This technique is especially useful for transforming recalcitrant species, chloroplasts, and thick-walled plant tissues directly.

Teacher's Note:
a) Describe the physical components: microcarriers (gold/tungsten) and high-pressure delivery.
b) Highlight its utility for plant cells with rigid cell walls.

Question 4 [4 Marks]
State any two differences between the following:
(i) YAC and BAC [2 Marks]

Answer:
1. Host organism: YAC (Yeast Artificial Chromosome) is propagated in yeast cells, whereas BAC (Bacterial Artificial Chromosome) is maintained in Escherichia coli host cells.
2. Insert capacity: YAC can accommodate extremely large DNA inserts (up to 1000 kb or more), whereas BAC typically accommodates smaller inserts ranging from 100 to 300 kb.

Teacher's Note:
a) Provide clear, contrasting points in distinct sentences.
b) Mention insert size and host system as key parameters.

(ii) Synthetic culture medium and semisynthetic medium [2 Marks]

Answer:
1. Composition: Synthetic culture media have a completely defined chemical composition where every ingredient and its exact concentration are known, whereas semisynthetic media contain undefined natural extracts like yeast extract or peptone.
2. Reproducibility: Synthetic media ensure high reproducibility across experiments, whereas semisynthetic media can vary slightly between batches due to natural ingredients.

Teacher's Note:
a) Emphasize whether the exact chemical makeup is known.
b) Contrast the use of defined chemical components against undefined natural supplements.

Question 5 [4 Marks]
(i) Describe the process of animal cloning. [4 Marks]

Answer:
1. Animal cloning, specifically somatic cell nuclear transfer (SCNT), begins with the enucleation of a mature oocyte (unfertilized egg cell).
2. A donor somatic cell (such as a mammary gland cell or fibroblast) is isolated from the animal to be cloned.
3. The entire donor somatic cell or its nucleus is fused with the enucleated oocyte using an electrical pulse or chemical stimulus.
4. The reconstructed egg is activated to initiate embryonic development in vitro and is subsequently implanted into a surrogate mother for gestation until birth.

Teacher's Note:
a) Detail the major steps: enucleation, nuclear transfer, fusion, activation, and surrogate implantation.
b) Mention the landmark example of Dolly the sheep to demonstrate conceptual clarity.

OR

(ii) Discuss the process of DNA isolation from a plant cell. [4 Marks]

Answer:
1. Cell lysis: Plant tissues are ground in a buffer and treated with detergents (like SDS) and enzymes (like cellulase) to break open cell walls and plasma membranes.
2. Protein and RNA removal: Proteases and RNases are added to degrade cellular proteins and RNA molecules present in the lysate.
3. Precipitation: Cold absolute ethanol or isopropanol is added to the aqueous phase to precipitate and aggregate the purified DNA molecules.
4. Spooling/Centrifugation: The precipitated DNA threads are collected by spooling onto a glass rod or recovered via centrifugation, washed with ethanol, and dissolved in TE buffer.

Teacher's Note:
a) List the sequence of actions: lysis, enzymatic digestion, precipitation, and recovery.
b) Emphasize the role of cold ethanol in precipitating nucleic acids.

Question 6 [4 Marks]
Give reasons for the following:
(i) Flavr savor tomato can be stored for longer time. [2 Marks]

Answer:
1. Flavr Savr tomatoes are genetically modified using antisense RNA technology to inhibit the expression of the polygalacturonase (PG) enzyme.
2. The PG enzyme is responsible for breaking down pectin in cell walls during fruit ripening; its suppression delays softening, allowing the fruit to remain firm and store longer.

Teacher's Note:
a) Mention the target enzyme: polygalacturonase (PG).
b) Explain how antisense technology prevents the degradation of cell wall pectin.

(ii) Golden rice is more nutritious than normal rice. [2 Marks]

Answer:
1. Golden rice is genetically engineered to biosynthesize beta-carotene (a precursor of vitamin A) in its endosperm.
2. This is achieved by introducing phytoene synthase and phytoene desaturase genes, which adds essential nutritional value to combat vitamin A deficiency in populations relying on rice as a staple diet.

Teacher's Note:
a) State the specific nutrient added: beta-carotene (provitamin A).
b) Briefly mention the transgenic metabolic pathway introduced into the rice endosperm.

Question 7 [4 Marks]
Briefly explain the methods of sterilizing the following:
(i) Instruments [1 Mark]

Answer: Instruments like forceps and scalpels are sterilized using an autoclave by subjecting them to high-pressure steam at 121 degrees Celsius and 15 psi for 15 to 20 minutes, or by dry heat sterilization in a hot air oven.

Teacher's Note:
a) Autoclaving is the gold standard for heat-stable lab instruments.
b) Mention standard operating parameters (temperature, pressure, and time).

(ii) Culture medium [1 Mark]

Answer: Culture media are sterilized by autoclaving at 121 degrees Celsius and 15 psi pressure for 15 to 20 minutes, ensuring the destruction of all microbial spores and vegetative cells.

Teacher's Note:
a) Ensure heat-labile components (like vitamins or antibiotics) are filter-sterilized separately.
b) Standard autoclave conditions must be explicitly stated.

(iii) Explants [1 Mark]

Answer: Explants are surface-sterilized by washing with chemical disinfectants such as sodium hypochlorite solution, mercuric chloride, or hydrogen peroxide for a specific duration, followed by thorough rinsing with sterile distilled water.

Teacher's Note:
a) Surface sterilization prevents tissue damage while eliminating surface-borne microbes.
b) Emphasize the importance of washing with sterile distilled water afterward.

(iv) Vitamins [1 Mark]

Answer: Vitamins are heat-sensitive components and are sterilized using membrane filtration (such as a 0.22 micrometer pore-size bacterial filter) rather than heat sterilization.

Teacher's Note:
a) Highlight that heat degrades vitamins, necessitating cold sterilization methods.
b) Specify membrane or syringe filters with 0.22 micrometer pore size.

Question 8 [4 Marks]
A group of researchers is studying ancient DNA samples obtained from archaeological remains in order to understand the genetic history of a particular population. The DNA samples are highly degraded due to age and environmental factors. Describe the technique that the researchers can employ to raise the amount of highly degraded DNA samples obtained from ancient remains. [4 Marks]

Answer:
1. The researchers should employ the Polymerase Chain Reaction (PCR) technique to amplify the target DNA sequences.
2. Step 1 - Denaturation: The double-stranded ancient DNA is heated to high temperatures (about 94 to 98 degrees Celsius) to separate it into single strands.
3. Step 2 - Annealing: The temperature is lowered to allow synthetic oligonucleotide primers to bind specifically to complementary sequences on the single-stranded DNA templates.
4. Step 3 - Extension: Thermostable DNA polymerase (such as Taq polymerase) synthesizes new DNA strands by adding deoxynucleoside triphosphates (dNTPs) starting from the primers, exponentially increasing the amount of the target DNA.

Teacher's Note:
a) Name PCR and explain its three core thermal cycling steps.
b) Mention the necessity of thermostable DNA polymerase and sequence-specific primers for amplifying degraded template DNA.

SECTION C - 28 MARKS

Question 9

(i) Discuss the role of any four enzymes involved in DNA replication in prokaryotes. [4 Marks]

Answer:
1. Helicase: Unwinds the double-stranded DNA helix by breaking hydrogen bonds between complementary bases at the replication fork.
2. DNA Polymerase III: The primary replicative enzyme that synthesizes the new DNA strand by adding nucleotides in the 5' to 3' direction.
3. DNA Ligase: Seals nicked phosphodiester backbones by joining Okazaki fragments on the lagging strand.
4. Primase: Synthesizes short RNA primers required by DNA polymerase to initiate synthesis.

Teacher's Note:
a) Choose four distinct, major prokaryotic replication enzymes.
b) Clearly describe the precise biochemical function of each enzyme.

(ii) Mention any three differences between Southern blotting and Northern blotting. [3 Marks]

Answer:

Teacher's Note:
a) Use a table to clearly contrast target molecules and applications.
b) Remember that Southern detects DNA while Northern detects RNA.

OR

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

Answer:
1. Isolation: Pure donor DNA containing the gene of interest and vector DNA (such as a plasmid) are isolated.
2. Restriction digestion: Both the vector and foreign DNA are cleaved using the same restriction endonuclease enzyme to generate compatible sticky or blunt ends.
3. Ligation: The digested foreign DNA fragment and vector are mixed together in the presence of DNA ligase enzyme to form covalent phosphodiester bonds, creating a recombinant DNA (rDNA) molecule.
4. Introduction: The constructed rDNA is introduced into a suitable host organism through transformation.

Teacher's Note:
a) Outline the step-by-step procedural workflow of gene cloning.
b) Highlight the role of restriction enzymes and DNA ligase.

(ii) Mention any three differences between BLAST and FASTA. [3 Marks]

Answer:

Teacher's Note:
a) Define both computational tools clearly in tabular format.
b) Mention algorithms and search speeds as core points of differentiation.

Question 10

(i) Discuss the levels of stem cells on the basis of their developmental potential. [4 Marks]

Answer:
1. Totipotent stem cells: Can differentiate into all cell types of the body plus extra-embryonic tissues (e.g., zygote and early cleavage-stage blastomeres).
2. Pluripotent stem cells: Can give rise to all derivatives of the three germ layers (ectoderm, mesoderm, and endoderm) but not extra-embryonic tissues (e.g., embryonic stem cells).
3. Multipotent stem cells: Can differentiate into a restricted family of related cell types (e.g., hematopoietic stem cells producing various blood cells).
4. Unipotent stem cells: Can produce only one cell type, their own lineage, while retaining self-renewal capacity (e.g., spermatogonial stem cells).

Teacher's Note:
a) List the four tiers of stem cell potency in descending order of differentiation potential.
b) Provide clear biological examples for each category.

(ii) Explain the clover leaf model of tRNA. [3 Marks]

Answer:
1. The cloverleaf secondary structure of tRNA features specific base-paired stems and single-stranded loops.
2. Acceptor arm: Carries the CCA stem at the 3' end where the specific amino acid binds.
3. Anticodon loop: Contains the anticodon triplet that recognizes and pairs with the complementary mRNA codon.
4. D-loop and T-psi-C loops: The D-loop is involved in recognition by aminoacyl-tRNA synthetase, and the T-psi-C loop binds to the ribosome.

Teacher's Note:
a) Describe the structural features of the cloverleaf model.
b) Clearly mention the functions of the acceptor stem and anticodon loop.

Question 11

(i) Figure 1 shows growth kinetics of one of the microbial cultures. Study the figure given below and answer the questions that follow: [4 Marks]

[Figure: Line graph showing microbial growth kinetics with 6 distinct phases labelled a, b, c, d, e, and f on a Growth versus Time plot. Phase a is lag phase, b is acceleration phase, c is exponential (log) phase, d is deceleration phase, e is stationary phase, and f is death phase.]

(a) What type of microbial culture is depicted in Figure 1? [1 Mark]

Answer: Batch culture

Teacher's Note:
a) Batch culture exhibits the classic closed system growth curve with lag, log, stationary, and death phases.
b) Distinguish batch culture from continuous (chemostat) culture systems.

(b) What happens to cell mass and cell culture in phase "c"? [1 Mark]

Answer: In phase "c" (exponential or log phase), both cell mass and the number of microbial cells increase exponentially at a maximal and constant growth rate.

Teacher's Note:
a) Phase "c" represents exponential growth.
b) Mention rapid cell division and exponential increase in biomass.

(c) Which phase yields maximum product? Give one reason to support your answer. [1 Mark]

Answer: Stationary phase (phase "e"), because secondary metabolites (like antibiotics) accumulate during this phase when nutrient depletion slows growth.

Teacher's Note:
a) Primary metabolites are produced in log phase, whereas most industrial secondary metabolites are maximized in stationary phase.
b) State the physiological reason clearly.

(d) In which phase do the cells adapt to grow in the culture medium? Give reasons. [1 Mark]

Answer: Lag phase (phase "a"), because cells synthesize new enzymes, repair macromolecules, and adjust their metabolic machinery to the fresh environment before active division begins.

Teacher's Note:
a) Identify the lag phase as the period of adaptation.
b) Explain that cells are metabolically active but not dividing.

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

[Figure: Ultracentrifugation tubes showing DNA density gradient bands. Generation Zero shows one single heavy band at the bottom; Generation 1 shows one intermediate midweight band; Generation 2 shows two bands - one light band near the top and one midweight band in the middle.]

(a) What is represented by heavy band in Generation Zero of Figure 2? [1 Mark]

Answer: DNA containing heavy nitrogenisotope (¹⁵N)

Teacher's Note:
a) Relate this to the Meselson and Stahl experiment proving semi-conservative DNA replication.
b) Explicitly mention ¹⁵N labelled DNA.

(b) Which method was used to determine the density of DNA? [1 Mark]

Answer: Cesium chloride (CsCl) density gradient equilibrium ultracentrifugation

Teacher's Note:
a) Name the exact technique: CsCl density gradient centrifugation.
b) Ensure all key terms are included for full credit.

(c) What is the result for Generation 1? [1 Mark]

Answer: A single hybrid (midweight) band consisting of DNA molecules with one ¹⁵N strand and one ¹⁴N strand.

Teacher's Note:
a) State the appearance (hybrid/midweight band).
b) Explain that it supports the semi-conservative mode of replication.

Question 12

A scientist is conducting an experiment to determine whether DNA is the genetic material responsible for inheritance. She has two groups of bacteria, Group A and Group B, and she is going to treat each group differently.
The scientist treats Group A bacteria with an enzyme that specifically degrades DNA. She treats Group B bacteria with an enzyme that specifically degrades RNA.
After treating Group A with the DNA-degrading enzyme, the scientist isolates the remaining cellular components, including proteins and RNA.
After treating Group B with the RNA-degrading enzyme, the scientist isolates the remaining cellular components, including proteins and DNA.

(i) What would be the expected outcome in the growth of the bacterial colony of Group A bacteria after DNA degrading enzyme is used? [1 Mark]

Answer: Transformation or genetic inheritance is abolished, meaning virulent traits are not transferred to non-virulent strains (or bacterial transformation does not occur).

Teacher's Note:
a) This reflects the classic Avery, MacLeod, and McCarty experiment.
b) Degradation of DNA prevents the transfer of genetic characteristics.

(ii) What would be the expected outcome in the growth of the bacterial colony of Group B bacteria after RNA degrading enzyme is used? [1 Mark]

Answer: Transformation still occurs normally and bacterial colonies grow with transformed genetic traits.

Teacher's Note:
a) RNase treatment does not affect DNA-mediated transformation.
b) Proves that RNA is not the genetic material in this system.

(iii) Explain the process that would be taken to analyse the nucleic acid(s) content after treating Group B bacteria with RNA degrading enzyme. [3 Marks]

Answer:
1. Sample preparation: The isolated cellular extract containing DNA and proteins is treated with protease to remove proteins.
2. Precipitation: Cold ethanol is added to precipitate and spool the high molecular weight DNA.
3. Analysis: The isolated nucleic acid is analyzed using diphenylamine test (which turns blue for DNA) or agarose gel electrophoresis to confirm that intact DNA is present.

Teacher's Note:
a) Outline protein digestion, DNA precipitation, and biochemical confirmation.
b) Emphasize that RNA was degraded, leaving DNA intact for analysis.

(iv) Explain the process that would be taken to analyse the nucleic acid/s content after treating Group A bacteria with DNA degrading enzyme. [2 Marks]

Answer:
1. The isolated extract (containing RNA and proteins, with DNA degraded) is subjected to tests such as orcinol assay for RNA.
2. Agarose gel electrophoresis of the sample shows the absence of the high molecular weight DNA band, confirming that DNA was specifically hydrolyzed by the DNA-degrading enzyme.

Teacher's Note:
a) State that DNase treatment destroys DNA, leaving RNA intact.
b) Explain how electrophoresis confirms the absence of intact DNA bands.